XEmacs 21.4.19 (Constant Variable).

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* Lispref: (lispref).           XEmacs Lisp Reference Manual.
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   Edition History:

   GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU
Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid
Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994
XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995
GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp
Programmer's Manual (for 19.13) Third Edition, July 1995 XEmacs Lisp
Reference Manual (for 19.14 and 20.0) v3.1, March 1996 XEmacs Lisp
Reference Manual (for 19.15 and 20.1, 20.2, 20.3) v3.2, April, May,
November 1997 XEmacs Lisp Reference Manual (for 21.0) v3.3, April 1998

   Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software
Foundation, Inc.  Copyright (C) 1994, 1995 Sun Microsystems, Inc.
Copyright (C) 1995, 1996 Ben Wing.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the section entitled "GNU General Public License" is included
exactly as in the original, and provided that the entire resulting
derived work is distributed under the terms of a permission notice
identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that the section entitled "GNU General Public License"
may be included in a translation approved by the Free Software
Foundation instead of in the original English.

\1f
File: lispref.info,  Node: Face Properties,  Next: Face Convenience Functions,  Prev: Basic Face Functions,  Up: Faces

49.1.3 Face Properties
----------------------

You can examine and modify the properties of an existing face with the
following functions.

   The following symbols have predefined meanings:

`foreground'
     The foreground color of the face.

`background'
     The background color of the face.

`font'
     The font used to display text covered by this face.

`display-table'
     The display table of the face.

`background-pixmap'
     The pixmap displayed in the background of the face.  Only used by
     faces on GUI devices, currently X11, GTK, and Microsoft Windows.

`underline'
     Underline all text covered by this face.

`highlight'
     Highlight all text covered by this face.  Only used by faces on TTY
     devices.

`dim'
     Dim all text covered by this face.  Only used by faces on TTY
     devices.

`blinking'
     Blink all text covered by this face.  Only used by faces on TTY
     devices.

`reverse'
     Reverse the foreground and background colors.  Only used by faces
     on TTY devices.

`doc-string'
     Description of what the face's normal use is.  NOTE: This is not a
     specifier, unlike all the other built-in properties, and cannot
     contain locale-specific values.

 -- Function: set-face-property face property value &optional locale
          tag-set how-to-add
     This function changes a property of a FACE.

     For built-in properties, the actual value of the property is a
     specifier and you cannot change this; but you can change the
     specifications within the specifier, and that is what this
     function will do.  For user-defined properties, you can use this
     function to either change the actual value of the property or, if
     this value is a specifier, change the specifications within it.

     If PROPERTY is a built-in property, the specifications to be added
     to this property can be supplied in many different ways:

          If VALUE is a simple instantiator (e.g. a string naming a
          font or color) or a list of instantiators, then the
          instantiator(s) will be added as a specification of the
          property for the given LOCALE (which defaults to `global' if
          omitted).

          If VALUE is a list of specifications (each of which is a cons
          of a locale and a list of instantiators), then LOCALE must be
          `nil' (it does not make sense to explicitly specify a locale
          in this case), and specifications will be added as given.

          If VALUE is a specifier (as would be returned by
          `face-property' if no LOCALE argument is given), then some or
          all of the specifications in the specifier will be added to
          the property.  In this case, the function is really
          equivalent to `copy-specifier' and LOCALE has the same
          semantics (if it is a particular locale, the specification
          for the locale will be copied; if a locale type,
          specifications for all locales of that type will be copied;
          if `nil' or `all', then all specifications will be copied).

     HOW-TO-ADD should be either `nil' or one of the symbols `prepend',
     `append', `remove-tag-set-prepend', `remove-tag-set-append',
     `remove-locale', `remove-locale-type', or `remove-all'.  See
     `copy-specifier' and `add-spec-to-specifier' for a description of
     what each of these means.  Most of the time, you do not need to
     worry about this argument; the default behavior usually is fine.

     In general, it is OK to pass an instance object (e.g. as returned
     by `face-property-instance') as an instantiator in place of an
     actual instantiator.  In such a case, the instantiator used to
     create that instance object will be used (for example, if you set
     a font-instance object as the value of the `font' property, then
     the font name used to create that object will be used instead).
     If some cases, however, doing this conversion does not make sense,
     and this will be noted in the documentation for particular types
     of instance objects.

     If PROPERTY is not a built-in property, then this function will
     simply set its value if LOCALE is `nil'.  However, if LOCALE is
     given, then this function will attempt to add VALUE as the
     instantiator for the given LOCALE, using `add-spec-to-specifier'.
     If the value of the property is not a specifier, it will
     automatically be converted into a `generic' specifier.

 -- Function: remove-face-property face property &optional locale
          tag-set exact-p
     This function removes a property of a FACE.

     For built-in properties, this is analogous to `remove-specifier'.
     For more information, *Note Other Specification Functions::.

     When PROPERTY is not a built-in property, this function will just
     remove its value if LOCALE is `nil' or `all'.  However, if LOCALE
     is other than that, this function will attempt to remove VALUE as
     the instantiator for the given LOCALE with `remove-specifier'.  If
     the value of the property is not a specifier, it will be converted
     into a `generic' specifier automatically.

 -- Function: face-property face property &optional locale tag-set
          exact-p
     This function returns FACE's value of the given PROPERTY.

     If LOCALE is omitted, the FACE's actual value for PROPERTY will be
     returned.  For built-in properties, this will be a specifier
     object of a type appropriate to the property (e.g. a font or color
     specifier).  For other properties, this could be anything.

     If LOCALE is supplied, then instead of returning the actual value,
     the specification(s) for the given locale or locale type will be
     returned.  This will only work if the actual value of PROPERTY is
     a specifier (this will always be the case for built-in properties,
     but not or not may apply to user-defined properties).  If the
     actual value of PROPERTY is not a specifier, this value will
     simply be returned regardless of LOCALE.

     The return value will be a list of instantiators (e.g. strings
     specifying a font or color name), or a list of specifications,
     each of which is a cons of a locale and a list of instantiators.
     Specifically, if LOCALE is a particular locale (a buffer, window,
     frame, device, or `global'), a list of instantiators for that
     locale will be returned.  Otherwise, if LOCALE is a locale type
     (one of the symbols `buffer', `window', `frame', or `device'), the
     specifications for all locales of that type will be returned.
     Finally, if LOCALE is `all', the specifications for all locales of
     all types will be returned.

     The specifications in a specifier determine what the value of
     PROPERTY will be in a particular "domain" or set of circumstances,
     which is typically a particular Emacs window along with the buffer
     it contains and the frame and device it lies within.  The value is
     derived from the instantiator associated with the most specific
     locale (in the order buffer, window, frame, device, and `global')
     that matches the domain in question.  In other words, given a
     domain (i.e. an Emacs window, usually), the specifier for PROPERTY
     will first be searched for a specification whose locale is the
     buffer contained within that window; then for a specification
     whose locale is the window itself; then for a specification whose
     locale is the frame that the window is contained within; etc.  The
     first instantiator that is valid for the domain (usually this
     means that the instantiator is recognized by the device [i.e. the
     X server or TTY device] that the domain is on).  The function
     `face-property-instance' actually does all this, and is used to
     determine how to display the face.

 -- Function: face-property-instance face property &optional domain
          default no-fallback
     This function returns the instance of FACE's PROPERTY in the
     specified DOMAIN.

     Under most circumstances, DOMAIN will be a particular window, and
     the returned instance describes how the specified property
     actually is displayed for that window and the particular buffer in
     it.  Note that this may not be the same as how the property
     appears when the buffer is displayed in a different window or
     frame, or how the property appears in the same window if you
     switch to another buffer in that window; and in those cases, the
     returned instance would be different.

     The returned instance will typically be a color-instance,
     font-instance, or pixmap-instance object, and you can query it
     using the appropriate object-specific functions.  For example, you
     could use `color-instance-rgb-components' to find out the RGB
     (red, green, and blue) components of how the `background' property
     of the `highlight' face is displayed in a particular window.  The
     results might be different from the results you would get for
     another window (perhaps the user specified a different color for
     the frame that window is on; or perhaps the same color was
     specified but the window is on a different X server, and that X
     server has different RGB values for the color from this one).

     DOMAIN defaults to the selected window if omitted.

     DOMAIN can be a frame or device, instead of a window.  The value
     returned for a such a domain is used in special circumstances when
     a more specific domain does not apply; for example, a frame value
     might be used for coloring a toolbar, which is conceptually
     attached to a frame rather than a particular window.  The value is
     also useful in determining what the value would be for a
     particular window within the frame or device, if it is not
     overridden by a more specific specification.

     If PROPERTY does not name a built-in property, its value will
     simply be returned unless it is a specifier object, in which case
     it will be instanced using `specifier-instance'.

     Optional arguments DEFAULT and NO-FALLBACK are the same as in
     `specifier-instance'.  *Note Specifiers::.

\1f
File: lispref.info,  Node: Face Convenience Functions,  Next: Other Face Display Functions,  Prev: Face Properties,  Up: Faces

49.1.4 Face Convenience Functions
---------------------------------

 -- Command: set-face-foreground face color &optional locale tag-set
          how-to-add
 -- Command: set-face-background face color &optional locale tag-set
          how-to-add
     These functions set the foreground (respectively, background)
     color of face FACE to COLOR.  The argument COLOR should be a
     string (the name of a color) or a color object as returned by
     `make-color' (*note Colors::).

 -- Command: set-face-background-pixmap face pixmap &optional locale
          tag-set how-to-add
     This function sets the background pixmap of face FACE to PIXMAP.
     The argument PIXMAP should be a string (the name of a bitmap or
     pixmap file; the directories listed in the variable
     `x-bitmap-file-path' will be searched) or a glyph object as
     returned by `make-glyph' (*note Glyphs::).  The argument may also
     be a list of the form `(WIDTH HEIGHT DATA)' where WIDTH and HEIGHT
     are the size in pixels, and DATA is a string, containing the raw
     bits of the bitmap.

     Similarly to how the glyph's image specifier works *Note Creating
     Glyphs::, you don't create your own image specifier, but rather add
     specifications to the existing one.  Note that the image instance
     that is generated in order to actually display the background
     pixmap is of type `mono-pixmap', meaning that it's a two-color
     image and the foreground and background of the image get filled in
     with the corresponding colors from the face.  (#### Is this still
     true?)

 -- Command: set-face-font face font &optional locale tag-set how-to-add
     This function sets the font of face FACE.  The argument FONT
     should be a string or a font object as returned by `make-font'
     (*note Fonts::).

 -- Command: set-face-underline-p face underline-p &optional locale
          tag-set how-to-add
     This function sets the underline property of face FACE.

 -- Function: face-foreground face &optional locale tag-set exact-p
 -- Function: face-background face &optional locale tag-set exact-p
     These functions return the foreground (respectively, background)
     color specifier of face FACE.  *Note Colors::.

 -- Function: face-background-pixmap face &optional locale tag-set
          exact-p
     This function returns the background-pixmap image specifier of face
     FACE.

 -- Function: face-font face &optional locale tag-set exact-p
     This function returns the font specifier of face FACE.  (Note:
     This is not the same as the function `face-font' in FSF Emacs.)

     *Note Fonts::.

 -- Function: face-font-name face &optional domain
     This function returns the name of the font of face FACE, or `nil'
     if it is unspecified.  This is basically equivalent to `(font-name
     (face-font FACE) DOMAIN)' except that it does not cause an error
     if FACE's font is `nil'. (This function is named `face-font' in
     FSF Emacs.)

 -- Function: face-underline-p face &optional locale
     This function returns the underline property of face FACE.

 -- Function: face-foreground-instance face &optional domain
 -- Function: face-background-instance face &optional domain
     These functions return the foreground (respectively, background)
     color specifier of face FACE.  *Note Colors::.

 -- Function: face-background-pixmap-instance face &optional domain
     This function return the background-pixmap glyph object of face
     FACE.

 -- Function: face-font-instance face &optional domain
     This function returns the font specifier of face FACE.  *Note
     Fonts::.

\1f
File: lispref.info,  Node: Other Face Display Functions,  Prev: Face Convenience Functions,  Up: Faces

49.1.5 Other Face Display Functions
-----------------------------------

 -- Command: invert-face face &optional locale
     Swap the foreground and background colors of face FACE.  If the
     face doesn't specify both foreground and background, then its
     foreground and background are set to the default background and
     foreground.

 -- Function: face-equal face1 face2 &optional domain
     This returns `t' if the faces FACE1 and FACE2 will display in the
     same way.  DOMAIN is as in `face-property-instance'.

 -- Function: face-differs-from-default-p face &optional domain
     This returns `t' if the face FACE displays differently from the
     default face.  DOMAIN is as in `face-property-instance'.

\1f
File: lispref.info,  Node: Fonts,  Next: Colors,  Prev: Faces,  Up: Faces and Window-System Objects

49.2 Fonts
==========

This section describes how to work with font specifier and font
instance objects, which encapsulate fonts in the window system.

* Menu:

* Font Specifiers::             Specifying how a font will appear.
* Font Instances::              What a font specifier gets instanced as.
* Font Instance Names::         The name of a font instance.
* Font Instance Size::          The size of a font instance.
* Font Instance Characteristics:: Display characteristics of font instances.
* Font Convenience Functions::  Convenience functions that automatically
                                  instance and retrieve the properties
                                  of a font specifier.

\1f
File: lispref.info,  Node: Font Specifiers,  Next: Font Instances,  Up: Fonts

49.2.1 Font Specifiers
----------------------

 -- Function: font-specifier-p object
     This predicate returns `t' if OBJECT is a font specifier, and
     `nil' otherwise.

 -- Function: make-font-specifier spec-list
     Return a new `font' specifier object with the given specification
     list.  SPEC-LIST can be a list of specifications (each of which is
     a cons of a locale and a list of instantiators), a single
     instantiator, or a list of instantiators.  *Note Specifiers::, for
     more information about specifiers.

     Valid instantiators for font specifiers are:

        * A string naming a font (e.g. under X this might be
          "-*-courier-medium-r-*-*-*-140-*-*-*-*-iso8859-*" for a
          14-point upright medium-weight Courier font).

        * A font instance (use that instance directly if the device
          matches, or use the string that generated it).

        * A vector of no elements (only on TTY's; this means to set no
          font at all, thus using the "natural" font of the terminal's
          text).

        * A vector of one element (a face to inherit from).

\1f
File: lispref.info,  Node: Font Instances,  Next: Font Instance Names,  Prev: Font Specifiers,  Up: Fonts

49.2.2 Font Instances
---------------------

 -- Function: font-instance-p object
     This predicate returns `t' if OBJECT is a font instance, and `nil'
     otherwise.

 -- Function: make-font-instance name &optional device noerror
     This function creates a new font-instance object of the specified
     name.  DEVICE specifies the device this object applies to and
     defaults to the selected device.  An error is signalled if the
     font is unknown or cannot be allocated; however, if NOERROR is
     non-`nil', `nil' is simply returned in this case.

     The returned object is a normal, first-class lisp object.  The way
     you "deallocate" the font is the way you deallocate any other lisp
     object: you drop all pointers to it and allow it to be garbage
     collected.  When these objects are GCed, the underlying X data is
     deallocated as well.

\1f
File: lispref.info,  Node: Font Instance Names,  Next: Font Instance Size,  Prev: Font Instances,  Up: Fonts

49.2.3 Font Instance Names
--------------------------

 -- Function: list-fonts pattern &optional device
     This function returns a list of font names matching the given
     pattern.  DEVICE specifies which device to search for names, and
     defaults to the currently selected device.

 -- Function: font-instance-name font-instance
     This function returns the name used to allocate FONT-INSTANCE.

 -- Function: font-instance-truename font-instance
     This function returns the canonical name of the given font
     instance.  Font names are patterns which may match any number of
     fonts, of which the first found is used.  This returns an
     unambiguous name for that font (but not necessarily its only
     unambiguous name).

\1f
File: lispref.info,  Node: Font Instance Size,  Next: Font Instance Characteristics,  Prev: Font Instance Names,  Up: Fonts

49.2.4 Font Instance Size
-------------------------

 -- Function: x-font-size font
     This function returns the nominal size of the given font.  This is
     done by parsing its name, so it's likely to lose.  X fonts can be
     specified (by the user) in either pixels or 10ths of points, and
     this returns the first one it finds, so you have to decide which
     units the returned value is measured in yourself ...

 -- Function: x-find-larger-font font &optional device
     This function loads a new, slightly larger version of the given
     font (or font name).  Returns the font if it succeeds, `nil'
     otherwise.  If scalable fonts are available, this returns a font
     which is 1 point larger.  Otherwise, it returns the next larger
     version of this font that is defined.

 -- Function: x-find-smaller-font font &optional device
     This function loads a new, slightly smaller version of the given
     font (or font name).  Returns the font if it succeeds, `nil'
     otherwise.  If scalable fonts are available, this returns a font
     which is 1 point smaller.  Otherwise, it returns the next smaller
     version of this font that is defined.

\1f
File: lispref.info,  Node: Font Instance Characteristics,  Next: Font Convenience Functions,  Prev: Font Instance Size,  Up: Fonts

49.2.5 Font Instance Characteristics
------------------------------------

 -- Function: font-instance-properties font-instance
     This function returns the properties (an alist or `nil') of
     FONT-INSTANCE.

 -- Function: x-make-font-bold font &optional device
     Given an X font specification, this attempts to make a "bold" font.
     If it fails, it returns `nil'.

 -- Function: x-make-font-unbold font &optional device
     Given an X font specification, this attempts to make a non-bold
     font.  If it fails, it returns `nil'.

 -- Function: x-make-font-italic font &optional device
     Given an X font specification, this attempts to make an "italic"
     font.  If it fails, it returns `nil'.

 -- Function: x-make-font-unitalic font &optional device
     Given an X font specification, this attempts to make a non-italic
     font.  If it fails, it returns `nil'.

 -- Function: x-make-font-bold-italic font &optional device
     Given an X font specification, this attempts to make a
     "bold-italic" font.  If it fails, it returns `nil'.

\1f
File: lispref.info,  Node: Font Convenience Functions,  Prev: Font Instance Characteristics,  Up: Fonts

49.2.6 Font Convenience Functions
---------------------------------

 -- Function: font-name font &optional domain
     This function returns the name of the FONT in the specified
     DOMAIN, if any.  FONT should be a font specifier object and DOMAIN
     is normally a window and defaults to the selected window if
     omitted.  This is equivalent to using `specifier-instance' and
     applying `font-instance-name' to the result.

 -- Function: font-truename font &optional domain
     This function returns the truename of the FONT in the specified
     DOMAIN, if any.  FONT should be a font specifier object and DOMAIN
     is normally a window and defaults to the selected window if
     omitted.  This is equivalent to using `specifier-instance' and
     applying `font-instance-truename' to the result.

 -- Function: font-properties font &optional domain
     This function returns the properties of the FONT in the specified
     DOMAIN, if any.  FONT should be a font specifier object and DOMAIN
     is normally a window and defaults to the selected window if
     omitted.  This is equivalent to using `specifier-instance' and
     applying `font-instance-properties' to the result.

\1f
File: lispref.info,  Node: Colors,  Prev: Fonts,  Up: Faces and Window-System Objects

49.3 Colors
===========

* Menu:

* Color Specifiers::            Specifying how a color will appear.
* Color Instances::             What a color specifier gets instanced as.
* Color Instance Properties::   Properties of color instances.
* Color Convenience Functions:: Convenience functions that automatically
                                  instance and retrieve the properties
                                  of a color specifier.

\1f
File: lispref.info,  Node: Color Specifiers,  Next: Color Instances,  Up: Colors

49.3.1 Color Specifiers
-----------------------

 -- Function: color-specifier-p object
     This function returns non-`nil' if OBJECT is a color specifier.

 -- Function: make-color-specifier spec-list
     Return a new `color' specifier object with the given specification
     list.  SPEC-LIST can be a list of specifications (each of which is
     a cons of a locale and a list of instantiators), a single
     instantiator, or a list of instantiators.  *Note Specifiers::, for
     a detailed description of how specifiers work.

     Valid instantiators for color specifiers are:

        * A string naming a color (e.g. under X this might be
          "lightseagreen2" or "#F534B2").

        * A color instance (use that instance directly if the device
          matches, or use the string that generated it).

        * A vector of no elements (only on TTY's; this means to set no
          color at all, thus using the "natural" color of the
          terminal's text).

        * A vector of one or two elements: a face to inherit from, and
          optionally a symbol naming which property of that face to
          inherit, either `foreground' or `background' (if omitted,
          defaults to the same property that this color specifier is
          used for; if this specifier is not part of a face, the
          instantiator would not be valid).

 -- Function: make-face-boolean-specifier spec-list
     Return a new `face-boolean' specifier object with the given spec
     list.  SPEC-LIST can be a list of specifications (each of which is
     a cons of a locale and a list of instantiators), a single
     instantiator, or a list of instantiators.  *Note Specifiers::, for
     a detailed description of how specifiers work.

     Valid instantiators for face-boolean specifiers are

        * t or nil.

        * A vector of two or three elements: a face to inherit from,
          optionally a symbol naming the property of that face to
          inherit from (if omitted, defaults to the same property that
          this face-boolean specifier is used for; if this specifier is
          not part of a face, the instantiator would not be valid), and
          optionally a value which, if non-`nil', means to invert the
          sense of the inherited property.


\1f
File: lispref.info,  Node: Color Instances,  Next: Color Instance Properties,  Prev: Color Specifiers,  Up: Colors

49.3.2 Color Instances
----------------------

A "color-instance object" is an object describing the way a color
specifier is instanced in a particular domain.  Functions such as
`face-background-instance' return a color-instance object.  For example,

     (face-background-instance 'default (next-window))
         => #<color-instance moccasin 47=(FFFF,E4E4,B5B5) 0x678d>

   The color-instance object returned describes the way the background
color of the `default' face is displayed in the next window after the
selected one.

 -- Function: color-instance-p object
     This function returns non-`nil' if OBJECT is a color-instance.

\1f
File: lispref.info,  Node: Color Instance Properties,  Next: Color Convenience Functions,  Prev: Color Instances,  Up: Colors

49.3.3 Color Instance Properties
--------------------------------

 -- Function: color-instance-name color-instance
     This function returns the name used to allocate COLOR-INSTANCE.

 -- Function: color-instance-rgb-components color-instance
     This function returns a three element list containing the red,
     green, and blue color components of COLOR-INSTANCE.

          (color-instance-rgb-components
            (face-background-instance 'default (next-window)))
              => (65535 58596 46517)

\1f
File: lispref.info,  Node: Color Convenience Functions,  Prev: Color Instance Properties,  Up: Colors

49.3.4 Color Convenience Functions
----------------------------------

 -- Function: color-name color &optional domain
     This function returns the name of the COLOR in the specified
     DOMAIN, if any.  COLOR should be a color specifier object and
     DOMAIN is normally a window and defaults to the selected window if
     omitted.  This is equivalent to using `specifier-instance' and
     applying `color-instance-name' to the result.

 -- Function: color-rgb-components color &optional domain
     This function returns the RGB components of the COLOR in the
     specified DOMAIN, if any.  COLOR should be a color specifier
     object and DOMAIN is normally a window and defaults to the
     selected window if omitted.  This is equivalent to using
     `specifier-instance' and applying `color-instance-rgb-components'
     to the result.

          (color-rgb-components (face-background 'default (next-window)))
              => (65535 58596 46517)

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File: lispref.info,  Node: Glyphs,  Next: Annotations,  Prev: Faces and Window-System Objects,  Up: Top

50 Glyphs
*********

A "glyph" is an object that is used for pixmaps, widgets, and images of
all sorts, as well as for things that "act" like pixmaps, such as
non-textual strings ("annotations") displayed in a buffer or in the
margins.  It is used in begin-glyphs and end-glyphs attached to
extents, marginal and textual annotations, overlay arrows
(`overlay-arrow-*' variables), toolbar buttons, mouse pointers, frame
icons, truncation and continuation markers, and the like.  Basically,
any place there is an image or something that acts like an image, there
will be a glyph object representing it.

 -- Function: glyphp object
     This function returns `t' if OBJECT is a glyph.

* Menu:

* Glyph Intro::         Glyphs are abstract image specifications.
* Images::              Specifying the appearance of glyphs.
* Using Glyphs::        Creating and displaying glyphs.
* Manipulating Glyphs:: Getting and setting glyph properties.
* Glyph Examples::      Examples of how to work with glyphs.

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File: lispref.info,  Node: Glyph Intro,  Next: Images,  Up: Glyphs

50.1 Glyph Introduction
=======================

In XEmacs, "glyph" does *not* refer to a single unit of textual display
(the XEmacs term for that is "rune", and runes are confined to the
internal implementation of redisplay), but rather is an object
encapsulating a graphical element, such as an image or widget (an
active GUI element such as a button or text entry field; X11 calls this
a "widget", while MS Windows uses the term "control").  This graphical
element could appear in a buffer, a margin, a gutter, or a toolbar, or
even externally to XEmacs as a mouse pointer or an icon, for example.

   On the other hand, by contrast with GNU Emacs 21, an XEmacs glyph is
not "just" an image.  The actual image that is displayed (as opposed to
its position or clipping) is defined by an "image specifier" object
contained within the glyph.  The separation between an image specifier
object and a glyph object is made because the glyph includes other
properties than just the actual image: e.g. the face it is displayed in,
the alignment of the image, _etc_.  Also, an image specifier is used in
at least one place in XEmacs in lieu of a glyph, namely the backing
pixmap of a face.

   An image specifier is used because glyphs often have locale-specific
semantics.  The most important example is semantics determined by the
display device: you can't usefully display a JPEG on stdout, or a color
image on a monochrome display.  But because the image property is a
specifier in XEmacs, you can specify that a given glyph appear as a
monochrome image on monochrome displays, a color image on color
displays, and as a string on TTYs.  (Specifying a string for the `tty'
device locale would give behavior like the `ALT' attribute of an `IMG'
element in HTML.)  Another is semantics determined by the buffer or
mode.  (Unfortunately, currently there are no compelling examples of
this for glyphs.)

   All this means that only one global glyph needs to exist for a
particular purpose (e.g. the icon used to represent an iconified frame,
the mouse pointer used over particular areas of a frame, etc.).  Often
you need not (and should not!) create your own glyph, but rather modify
an existing one.

   In working with glyphs it is important to keep in mind the
distinction between a locale and a domain.  A "locale" is specified by
the programmer, and is an abstract link between a specification (for a
glyph, its visual appearance) and a displayable object.  The displayable
object may be a buffer or a window, or an object containing buffers or
windows such as frame, device, or console.  A "domain" is an actual
display context, which must be concrete enough to enable XEmacs to
identify the device type.  (Buffers may be displayed in windows on
different devices, even simultaneously, so a buffer cannot be a domain.
Similarly, the global locale cannot be a domain.)  *Note Specifiers::,
for more information about specifier locales and domains.

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File: lispref.info,  Node: Images,  Next: Using Glyphs,  Prev: Glyph Intro,  Up: Glyphs

50.2 Images
===========

* Menu:

* Image Specifiers::                    Specifying an image's appearance.
* Image Instantiator Conversion::       Lazy realization of graphics.
* Image Instantiator Formats::          A catalog of image descriptors.
* Image Instances::                     Classes of graphical objects.

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File: lispref.info,  Node: Image Specifiers,  Next: Image Instantiator Conversion,  Up: Images

50.2.1 Image Specifiers
-----------------------

An image specifier is a description of the actual graphical realization
of a glyph.  For example, a typical image description is _the file
system path to a PNG file_.  Since redisplay doesn't know about files,
and in any case the image may need to be manipulated (_e.g._, a face's
background pixmap must be clipped and tiled), the PNG file must be
converted internally to a window system bitmap or pixmap object.  We
describe this process by writing that when XEmacs displays the image,
it "instantiates" the "image instantiator" into an "image instance".
Image instances are an internal object type (similar to font instances
and color instances), describing how the image appears in a particular
domain.  On the other hand, image instantiators, which are just
descriptions of how the image should appear, are represented using Lisp
strings or vectors.

   Furthermore the graphical realization will vary, and for some devices
may not even be a bitmapped graphic.  These variations may be controlled
by the program by specifying different "image instantiators" in
different locales.  This is implemented with an "image specifier", a
specifier whose specifications are image instantiators.

   Image specifiers are rarely if ever found by themselves.  However, an
image specifier results from calling `glyph-image' on a glyph, or
retrieving the `background-pixmap' property of a face, and you can
check if some random object is an image specifier.

 -- Function: image-specifier-p object
     This function returns non-`nil' if OBJECT is an image specifier.

 -- Function: make-image-specifier spec-list
     This function creates a new image specifier object and initializes
     it according to SPEC-LIST.  *Note Specifiers::.

   This function exists mainly for completeness.  In practice, you
rarely, if ever, need to actually create an image specifier.  Instead,
they are implicitly created by the initialization of glyphs and faces,
and the specifier member of these objects cannot be changed after
initialization; you may only set the specifications it contains.

   Image instantiators come in many formats: `xbm', `xpm', `gif',
`jpeg', etc.  These denote the format of the data describing the image.
The resulting image instances also come in many types--`mono-pixmap',
`color-pixmap', `text', `pointer', etc.  This refers to the behavior of
the image and the sorts of places it can appear. (For example, a
color-pixmap image has fixed colors specified for it, while a
mono-pixmap image comes in two unspecified shades "foreground" and
"background" that are determined from the face of the glyph or
surrounding text; a text image appears as a string of text and has an
unspecified foreground, background, and font; a pointer image behaves
like a mono-pixmap image but can only be used as a mouse pointer
[mono-pixmap images cannot be used as mouse pointers]; etc.)

   It is important to keep the distinction between image instantiator
format and image instance type in mind.  Typically, a given image
instantiator format can result in many different image instance types.
For example, `xpm' can be instanced as `color-pixmap', `mono-pixmap',
or `pointer'; whereas `cursor-font' can be instanced only as `pointer'.
On the other hand, a particular image instance type can be generated
by many different image instantiator formats (e.g.  `color-pixmap' can
be generated by `xpm', `gif', `jpeg', etc.).

   *Note Image Instances::, for a more detailed discussion of image
instance types.

   An image instantiator should be a string or a vector of the form

      `[FORMAT :KEYWORD VALUE ...]'

   i.e. a format symbol followed by zero or more alternating
keyword-value pairs.

   The form of an instantiator can be checked with
`valid-instantiator-p' with a TYPE of `image', *Note Specifier
Validation Functions::.

   For a complete list of the format symbols and their usage, *Note
Image Instantiator Formats::.

   If the instantiator is a string, it will be converted into a vector
by looking it up according to the specs in the
`console-type-image-conversion-list' for the console type of the domain
(usually a window; sometimes a frame or device) over which the image is
being instantiated.

   If the instantiator specifies data from a file, the data will be
read in at the time that the instantiator is added to the image
specifier (which may be well before the image is actually displayed),
and the instantiator will be converted into one of the inline-data
forms, with the filename retained using a `:file' keyword.  This
implies that the file must exist when the instantiator is added to the
image, but does not need to exist at any other time (e.g. it may safely
be a temporary file).

   The available keywords are given below.  Note that some keywords are
generally available (for example, the `:data' keyword may be used with
any format except `nothing'), while others are only available for one
format (`resource-id' is unique to the `mswindows-resource' format).

`:data'
     Inline image data.  If available for a given format, it may be
     specified directly by the program, or it may be a cache of file
     data previously read.  When present, it is used to instantiate the
     image in preference to the file named by the `:file' property.

     The format of inline data is image-format-specific.  For example,
     in pixmap formats, the value should be a string, which is
     interpreted as an octet-stream representing a bitmap or pixmap.
     But for text formats, it's string containing the text to be
     displayed, and for resource formats, it's a string containing the
     name of the resource.

`:file'
     Data contained in a file.  The value is the name of this file.  If
     both `:data' and `:file' are specified, the image is created from
     what is specified in `:data' and the string in `:file' becomes the
     value of the `image-instance-file-name' function when applied to
     the resulting image-instance.  Note that there is nothing to stop a
     program from changing either the `:file' or the `:data' property,
     and there is no way to detect such mischief.  This means that the
     data will _not_ be automatically reread if you change the `file'
     property; you must force it by removing the `:data' property.
     (One way to do this is replacing the whole specification with a new
     vector.)  This keyword is not valid for instantiator formats
     `nothing', `string', `formatted-string', `cursor-font', `font',
     and `autodetect'.

`:mask-data'
     Inline data for `xbm' and `xface'.  This specifies a mask to be
     used with the bitmap.  Pixels which are not set in the mask will
     not be written to the imaging device.  The format is a list of
     width, height, and bits, as for `:data'.

`:mask-file'
     For `xbm' and `xface'.  This specifies a file containing the mask
     data.  If neither a mask file nor inline mask data is given for an
     XBM image, and the XBM image comes from a file, XEmacs will look
     for a mask file with the same name as the image file but with
     `Mask' or `msk' appended.  For example, if you specify the XBM file
     `left_ptr' [usually located in `/usr/include/X11/bitmaps'], the
     associated mask file `left_ptrmsk' will automatically be picked up.

`:resource-id'
     Only for `mswindows-resource'.  This must be either an integer
     (which directly specifies a resource number) or a string.  See the
     description of `mswindows-resource' for valid strings.  *Note
     Image Instantiator Formats::.

`:foreground'
`:background'
     For `xbm', `xface', `cursor-font', and `font'.  These keywords
     allow you to explicitly specify foreground and background colors.
     The value should be anything acceptable to `make-color-instance'.
     This will cause an external format that would by default be
     instantiated as a `mono-pixmap' to instead be instantiated as a
     two-color color-pixmap.  This can be used to override the colors
     specified by a glyph's face, for example.  If the image is
     instantiated as a pointer, they specify its foreground and/or
     background, instead of the defaults of black and white.

`:hotspot-x'
`:hotspot-y'
     For `xbm' and `xface'.  These keywords specify a hotspot if the
     image is instantiated as a `pointer'.  Note that if the XBM image
     file specifies a hotspot, it will automatically be picked up if no
     explicit hotspot is given.

`:color-symbols'
     Only for `xpm'.  This specifies an alist that maps strings that
     specify symbolic color names to the actual color to be used for
     that symbolic color (in the form of a string or a color-specifier
     object).  If this is not specified, the contents of
     `xpm-color-symbols' are used to generate the alist.

`:resource-type'
     Only for `mswindows-resource'.  This must be a symbol, either
     `cursor', `icon', or `bitmap', specifying the type of resource to
     be retrieved.

`:face'
     For `inherit' and the widget formats.  This specifies the face to
     inherit from.  For widgets this specifies the face to use for
     display.  It defaults to gui-element-face.

`:selected'
`:active'
`:suffix'
`:keys'
`:style'
`:filter'
`:config'
`:included'
`:key-sequence'
`:accelerator'
`:label'
`:callback'
     These keywords, accepted as menu item specs, are also accepted by
     images instantiated as `widget'.  For their semantics, *Note Menu
     Format::.

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File: lispref.info,  Node: Image Instantiator Conversion,  Next: Image Instantiator Formats,  Prev: Image Specifiers,  Up: Images

50.2.2 Image Instantiator Conversion
------------------------------------

Conversion is applied to image instantiators at the time they are added
to an image specifier or at the time they are passed to
`make-image-instance'.

 -- Function: set-console-type-image-conversion-list console-type list
     This function sets the image-conversion-list for consoles of the
     given CONSOLE-TYPE.  The image-conversion-list specifies how image
     instantiators that are strings should be interpreted.  Each
     element of the list should be a list of two elements (a regular
     expression string and a vector) or a list of three elements (the
     preceding two plus an integer index into the vector).  The string
     is converted to the vector associated with the first matching
     regular expression.  If a vector index is specified, the string
     itself is substituted into that position in the vector.

     Note: The conversion above is applied when the image instantiator
     is added to an image specifier, not when the specifier is actually
     instantiated.  Therefore, changing the image-conversion-list only
     affects newly-added instantiators.  Existing instantiators in
     glyphs and image specifiers will not be affected.

 -- Function: console-type-image-conversion-list console-type
     This function returns the image-conversion-list for consoles of
     the given CONSOLE-TYPE.

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File: lispref.info,  Node: Image Instantiator Formats,  Next: Image Instances,  Prev: Image Instantiator Conversion,  Up: Images

50.2.3 Image Instantiator Formats
---------------------------------

The "format" field of an image instantiator should be a symbol denoting
a valid format.  Which formats are valid will depend on the features
(such as image decoding libraries) available, on platform support (MS
Windows resource IDs make no sense on other platforms), and on the
locale.

 -- Function: valid-image-instantiator-format-p format &optional locale
     This function returns non-`nil' if FORMAT is a valid image
     instantiator format.

     If LOCALE is non-`nil' then the format is checked in that locale.
     If LOCALE is `nil' the current console is used.

     Note that the return value for many formats listed above depends on
     whether XEmacs was compiled with support for that format.

 -- Function: image-instantiator-format-list
     This function returns a list of valid image-instantiator formats.

   Here is a table of image-instantiator formats, giving the keywords
that are usable with each, and the kinds of instances that may result.

`nothing'
     Don't display anything; no keywords are valid for this format.
     Can only be instanced as `nothing'.

`string'
     Display this image as a text string.  Can only be instanced as
     `text', although support for instancing as `mono-pixmap' should be
     added.  The valid keyword is `:data'.  The value should be a
     string, and it is interpreted as a string of characters.

`formatted-string'
     Display this image as a text string with replaceable fields,
     similar to a modeline format string.  The valid keyword is `:data'.
     The value should be a string, and it is interpreted as a string of
     characters containing format sequences.

     Not currently implemented.

`xbm'
     An X bitmap; available only if X support was compiled into this
     XEmacs.

     If used in a buffer glyph, icon glyph, or face background pixmap,
     it will be instantiated as `mono-pixmap' unless the `:foreground'
     or `:background' keywords are present.  In the latter case it will
     be instantiated as `color-pixmap' with the two specified colors.
     (Probably if `:foreground' or `:background' is omitted, it
     defaults to black or white respectively.)  If used in a pointer
     glyph, it will be instantiated as an `pointer'.

     The valid keywords and their values are
    `:data'
          A list containing the height and width of the bitmap as
          integers, and a string interpreted as a bit vector according
          to the X11 standard XBM bitmap format, in that order.

    `:file'
          The name of a file containing standard XBM-format data.  If
          it contains a hotspot specification, it will be parsed and
          used if the hotspot is not explicitly specified.

    `:mask-data'
          A list containing the height and width of the bitmap as
          integers, and a string interpreted as a bit vector according
          to the X11 standard XBM bitmap format, in that order.  This
          bitmap is interpreted as the clipping region for the bitmap
          contained in the `:data' property.

    `:mask-file'
          The name of a file containing standard XBM-format data.
          Interpreted as the clipping region for the bitmap contained
          in the `:data' property.

    `:foreground'
    `:background'
          These keywords allow you to explicitly specify foreground and
          background colors.  The values should be acceptable to
          `make-color-instance'.

    `:hotspot-x'
    `:hotspot-y'
          Integers denoting the hotspot (mouse pointer position), with
          (0,0) at the top left corner.  If given, these override any
          specification in the XBM file.

`xpm'
     An XPM pixmap; only available if XPM support was compiled into
     this XEmacs.

     Can be instanced as `color-pixmap', `mono-pixmap', or `pointer'.

     XPM is an add-on library for X that was designed to rectify the
     shortcomings of the XBM format.  Many icons and labels used in the
     XEmacs GUI are still distributed in XPM format (although we are
     moving to standardize on the PNG format).  It is therefore highly
     desirable that XPM be available in your XEmacs.

     Most implementations of X include the XPM library as a standard
     part.  If your vendor does not, it is highly recommended that you
     download it and install it.  You can get it from the XEmacs FTP
     site and mirrors, as well as from most sites that distribute X11.

     The valid keywords and their values are
    `:data'
          A string interpreted as the contents of a standard XPM file.

    `:file'
          The name of a file containing standard XPM-format data.  If
          it contains a hotspot specification, it will be parsed and
          used if the hotspot is not explicitly specified.

    `:hotspot-x'
    `:hotspot-y'
          Integers denoting the hotspot (mouse pointer position), with
          (0,0) at the top left corner.  If given, these override any
          specification in the XBM file.  (This may not be true.  The
          original documentation doesn't mention them in connection
          with XPM, but a pointer needs a hotspot.)

    `:color-symbols'
          An alist that maps the one- or two-character strings that
          specify symbolic color names in the XPM file to the actual
          color to be used for that symbolic color (in the form of a
          string acceptable as a color instantiator, *Note Color
          Specifiers::, or a color-specifier object).  If this is not
          specified, the contents of `xpm-color-symbols' are used to
          generate the alist.

`xface'
     An X-Face bitmap, used to encode people's faces in e-mail messages;
     only available if X-Face support was compiled into this XEmacs.

     Will be instanced as `mono-pixmap', `color-pixmap', or `pointer',
     depending on the target instance type and the presence of color
     keywords.

     The valid keywords and their values are
    `:data'
          A list containing the height and width of the bitmap as
          integers, and a string interpreted as a bit vector according
          to the X11 standard XBM bitmap format, in that order.

    `:file'
          The name of a file containing standard XBM-format data.  If
          it contains a hotspot specification, it will be parsed and
          used if the hotspot is not explicitly specified.

    `:mask-data'
          A list containing the height and width of the bitmap as
          integers, and a string interpreted as a bit vector according
          to the X11 standard XBM bitmap format, in that order.  This
          bitmap is interpreted as the clipping region for the bitmap
          contained in the `:data' property.

    `:mask-file'
          The name of a file containing standard XBM-format data.
          Interpreted as the clipping region for the bitmap contained
          in the `:data' property.

    `:foreground'
    `:background'
          These keywords allow you to explicitly specify foreground and
          background colors.  The values should be acceptable to
          `make-color-instance'.

    `:hotspot-x'
    `:hotspot-y'
          Integers denoting the hotspot (mouse pointer position), with
          (0,0) at the top left corner.  If given, these override any
          specification in the XBM file.

`gif'
`jpeg'
`png'
`tiff'
     These are GIF87- or GIF89-format, JPEG-format, PNG/GIF24-format,
     and TIFF-format images, respectively.  They are available only if
     appropriate decoding support was built into XEmacs.  XEmacs
     includes GIF decoding functions as a standard part of it, so if
     you have X support, you will normally have GIF support, unless you
     explicitly disable it at configure time.  If you have development
     support (both the libraries and the relevant C header files)
     available when XEmacs is built, the JPEG, PNG, and TIFF libraries
     will automatically be detected (in the "usual places") and linked
     into the build.

     Note that PNG is the standard format for images distributed with
     XEmacs, so it is highly recommended that PNG support be built in.

     All of these instantiators will be instanced as `color-pixmap'.

     The valid keywords and their values are
    `:data'
          A string interpreted as the contents of a file containing
          data in the appropriate standard format.

    `:file'
          The name of a file containing standard-format data.

`cursor-font'
     Most window systems provide a set of standard cursors, which in
     X11 is called a cursor font.  Can only be instanced as `pointer'.
     This should probably be fixed.

     The valid keyword is `:data'.  Its value should be a string
     containing one of the standard cursor-font names, such as `watch'
     or `right_ptr' under X.  More specifically, in the X Window System
     it may be any of the standard cursor names from appendix B of the
     Xlib manual, provided in the file `<X11/cursorfont.h>' by most
     distributions, minus the `XC_' prefix.  For MS Windows, use
     `mswindows-resource' instantiator format, not `cursor-font'.
     Other window systems may have different lists.

`font'
     A glyph from a font; i.e. the name of a font, and glyph index into
     it of the form `FONT fontname index [[mask-font] mask-index]'.
     Only if X support was compiled into this XEmacs.  Currently can
     only be instanced as `pointer'.  This should probably be fixed.

`mswindows-resource'
     An MS Windows pointer resource.  Specifies a resource to retrieve
     directly from the system (an OEM resource) or from a file,
     particularly an executable file.  Can be instanced as `pointer' or
     `color-pixmap'.

     The valid keywords and their values are

    `:resource-type'
          A string naming the type (`cursor', `bitmap', or `icon') of
          the resource.  Required.

    `:file'
          A string containing the name of the file containing the
          resource (often an executable).  If a system resource,
          `:file' should be omitted.

    `:resource-id'
          A string containing the name of a resource.   Required if
          `:file' is not specified.

          This must be either an integer (which directly specifies a
          resource number) or a string.  Valid strings are

          For bitmaps:

          "close", "uparrow", "dnarrow", "rgarrow", "lfarrow",
          "reduce", "zoom", "restore", "reduced", "zoomd", "restored",
          "uparrowd", "dnarrowd", "rgarrowd", "lfarrowd", "mnarrow",
          "combo", "uparrowi", "dnarrowi", "rgarrowi", "lfarrowi",
          "size", "btsize", "check", "checkboxes", and "btncorners".

          For cursors:

          "normal", "ibeam", "wait", "cross", "up", "sizenwse",
          "sizenesw", "sizewe", "sizens", "sizeall", and "no".

          For icons:

          "sample", "hand", "ques", "bang", "note", and "winlogo".

`subwindow'
     An embedded windowing system window.  Can only be instanced as
     `subwindow'.  Not implemented.

`button'
     A button widget; either a push button, radio button or toggle
     button.  Can only be instanced as `widget'.

`combo-box'
     A drop list of selectable items in a widget, for editing text.
     Can only be instanced as `widget'.

`edit-field'
     A text editing widget.  Can only be instanced as `widget'.

`label'
     A static, text-only, widget; for displaying text.  Can only be
     instanced as `widget'.

`layout'
     A widget for controlling the positioning of children underneath it.
     Through the use of nested layouts, a widget hierarchy can be
     created which can have the appearance of any standard dialog box
     or similar arrangement; all of this is counted as one "glyph" and
     could appear in many of the places that expect a single glyph.
     Can only be instanced as `widget'.

`native-layout'
     The native version of a layout widget.  Can only be instanced as
     `widget'.

`progress-gauge'
     A sliding widget, for showing progress.  Can only be instanced as
     `widget'.

`tab-control'
     A tab widget; a series of user selectable tabs.  Can only be
     instanced as `widget'.

`tree-view'
     A folding widget.  Can only be instanced as `widget'.

`scrollbar'
     A scrollbar widget.  Can only be instanced as `widget'.

`autodetect'
     XEmacs tries to guess what format the data is in.  If X support
     exists, the data string will be checked to see if it names a
     filename.  If so, and this filename contains XBM or XPM data, the
     appropriate sort of pixmap or pointer will be created. [This
     includes picking up any specified hotspot or associated mask
     file.] Otherwise, if `pointer' is one of the allowable
     image-instance types and the string names a valid cursor-font
     name, the image will be created as a pointer.  Otherwise, the
     image will be displayed as text.  If no X support exists, the
     image will always be displayed as text.

`inherit'
     Inherit from the background-pixmap property of a face.  Can only be
     instanced as `mono-pixmap'.

   There are two convenience variables for use with the XBM and XPM
image formats.

 -- Variable: xpm-color-symbols
     This variable holds definitions of logical color-names used when
     reading XPM files.  Elements of this list should be of the form
     `(COLOR-NAME FORM-TO-EVALUATE)'.  The COLOR-NAME should be a
     string, which is the name of the color to define; the
     FORM-TO-EVALUATE should evaluate to a color specifier object, or a
     string to be passed to `make-color-instance' (*note Colors::).  If
     a loaded XPM file references a symbolic color called COLOR-NAME,
     it will display as the computed color instead.

     The default value of this variable defines the logical color names
     `"foreground"' and `"background"' to be the colors of the
     `default' face.

 -- Variable: x-bitmap-file-path
     A list of the directories in which X bitmap files may be found.
     If `nil', this is initialized from the `"*bitmapFilePath"'
     resource.  This is used by the `make-image-instance' function
     (however, note that if the environment variable `XBMLANGPATH' is
     set, it is consulted first).

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File: lispref.info,  Node: Image Instances,  Prev: Image Instantiator Formats,  Up: Images

50.2.4 Image Instances
----------------------

Image-instance objects encapsulate the way a particular image (pixmap,
etc.) is displayed on a particular device.

   In most circumstances, you do not need to directly create image
instances; use a glyph instead.  However, it may occasionally be useful
to explicitly create image instances, if you want more control over the
instantiation process.

 -- Function: image-instance-p object
     This function returns non-`nil' if OBJECT is an image instance.

* Menu:

* Image Instance Types::         Each image instances has a particular type.
* Image Instance Functions::     Functions for working with image instances.

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File: lispref.info,  Node: Image Instance Types,  Next: Image Instance Functions,  Up: Image Instances

50.2.4.1 Image Instance Types
.............................

Image instances come in a number of different types.  The type of an
image instance specifies the nature of the image: Whether it is a text
string, a mono pixmap, a color pixmap, etc.

   The valid image instance types are

`nothing'
     Nothing is displayed.

`text'
     Displayed as text.  The foreground and background colors and the
     font of the text are specified independent of the pixmap.
     Typically these attributes will come from the face of the
     surrounding text, unless a face is specified for the glyph in
     which the image appears.

`mono-pixmap'
     Displayed as a mono pixmap (a pixmap with only two colors where the
     foreground and background can be specified independent of the
     pixmap; typically the pixmap assumes the foreground and background
     colors of the text around it, unless a face is specified for the
     glyph in which the image appears).

`color-pixmap'
     Displayed as a color pixmap.

`pointer'
     Used as the mouse pointer for a window.

`subwindow'
     A child window that is treated as an image.  This allows (e.g.)
     another program to be responsible for drawing into the window.
     Not currently implemented.

`widget'
     An active GUI element implemented as a "widget" or "control" of the
     underlying window system.

   The following functions are used to check whether an image instance
type is valid in the running XEmacs.

 -- Function: valid-image-instance-type-p type
     This function returns non-`nil' if TYPE is a valid image instance
     type.

 -- Function: image-instance-type-list
     This function returns a list of the valid image instance types.

   The following functions are used to determine the type of an image
instance.

 -- Function: image-instance-type image-instance
     Return the type of the given image instance.  The return value
     will be one of `nothing', `text', `mono-pixmap', `color-pixmap',
     `pointer', `subwindow', or `widget'.

 -- Function: text-image-instance-p object
     Return non-`nil' if OBJECT is an image instance of type `text'.

 -- Function: mono-pixmap-image-instance-p object
     Return non-`nil' if OBJECT is an image instance of type
     `mono-pixmap'.

 -- Function: color-pixmap-image-instance-p object
     Return non-`nil' if OBJECT is an image instance of type
     `color-pixmap'.

 -- Function: pointer-image-instance-p object
     Return non-`nil' if OBJECT is an image instance of type `pointer'.

 -- Function: subwindow-image-instance-p object
     Return non-`nil' if OBJECT is an image instance of type
     `subwindow'.

 -- Function: nothing-image-instance-p object
     Return non-`nil' if OBJECT is an image instance of type `nothing'.

 -- Function: widget-image-instance-p object
     Return non-`nil' if OBJECT is an image instance of type `widget'.

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File: lispref.info,  Node: Image Instance Functions,  Prev: Image Instance Types,  Up: Image Instances

50.2.4.2 Image Instance Functions
.................................

 -- Function: make-image-instance data &optional domain dest-types
          noerror
     This function creates a new image-instance object.

     DATA is an image instantiator, which describes the image (*note
     Image Specifiers::).

     DEST-TYPES should be a list of allowed image instance types that
     can be generated.  The DEST-TYPES list is unordered.  If multiple
     destination types are possible for a given instantiator, the "most
     natural" type for the instantiator's format is chosen.  These are

    `XBM'
    `xface'
          `mono-pixmap', then `color-pixmap', then `pointer'.

    `XPM'
    `GIF'
    `JPEG'
    `PNG'
    `TIFF'
          `color-pixmap', then `mono-pixmap', then `pointer'.

    `string'
    `formatted-string formats'
          `text', then `mono-pixmap' (not currently implemented), then
          `color-pixmap' (not currently implemented).

    `mswindows-resource'
          For pointer resources, `pointer'.

          For the others, `color-pixmap'.

     The other formats can only be instantiated as one type.

     If you want to control more specifically the order of the types
     into which an image is instantiated, call `make-image-instance'
     repeatedly until it succeeds, passing less and less preferred
     destination types each time.

     If DEST-TYPES is omitted, all possible types are allowed.

     DOMAIN specifies the domain to which the image instance will be
     attached.  This domain is termed the "governing domain".  The type
     of the governing domain depends on the image instantiator format.
     (Although, more correctly, it should probably depend on the image
     instance type.)  For example, pixmap image instances are specific
     to a device, but widget image instances are specific to a
     particular XEmacs window because in order to display such a widget
     when two windows onto the same buffer want to display the widget,
     two separate underlying widgets must be created.  (That's because
     a widget is actually a child window-system window, and all
     window-system windows have a unique existence on the screen.)
     This means that the governing domain for a pixmap image instance
     will be some device (most likely, the only existing device),
     whereas the governing domain for a widget image instance will be
     some XEmacs window.

     If you specify an overly general DOMAIN (e.g. a frame when a
     window was wanted), an error is signaled.  If you specify an overly
     specific DOMAIN (e.g. a window when a device was wanted), the
     corresponding general domain is fetched and used instead.  For
     `make-image-instance', it makes no difference whether you specify
     an overly specific domain or the properly general domain derived
     from it.  However, it does matter when creating an image instance
     by instantiating a specifier or glyph (e.g. with
     `glyph-image-instance'), because the more specific domain causes
     spec lookup to start there and proceed to more general domains.
     (It would also matter when creating an image instance with an
     instantiator format of `inherit', but we currently disallow this.)

     If omitted, DOMAIN defaults to the selected window.

     NOERROR controls what happens when the image cannot be generated.
     If `nil', an error message is generated.  If `t', no messages are
     generated and this function returns `nil'.  If anything else, a
     warning message is generated and this function returns `nil'.

 -- Function: colorize-image-instance image-instance foreground
          background
     This function makes the image instance be displayed in the given
     colors.  Image instances come in two varieties: bitmaps, which are
     1 bit deep which are rendered in the prevailing foreground and
     background colors; and pixmaps, which are of arbitrary depth
     (including 1) and which have the colors explicitly specified.
     This function converts a bitmap to a pixmap.  If the image
     instance was a pixmap already, nothing is done (and `nil' is
     returned).  Otherwise `t' is returned.

   The following functions are

 -- Function: image-instance-name image-instance
     This function returns the name of the given image instance.  The
     name is typically taken from the `:file' property of the
     instantiator if present, otherwise from the `:data' property.

 -- Function: image-instance-domain image-instance
     Return the governing domain of the given IMAGE-INSTANCE.  The
     governing domain of an image instance is the domain that the image
     instance is specific to.  It is _NOT_ necessarily the domain that
     was given to the call to `specifier-instance' that resulted in the
     creation of this image instance.  See `make-image-instance' for
     more information on governing domains.

 -- Function: image-instance-string image-instance
     This function returns the string of the given image instance.
     This will only be non-`nil' for text image instances.

 -- Function: image-instance-file-name image-instance
     This function returns the file name from which IMAGE-INSTANCE was
     read, if known.

 -- Function: image-instance-mask-file-name image-instance
     This function returns the file name from which IMAGE-INSTANCE's
     mask was read, if known.

   Pixmaps are considered to be three-dimensional.  The height and
width of the pixel array that is displayed, and the color depth of its
pixels, are accessed with these functions.

 -- Function: image-instance-depth image-instance
     This function returns the depth of the image instance.  This is 0
     for a mono pixmap, or a positive integer for a color pixmap.

 -- Function: image-instance-height image-instance
     This function returns the height of the image instance, in pixels.

 -- Function: image-instance-width image-instance
     This function returns the width of the image instance, in pixels.

   The hotspot is a point relative to the origin of the pixmap.  When
an image is used as a mouse pointer, the hotspot is the point on the
image that sits over the location that the pointer points to.  This is,
for example, the tip of the arrow or the center of the crosshairs.

   These functions access the coordinates of the hotspot.  They simply
return `nil' for a non-pointer image instance.

 -- Function: image-instance-hotspot-x image-instance
     This function returns the X coordinate of the image instance's
     hotspot, if known.

 -- Function: image-instance-hotspot-y image-instance
     This function returns the Y coordinate of the image instance's
     hotspot, if known.

   Mono pixmaps and pointers may have their foreground and background
colors set when instanced.  Use these functions to access color
information.

 -- Function: image-instance-foreground image-instance
     This function returns the foreground color of IMAGE-INSTANCE, if
     applicable.  This will be a color instance or `nil'.  (It will only
     be non-`nil' for colorized mono pixmaps and for pointers.)

 -- Function: image-instance-background image-instance
     This function returns the background color of IMAGE-INSTANCE, if
     applicable.  This will be a color instance or `nil'.  (It will only
     be non-`nil' for colorized mono pixmaps and for pointers.)

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File: lispref.info,  Node: Using Glyphs,  Next: Manipulating Glyphs,  Prev: Images,  Up: Glyphs

50.3 Using Glyphs
=================

Glyph usage is unfortunately somewhat arcane.  (For discussion of
rationale, *Note Glyphs: (Internals)Glyphs.)  Because they are not
"text," they cannot be inserted directly into a buffer.  Instead, they
are values of properties of extents attached to buffers or strings,
values of global variables such as mouse pointers, or as a component of
a complex data structure such as a toolbar initializer.  Although these
uses could probably streamlined, each structure has its own
requirements.  Since glyphs are very flexible, it is possible to create
applications like the `edit-toolbar' and `xpm-mode' libraries which
display glyphs in a buffer (for reference while editing) that are
normally used in a different context.

   Usage of glyphs can roughly be categorized as follows:

*Buffer glyphs*
     Glyphs that are inserted in a buffer may be used for their own
     sake (for example, image display in `w3'), as an accurate
     representation of text that can't be displayed in usual fonts
     (equation display in `preview-latex'), or as annotations (such as
     a marginal indication of a bookmark).  Glyphs are attached to
     buffers via extents.

*Redisplay glyphs*
     Glyphs can be used to create XEmacs-specific "fonts".  For example,
     the character that indicates truncation of lines is implemented as
     the `truncation-glyph'.  It is also possible to have XEmacs
     display a certain character using a custom glyph, via display
     tables.

*Frame glyphs*
     Glyphs are used to control the appearance of various other
     components of the frame.  They can be inserted in the modeline,
     like the favicons used in Web browsers.  They are used to specify
     the labels on toolbar buttons.  Finally, they can be inserted in
     the gutters.  (The difference between a glyph inserted in a gutter
     and a marginal annotation is that the marginal annotation is tied
     to the text in the buffer.  If the buffer line scrolls out of
     view, the marginal annotation will, as well.  A gutter glyph does
     not move with the text.)

     Unfortunately, all these uses are special cases, and have their own
     APIs, in contrast to glyphs in a buffer.

*External glyphs*
     External glyphs simply allow a consistent API for images.  The
     images are then passed to external software such as the window
     system itself (mouse cursor shapes) and the window manager (icons
     to represent minimized windows).  XEmacs has no role in managing
     their use.

*Subwindow and widget glyphs*
     These do not constitute a context of use, but rather an important
     class of glyph types.  The difference between these and other
     glyphs is that while their geometry is determined by XEmacs, their
     behavior is managed separately, by internal mechanisms in the case
     of widgets, and (possibly) by another process in the case of
     subwindows.

   Some simple concrete examples showing how to insert a glyph in a
buffer are presented later.  *Note Glyph Examples::.

   "Creating Glyphs" explains how to create glyphs.  Creating a glyph
using `make-glyph' does not specify _where_ the glyph will be used, it
only specifies _what_ the glyph will look like.  The next four sections
explain how to embed glyphs in different display contexts.  Finally,
the last two sections explain the special considerations of using
glyphs whose behavior is not determined by the code creating them, but
by the glyph itself (a "widget" in X11 or "control" in MS Windows or
Aqua), or even by a separate process.

* Menu:

* Creating Glyphs::     Creating new glyphs.
* Buffer Glyphs::       Annotations are glyphs that appear in a buffer.
* Redisplay Glyphs::    Glyphs controlling various redisplay functions.
* Frame Glyphs::        Displaying glyphs in GUI components of the frame.
* External Glyphs::     Icons and mouse pointers for the window system.
* Native GUI Widgets::  Complex active elements treated as a single glyph.
* Subwindows::          Externally-controlled subwindows in buffers.

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File: lispref.info,  Node: Creating Glyphs,  Next: Buffer Glyphs,  Up: Using Glyphs

50.3.1 Creating Glyphs
----------------------

 -- Function: make-glyph &optional spec-list type
     This function creates a new glyph object of type TYPE.

     The optional SPEC-LIST is used to initialize the glyph's image.
     It can be any spec-list of "image instantiator" accepted by
     `canonicalize-spec-list', *Note Adding Specifications::.  An
     individual image instantiator may be a string, which is converted
     to a vector according to `console-type-image-conversion-list', or a
     vector.  The vector's first element specifies the _external_ format
     of the data, such as a string, a PNG file, or an MS Windows
     resource.  This is followed by properties (keyword-value pairs)
     specifying such information as the name of a file containing an
     image, or pixmap data directly.  *Note Image Specifiers::.

     The optional TYPE specifies the type of the glyph.  TYPE should be
     one of `buffer' (used for glyphs in an extent, the modeline, the
     toolbar, or elsewhere in a frame), `pointer' (used for the
     mouse-pointer), or `icon' (used for a frame's icon), and defaults
     to `buffer'.

   SPEC-LIST is the initializer for the glyph's `image' property, which
is an image specifier.  (Note that "image" as used in the context of a
glyph's `image' property or in the terms "image specifier", "image
instantiator", or "image instance" does not refer to what people
normally think of as an image (which in XEmacs is called a "pixmap"),
but to any graphical element--a pixmap, a widget, or even a block of
text, when used in the places that call for a glyph.)

   The most common form of SPEC-LIST is a single image instantiator.
(*Compatibility note:* in GNU Emacs 21, a string used to instantiate an
image is interpreted as the name of an image file, which is searched
for and instantiated.)  The conversion controlled by
`console-type-image-conversion-list' typically attempts to look up the
string as a file name in XEmacs's data directory path, and if this
fails, defaults to displaying the string as a text image instance
(_i.e._. the string itself.

   Fine control of a particular specification is provided by using a
vector as the image instantiator.  More complicated instantiators allow
lists of instantiators to be specified (which are tried in order), or
mappings from locales to lists of instantiators, _etc_.  *Note
Specifiers::, for more information about specification formats.

   As well as using SPEC-LIST to initialize the glyph, you can set
specifications using `set-glyph-image'.  The glyph itself is not
actually a specifier, but rather is an object containing an image
specifier (as well as other properties seldom set by user code).
Therefore, you cannot set or access specifications for the glyph's image
by directly using `set-specifier', `specifier-instance' or the like on
the glyph; instead use them on `(glyph-image GLYPH)' or use the
convenience functions `set-glyph-image', `glyph-image-instance', and
`glyph-image'.

   Glyph types reflect the fact that glyphs are used in contexts like
pointers and window manager icons, which are defined by external
programs such as the window system or window manager.  These require
somewhat different _internal_ format, which is opaque to the user.

   It is extremely rare that you will ever have to specify a value for
TYPE, which should be one of `buffer' (used for glyphs in an extent,
the modeline, the toolbar, or elsewhere in a buffer), `pointer' (used
for the mouse-pointer), or `icon' (used for a frame's icon), and
defaults to `buffer'.  The only cases where it needs to be specified is
when creating icon or pointer glyphs, and in both cases the necessary
glyphs have already been created at startup and are accessed through
the appropriate variables, e.g. `text-pointer-glyph' (or in general, any
`*-pointer-glyph') and `frame-icon-glyph'.  User code should never need
to create `pointer' or `icon' glyphs.  *Note Glyph Types::.

   There are a few other glyph creation functions, normally used only
internally or at XEmacs initialization.

 -- Function: make-glyph-internal &optional type
     This function creates a new, uninitialized glyph of type TYPE.

 -- Function: make-pointer-glyph &optional spec-list
     Return a new `pointer-glyph' object with the specification list
     SPEC-LIST.  This function is equivalent to calling `make-glyph'
     with a TYPE of `pointer'.

   `make-pointer-glyph' is normally used only by XEmacs initialization
code.  It is extremely unlikely that you will ever need to create a
pointer glyph.  Instead, you probably want to be calling
`set-glyph-image' on an existing glyph, e.g. `text-pointer-glyph'.

 -- Function: make-icon-glyph &optional spec-list
     Return a new `icon-glyph' object with the specification list
     SPEC-LIST.  This function is equivalent to calling `make-glyph'
     with a TYPE of `icon'.

   `make-icon-glyph' is normally used only by XEmacs initialization
code.  It is extremely unlikely that you will ever need to create a icon
glyph.  Instead, you probably want to be calling `set-glyph-image' on
the existing glyph, `frame-icon-glyph'.

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File: lispref.info,  Node: Buffer Glyphs,  Next: Redisplay Glyphs,  Prev: Creating Glyphs,  Up: Using Glyphs

50.3.2 Buffer Glyphs
--------------------

Creating a glyph using `make-glyph' does not specify _where_ the glyph
will be used, it only specifies _what_ the glyph will look like.  Once
you have created a glyph, you specify where it will be used by
attaching it to an extent as a _begin-glyph_ or _end-glyph_.

`buffer text'
     To insert a glyph into a buffer, create an extent in the buffer
     and then use `set-extent-begin-glyph' or `set-extent-end-glyph' to
     set a glyph to be displayed at the corresponding edge of the
     extent.  (It is common to create zero-width extents for this
     purpose.)

`margins'
     To insert a glyph into the left or right margin of a buffer, first
     make sure the margin is visible by setting a value for the
     specifiers `left-margin-width' or `right-margin-width'.  (Not
     strictly necessary when using margin glyphs with layout policy
     `whitespace'.)  Follow the same procedure above for inserting a
     glyph in a buffer, then set a non-default layout policy for the
     glyph using `set-extent-begin-glyph-layout' or
     `set-extent-end-glyph-layout'.  Alternatively, use the high-level
     annotations API (see `make-annotation').  (In fact, you can also
     use the annotations API for glyphs in a buffer, by setting a
     layout policy of `text'.)


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File: lispref.info,  Node: Redisplay Glyphs,  Next: Frame Glyphs,  Prev: Buffer Glyphs,  Up: Using Glyphs

50.3.3 Redisplay Glyphs
-----------------------

To use a glyph to control the shape of miscellaneous redisplay effects
such as the truncation and continuation markers, set the appropriate
existing glyph variables with `set-glyph-image'.  See
`continuation-glyph', `control-arrow-glyph', `hscroll-glyph',
`invisible-text-glyph', `octal-escape-glyph', and `truncation-glyph'.
See also `overlay-arrow-string', an odd redisplay leftover which can be
set to a glyph you created, and will cause the glyph to be displayed on
top of the text position specified in the marker stored in
`overlay-arrow-position'.

   To use a glyph in a display table (i.e. to control the appearance of
any individual character), create the appropriate character glyphs and
then set a specification for the specifier `current-display-table',
which controls the appearance of characters.  You can also set an
overriding display table for use with text displayed in a particular
face; see `set-face-display-table' and `make-display-table'.  ####
Note: Display tables do not currently support general Mule characters.
They will be overhauled at some point to support this and to provide
other features required under Mule.  *Note Display Tables::.

   Glyphs are not actually used as the background pixmaps of faces, but
the API is similar.  The background pixmap of a face is actually an
image specifier - probably the only place in XEmacs where an image
specifier occurs outside of a glyph.  If you would like to use a
glyph's image as a background pixmap, you can extract it with
`glyph-image', and then add it to a face.  *Note Face Convenience
Functions::.

 -- Glyph: truncation-glyph
     This variable specifies what is displayed at the end of truncated
     lines.

 -- Glyph: continuation-glyph
     This variable specifies what is displayed at the end of wrapped
     lines.

 -- Glyph: octal-escape-glyph
     This variable specifies what to prefix character codes displayed
     in octal with.

 -- Glyph: hscroll-glyph
     This variable specifies what to display at the beginning of
     horizontally scrolled lines.

 -- Glyph: invisible-text-glyph
     This variable specifies what to use to indicate the presence of
     invisible text.  This is the glyph that is displayed when an
     ellipsis is called for, according to `selective-display-ellipses'
     or `buffer-invisibility-spec').  Normally this is three dots
     ("...").

 -- Glyph: control-arrow-glyph
     This variable specifies what to use as an arrow for control
     characters.

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File: lispref.info,  Node: Frame Glyphs,  Next: External Glyphs,  Prev: Redisplay Glyphs,  Up: Using Glyphs

50.3.4 Frame Glyphs
-------------------

There are also a number of special objects whose appearance is specified
by a glyph.  Most of these a global objects that you update with
`set-glyph-image', such as mouse pointers.  Frame icons, toolbar button
icons, and the modeline are the main non-text objects which accept
glyphs as elements.

`modeline'
     A glyph may be displayed in the modeline by inserting the glyph as
     one of the elements of the modeline format.  (Unfortunately you
     can't currently put a begin glyph or end glyph on one of the
     modeline extents--they're ignored.)

`toolbar'
     To insert a glyph into a toolbar, specify it as the icon part of a
     toolbar button, which in turn must be part of a toolbar
     instantiator (typically set on the specifier `default-toolbar').
     See `default-toolbar' for more information. (As a convenience, you
     may use a symbol in place of the glyph list in the toolbar button
     instantiator; the symbol is evalled to get the glyph list.  This
     facilitates both creating the toolbar instantiator and modifying
     individual glyphs in a toolbar later on.  For example, you can
     change the way that the Mail toolbar button looks by modifying the
     value of the variable `toolbar-mail-icon' (in general,
     `toolbar-*-icon') and then calling `(set-specifier-dirty-flag
     default-toolbar)'.  (#### Unfortunately this doesn't quite work
     the way it should; the change will appear in new frames, but not
     existing ones, because once an image has been displayed the pixmap
     replaces the symbol for those domains.)

`gutter'
     To insert a glyph into a gutter, use `set-extent-begin-glyph' or
     `set-extent-end-glyph' to set a glyph to be displayed at the
     corresponding edge of extent in a string, similar to the way you
     insert glyphs in a buffer.  Then insert the string into the gutter
     *Note Specifying a Gutter::.  Glyphs that are frequently used in
     this way are `tab control' and `progress bar' glyphs.


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File: lispref.info,  Node: External Glyphs,  Next: Native GUI Widgets,  Prev: Frame Glyphs,  Up: Using Glyphs

50.3.5 External Glyphs
----------------------

There are two special kinds of glyph that are not displayed by XEmacs.
Instead, they are used to set the appearance of iconified frames and the
mouse pointer.  Because these uses are constrained by the window system,
icons and pointers have their own special types *Note Glyph Types::.

   You may use a glyph as the icon for a frame.  Do not create a new
glyph; instead, change the specifications for the existing glyph
`frame-icon-glyph' with `set-glyph-image'.  This is a unique,
predefined object.  Although the natural usage is to set specifications
for the global locale or a frame locale, you can also arrange for a
special icon when a frame's selected window displays a particular buffer
by using a buffer locale.

   The shape of the mouse pointer when over a particular section of a
frame is controlled using various glyph variables.  Since the image of
a glyph is a specifier, it can be controlled on a per-buffer,
per-frame, per-window, or per-device basis.

   To use a glyph as the mouse pointer, in general you do not create a
new glyph, but rather you change the specifications of various existing
glyphs, such as `text-pointer-glyph' for the pointer used over text,
`modeline-pointer-glyph' for the pointer used over the modeline, etc.
Do an apropos over `pointer-glyph' to find all of them.  (Note also
that you can temporarily set the mouse pointer to some specific shape
by using `set-frame-pointer', which takes an image instance, as
obtained from calling `glyph-image-instance' on a glyph of type
`pointer' - either one of the above-mentioned variables or one you
created yourself.  (See below for what it means to create a glyph of
type `pointer'.)  This pointer will last only until the next mouse
motion event is processed or certain other things happen, such as
creating or deleting a window. (In fact, the above-mentioned pointer
glyph variables are implemented as part of the default handler for
mouse motion events.  If you want to customize this behavior, take a
look at `mode-motion-hook', or `mouse-motion-handler' if you really
want to get low-level.)

   You should use `set-glyph-image' to set the following variables,
_not_ `setq'.

 -- Glyph: text-pointer-glyph
     This variable specifies the shape of the mouse pointer when over
     text.

 -- Glyph: nontext-pointer-glyph
     This variable specifies the shape of the mouse pointer when over a
     buffer, but not over text.  If unspecified in a particular domain,
     `text-pointer-glyph' is used.

 -- Glyph: modeline-pointer-glyph
     This variable specifies the shape of the mouse pointer when over
     the modeline.  If unspecified in a particular domain,
     `nontext-pointer-glyph' is used.

 -- Glyph: selection-pointer-glyph
     This variable specifies the shape of the mouse pointer when over a
     selectable text region.  If unspecified in a particular domain,
     `text-pointer-glyph' is used.

 -- Glyph: gc-pointer-glyph
     This variable specifies the shape of the mouse pointer when a
     garbage collection is in progress.  If the selected window is on a
     window system and this glyph specifies a value (i.e. a pointer
     image instance) in the domain of the selected window, the pointer
     will be changed as specified during garbage collection.
     Otherwise, a message will be printed in the echo area, as
     controlled by `gc-message'.

 -- Glyph: busy-pointer-glyph
     This variable specifies the shape of the mouse pointer when XEmacs
     is busy.  If unspecified in a particular domain, the pointer is
     not changed when XEmacs is busy.

 -- Glyph: menubar-pointer-glyph
     This variable specifies the shape of the mouse pointer when over
     the menubar.  If unspecified in a particular domain, the
     window-system-provided default pointer is used.

 -- Glyph: scrollbar-pointer-glyph
     This variable specifies the shape of the mouse pointer when over a
     scrollbar.  If unspecified in a particular domain, the
     window-system-provided default pointer is used.

 -- Glyph: toolbar-pointer-glyph
     This variable specifies the shape of the mouse pointer when over a
     toolbar.  If unspecified in a particular domain,
     `nontext-pointer-glyph' is used.

   Internally, these variables are implemented in
`default-mouse-motion-handler', and thus only take effect when the
mouse moves.  That function calls `set-frame-pointer', which sets the
current mouse pointer for a frame.

 -- Function: set-frame-pointer frame image-instance
     This function sets the mouse pointer of FRAME to the given pointer
     image instance.  You should not call this function directly.  (If
     you do, the pointer will change again the next time the mouse
     moves.)

\1f
File: lispref.info,  Node: Native GUI Widgets,  Next: Subwindows,  Prev: External Glyphs,  Up: Using Glyphs

50.3.6 Native GUI Widgets
-------------------------

A "native widget" is a primitive GUI object defined either by the host
GUI platform or an external toolkit, and accessed from Lisp as a
"glyph."

* Menu:

* Introduction to Widgets::     Native widgets provide tight integration of
                                GUI features with the platform GUI.
* Lisp API to Native Widgets::  Native widgets are glyphs.
* Layouts::                     Specifying composite widgets from Lisp.
* Primitive Widgets::           Catalogue of available native widgets.

\1f
File: lispref.info,  Node: Introduction to Widgets,  Next: Lisp API to Native Widgets,  Up: Native GUI Widgets

50.3.6.1 Introduction to Native Widgets and Subwindow Glyphs
............................................................

Traditionally Emacsen have hidden the GUI apparatus from the Lisp
programmer, but in XEmacs 21.4 the ability to embed autonomous GUI
objects, called "native widgets", in text was added to Lisp.  They are
handled as _glyphs_.  Unlike traditional XEmacs glyphs such images and
strings, native widgets are opaque to XEmacs, and must be able to
redraw themselves because they are implemented as subwindows, not as
graphics drawn by XEmacs into the text window.

   Primitive widgets are coded in C using the underlying GUI toolkit,
and thus are beyond the scope of the _XEmacs Lisp Reference Manual_.
However, composite widgets can be created in Lisp using "layouts,"
which are horizontal or vertical arrays of subwidgets.  For example, the
search dialog is formatted using layouts.

\1f
File: lispref.info,  Node: Lisp API to Native Widgets,  Next: Layouts,  Prev: Introduction to Widgets,  Up: Native GUI Widgets

50.3.6.2 Lisp API to Native Widgets
...................................

Native widgets are manipulated as _glyphs_ (*note Glyphs::).  Thus they
are created using `make-glyph', with a format of one of the widget
types and a `:data' property specific to the widget being instanced.

   However, there is a technical difference between widgets and other
kinds of glyphs that is theoretically important.  Because widgets are
active (that is, they can respond to user input events themselves), it
is possible for the user to become aware that two appearances of the
"same" glyph are actually separate instances.  For example, if a user
changes an image glyph from red to blue, and the buffer containing the
glyph appears in more than one window, the user will perceive all the
appearances to change from red to blue simultaneously.  However, suppose
the glyph is a button glyph (_e.g._, as used in the Customize buffer
for the Set, Save, and Done buttons).  Then if the Customize buffer
appears in several windows at the same time, and the user clicks on the
button, she will only perceive the button to be depressed in the window
where she clicked the button.

   It seems from this example that it is unlikely to be a problem in
practice.  When the user is faced with an active widget, it seems likely
that attention will focus on the widget being manipulated, and having
other instances of the widget respond simultaneously might be more
disconcerting than the actual case.

\1f
File: lispref.info,  Node: Layouts,  Next: Primitive Widgets,  Prev: Lisp API to Native Widgets,  Up: Native GUI Widgets

50.3.6.3 Layouts
................

An XEmacs "layout" is a one-dimensional array of glyphs.  It is a
widget for controlling the positioning of children underneath it.
Through the use of nested layouts, a widget hierarchy can be created
which can have the appearance of any standard dialog box or similar
arrangement; all of this is counted as one "glyph" and could appear in
many of the places that expect a single glyph.  (There are also "native
layouts", but these are undocumented, as are their uses.)

   A layout descriptor is an image instantiator, _i.e._, a vector of
the form `[FORMAT KEY-1 VALUE-1 KEY-2 VALUE-2 ...]' with format
`layout', and properties

`:orientation'
     Specifies the orientation of the contained array of glyphs.  The
     value must be one of the symbols `horizontal' or `vertical'.

`:horizontally-justify'
     Specifies the horizontal justification of the items in the array.
     The value must be one of the symbols `:right', `:center', or
     `:left'.

`:vertically-justify'
     Specifies the vertical justification of the items in the array.
     The value must be one of the symbols `:top', `:center', or
     `:bottom'.

`:justify'
     Specifies justification.  #### not understood.

`:border'
     A glyph to place in the border.  The value must be an image
     instantiator.

`:items'
     The glyphs controlled by the layout.  The value must be a list of
     image instantiators.

   Here is the specification of the search dialog widget created by
`make-search-dialog' in the `dialog-items' library, which makes use of
recursive layouts.

     (make-glyph
      `[layout
        :orientation horizontal
        :vertically-justify top
        :horizontally-justify center
        :border [string :data "Search"]
        :items
        ([layout :orientation vertical
                 :justify top   ; implies left also
                 :items
                 ([string :data "Search for:"]
                [button :descriptor "Match Case"
                        :style toggle
                        :selected (not case-fold-search)
                        :callback (setq case-fold-search
                                        (not case-fold-search))]
                [button :descriptor "Regular Expression"
                        :style toggle
                        :selected search-dialog-regexp
                        :callback (setq search-dialog-regexp
                                        (not search-dialog-regexp))]
                [button :descriptor "Forwards"
                        :style radio
                        :selected search-dialog-direction
                        :callback (setq search-dialog-direction t)]
                [button :descriptor "Backwards"
                        :style radio
                        :selected (not search-dialog-direction)
                        :callback (setq search-dialog-direction nil)]
                )]
         [layout :orientation vertical
                 :vertically-justify top
                 :horizontally-justify right
                 :items
                 ([edit-field :width 15 :descriptor "" :active t
                            :initial-focus t]
                [button :width 10 :descriptor "Find Next"
                        :callback-ex
                        (lambda (image-instance event)
                          (search-dialog-callback ,parent
                                                  image-instance
                                                  event))]
                [button :width 10 :descriptor "Cancel"
                        :callback-ex
                        (lambda (image-instance event)
                          (isearch-dehighlight)
                          (delete-frame
                           (event-channel event)))])])])

\1f
File: lispref.info,  Node: Primitive Widgets,  Prev: Layouts,  Up: Native GUI Widgets

50.3.6.4 Primitive Widgets
..........................

`button'
     A button widget; either a push button, radio button or toggle
     button.

`combo-box'
     A drop list of selectable items in a widget, for editing text.

`edit-field'
     A text editing widget.

`label'
     A static, text-only, widget; for displaying text.

`progress-gauge'
     A sliding widget, for showing progress.

`tab-control'
     A tab widget; a series of user selectable tabs.

`tree-view'
     A folding widget.

`scrollbar'
     A scrollbar widget.  (#### Probably not the same as the scrollbar
     controlling an Emacs window.)

\1f
File: lispref.info,  Node: Subwindows,  Prev: Native GUI Widgets,  Up: Using Glyphs

50.3.7 Subwindows
-----------------

Subwindows are not currently implemented.

 -- Function: subwindowp object
     This function returns non-`nil' if OBJECT is a subwindow.

\1f
File: lispref.info,  Node: Manipulating Glyphs,  Next: Glyph Examples,  Prev: Using Glyphs,  Up: Glyphs

50.4 Manipulating Glyphs
========================

Each glyphs has properties that may be accessed.  Most of these can
also be set after the glyph is initialized, with the exception of the
glyph's type.  This is not a real restriction, as it is almost never
useful to create glyphs of types other than `buffer'.

* Menu:

* Glyph Properties::    Accessing and modifying a glyph's properties.
* Glyph Convenience Functions::  Accessing particular properties of a glyph.
* Glyph Dimensions::    Determining the height, width, etc. of a glyph.
* Glyph Types::         Each glyph has a particular type.

\1f
File: lispref.info,  Node: Glyph Properties,  Next: Glyph Convenience Functions,  Up: Manipulating Glyphs

50.4.1 Glyph Properties
-----------------------

Each glyph has a list of properties, which control all of the aspects of
the glyph's appearance.  The following symbols have predefined meanings:

`image'
     The image used to display the glyph.

`baseline'
     Percent above baseline that glyph is to be displayed.  Only for
     glyphs displayed inside of a buffer.

`contrib-p'
     Whether the glyph contributes to the height of the line it's on.
     Only for glyphs displayed inside of a buffer.

`face'
     Face of this glyph (_not_ a specifier).

 -- Function: set-glyph-property glyph property value &optional locale
          tag-set how-to-add
     This function changes a property of a GLYPH.

     For built-in properties, the actual value of the property is a
     specifier and you cannot change this; but you can change the
     specifications within the specifier, and that is what this
     function will do.  The glyph face is an exception; it is a face
     name (a symbol) or a face object, not a specifier.  (The face
     properties themselves are typically specifiers.)  For user-defined
     properties, you can use this function to either change the actual
     value of the property or, if this value is a specifier, change the
     specifications within it.

     If PROPERTY is a built-in property, the specifications to be added
     to this property can be supplied in many different ways:

        * If VALUE is a simple instantiator (e.g. a string naming a
          pixmap filename) or a list of instantiators, then the
          instantiator(s) will be added as a specification of the
          property for the given LOCALE (which defaults to `global' if
          omitted).

        * If VALUE is a list of specifications (each of which is a cons
          of a locale and a list of instantiators), then LOCALE must be
          `nil' (it does not make sense to explicitly specify a locale
          in this case), and specifications will be added as given.

        * If VALUE is a specifier (as would be returned by
          `glyph-property' if no LOCALE argument is given), then some
          or all of the specifications in the specifier will be added
          to the property.  In this case, the function is really
          equivalent to `copy-specifier' and LOCALE has the same
          semantics (if it is a particular locale, the specification
          for the locale will be copied; if a locale type,
          specifications for all locales of that type will be copied;
          if `nil' or `all', then all specifications will be copied).

     HOW-TO-ADD should be either `nil' or one of the symbols `prepend',
     `append', `remove-tag-set-prepend', `remove-tag-set-append',
     `remove-locale', `remove-locale-type', or `remove-all'.  See
     `copy-specifier' and `add-spec-to-specifier' for a description of
     what each of these means.  Most of the time, you do not need to
     worry about this argument; the default behavior usually is fine.

     In general, it is OK to pass an instance object (e.g. as returned
     by `glyph-property-instance') as an instantiator in place of an
     actual instantiator.  In such a case, the instantiator used to
     create that instance object will be used (for example, if you set
     a font-instance object as the value of the `font' property, then
     the font name used to create that object will be used instead).
     In some cases, however, doing this conversion does not make sense,
     and this will be noted in the documentation for particular types
     of instance objects.

     If PROPERTY is not a built-in property, then this function will
     simply set its value if LOCALE is `nil'.  However, if LOCALE is
     given, then this function will attempt to add VALUE as the
     instantiator for the given LOCALE, using `add-spec-to-specifier'.
     If the value of the property is not a specifier, it will
     automatically be converted into a `generic' specifier.

 -- Function: glyph-property glyph property &optional locale
     This function returns GLYPH's value of the given PROPERTY.

     If LOCALE is omitted, the GLYPH's actual value for PROPERTY will
     be returned.  For built-in properties, this will be a specifier
     object of a type appropriate to the property (e.g. a font or color
     specifier).  For other properties, this could be anything.

     If LOCALE is supplied, then instead of returning the actual value,
     the specification(s) for the given locale or locale type will be
     returned.  This will only work if the actual value of PROPERTY is
     a specifier (this will always be the case for built-in properties,
     but may or may not apply to user-defined properties).  If the
     actual value of PROPERTY is not a specifier, this value will
     simply be returned regardless of LOCALE.

     The return value will be a list of instantiators (e.g. vectors
     specifying pixmap data), or a list of specifications, each of
     which is a cons of a locale and a list of instantiators.
     Specifically, if LOCALE is a particular locale (a buffer, window,
     frame, device, or `global'), a list of instantiators for that
     locale will be returned.  Otherwise, if LOCALE is a locale type
     (one of the symbols `buffer', `window', `frame', or `device'), the
     specifications for all locales of that type will be returned.
     Finally, if LOCALE is `all', the specifications for all locales of
     all types will be returned.

     The specifications in a specifier determine what the value of
     PROPERTY will be in a particular "domain" or set of circumstances,
     which is typically a particular Emacs window along with the buffer
     it contains and the frame and device it lies within.  The value is
     derived from the instantiator associated with the most specific
     locale (in the order buffer, window, frame, device, and `global')
     that matches the domain in question.  In other words, given a
     domain (i.e. an Emacs window, usually), the specifier for PROPERTY
     will first be searched for a specification whose locale is the
     buffer contained within that window; then for a specification
     whose locale is the window itself; then for a specification whose
     locale is the frame that the window is contained within; etc.  The
     first instantiator that is valid for the domain (usually this
     means that the instantiator is recognized by the device [i.e. the
     X server or TTY device] that the domain is on).  The function
     `glyph-property-instance' actually does all this, and is used to
     determine how to display the glyph.

 -- Function: glyph-property-instance glyph property &optional domain
          default no-fallback
     This function returns the instance of GLYPH's PROPERTY in the
     specified DOMAIN.

     Under most circumstances, DOMAIN will be a particular window, and
     the returned instance describes how the specified property
     actually is displayed for that window and the particular buffer in
     it.  Note that this may not be the same as how the property
     appears when the buffer is displayed in a different window or
     frame, or how the property appears in the same window if you
     switch to another buffer in that window; and in those cases, the
     returned instance would be different.

     The returned instance is an image-instance object, and you can
     query it using the appropriate image instance functions.  For
     example, you could use `image-instance-depth' to find out the
     depth (number of color planes) of a pixmap displayed in a
     particular window.  The results might be different from the
     results you would get for another window (perhaps the user
     specified a different image for the frame that window is on; or
     perhaps the same image was specified but the window is on a
     different X server, and that X server has different color
     capabilities from this one).

     DOMAIN defaults to the selected window if omitted.

     DOMAIN can be a frame or device, instead of a window.  The value
     returned for such a domain is used in special circumstances when a
     more specific domain does not apply; for example, a frame value
     might be used for coloring a toolbar, which is conceptually
     attached to a frame rather than a particular window.  The value is
     also useful in determining what the value would be for a
     particular window within the frame or device, if it is not
     overridden by a more specific specification.

     If PROPERTY does not name a built-in property, its value will
     simply be returned unless it is a specifier object, in which case
     it will be instanced using `specifier-instance'.

     Optional arguments DEFAULT and NO-FALLBACK are the same as in
     `specifier-instance'.  *Note Specifiers::.

 -- Function: remove-glyph-property glyph property &optional locale
          tag-set exact-p
     This function removes a property from a glyph.  For built-in
     properties, this is analogous to `remove-specifier'.  *Note
     remove-specifier-p: Specifiers, for the meaning of the LOCALE,
     TAG-SET, and EXACT-P arguments.

\1f
File: lispref.info,  Node: Glyph Convenience Functions,  Next: Glyph Dimensions,  Prev: Glyph Properties,  Up: Manipulating Glyphs

50.4.2 Glyph Convenience Functions
----------------------------------

The following functions are provided for working with specific
properties of a glyph.  Note that these are exactly like calling the
general functions described above and passing in the appropriate value
for PROPERTY.

   Remember that if you want to determine the "value" of a specific
glyph property, you probably want to use the `*-instance' functions.
For example, to determine whether a glyph contributes to its line
height, use `glyph-contrib-p-instance', not `glyph-contrib-p'. (The
latter will return a boolean specifier or a list of specifications, and
you probably aren't concerned with these.)

 -- Function: glyph-image glyph &optional locale
     This function is equivalent to calling `glyph-property' with a
     property of `image'.  The return value will be an image specifier
     if LOCALE is `nil' or omitted; otherwise, it will be a
     specification or list of specifications.

 -- Function: set-glyph-image glyph spec &optional locale tag-set
          how-to-add
     This function is equivalent to calling `set-glyph-property' with a
     property of `image'.

 -- Function: glyph-image-instance glyph &optional domain default
          no-fallback
     This function returns the instance of GLYPH's image in the given
     DOMAIN, and is equivalent to calling `glyph-property-instance'
     with a property of `image'.  The return value will be an image
     instance.

     Normally DOMAIN will be a window or `nil' (meaning the selected
     window), and an instance object describing how the image appears
     in that particular window and buffer will be returned.

 -- Function: glyph-contrib-p glyph &optional locale
     This function is equivalent to calling `glyph-property' with a
     property of `contrib-p'.  The return value will be a boolean
     specifier if LOCALE is `nil' or omitted; otherwise, it will be a
     specification or list of specifications.

 -- Function: set-glyph-contrib-p glyph spec &optional locale tag-set
          how-to-add
     This function is equivalent to calling `set-glyph-property' with a
     property of `contrib-p'.

 -- Function: glyph-contrib-p-instance glyph &optional domain default
          no-fallback
     This function returns whether the glyph contributes to its line
     height in the given DOMAIN, and is equivalent to calling
     `glyph-property-instance' with a property of `contrib-p'.  The
     return value will be either `nil' or `t'. (Normally DOMAIN will be
     a window or `nil', meaning the selected window.)

 -- Function: glyph-baseline glyph &optional locale
     This function is equivalent to calling `glyph-property' with a
     property of `baseline'.  The return value will be a specifier if
     LOCALE is `nil' or omitted; otherwise, it will be a specification
     or list of specifications.

 -- Function: set-glyph-baseline glyph spec &optional locale tag-set
          how-to-add
     This function is equivalent to calling `set-glyph-property' with a
     property of `baseline'.

 -- Function: glyph-baseline-instance glyph &optional domain default
          no-fallback
     This function returns the instance of GLYPH's baseline value in
     the given DOMAIN, and is equivalent to calling
     `glyph-property-instance' with a property of `baseline'.  The
     return value will be an integer or `nil'.

     Normally DOMAIN will be a window or `nil' (meaning the selected
     window), and an instance object describing the baseline value
     appears in that particular window and buffer will be returned.

 -- Function: glyph-face glyph
     This function returns the face of GLYPH. (Remember, this is not a
     specifier, but a simple property.)

 -- Function: set-glyph-face glyph face
     This function changes the face of GLYPH to FACE.

\1f
File: lispref.info,  Node: Glyph Dimensions,  Next: Glyph Types,  Prev: Glyph Convenience Functions,  Up: Manipulating Glyphs

50.4.3 Glyph Dimensions
-----------------------

 -- Function: glyph-width glyph &optional window
     This function returns the width of GLYPH on WINDOW.  This may not
     be exact as it does not take into account all of the context that
     redisplay will.

 -- Function: glyph-ascent glyph &optional window
     This function returns the ascent value of GLYPH on WINDOW.  This
     may not be exact as it does not take into account all of the
     context that redisplay will.

 -- Function: glyph-descent glyph &optional window
     This function returns the descent value of GLYPH on WINDOW.  This
     may not be exact as it does not take into account all of the
     context that redisplay will.

 -- Function: glyph-height glyph &optional window
     This function returns the height of GLYPH on WINDOW.  (This is
     equivalent to the sum of the ascent and descent values.)  This may
     not be exact as it does not take into account all of the context
     that redisplay will.

\1f
File: lispref.info,  Node: Glyph Types,  Prev: Glyph Dimensions,  Up: Manipulating Glyphs

50.4.4 Glyph Types
------------------

Each glyph has a particular type, which controls how the glyph's image
is generated.  Each glyph type has a corresponding list of allowable
image instance types that can be generated.  When you call
`glyph-image-instance' to retrieve the image instance of a glyph,
XEmacs does the equivalent of calling `make-image-instance' and passing
in DEST-TYPES the list of allowable image instance types for the
glyph's type.

   * `buffer' glyphs can be used as the begin-glyph or end-glyph of an
     extent, in the modeline, and in the toolbar.  Their image can be
     instantiated as `nothing', `mono-pixmap', `color-pixmap', `text',
     and `subwindow'.

   * `pointer' glyphs can be used to specify the mouse pointer.  Their
     image can be instantiated as `pointer'.

   * `icon' glyphs can be used to specify the icon used when a frame is
     iconified.  Their image can be instantiated as `mono-pixmap' and
     `color-pixmap'.

 -- Function: glyph-type glyph
     This function returns the type of the given glyph.  The return
     value will be a symbol, one of `buffer', `pointer', or `icon'.

 -- Function: valid-glyph-type-p glyph-type
     Given a GLYPH-TYPE, this function returns non-`nil' if it is valid.

 -- Function: glyph-type-list
     This function returns a list of valid glyph types.

 -- Function: buffer-glyph-p object
     This function returns non-`nil' if OBJECT is a glyph of type
     `buffer'.

 -- Function: icon-glyph-p object
     This function returns non-`nil' if OBJECT is a glyph of type
     `icon'.

 -- Function: pointer-glyph-p object
     This function returns non-`nil' if OBJECT is a glyph of type
     `pointer'.

\1f
File: lispref.info,  Node: Glyph Examples,  Prev: Manipulating Glyphs,  Up: Glyphs

50.5 Glyph Examples
===================

For many applications, displaying graphics is a simple process: you
create a glyph, and then you insert it into a buffer.

   The easiest way to create a glyph is to use a file that contains a
graphical image, such as a JPEG, TIFF, or PNG file:

     ;; Create a glyph from a JPEG file:
     (setq foo (make-glyph [jpeg :file "/tmp/file1.jpg"]))

     ;; Create a glyph from a XPM file:
     (setq foo (make-glyph [xpm :file "/tmp/file2.xpm"]))

     ;; Create a glyph from a PNG file:
     (setq foo (make-glyph [png :file "/tmp/file3.png"]))

     ;; Create a glyph from a TIFF file:
     (setq foo (make-glyph [tiff :file "/tmp/file4.tiff"]))

   The parameters passed to `make-glyph' are called "Image Specifiers",
and can handle more image types than those shown above.  You can also
put the raw image data into a string (e.g., if you put the contents of
a JPEG file into a string), and use that to create a glyph.  *Note
Image Specifiers::, for more information.

     *Caution*: In order for XEmacs to read a particular graphics file
     format, support for that format must have been compiled into
     XEmacs.  It's possible, although somewhat unlikely, for XEmacs to
     have been compiled without support for any of the various graphics
     file formats.  To see what graphics formats your particular
     version of XEmacs supports, use `M-x describe-installation'.

     To programmatically query whether or not a particular file format
     is supported, you can use the `featurep' function, with one of:
     `gif', `tiff', `jpeg', `xpm', `xbm', `png', or `xface'.  For an
     up-to-date list, *Note Image Specifiers::.  Example:

          ;; Returns `t' if TIFF is supported:
          (featurep 'tiff)

     Another example is:

          ;; Returns a list of `t' or `nil', depending on whether or not the
          ;; corresponding feature is supported:
          (mapcar #'(lambda (format-symbol) (featurep format-symbol))
                  '(gif tiff jpeg xpm png))


   Once you have a glyph, you can then insert it into a buffer.
Example:

     ;; Use this function to insert a glyph at the left edge of point in the
     ;; current buffer.  Any existing glyph at this location is replaced.
     (defun insert-glyph (gl)
       "Insert a glyph at the left edge of point."
       (let ( (prop 'myimage)        ;; myimage is an arbitrary name, chosen
                                     ;; to (hopefully) not conflict with any
                                     ;; other properties.  Change it if
                                     ;; necessary.
              extent )
         ;; First, check to see if one of our extents already exists at
         ;; point.  For ease-of-programming, we are creating and using our
         ;; own extents (multiple extents are allowed to exist/overlap at the
         ;; same point, and it's quite possible for other applications to
         ;; embed extents in the current buffer without your knowledge).
         ;; Basically, if an extent, with the property stored in "prop",
         ;; exists at point, we assume that it is one of ours, and we re-use
         ;; it (this is why it is important for the property stored in "prop"
         ;; to be unique, and only used by us).
         (if (not (setq extent (extent-at (point) (current-buffer) prop)))
           (progn
             ;; If an extent does not already exist, create a zero-length
             ;; extent, and give it our special property.
             (setq extent (make-extent (point) (point) (current-buffer)))
             (set-extent-property extent prop t)
             ))
         ;; Display the glyph by storing it as the extent's "begin-glyph".
         (set-extent-property extent 'begin-glyph gl)
         ))

     ;; You can then use this function like:
     (insert-glyph (make-glyph [jpeg :file "/tmp/file1.jpg"]))
     ;; This will insert the glyph at point.

     ;; Here's an example of how to insert two glyphs side-by-side, at point
     ;; (using the above code):
     (progn
       (insert-glyph (make-glyph [jpeg :file "/tmp/file1.jpg"]))
       ;; Create a new extent at point.  We can't simply call "insert-glyph",
       ;; as "insert-glyph" will simply replace the first glyph with the
       ;; second.
       (setq extent (make-extent (point) (point) (current-buffer)))
       ;; Here, we're only setting the 'myimage property in case we need
       ;; to later identify/locate/reuse this particular extent.
       (set-extent-property extent 'myimage t)
       (set-extent-property extent 'begin-glyph
                            (make-glyph [jpeg :file "/tmp/file2.jpg"]))
       )

   Here are the gory details:

   * Glyphs are displayed by attaching them to extents (see *Note
     Extents::), either to the beginning or the end of extents.

     Note that extents can be used for many things, and not just for
     displaying images (although, in the above example, we are creating
     our own extent for the sole purpose of displaying an image).
     Also, note that multiple extents are allowed to exist at the same
     position, and they can overlap.

   * Glyphs are often displayed inside the text area (alongside text).
     This is the default.

     Although glyphs can also be displayed in the margins, how to do
     this will not be described here.  For more information on this, see
     *Note Annotation Basics:: (look for information on "layout types")
     and *Note Extent Properties:: (look for `begin-glyph-layout' and
     `end-glyph-layout').

   * The easiest way to insert a glyph into text is to create a
     zero-length extent at the point where you want the glyph to appear.

     Note that zero-length extents are attached to the character to the
     right of the extent; deleting this character will also delete the
     extent.

   * It's often a good idea to assign a unique property to the
     newly-created extent, in case you later want to locate it, and
     replace any existing glyph with a different one (or just delete
     the existing one).  In the above example, we are using "myimage"
     as our (hopefully) unique property name.

     If you need to locate all of the extents, you'll have to use
     functions like `extent-list' or `next-extent', or provide
     additional parameters to the `extent-at' function.  Assigning a
     unique property to the extent makes it easy to locate your
     extents; for example, `extent-list' can return only those extents
     with a particular property.  *Note Finding Extents::, and *Note
     Mapping Over Extents::, for more information.

   * Glyphs are displayed by assigning then to the `begin-glyph' or
     `end-glyph' property of the extent.  For zero-length extents, it
     doesn't really matter if you assign the glyph to the `begin-glyph'
     or `end-glyph' property, as they are both at the same location;
     however, for non-zero-length extents (extents that cover one or
     more characters of text), it does matter which one you use.

     Assigning `nil' to the `begin-glyph' or `end-glyph' property will
     delete any existing glyph.  In this case, you may also want to
     delete the extent, assuming that the extent is used for no other
     purpose.

   * If you happen to insert two glyphs, side-by-side, note that the
     example `insert-glyph' function will have trouble, if it's again
     used at the same point (it can only locate one of the two extents).
     *Note Finding Extents::, and *Note Mapping Over Extents::, for more
     information on locating extents in a buffer.

   * Among other things, glyphs provide a way of displaying graphics
     alongside text.  Note, however, that glyphs only provide a way of
     displaying graphics; glyphs are not actually part of the text, and
     are only displayed alongside the text.  If you save the text in
     the buffer, the graphics are not saved.  The low-level glyph code
     does not provide a way of saving graphics with the text.  If you
     need to save graphics and text, you have to write your own code to
     do this, and this topic is outside the scope of this discussion.


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File: lispref.info,  Node: Annotations,  Next: Display,  Prev: Glyphs,  Up: Top

51 Annotations
**************

An "annotation" is a pixmap or string that is not part of a buffer's
text but is displayed next to a particular location in a buffer.
Annotations can be displayed intermixed with text, in any whitespace at
the beginning or end of a line, or in a special area at the left or
right side of the frame called a "margin", whose size is controllable.
Annotations are implemented using extents (*note Extents::); but you
can work with annotations without knowing how extents work.

* Menu:

* Annotation Basics::           Introduction to annotations.
* Annotation Primitives::       Creating and deleting annotations.
* Annotation Properties::       Retrieving and changing the characteristics
                                  of an annotation.
* Margin Primitives::           Controlling the size of the margins.
* Locating Annotations::        Looking for annotations in a buffer.
* Annotation Hooks::            Hooks called at certain times during an
                                  annotation's lifetime.

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File: lispref.info,  Node: Annotation Basics,  Next: Annotation Primitives,  Up: Annotations

51.1 Annotation Basics
======================

Marginal annotations are notes associated with a particular location in
a buffer.  They may be displayed in a margin created on the left-hand or
right-hand side of the frame, in any whitespace at the beginning or end
of a line, or inside of the text itself.  Every annotation may have an
associated action to be performed when the annotation is selected.  The
term "annotation" is used to refer to an individual note.  The term
"margin" is generically used to refer to the whitespace before the
first character on a line or after the last character on a line.

   Each annotation has the following characteristics:
GLYPH
     This is a glyph object and is used as the displayed representation
     of the annotation.

DOWN-GLYPH
     If given, this glyph is used as the displayed representation of
     the annotation when the mouse is pressed down over the annotation.

FACE
     The face with which to display the glyph.

SIDE
     Which side of the text (left or right) the annotation is displayed
     at.

ACTION
     If non-`nil', this field must contain a function capable of being
     the first argument to `funcall'.  This function is normally
     evaluated with a single argument, the value of the DATA field,
     each time the annotation is selected.  However, if the WITH-EVENT
     parameter to `make-annotation' is non-`nil', the function is
     called with two arguments.  The first argument is the same as
     before, and the second argument is the event (a button-up event,
     usually) that activated the annotation.

DATA
     Not used internally.  This field can contain any E-Lisp object.
     It is passed as the first argument to ACTION described above.

MENU
     A menu displayed when the right mouse button is pressed over the
     annotation.

   The margin is divided into "outside" and "inside".  The outside
margin is space on the left or right side of the frame which normal text
cannot be displayed in.  The inside margin is that space between the
leftmost or rightmost point at which text can be displayed and where the
first or last character actually is.

   There are four different "layout types" which affect the exact
location an annotation appears.

`outside-margin'
     The annotation is placed in the outside margin area. as close as
     possible to the edge of the frame.  If the outside margin is not
     wide enough for an annotation to fit, it is not displayed.

`inside-margin'
     The annotation is placed in the inside margin area, as close as
     possible to the edge of the frame.  If the inside margin is not
     wide enough for the annotation to fit, it will be displayed using
     any available outside margin space if and only if the specifier
     `use-left-overflow' or `use-right-overflow' (depending on which
     side the annotation appears in) is non-`nil'.

`whitespace'
     The annotation is placed in the inside margin area, as close as
     possible to the first or last non-whitespace character on a line.
     If the inside margin is not wide enough for the annotation to fit,
     it will be displayed if and only if the specifier
     `use-left-overflow' or `use-right-overflow' (depending on which
     side the annotation appears in) is non-`nil'.

`text'
     The annotation is placed at the position it is inserted.  It will
     create enough space for itself inside of the text area.  It does
     not take up a place in the logical buffer, only in the display of
     the buffer.

   The current layout policy is that all `whitespace' annotations are
displayed first.  Next, all `inside-margin' annotations are displayed
using any remaining space.  Finally as many `outside-margin'
annotations are displayed as possible.  The `text' annotations will
always display as they create their own space to display in.

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File: lispref.info,  Node: Annotation Primitives,  Next: Annotation Properties,  Prev: Annotation Basics,  Up: Annotations

51.2 Annotation Primitives
==========================

 -- Function: make-annotation glyph &optional position layout buffer
          with-event d-glyph rightp
     This function creates a marginal annotation at position POSITION in
     BUFFER.  The annotation is displayed using GLYPH, which should be
     a glyph object or a string, and is positioned using layout policy
     LAYOUT.  If POSITION is `nil', point is used.  If LAYOUT is `nil',
     `whitespace' is used.  If BUFFER is `nil', the current buffer is
     used.

     If WITH-EVENT is non-`nil', then when an annotation is activated,
     the triggering event is passed as the second arg to the annotation
     function.  If D-GLYPH is non-`nil' then it is used as the glyph
     that will be displayed when button1 is down.  If RIGHTP is
     non-`nil' then the glyph will be displayed on the right side of
     the buffer instead of the left.

     The newly created annotation is returned.

 -- Function: delete-annotation annotation
     This function removes ANNOTATION from its buffer.  This does not
     modify the buffer text.

 -- Function: annotationp annotation
     This function returns `t' if ANNOTATION is an annotation, `nil'
     otherwise.

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File: lispref.info,  Node: Annotation Properties,  Next: Margin Primitives,  Prev: Annotation Primitives,  Up: Annotations

51.3 Annotation Properties
==========================

 -- Function: annotation-glyph annotation
     This function returns the glyph object used to display ANNOTATION.

 -- Function: set-annotation-glyph annotation glyph &optional layout
          side
     This function sets the glyph of ANNOTATION to GLYPH, which should
     be a glyph object.  If LAYOUT is non-`nil', set the layout policy
     of ANNOTATION to LAYOUT.  If SIDE is `left' or `right', change the
     side of the buffer at which the annotation is displayed to the
     given side.  The new value of `annotation-glyph' is returned.

 -- Function: annotation-down-glyph annotation
     This function returns the glyph used to display ANNOTATION when
     the left mouse button is depressed on the annotation.

 -- Function: set-annotation-down-glyph annotation glyph
     This function returns the glyph used to display ANNOTATION when
     the left mouse button is depressed on the annotation to GLYPH,
     which should be a glyph object.

 -- Function: annotation-face annotation
     This function returns the face associated with ANNOTATION.

 -- Function: set-annotation-face annotation face
     This function sets the face associated with ANNOTATION to FACE.

 -- Function: annotation-layout annotation
     This function returns the layout policy of ANNOTATION.

 -- Function: set-annotation-layout annotation layout
     This function sets the layout policy of ANNOTATION to LAYOUT.

 -- Function: annotation-side annotation
     This function returns the side of the buffer that ANNOTATION is
     displayed on.  Return value is a symbol, either `left' or `right'.

 -- Function: annotation-data annotation
     This function returns the data associated with ANNOTATION.

 -- Function: set-annotation-data annotation data
     This function sets the data field of ANNOTATION to DATA.  DATA is
     returned.

 -- Function: annotation-action annotation
     This function returns the action associated with ANNOTATION.

 -- Function: set-annotation-action annotation action
     This function sets the action field of ANNOTATION to ACTION.
     ACTION is returned..

 -- Function: annotation-menu annotation
     This function returns the menu associated with ANNOTATION.

 -- Function: set-annotation-menu annotation menu
     This function sets the menu associated with ANNOTATION to MENU.
     This menu will be displayed when the right mouse button is pressed
     over the annotation.

 -- Function: annotation-visible annotation
     This function returns `t' if there is enough available space to
     display ANNOTATION, `nil' otherwise.

 -- Function: annotation-width annotation
     This function returns the width of ANNOTATION in pixels.

 -- Function: hide-annotation annotation
     This function removes ANNOTATION's glyph, making it invisible.

 -- Function: reveal-annotation annotation
     This function restores ANNOTATION's glyph, making it visible.

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File: lispref.info,  Node: Locating Annotations,  Next: Annotation Hooks,  Prev: Margin Primitives,  Up: Annotations

51.4 Locating Annotations
=========================

 -- Function: annotations-in-region start end buffer
     This function returns a list of all annotations in BUFFER which
     are between START and END inclusively.

 -- Function: annotations-at &optional position buffer
     This function returns a list of all annotations at POSITION in
     BUFFER.  If POSITION is `nil' point is used.  If BUFFER is `nil'
     the current buffer is used.

 -- Function: annotation-list &optional buffer
     This function returns a list of all annotations in BUFFER.  If
     BUFFER is `nil', the current buffer is used.

 -- Function: all-annotations
     This function returns a list of all annotations in all buffers in
     existence.

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File: lispref.info,  Node: Margin Primitives,  Next: Locating Annotations,  Prev: Annotation Properties,  Up: Annotations

51.5 Margin Primitives
======================

The margin widths are controllable on a buffer-local, window-local,
frame-local, device-local, or device-type-local basis through the use
of specifiers.  *Note Specifiers::.

 -- Specifier: left-margin-width
     This is a specifier variable controlling the width of the left
     outside margin, in characters.  Use `set-specifier' to change its
     value.

 -- Specifier: right-margin-width
     This is a specifier variable controlling the width of the right
     outside margin, in characters.  Use `set-specifier' to change its
     value.

 -- Specifier: use-left-overflow
     If non-`nil', use the left outside margin as extra whitespace when
     displaying `whitespace' and `inside-margin' annotations.  Defaults
     to `nil'.  This is a specifier variable; use `set-specifier' to
     change its value.

 -- Specifier: use-right-overflow
     If non-`nil', use the right outside margin as extra whitespace when
     displaying `whitespace' and `inside-margin' annotations.  Defaults
     to `nil'.  This is a specifier variable; use `set-specifier' to
     change its value.

 -- Function: window-left-margin-pixel-width &optional window
     This function returns the width in pixels of the left outside
     margin of WINDOW.  If WINDOW is `nil', the selected window is
     assumed.

 -- Function: window-right-margin-pixel-width &optional window
     This function returns the width in pixels of the right outside
     margin of WINDOW.  If WINDOW is `nil', the selected window is
     assumed.

   The margin colors are controlled by the faces `left-margin' and
`right-margin'.  These can be set using the X resources
`Emacs.left-margin.background' and `Emacs.left-margin.foreground';
likewise for the right margin.

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File: lispref.info,  Node: Annotation Hooks,  Prev: Locating Annotations,  Up: Annotations

51.6 Annotation Hooks
=====================

The following three hooks are provided for use with the marginal
annotations:

`before-delete-annotation-hook'
     This hook is called immediately before an annotation is destroyed.
     It is passed a single argument, the annotation being destroyed.

`after-delete-annotation-hook'
     This normal hook is called immediately after an annotation is
     destroyed.

`make-annotation-hook'
     This hook is called immediately after an annotation is created.
     It is passed a single argument, the newly created annotation.

\1f
File: lispref.info,  Node: Display,  Next: Hash Tables,  Prev: Annotations,  Up: Top

52 Emacs Display
****************

This chapter describes a number of other features related to the display
that XEmacs presents to the user.

* Menu:

* Refresh Screen::      Clearing the screen and redrawing everything on it.
* Truncation::          Folding or wrapping long text lines.
* The Echo Area::       Where messages are displayed.
* Warnings::            Display of Warnings.
* Invisible Text::      Hiding part of the buffer text.
* Selective Display::   Hiding part of the buffer text (the old way).
* Overlay Arrow::       Display of an arrow to indicate position.
* Temporary Displays::  Displays that go away automatically.
* Blinking::            How XEmacs shows the matching open parenthesis.
* Usual Display::       The usual conventions for displaying nonprinting chars.
* Display Tables::      How to specify other conventions.
* Beeping::             Audible signal to the user.

\1f
File: lispref.info,  Node: Refresh Screen,  Next: Truncation,  Up: Display

52.1 Refreshing the Screen
==========================

The function `redraw-frame' redisplays the entire contents of a given
frame.  *Note Frames::.

 -- Function: redraw-frame &optional frame no-preempt
     This function clears and redisplays frame FRAME.

     FRAME defaults to the selected frame if omitted.

     Normally, redisplay is preempted as normal if input arrives.
     However, if optional second arg NO-PREEMPT is non-`nil', redisplay
     will not stop for input and is guaranteed to proceed to completion.

   Even more powerful is `redraw-display':

 -- Command: redraw-display &optional device
     This function redraws all frames on DEVICE marked as having their
     image garbled.  DEVICE defaults to the selected device.  If DEVICE
     is `t', all devices will have their frames checked.

   Processing user input takes absolute priority over redisplay.  If you
call these functions when input is available, they do nothing
immediately, but a full redisplay does happen eventually--after all the
input has been processed.

   Normally, suspending and resuming XEmacs also refreshes the screen.
Some terminal emulators record separate contents for display-oriented
programs such as XEmacs and for ordinary sequential display.  If you are
using such a terminal, you might want to inhibit the redisplay on
resumption.  *Note Suspending XEmacs::.

 -- Variable: no-redraw-on-reenter
     This variable controls whether XEmacs redraws the entire screen
     after it has been suspended and resumed.  Non-`nil' means yes,
     `nil' means no.

   The above functions do not actually cause the display to be updated;
rather, they clear out the internal display records that XEmacs
maintains, so that the next time the display is updated it will be
redrawn from scratch.  Normally this occurs the next time that
`next-event' or `sit-for' is called; however, a display update will not
occur if there is input pending.  *Note Command Loop::.

 -- Function: force-cursor-redisplay &optional frame
     This function causes an immediate update of the cursor on FRAME,
     which defaults to the selected frame.

\1f
File: lispref.info,  Node: Truncation,  Next: The Echo Area,  Prev: Refresh Screen,  Up: Display

52.2 Truncation
===============

When a line of text extends beyond the right edge of a window, the line
can either be truncated or continued on the next line.  When a line is
truncated, this is normally shown with a `\' in the rightmost column of
the window on X displays, and with a `$' on TTY devices.  When a line
is continued or "wrapped" onto the next line, this is shown with a
curved arrow in the rightmost column of the window (or with a `\' on
TTY devices).  The additional screen lines used to display a long text
line are called "continuation" lines.

   Normally, whenever line truncation is in effect for a particular
window, a horizontal scrollbar is displayed in that window if the
device supports scrollbars.  *Note Scrollbars::.

   Note that continuation is different from filling; continuation
happens on the screen only, not in the buffer contents, and it breaks a
line precisely at the right margin, not at a word boundary.  *Note
Filling::.

 -- User Option: truncate-lines
     This buffer-local variable controls how XEmacs displays lines that
     extend beyond the right edge of the window.  If it is non-`nil',
     then XEmacs does not display continuation lines; rather each line
     of text occupies exactly one screen line, and a backslash appears
     at the edge of any line that extends to or beyond the edge of the
     window.  The default is `nil'.

     If the variable `truncate-partial-width-windows' is non-`nil',
     then truncation is always used for side-by-side windows (within one
     frame) regardless of the value of `truncate-lines'.

 -- User Option: default-truncate-lines
     This variable is the default value for `truncate-lines', for
     buffers that do not have local values for it.

 -- User Option: truncate-partial-width-windows
     This variable controls display of lines that extend beyond the
     right edge of the window, in side-by-side windows (*note Splitting
     Windows::).  If it is non-`nil', these lines are truncated;
     otherwise, `truncate-lines' says what to do with them.

   The backslash and curved arrow used to indicate truncated or
continued lines are only defaults, and can be changed.  These images
are actually glyphs (*note Glyphs::).  XEmacs provides a great deal of
flexibility in how glyphs can be controlled. (This differs from FSF
Emacs, which uses display tables to control these images.)

   For details, *Note Redisplay Glyphs::.

\1f
File: lispref.info,  Node: The Echo Area,  Next: Warnings,  Prev: Truncation,  Up: Display

52.3 The Echo Area
==================

The "echo area" is used for displaying messages made with the `message'
primitive, and for echoing keystrokes.  It is not the same as the
minibuffer, despite the fact that the minibuffer appears (when active)
in the same place on the screen as the echo area.  The `XEmacs Lisp
Reference Manual' specifies the rules for resolving conflicts between
the echo area and the minibuffer for use of that screen space (*note
The Minibuffer: (xemacs)Minibuffer.).  Error messages appear in the
echo area; see *Note Errors::.

   You can write output in the echo area by using the Lisp printing
functions with `t' as the stream (*note Output Functions::), or as
follows:

 -- Function: message string &rest arguments
     This function displays a one-line message in the echo area.  The
     argument STRING is similar to a C language `printf' control
     string.  See `format' in *Note String Conversion::, for the details
     on the conversion specifications.  `message' returns the
     constructed string.

     In batch mode, `message' prints the message text on the standard
     error stream, followed by a newline.

     If STRING is `nil', `message' clears the echo area.  If the
     minibuffer is active, this brings the minibuffer contents back onto
     the screen immediately.

          (message "Minibuffer depth is %d."
                   (minibuffer-depth))
           -| Minibuffer depth is 0.
          => "Minibuffer depth is 0."

          ---------- Echo Area ----------
          Minibuffer depth is 0.
          ---------- Echo Area ----------

   In addition to only displaying a message, XEmacs allows you to
"label" your messages, giving you fine-grained control of their
display.  Message label is a symbol denoting the message type.  Some
standard labels are:

   * `message'--default label used by the `message' function;

   * `error'--default label used for reporting errors;

   * `progress'--progress indicators like `Converting... 45%' (not
     logged by default);

   * `prompt'--prompt-like messages like `Isearch: foo' (not logged by
     default);

   * `command'--helper command messages like `Mark set' (not logged by
     default);

   * `no-log'--messages that should never be logged

   Several messages may be stacked in the echo area at once.  Lisp
programs may access these messages, or remove them as appropriate, via
the message stack.

 -- Function: display-message label message &optional frame stdout-p
     This function displays MESSAGE (a string) labeled as LABEL, as
     described above.

     The FRAME argument specifies the frame to whose minibuffer the
     message should be printed.  This is currently unimplemented.  The
     STDOUT-P argument is used internally.

          (display-message 'command "Mark set")

 -- Function: lmessage label string &rest arguments
     This function displays a message STRING with label LABEL.  It is
     similar to `message' in that it accepts a `printf'-like strings
     and any number of arguments.

          ;; Display a command message.
          (lmessage 'command "Comment column set to %d" comment-column)

          ;; Display a progress message.
          (lmessage 'progress "Fontifying %s... (%d)" buffer percentage)

          ;; Display a message that should not be logged.
          (lmessage 'no-log "Done")

 -- Function: clear-message &optional label frame stdout-p no-restore
     This function remove any message with the given LABEL from the
     message-stack, erasing it from the echo area if it's currently
     displayed there.

     If a message remains at the head of the message-stack and
     NO-RESTORE is `nil', it will be displayed.  The string which
     remains in the echo area will be returned, or `nil' if the
     message-stack is now empty.  If LABEL is `nil', the entire
     message-stack is cleared.

          ;; Show a message, wait for 2 seconds, and restore old minibuffer
          ;; contents.
          (message "A message")
           -| A message
          => "A Message"
          (lmessage 'my-label "Newsflash!  Newsflash!")
           -| Newsflash!  Newsflash!
          => "Newsflash!  Newsflash!"
          (sit-for 2)
          (clear-message 'my-label)
           -| A message
          => "A message"

     Unless you need the return value or you need to specify a label,
     you should just use `(message nil)'.

 -- Function: current-message &optional frame
     This function returns the current message in the echo area, or
     `nil'.  The FRAME argument is currently unused.

   Some of the messages displayed in the echo area are also recorded in
the ` *Message-Log*' buffer.  Exactly which messages will be recorded
can be tuned using the following variables.

 -- User Option: log-message-max-size
     This variable specifies the maximum size of the ` *Message-log*'
     buffer.

 -- Variable: log-message-ignore-labels
     This variable specifies the labels whose messages will not be
     logged.  It should be a list of symbols.

 -- Variable: log-message-ignore-regexps
     This variable specifies the regular expressions matching messages
     that will not be logged.  It should be a list of regular
     expressions.

     Normally, packages that generate messages that might need to be
     ignored should label them with `progress', `prompt', or `no-log',
     so they can be filtered by `log-message-ignore-labels'.

 -- Variable: echo-keystrokes
     This variable determines how much time should elapse before command
     characters echo.  Its value must be a number, which specifies the
     number of seconds to wait before echoing.  If the user types a
     prefix key (such as `C-x') and then delays this many seconds
     before continuing, the prefix key is echoed in the echo area.  Any
     subsequent characters in the same command will be echoed as well.

     If the value is zero, then command input is not echoed.

 -- Variable: cursor-in-echo-area
     This variable controls where the cursor appears when a message is
     displayed in the echo area.  If it is non-`nil', then the cursor
     appears at the end of the message.  Otherwise, the cursor appears
     at point--not in the echo area at all.

     The value is normally `nil'; Lisp programs bind it to `t' for
     brief periods of time.

\1f
File: lispref.info,  Node: Warnings,  Next: Invisible Text,  Prev: The Echo Area,  Up: Display

52.4 Warnings
=============

XEmacs contains a facility for unified display of various warnings.
Unlike errors, warnings are displayed in the situations when XEmacs
encounters a problem that is recoverable, but which should be fixed for
safe future operation.

   For example, warnings are printed by the startup code when it
encounters problems with X keysyms, when there is an error in `.emacs',
and in other problematic situations.  Unlike messages, warnings are
displayed in a separate buffer, and include an explanatory message that
may span across several lines.  Here is an example of how a warning is
displayed:

     (1) (initialization/error) An error has occurred while loading ~/.emacs:

     Symbol's value as variable is void: bogus-variable

     To ensure normal operation, you should investigate the cause of the error
     in your initialization file and remove it.  Use the `-debug-init' option
     to XEmacs to view a complete error backtrace.

   Each warning has a "class" and a "priority level".  The class is a
symbol describing what sort of warning this is, such as
`initialization', `resource' or `key-mapping'.

   The warning priority level specifies how important the warning is.
The recognized warning levels, in increased order of priority, are:
`debug', `info', `notice', `warning', `error', `critical', `alert' and
`emergency'.

 -- Function: display-warning class message &optional level
     This function displays a warning message MESSAGE (a string).
     CLASS should be a warning class symbol, as described above, or a
     list of such symbols.  LEVEL describes the warning priority level.
     If unspecified, it default to `warning'.

          (display-warning 'resource
            "Bad resource specification encountered:
          something like

              Emacs*foo: bar

          You should replace the * with a . in order to get proper behavior when
          you use the specifier and/or `set-face-*' functions.")

          ---------- Warning buffer ----------
          (1) (resource/warning) Bad resource specification encountered:
          something like

              Emacs*foo: bar

          You should replace the * with a . in order to get proper behavior when
          you use the specifier and/or `set-face-*' functions.
          ---------- Warning buffer ----------

 -- Function: lwarn class level message &rest args
     This function displays a formatted labeled warning message.  As
     above, CLASS should be the warning class symbol, or a list of such
     symbols, and LEVEL should specify the warning priority level
     (`warning' by default).

     Unlike in `display-warning', MESSAGE may be a formatted message,
     which will be, together with the rest of the arguments, passed to
     `format'.

          (lwarn 'message-log 'warning
            "Error caught in `remove-message-hook': %s"
            (error-message-string e))

 -- Variable: log-warning-minimum-level
     This variable specifies the minimum level of warnings that should
     be generated.  Warnings with level lower than defined by this
     variable are completely ignored, as if they never happened.

 -- Variable: display-warning-minimum-level
     This variable specifies the minimum level of warnings that should
     be displayed.  Unlike `log-warning-minimum-level', setting this
     function does not suppress warnings entirely--they are still
     generated in the `*Warnings*' buffer, only they are not displayed
     by default.

 -- Variable: log-warning-suppressed-classes
     This variable specifies a list of classes that should not be
     logged or displayed.  If any of the class symbols associated with
     a warning is the same as any of the symbols listed here, the
     warning will be completely ignored, as it they never happened.

 -- Variable: display-warning-suppressed-classes
     This variable specifies a list of classes that should not be
     logged or displayed.  If any of the class symbols associated with
     a warning is the same as any of the symbols listed here, the
     warning will not be displayed.  The warning will still logged in
     the *Warnings* buffer (unless also contained in
     `log-warning-suppressed-classes'), but the buffer will not be
     automatically popped up.

\1f
File: lispref.info,  Node: Invisible Text,  Next: Selective Display,  Prev: Warnings,  Up: Display

52.5 Invisible Text
===================

You can make characters "invisible", so that they do not appear on the
screen, with the `invisible' property.  This can be either a text
property or a property of an overlay.

   In the simplest case, any non-`nil' `invisible' property makes a
character invisible.  This is the default case--if you don't alter the
default value of `buffer-invisibility-spec', this is how the
`invisibility' property works.  This feature is much like selective
display (*note Selective Display::), but more general and cleaner.

   More generally, you can use the variable `buffer-invisibility-spec'
to control which values of the `invisible' property make text
invisible.  This permits you to classify the text into different subsets
in advance, by giving them different `invisible' values, and
subsequently make various subsets visible or invisible by changing the
value of `buffer-invisibility-spec'.

   Controlling visibility with `buffer-invisibility-spec' is especially
useful in a program to display the list of entries in a data base.  It
permits the implementation of convenient filtering commands to view
just a part of the entries in the data base.  Setting this variable is
very fast, much faster than scanning all the text in the buffer looking
for properties to change.

 -- Variable: buffer-invisibility-spec
     This variable specifies which kinds of `invisible' properties
     actually make a character invisible.

    `t'
          A character is invisible if its `invisible' property is
          non-`nil'.  This is the default.

    a list
          Each element of the list makes certain characters invisible.
          Ultimately, a character is invisible if any of the elements
          of this list applies to it.  The list can have two kinds of
          elements:

         `ATOM'
               A character is invisible if its `invisible' property
               value is ATOM or if it is a list with ATOM as a member.

         `(ATOM . t)'
               A character is invisible if its `invisible' property
               value is ATOM or if it is a list with ATOM as a member.
               Moreover, if this character is at the end of a line and
               is followed by a visible newline, it displays an
               ellipsis.

   Ordinarily, commands that operate on text or move point do not care
whether the text is invisible.  However, the user-level line motion
commands explicitly ignore invisible newlines.  Since this causes a
slow-down of these commands it is turned off by default, controlled by
the variable `line-move-ignore-invisible'.

\1f
File: lispref.info,  Node: Selective Display,  Next: Overlay Arrow,  Prev: Invisible Text,  Up: Display

52.6 Selective Display
======================

"Selective display" is a pair of features that hide certain lines on
the screen.

   The first variant, explicit selective display, is designed for use in
a Lisp program.  The program controls which lines are hidden by altering
the text.  Outline mode has traditionally used this variant.  It has
been partially replaced by the invisible text feature (*note Invisible
Text::); there is a new version of Outline mode which uses that instead.

   In the second variant, the choice of lines to hide is made
automatically based on indentation.  This variant is designed to be a
user-level feature.

   The way you control explicit selective display is by replacing a
newline (control-j) with a carriage return (control-m).  The text that
was formerly a line following that newline is now invisible.  Strictly
speaking, it is temporarily no longer a line at all, since only newlines
can separate lines; it is now part of the previous line.

   Selective display does not directly affect editing commands.  For
example, `C-f' (`forward-char') moves point unhesitatingly into
invisible text.  However, the replacement of newline characters with
carriage return characters affects some editing commands.  For example,
`next-line' skips invisible lines, since it searches only for newlines.
Modes that use selective display can also define commands that take
account of the newlines, or that make parts of the text visible or
invisible.

   When you write a selectively displayed buffer into a file, all the
control-m's are output as newlines.  This means that when you next read
in the file, it looks OK, with nothing invisible.  The selective display
effect is seen only within XEmacs.

 -- Variable: selective-display
     This buffer-local variable enables selective display.  This means
     that lines, or portions of lines, may be made invisible.

        * If the value of `selective-display' is `t', then any portion
          of a line that follows a control-m is not displayed.

        * If the value of `selective-display' is a positive integer,
          then lines that start with more than that many columns of
          indentation are not displayed.

     When some portion of a buffer is invisible, the vertical movement
     commands operate as if that portion did not exist, allowing a
     single `next-line' command to skip any number of invisible lines.
     However, character movement commands (such as `forward-char') do
     not skip the invisible portion, and it is possible (if tricky) to
     insert or delete text in an invisible portion.

     In the examples below, we show the _display appearance_ of the
     buffer `foo', which changes with the value of `selective-display'.
     The _contents_ of the buffer do not change.

          (setq selective-display nil)
               => nil

          ---------- Buffer: foo ----------
          1 on this column
           2on this column
            3n this column
            3n this column
           2on this column
          1 on this column
          ---------- Buffer: foo ----------

          (setq selective-display 2)
               => 2

          ---------- Buffer: foo ----------
          1 on this column
           2on this column
           2on this column
          1 on this column
          ---------- Buffer: foo ----------

 -- Variable: selective-display-ellipses
     If this buffer-local variable is non-`nil', then XEmacs displays
     `...' at the end of a line that is followed by invisible text.
     This example is a continuation of the previous one.

          (setq selective-display-ellipses t)
               => t

          ---------- Buffer: foo ----------
          1 on this column
           2on this column ...
           2on this column
          1 on this column
          ---------- Buffer: foo ----------

     You can use a display table to substitute other text for the
     ellipsis (`...').  *Note Display Tables::.

\1f
File: lispref.info,  Node: Overlay Arrow,  Next: Temporary Displays,  Prev: Selective Display,  Up: Display

52.7 The Overlay Arrow
======================

The "overlay arrow" is useful for directing the user's attention to a
particular line in a buffer.  For example, in the modes used for
interface to debuggers, the overlay arrow indicates the line of code
about to be executed.

 -- Variable: overlay-arrow-string
     This variable holds the string to display to call attention to a
     particular line, or `nil' if the arrow feature is not in use.
     Despite its name, the value of this variable can be either a string
     or a glyph (*note Glyphs::).

 -- Variable: overlay-arrow-position
     This variable holds a marker that indicates where to display the
     overlay arrow.  It should point at the beginning of a line.  The
     arrow text appears at the beginning of that line, overlaying any
     text that would otherwise appear.  Since the arrow is usually
     short, and the line usually begins with indentation, normally
     nothing significant is overwritten.

     The overlay string is displayed only in the buffer that this marker
     points into.  Thus, only one buffer can have an overlay arrow at
     any given time.

   You can do the same job by creating an extent with a `begin-glyph'
property.  *Note Extent Properties::.

\1f
File: lispref.info,  Node: Temporary Displays,  Next: Blinking,  Prev: Overlay Arrow,  Up: Display

52.8 Temporary Displays
=======================

Temporary displays are used by commands to put output into a buffer and
then present it to the user for perusal rather than for editing.  Many
of the help commands use this feature.

 -- Special Form: with-output-to-temp-buffer buffer-name forms...
     This function executes FORMS while arranging to insert any output
     they print into the buffer named BUFFER-NAME.  The buffer is then
     shown in some window for viewing, displayed but not selected.

     The string BUFFER-NAME specifies the temporary buffer, which need
     not already exist.  The argument must be a string, not a buffer.
     The buffer is erased initially (with no questions asked), and it is
     marked as unmodified after `with-output-to-temp-buffer' exits.

     `with-output-to-temp-buffer' binds `standard-output' to the
     temporary buffer, then it evaluates the forms in FORMS.  Output
     using the Lisp output functions within FORMS goes by default to
     that buffer (but screen display and messages in the echo area,
     although they are "output" in the general sense of the word, are
     not affected).  *Note Output Functions::.

     The value of the last form in FORMS is returned.

          ---------- Buffer: foo ----------
           This is the contents of foo.
          ---------- Buffer: foo ----------

          (with-output-to-temp-buffer "foo"
              (print 20)
              (print standard-output))
          => #<buffer foo>

          ---------- Buffer: foo ----------
          20

          #<buffer foo>

          ---------- Buffer: foo ----------

 -- Variable: temp-buffer-show-function
     If this variable is non-`nil', `with-output-to-temp-buffer' calls
     it as a function to do the job of displaying a help buffer.  The
     function gets one argument, which is the buffer it should display.

     In Emacs versions 18 and earlier, this variable was called
     `temp-buffer-show-hook'.

 -- Function: momentary-string-display string position &optional char
          message
     This function momentarily displays STRING in the current buffer at
     POSITION.  It has no effect on the undo list or on the buffer's
     modification status.

     The momentary display remains until the next input event.  If the
     next input event is CHAR, `momentary-string-display' ignores it
     and returns.  Otherwise, that event remains buffered for
     subsequent use as input.  Thus, typing CHAR will simply remove the
     string from the display, while typing (say) `C-f' will remove the
     string from the display and later (presumably) move point forward.
     The argument CHAR is a space by default.

     The return value of `momentary-string-display' is not meaningful.

     You can do the same job in a more general way by creating an extent
     with a begin-glyph property.  *Note Extent Properties::.

     If MESSAGE is non-`nil', it is displayed in the echo area while
     STRING is displayed in the buffer.  If it is `nil', a default
     message says to type CHAR to continue.

     In this example, point is initially located at the beginning of the
     second line:

          ---------- Buffer: foo ----------
          This is the contents of foo.
          -!-Second line.
          ---------- Buffer: foo ----------

          (momentary-string-display
            "**** Important Message! ****"
            (point) ?\r
            "Type RET when done reading")
          => t

          ---------- Buffer: foo ----------
          This is the contents of foo.
          **** Important Message! ****Second line.
          ---------- Buffer: foo ----------

          ---------- Echo Area ----------
          Type RET when done reading
          ---------- Echo Area ----------

     This function works by actually changing the text in the buffer.
     As a result, if you later undo in this buffer, you will see the
     message come and go.

\1f
File: lispref.info,  Node: Blinking,  Next: Usual Display,  Prev: Temporary Displays,  Up: Display

52.9 Blinking Parentheses
=========================

This section describes the mechanism by which XEmacs shows a matching
open parenthesis when the user inserts a close parenthesis.

 -- Variable: blink-paren-function
     The value of this variable should be a function (of no arguments)
     to be called whenever a character with close parenthesis syntax is
     inserted.  The value of `blink-paren-function' may be `nil', in
     which case nothing is done.

          *Please note:* This variable was named `blink-paren-hook' in
          older Emacs versions, but since it is not called with the
          standard convention for hooks, it was renamed to
          `blink-paren-function' in version 19.

 -- Variable: blink-matching-paren
     If this variable is `nil', then `blink-matching-open' does nothing.

 -- Variable: blink-matching-paren-distance
     This variable specifies the maximum distance to scan for a matching
     parenthesis before giving up.

 -- Variable: blink-matching-paren-delay
     This variable specifies the number of seconds for the cursor to
     remain at the matching parenthesis.  A fraction of a second often
     gives good results, but the default is 1, which works on all
     systems.

 -- Command: blink-matching-open
     This function is the default value of `blink-paren-function'.  It
     assumes that point follows a character with close parenthesis
     syntax and moves the cursor momentarily to the matching opening
     character.  If that character is not already on the screen, it
     displays the character's context in the echo area.  To avoid long
     delays, this function does not search farther than
     `blink-matching-paren-distance' characters.

     Here is an example of calling this function explicitly.

          (defun interactive-blink-matching-open ()
            "Indicate momentarily the start of sexp before point."
            (interactive)
            (let ((blink-matching-paren-distance
                   (buffer-size))
                  (blink-matching-paren t))
              (blink-matching-open)))

\1f
File: lispref.info,  Node: Usual Display,  Next: Display Tables,  Prev: Blinking,  Up: Display

52.10 Usual Display Conventions
===============================

The usual display conventions define how to display each character
code.  You can override these conventions by setting up a display table
(*note Display Tables::).  Here are the usual display conventions:

   * Character codes 32 through 126 map to glyph codes 32 through 126.
     Normally this means they display as themselves.

   * Character code 9 is a horizontal tab.  It displays as whitespace
     up to a position determined by `tab-width'.

   * Character code 10 is a newline.

   * All other codes in the range 0 through 31, and code 127, display
     in one of two ways according to the value of `ctl-arrow'.  If it is
     non-`nil', these codes map to sequences of two glyphs, where the
     first glyph is the ASCII code for `^'.  (A display table can
     specify a glyph to use instead of `^'.)  Otherwise, these codes map
     just like the codes in the range 128 to 255.

   * Character codes 128 through 255 map to sequences of four glyphs,
     where the first glyph is the ASCII code for `\', and the others are
     digit characters representing the code in octal.  (A display table
     can specify a glyph to use instead of `\'.)

   The usual display conventions apply even when there is a display
table, for any character whose entry in the active display table is
`nil'.  Thus, when you set up a display table, you need only specify
the characters for which you want unusual behavior.

   These variables affect the way certain characters are displayed on
the screen.  Since they change the number of columns the characters
occupy, they also affect the indentation functions.

 -- User Option: ctl-arrow
     This buffer-local variable controls how control characters are
     displayed.  If it is non-`nil', they are displayed as a caret
     followed by the character: `^A'.  If it is `nil', they are
     displayed as a backslash followed by three octal digits: `\001'.

 -- Variable: default-ctl-arrow
     The value of this variable is the default value for `ctl-arrow' in
     buffers that do not override it.  *Note Default Value::.

 -- User Option: tab-width
     The value of this variable is the spacing between tab stops used
     for displaying tab characters in Emacs buffers.  The default is 8.
     Note that this feature is completely independent from the
     user-settable tab stops used by the command `tab-to-tab-stop'.
     *Note Indent Tabs::.

\1f
File: lispref.info,  Node: Display Tables,  Next: Beeping,  Prev: Usual Display,  Up: Display

52.11 Display Tables
====================

You can use the "display table" feature to control how all 256 possible
character codes display on the screen.  This is useful for displaying
European languages that have letters not in the ASCII character set.

   The display table maps each character code into a sequence of
"runes", each rune being an image that takes up one character position
on the screen.  You can also define how to display each rune on your
terminal, using the "rune table".

* Menu:

* Display Table Format::        What a display table consists of.
* Active Display Table::        How XEmacs selects a display table to use.
* Character Descriptors::       Format of an individual element of a
                                  display table.

\1f
File: lispref.info,  Node: Display Table Format,  Next: Active Display Table,  Up: Display Tables

52.11.1 Display Table Format
----------------------------

A display table is an array of 256 elements. (In FSF Emacs, a display
table is 262 elements.  The six extra elements specify the truncation
and continuation glyphs, etc.  This method is very kludgey, and in
XEmacs the variables `truncation-glyph', `continuation-glyph', etc. are
used.  *Note Truncation::.)

 -- Function: make-display-table
     This creates and returns a display table.  The table initially has
     `nil' in all elements.

   The 256 elements correspond to character codes; the Nth element says
how to display the character code N.  The value should be `nil', a
string, a glyph, or a vector of strings and glyphs (*note Character
Descriptors::).  If an element is `nil', it says to display that
character according to the usual display conventions (*note Usual
Display::).

   If you use the display table to change the display of newline
characters, the whole buffer will be displayed as one long "line."

   For example, here is how to construct a display table that mimics the
effect of setting `ctl-arrow' to a non-`nil' value:

     (setq disptab (make-display-table))
     (let ((i 0))
       (while (< i 32)
         (or (= i ?\t) (= i ?\n)
             (aset disptab i (concat "^" (char-to-string (+ i 64)))))
         (setq i (1+ i)))
       (aset disptab 127 "^?"))

\1f
File: lispref.info,  Node: Active Display Table,  Next: Character Descriptors,  Prev: Display Table Format,  Up: Display Tables

52.11.2 Active Display Table
----------------------------

The active display table is controlled by the variable
`current-display-table'.  This is a specifier, which means that you can
specify separate values for it in individual buffers, windows, frames,
and devices, as well as a global value.  It also means that you cannot
set this variable using `setq'; use `set-specifier' instead.  *Note
Specifiers::. (FSF Emacs uses `window-display-table',
`buffer-display-table', `standard-display-table', etc. to control the
display table.  However, specifiers are a cleaner and more powerful way
of doing the same thing.  FSF Emacs also uses a different format for
the contents of a display table, using additional indirection to a
"glyph table" and such.  Note that "glyph" has a different meaning in
XEmacs.)

 -- Variable: current-display-table
     The display table currently in use.  This is a specifier.

     Display tables are used to control how characters are displayed.
     Each time that redisplay processes a character, it is looked up in
     all the display tables that apply (obtained by calling
     `specifier-instance' on `current-display-table' and any overriding
     display tables specified in currently active faces).  The first
     entry found that matches the character determines how the
     character is displayed.  If there is no matching entry, the
     default display method is used. (Non-control characters are
     displayed as themselves and control characters are displayed
     according to the buffer-local variable `ctl-arrow'.  Control
     characters are further affected by `control-arrow-glyph' and
     `octal-escape-glyph'.)

     Each instantiator in this specifier and the display-table
     specifiers in faces is a display table or a list of such tables.
     If a list, each table will be searched in turn for an entry
     matching a particular character.  Each display table is one of

        * A vector, specifying values for characters starting at 0.

        * A char table, either of type `char' or `generic'.

        * A range table.

     Each entry in a display table should be one of

        * nil (this entry is ignored and the search continues).

        * A character (use this character; if it happens to be the same
          as the original character, default processing happens,
          otherwise redisplay attempts to display this character
          directly; #### At some point recursive display-table lookup
          will be implemented).

        * A string (display each character in the string directly; ####
          At some point recursive display-table lookup will be
          implemented).

        * A glyph (display the glyph; #### At some point recursive
          display-table lookup will be implemented when a string glyph
          is being processed).

        * A cons of the form (format "STRING") where STRING is a
          printf-like spec used to process the character. ####
          Unfortunately no formatting directives other than %% are
          implemented.

        * A vector (each element of the vector is processed recursively;
          in such a case, nil elements in the vector are simply
          ignored).

          #### At some point in the near future, display tables are
          likely to be expanded to include other features, such as
          referencing characters in particular fonts and allowing the
          character search to continue all the way up the chain of
          specifier instantiators.  These features are necessary to
          properly display Unicode characters.

   Individual faces can also specify an overriding display table; this
is set using `set-face-display-table'.  *Note Faces::.

   If no display table can be determined for a particular window, then
XEmacs uses the usual display conventions.  *Note Usual Display::.

\1f
File: lispref.info,  Node: Character Descriptors,  Prev: Active Display Table,  Up: Display Tables

52.11.3 Character Descriptors
-----------------------------

Each element of the display-table vector describes how to display a
particular character and is called a "character descriptor".  A
character descriptor can be:

a string
     Display this particular string wherever the character is to be
     displayed.

a glyph
     Display this particular glyph wherever the character is to be
     displayed.

a vector
     The vector may contain strings and/or glyphs.  Display the
     elements of the vector one after another wherever the character is
     to be displayed.

`nil'
     Display according to the standard interpretation (*note Usual
     Display::).

\1f
File: lispref.info,  Node: Beeping,  Prev: Display Tables,  Up: Display

52.12 Beeping
=============

You can make XEmacs ring a bell, play a sound, or blink the screen to
attract the user's attention.  Be conservative about how often you do
this; frequent bells can become irritating.  Also be careful not to use
beeping alone when signaling an error is appropriate.  (*Note Errors::.)

 -- Function: ding &optional dont-terminate sound device
     This function beeps, or flashes the screen (see `visible-bell'
     below).  It also terminates any keyboard macro currently executing
     unless DONT-TERMINATE is non-`nil'.  If SOUND is specified, it
     should be a symbol specifying which sound to make.  This sound
     will be played if `visible-bell' is `nil'. (This only works if
     sound support was compiled into the executable and you are running
     on the console of a Sun SparcStation, SGI, HP9000s700, or Linux
     PC. Otherwise you just get a beep.) The optional third argument
     specifies what device to make the sound on, and defaults to the
     selected device.

 -- Function: beep &optional dont-terminate sound device
     This is a synonym for `ding'.

 -- User Option: visible-bell
     This variable determines whether XEmacs should flash the screen to
     represent a bell.  Non-`nil' means yes, `nil' means no.  On TTY
     devices, this is effective only if the Termcap entry for the
     terminal type has the visible bell flag (`vb') set.

 -- Variable: sound-alist
     This variable holds an alist associating names with sounds.  When
     `beep' or `ding' is called with one of the name symbols, the
     associated sound will be generated instead of the standard beep.

     Each element of `sound-alist' is a list describing a sound.  The
     first element of the list is the name of the sound being defined.
     Subsequent elements of the list are alternating keyword/value
     pairs:

    `sound'
          A string of raw sound data, or the name of another sound to
          play.  The symbol `t' here means use the default X beep.

    `volume'
          An integer from 0-100, defaulting to `bell-volume'.

    `pitch'
          If using the default X beep, the pitch (Hz) to generate.

    `duration'
          If using the default X beep, the duration (milliseconds).

     For compatibility, elements of `sound-alist' may also be:

        * `( sound-name . <sound> )'

        * `( sound-name <volume> <sound> )'

     You should probably add things to this list by calling the function
     `load-sound-file'.

     Caveats:

        - You can only play audio data if running on the console screen
          of a Sun SparcStation, SGI, or HP9000s700.

        - The pitch, duration, and volume options are available
          everywhere, but many X servers ignore the `pitch' option.

     The following beep-types are used by XEmacs itself:

    `auto-save-error'
          when an auto-save does not succeed

    `command-error'
          when the XEmacs command loop catches an error

    `undefined-key'
          when you type a key that is undefined

    `undefined-click'
          when you use an undefined mouse-click combination

    `no-completion'
          during completing-read

    `y-or-n-p'
          when you type something other than 'y' or 'n'

    `yes-or-no-p'
          when you type something other than 'yes' or 'no'

    `default'
          used when nothing else is appropriate.

     Other lisp packages may use other beep types, but these are the
     ones that the C kernel of XEmacs uses.

 -- User Option: bell-volume
     This variable specifies the default volume for sounds, from 0 to
     100.

 -- Command: load-default-sounds
     This function loads and installs some sound files as beep-types.

 -- Command: load-sound-file filename sound-name &optional volume
     This function reads in an audio file and adds it to `sound-alist'.
     The sound file must be in the Sun/NeXT U-LAW format.  SOUND-NAME
     should be a symbol, specifying the name of the sound.  If VOLUME
     is specified, the sound will be played at that volume; otherwise,
     the value of `bell-volume' will be used.

 -- Function: play-sound sound &optional volume device
     This function plays sound SOUND, which should be a symbol
     mentioned in `sound-alist'.  If VOLUME is specified, it overrides
     the value (if any) specified in `sound-alist'.  DEVICE specifies
     the device to play the sound on, and defaults to the selected
     device.

 -- Command: play-sound-file file &optional volume device
     This function plays the named sound file at volume VOLUME, which
     defaults to `bell-volume'.  DEVICE specifies the device to play
     the sound on, and defaults to the selected device.

\1f
File: lispref.info,  Node: Hash Tables,  Next: Range Tables,  Prev: Display,  Up: Top

53 Hash Tables
**************

 -- Function: hash-table-p object
     This function returns `t' if OBJECT is a hash table, else `nil'.

* Menu:

* Introduction to Hash Tables:: Hash tables are fast data structures for
                                implementing simple tables (i.e. finite
                                mappings from keys to values).
* Working With Hash Tables::    Hash table functions.
* Weak Hash Tables::            Hash tables with special garbage-collection
                                behavior.

\1f
File: lispref.info,  Node: Introduction to Hash Tables,  Next: Working With Hash Tables,  Up: Hash Tables

53.1 Introduction to Hash Tables
================================

A "hash table" is a data structure that provides mappings from
arbitrary Lisp objects called "keys" to other arbitrary Lisp objects
called "values".  A key/value pair is sometimes called an "entry" in
the hash table.  There are many ways other than hash tables of
implementing the same sort of mapping, e.g.  association lists (*note
Association Lists::) and property lists (*note Property Lists::), but
hash tables provide much faster lookup when there are many entries in
the mapping.  Hash tables are an implementation of the abstract data
type "dictionary", also known as "associative array".

   Internally, hash tables are hashed using the "linear probing" hash
table implementation method.  This method hashes each key to a
particular spot in the hash table, and then scans forward sequentially
until a blank entry is found.  To look up a key, hash to the appropriate
spot, then search forward for the key until either a key is found or a
blank entry stops the search.  This method is used in preference to
double hashing because of changes in recent hardware.  The penalty for
non-sequential access to memory has been increasing, and this
compensates for the problem of clustering that linear probing entails.

   When hash tables are created, the user may (but is not required to)
specify initial properties that influence performance.

   Use the `:size' parameter to specify the number of entries that are
likely to be stored in the hash table, to avoid the overhead of resizing
the table.  But if the pre-allocated space for the entries is never
used, it is simply wasted and makes XEmacs slower.  Excess unused hash
table entries exact a small continuous performance penalty, since they
must be scanned at every garbage collection.  If the number of entries
in the hash table is unknown, simply avoid using the `:size' keyword.

   Use the `:rehash-size' and `:rehash-threshold' keywords to adjust
the algorithm for deciding when to rehash the hash table.  For
temporary hash tables that are going to be very heavily used, use a
small rehash threshold, for example, 0.4 and a large rehash size, for
example 2.0.  For permanent hash tables that will be infrequently used,
specify a large rehash threshold, for example 0.8.

   Hash tables can also be created by the lisp reader using structure
syntax, for example:
     #s(hash-table size 20 data (foo 1 bar 2))

   The structure syntax accepts the same keywords as `make-hash-table'
(without the `:' character), as well as the additional keyword `data',
which specifies the initial hash table contents.

 -- Function: make-hash-table &key `test' `size' `rehash-size'
          `rehash-threshold' `weakness'
     This function returns a new empty hash table object.

     Keyword `:test' can be `eq', `eql' (default) or `equal'.
     Comparison between keys is done using this function.  If speed is
     important, consider using `eq'.  When storing strings in the hash
     table, you will likely need to use `equal'.

     Keyword `:size' specifies the number of keys likely to be inserted.
     This number of entries can be inserted without enlarging the hash
     table.

     Keyword `:rehash-size' must be a float greater than 1.0, and
     specifies the factor by which to increase the size of the hash
     table when enlarging.

     Keyword `:rehash-threshold' must be a float between 0.0 and 1.0,
     and specifies the load factor of the hash table which triggers
     enlarging.

     Non-standard keyword `:weakness' can be `nil' (default), `t',
     `key-and-value', `key', `value' or `key-or-value'.  `t' is an
     alias for `key-and-value'.

     A key-and-value-weak hash table, also known as a fully-weak or
     simply as a weak hash table, is one whose pointers do not count as
     GC referents: for any key-value pair in the hash table, if the only
     remaining pointer to either the key or the value is in a weak hash
     table, then the pair will be removed from the hash table, and the
     key and value collected.  A non-weak hash table (or any other
     pointer) would prevent the object from being collected.

     A key-weak hash table is similar to a fully-weak hash table except
     that a key-value pair will be removed only if the key remains
     unmarked outside of weak hash tables.  The pair will remain in the
     hash table if the key is pointed to by something other than a weak
     hash table, even if the value is not.

     A value-weak hash table is similar to a fully-weak hash table
     except that a key-value pair will be removed only if the value
     remains unmarked outside of weak hash tables.  The pair will
     remain in the hash table if the value is pointed to by something
     other than a weak hash table, even if the key is not.

     A key-or-value-weak hash table is similar to a fully-weak hash
     table except that a key-value pair will be removed only if the
     value and the key remain unmarked outside of weak hash tables.
     The pair will remain in the hash table if the value or key are
     pointed to by something other than a weak hash table, even if the
     other is not.

 -- Function: copy-hash-table hash-table
     This function returns a new hash table which contains the same
     keys and values as HASH-TABLE.  The keys and values will not
     themselves be copied.

 -- Function: hash-table-count hash-table
     This function returns the number of entries in HASH-TABLE.

 -- Function: hash-table-test hash-table
     This function returns the test function of HASH-TABLE.  This can
     be one of `eq', `eql' or `equal'.

 -- Function: hash-table-size hash-table
     This function returns the current number of slots in HASH-TABLE,
     whether occupied or not.

 -- Function: hash-table-rehash-size hash-table
     This function returns the current rehash size of HASH-TABLE.  This
     is a float greater than 1.0; the factor by which HASH-TABLE is
     enlarged when the rehash threshold is exceeded.

 -- Function: hash-table-rehash-threshold hash-table
     This function returns the current rehash threshold of HASH-TABLE.
     This is a float between 0.0 and 1.0; the maximum "load factor" of
     HASH-TABLE, beyond which the HASH-TABLE is enlarged by rehashing.

 -- Function: hash-table-weakness hash-table
     This function returns the weakness of HASH-TABLE.  This can be one
     of `nil', `t', `key' or `value'.

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File: lispref.info,  Node: Working With Hash Tables,  Next: Weak Hash Tables,  Prev: Introduction to Hash Tables,  Up: Hash Tables

53.2 Working With Hash Tables
=============================

 -- Function: puthash key value hash-table
     This function hashes KEY to VALUE in HASH-TABLE.

 -- Function: gethash key hash-table &optional default
     This function finds the hash value for KEY in HASH-TABLE.  If
     there is no entry for KEY in HASH-TABLE, DEFAULT is returned
     (which in turn defaults to `nil').

 -- Function: remhash key hash-table
     This function removes the entry for KEY from HASH-TABLE.  Does
     nothing if there is no entry for KEY in HASH-TABLE.

 -- Function: clrhash hash-table
     This function removes all entries from HASH-TABLE, leaving it
     empty.

 -- Function: maphash function hash-table
     This function maps FUNCTION over entries in HASH-TABLE, calling it
     with two args, each key and value in the hash table.

     FUNCTION may not modify HASH-TABLE, with the one exception that
     FUNCTION may remhash or puthash the entry currently being
     processed by FUNCTION.

\1f
File: lispref.info,  Node: Weak Hash Tables,  Prev: Working With Hash Tables,  Up: Hash Tables

53.3 Weak Hash Tables
=====================

A "weak hash table" is a special variety of hash table whose elements
do not count as GC referents.  For any key-value pair in such a hash
table, if either the key or value (or in some cases, if one particular
one of the two) has no references to it outside of weak hash tables
(and similar structures such as weak lists), the pair will be removed
from the table, and the key and value collected.  A non-weak hash table
(or any other pointer) would prevent the objects from being collected.

   Weak hash tables are useful for keeping track of information in a
non-obtrusive way, for example to implement caching.  If the cache
contains objects such as buffers, markers, image instances, etc. that
will eventually disappear and get garbage-collected, using a weak hash
table ensures that these objects are collected normally rather than
remaining around forever, long past their actual period of use.
(Otherwise, you'd have to explicitly map over the hash table every so
often and remove unnecessary elements.)

   There are four types of weak hash tables:

key-and-value-weak hash tables
     In these hash tables, also known as fully weak or simply as weak
     hash tables, a pair disappears if either the key or the value is
     unreferenced outside of the table.

key-weak hash tables
     In these hash tables, a pair disappears if the key is unreferenced
     outside of the table, regardless of how the value is referenced.

value-weak hash tables
     In these hash tables, a pair disappears if the value is
     unreferenced outside of the table, regardless of how the key is
     referenced.

key-or-value-weak hash tables
     In these hash tables, a pair disappears if both the key and the
     value are unreferenced outside of the table.

   Also see *Note Weak Lists::.

   Weak hash tables are created by specifying the `:weakness' keyword to
`make-hash-table'.

\1f
File: lispref.info,  Node: Range Tables,  Next: Databases,  Prev: Hash Tables,  Up: Top

54 Range Tables
***************

A range table is a table that efficiently associated values with ranges
of integers.

   Note that range tables have a read syntax, like this:

     #s(range-table data ((-3 2) foo (5 20) bar))

   This maps integers in the range (-3, 2) to `foo' and integers in the
range (5, 20) to `bar'.

 -- Function: range-table-p object
     Return non-`nil' if OBJECT is a range table.

* Menu:

* Introduction to Range Tables:: Range tables efficiently map ranges of
                                 integers to values.
* Working With Range Tables::    Range table functions.

\1f
File: lispref.info,  Node: Introduction to Range Tables,  Next: Working With Range Tables,  Up: Range Tables

54.1 Introduction to Range Tables
=================================

 -- Function: make-range-table
     Make a new, empty range table.

 -- Function: copy-range-table range-table
     This function returns a new range table which contains the same
     values for the same ranges as RANGE-TABLE.  The values will not
     themselves be copied.

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File: lispref.info,  Node: Working With Range Tables,  Prev: Introduction to Range Tables,  Up: Range Tables

54.2 Working With Range Tables
==============================

 -- Function: get-range-table pos range-table &optional default
     This function finds value for position POS in RANGE-TABLE.  If
     there is no corresponding value, return DEFAULT (defaults to
     `nil').

 -- Function: put-range-table start end value range-table
     This function sets the value for range (START, END) to be VALUE in
     RANGE-TABLE.

 -- Function: remove-range-table start end range-table
     This function removes the value for range (START, END) in
     RANGE-TABLE.

 -- Function: clear-range-table range-table
     This function flushes RANGE-TABLE.

 -- Function: map-range-table function range-table
     This function maps FUNCTION over entries in RANGE-TABLE, calling
     it with three args, the beginning and end of the range and the
     corresponding value.

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File: lispref.info,  Node: Databases,  Next: Processes,  Prev: Range Tables,  Up: Top

55 Databases
************

 -- Function: databasep object
     This function returns non-`nil' if OBJECT is a database.

* Menu:

* Connecting to a Database::
* Working With a Database::
* Other Database Functions::

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File: lispref.info,  Node: Connecting to a Database,  Next: Working With a Database,  Up: Databases

55.1 Connecting to a Database
=============================

 -- Function: open-database file &optional type subtype access mode
     This function opens database FILE, using database method TYPE and
     SUBTYPE, with access rights ACCESS and permissions MODE.  ACCESS
     can be any combination of `r' `w' and `+', for read, write, and
     creation flags.

     TYPE can have the value `'dbm' or `'berkeley-db' to select the
     type of database file to use.  (Note:  XEmacs may not support both
     of these types.)

     For a TYPE of `'dbm', there are no subtypes, so SUBTYPE should be
     `nil'.

     For a TYPE of `'berkeley-db', the following subtypes are
     available:  `'hash', `'btree', and `'recno'.  See the manpages for
     the Berkeley DB functions for more information about these types.

 -- Function: close-database database
     This function closes database DATABASE.

 -- Function: database-live-p object
     This function returns `t' if OBJECT is an active database, else
     `nil'.

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File: lispref.info,  Node: Working With a Database,  Next: Other Database Functions,  Prev: Connecting to a Database,  Up: Databases

55.2 Working With a Database
============================

 -- Function: get-database key database &optional default
     This function finds the value for KEY in DATABASE.  If there is no
     corresponding value, DEFAULT is returned (`nil' if DEFAULT is
     omitted).

 -- Function: map-database function database
     This function maps FUNCTION over entries in DATABASE, calling it
     with two args, each key and value in the database.

 -- Function: put-database key value database &optional replace
     This function stores KEY and VALUE in DATABASE.  If optional
     fourth arg REPLACE is non-`nil', replace any existing entry in the
     database.

 -- Function: remove-database key database
     This function removes KEY from DATABASE.

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File: lispref.info,  Node: Other Database Functions,  Prev: Working With a Database,  Up: Databases

55.3 Other Database Functions
=============================

 -- Function: database-file-name database
     This function returns the filename associated with DATABASE.

 -- Function: database-last-error &optional database
     This function returns the last error associated with DATABASE.

 -- Function: database-subtype database
     This function returns the subtype of DATABASE, if any.

 -- Function: database-type database
     This function returns the type of DATABASE.

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File: lispref.info,  Node: Processes,  Next: System Interface,  Prev: Databases,  Up: Top

56 Processes
************

In the terminology of operating systems, a "process" is a space in
which a program can execute.  XEmacs runs in a process.  XEmacs Lisp
programs can invoke other programs in processes of their own.  These are
called "subprocesses" or "child processes" of the XEmacs process, which
is their "parent process".

   A subprocess of XEmacs may be "synchronous" or "asynchronous",
depending on how it is created.  When you create a synchronous
subprocess, the Lisp program waits for the subprocess to terminate
before continuing execution.  When you create an asynchronous
subprocess, it can run in parallel with the Lisp program.  This kind of
subprocess is represented within XEmacs by a Lisp object which is also
called a "process".  Lisp programs can use this object to communicate
with the subprocess or to control it.  For example, you can send
signals, obtain status information, receive output from the process, or
send input to it.

 -- Function: processp object
     This function returns `t' if OBJECT is a process, `nil' otherwise.

* Menu:

* Subprocess Creation::      Functions that start subprocesses.
* Synchronous Processes::    Details of using synchronous subprocesses.
* MS-DOS Subprocesses::      On MS-DOS, you must indicate text vs binary
                                for data sent to and from a subprocess.
* Asynchronous Processes::   Starting up an asynchronous subprocess.
* Deleting Processes::       Eliminating an asynchronous subprocess.
* Process Information::      Accessing run-status and other attributes.
* Input to Processes::       Sending input to an asynchronous subprocess.
* Signals to Processes::     Stopping, continuing or interrupting
                               an asynchronous subprocess.
* Output from Processes::    Collecting output from an asynchronous subprocess.
* Sentinels::                Sentinels run when process run-status changes.
* Process Window Size::      Changing the logical window size of a process.
* Transaction Queues::       Transaction-based communication with subprocesses.
* Network::                  Opening network connections.

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File: lispref.info,  Node: Subprocess Creation,  Next: Synchronous Processes,  Up: Processes

56.1 Functions that Create Subprocesses
=======================================

There are three functions that create a new subprocess in which to run
a program.  One of them, `start-process', creates an asynchronous
process and returns a process object (*note Asynchronous Processes::).
The other two, `call-process' and `call-process-region', create a
synchronous process and do not return a process object (*note
Synchronous Processes::).

   Synchronous and asynchronous processes are explained in the following
sections.  Since the three functions are all called in a similar
fashion, their common arguments are described here.

   In all cases, the function's PROGRAM argument specifies the program
to be run.  An error is signaled if the file is not found or cannot be
executed.  If the file name is relative, the variable `exec-path'
contains a list of directories to search.  Emacs initializes
`exec-path' when it starts up, based on the value of the environment
variable `PATH'.  The standard file name constructs, `~', `.', and
`..', are interpreted as usual in `exec-path', but environment variable
substitutions (`$HOME', etc.) are not recognized; use
`substitute-in-file-name' to perform them (*note File Name Expansion::).

   Each of the subprocess-creating functions has a BUFFER-OR-NAME
argument which specifies where the standard output from the program will
go.  If BUFFER-OR-NAME is `nil', that says to discard the output unless
a filter function handles it.  (*Note Filter Functions::, and *Note
Read and Print::.)  Normally, you should avoid having multiple
processes send output to the same buffer because their output would be
intermixed randomly.

   All three of the subprocess-creating functions have a `&rest'
argument, ARGS.  The ARGS must all be strings, and they are supplied to
PROGRAM as separate command line arguments.  Wildcard characters and
other shell constructs are not allowed in these strings, since they are
passed directly to the specified program.

   *Please note:* The argument PROGRAM contains only the name of the
program; it may not contain any command-line arguments.  You must use
ARGS to provide those.

   If you want to use features of the shell, then invoke the shell
directly using, for example, PROGRAM of `"sh"', and ARGS of `"-c"' and
"COMMAND LINE...".

   The subprocess gets its current directory from the value of
`default-directory' (*note File Name Expansion::).

   The subprocess inherits its environment from XEmacs; but you can
specify overrides for it with `process-environment'.  *Note System
Environment::.

 -- Variable: exec-directory
     The value of this variable is the name of a directory (a string)
     that contains programs that come with XEmacs, that are intended
     for XEmacs to invoke.  The program `wakeup' is an example of such
     a program; the `display-time' command uses it to get a reminder
     once per minute.

 -- User Option: exec-path
     The value of this variable is a list of directories to search for
     programs to run in subprocesses.  Each element is either the name
     of a directory (i.e., a string), or `nil', which stands for the
     default directory (which is the value of `default-directory').  

     The value of `exec-path' is used by `call-process' and
     `start-process' when the PROGRAM argument is not an absolute file
     name.

\1f
File: lispref.info,  Node: Synchronous Processes,  Next: MS-DOS Subprocesses,  Prev: Subprocess Creation,  Up: Processes

56.2 Creating a Synchronous Process
===================================

After a "synchronous process" is created, XEmacs waits for the process
to terminate before continuing.  Starting Dired is an example of this:
it runs `ls' in a synchronous process, then modifies the output
slightly.  Because the process is synchronous, the entire directory
listing arrives in the buffer before XEmacs tries to do anything with
it.

   While Emacs waits for the synchronous subprocess to terminate, the
user can quit by typing `C-g'.  The first `C-g' tries to kill the
subprocess with a `SIGINT' signal; but it waits until the subprocess
actually terminates before quitting.  If during that time the user
types another `C-g', that kills the subprocess instantly with `SIGKILL'
and quits immediately.  *Note Quitting::.

   The synchronous subprocess functions returned `nil' in version 18.
In version 19, they return an indication of how the process terminated.

 -- Function: call-process program &optional infile destination display
          &rest args
     This function calls PROGRAM in a separate process and waits for it
     to finish.

     The standard input for the process comes from file INFILE if
     INFILE is not `nil' and from `/dev/null' otherwise.  The argument
     DESTINATION says where to put the process output.  Here are the
     possibilities:

    a buffer
          Insert the output in that buffer, before point.  This
          includes both the standard output stream and the standard
          error stream of the process.

    a string
          Find or create a buffer with that name, then insert the
          output in that buffer, before point.

    `t'
          Insert the output in the current buffer, before point.

    `nil'
          Discard the output.

    0
          Discard the output, and return immediately without waiting
          for the subprocess to finish.

          In this case, the process is not truly synchronous, since it
          can run in parallel with Emacs; but you can think of it as
          synchronous in that Emacs is essentially finished with the
          subprocess as soon as this function returns.

    (REAL-DESTINATION ERROR-DESTINATION)
          Keep the standard output stream separate from the standard
          error stream; deal with the ordinary output as specified by
          REAL-DESTINATION, and dispose of the error output according
          to ERROR-DESTINATION.  The value `nil' means discard it, `t'
          means mix it with the ordinary output, and a string specifies
          a file name to redirect error output into.

          You can't directly specify a buffer to put the error output
          in; that is too difficult to implement.  But you can achieve
          this result by sending the error output to a temporary file
          and then inserting the file into a buffer.

     If DISPLAY is non-`nil', then `call-process' redisplays the buffer
     as output is inserted.  Otherwise the function does no redisplay,
     and the results become visible on the screen only when XEmacs
     redisplays that buffer in the normal course of events.

     The remaining arguments, ARGS, are strings that specify command
     line arguments for the program.

     The value returned by `call-process' (unless you told it not to
     wait) indicates the reason for process termination.  A number
     gives the exit status of the subprocess; 0 means success, and any
     other value means failure.  If the process terminated with a
     signal, `call-process' returns a string describing the signal.

     In the examples below, the buffer `foo' is current.

          (call-process "pwd" nil t)
               => nil

          ---------- Buffer: foo ----------
          /usr/user/lewis/manual
          ---------- Buffer: foo ----------

          (call-process "grep" nil "bar" nil "lewis" "/etc/passwd")
               => nil

          ---------- Buffer: bar ----------
          lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh

          ---------- Buffer: bar ----------

     The `insert-directory' function contains a good example of the use
     of `call-process':

          (call-process insert-directory-program nil t nil switches
                        (if full-directory-p
                            (concat (file-name-as-directory file) ".")
                          file))

 -- Function: call-process-region start end program &optional deletep
          destination displayp &rest args
     This function sends the text between START to END as standard
     input to a process running PROGRAM.  It deletes the text sent if
     DELETEP is non-`nil'; this is useful when BUFFER is `t', to insert
     the output in the current buffer.

     The arguments DESTINATION and DISPLAYP control what to do with the
     output from the subprocess, and whether to update the display as
     it comes in.  For details, see the description of `call-process',
     above.  If DESTINATION is the integer 0, `call-process-region'
     discards the output and returns `nil' immediately, without waiting
     for the subprocess to finish.

     The remaining arguments, ARGS, are strings that specify command
     line arguments for the program.

     The return value of `call-process-region' is just like that of
     `call-process': `nil' if you told it to return without waiting;
     otherwise, a number or string which indicates how the subprocess
     terminated.

     In the following example, we use `call-process-region' to run the
     `cat' utility, with standard input being the first five characters
     in buffer `foo' (the word `input').  `cat' copies its standard
     input into its standard output.  Since the argument DESTINATION is
     `t', this output is inserted in the current buffer.

          ---------- Buffer: foo ----------
          input-!-
          ---------- Buffer: foo ----------

          (call-process-region 1 6 "cat" nil t)
               => nil

          ---------- Buffer: foo ----------
          inputinput-!-
          ---------- Buffer: foo ----------

     The `shell-command-on-region' command uses `call-process-region'
     like this:

          (call-process-region
           start end
           shell-file-name      ; Name of program.
           nil                  ; Do not delete region.
           buffer               ; Send output to `buffer'.
           nil                  ; No redisplay during output.
           "-c" command)        ; Arguments for the shell.

\1f
File: lispref.info,  Node: MS-DOS Subprocesses,  Next: Asynchronous Processes,  Prev: Synchronous Processes,  Up: Processes

56.3 MS-DOS Subprocesses
========================

On MS-DOS, you must indicate whether the data going to and from a
synchronous subprocess are text or binary.  Text data requires
translation between the end-of-line convention used within Emacs (a
single newline character) and the convention used outside Emacs (the
two-character sequence, CRLF).

   The variable `binary-process-input' applies to input sent to the
subprocess, and `binary-process-output' applies to output received from
it.  A non-`nil' value means the data is non-text; `nil' means the data
is text, and calls for conversion.

 -- Variable: binary-process-input
     If this variable is `nil', convert newlines to CRLF sequences in
     the input to a synchronous subprocess.

 -- Variable: binary-process-output
     If this variable is `nil', convert CRLF sequences to newlines in
     the output from a synchronous subprocess.

   *Note Files and MS-DOS::, for related information.

\1f
File: lispref.info,  Node: Asynchronous Processes,  Next: Deleting Processes,  Prev: MS-DOS Subprocesses,  Up: Processes

56.4 Creating an Asynchronous Process
=====================================

After an "asynchronous process" is created, Emacs and the Lisp program
both continue running immediately.  The process may thereafter run in
parallel with Emacs, and the two may communicate with each other using
the functions described in following sections.  Here we describe how to
create an asynchronous process with `start-process'.

 -- Function: start-process name buffer-or-name program &rest args
     This function creates a new asynchronous subprocess and starts the
     program PROGRAM running in it.  It returns a process object that
     stands for the new subprocess in Lisp.  The argument NAME
     specifies the name for the process object; if a process with this
     name already exists, then NAME is modified (by adding `<1>', etc.)
     to be unique.  The buffer BUFFER-OR-NAME is the buffer to
     associate with the process.

     The remaining arguments, ARGS, are strings that specify command
     line arguments for the program.

     In the example below, the first process is started and runs
     (rather, sleeps) for 100 seconds.  Meanwhile, the second process
     is started, and given the name `my-process<1>' for the sake of
     uniqueness.  It inserts the directory listing at the end of the
     buffer `foo', before the first process finishes.  Then it
     finishes, and a message to that effect is inserted in the buffer.
     Much later, the first process finishes, and another message is
     inserted in the buffer for it.

          (start-process "my-process" "foo" "sleep" "100")
               => #<process my-process>

          (start-process "my-process" "foo" "ls" "-l" "/user/lewis/bin")
               => #<process my-process<1>>

          ---------- Buffer: foo ----------
          total 2
          lrwxrwxrwx  1 lewis     14 Jul 22 10:12 gnuemacs --> /emacs
          -rwxrwxrwx  1 lewis     19 Jul 30 21:02 lemon

          Process my-process<1> finished

          Process my-process finished
          ---------- Buffer: foo ----------

 -- Function: start-process-shell-command name buffer-or-name command
          &rest command-args
     This function is like `start-process' except that it uses a shell
     to execute the specified command.  The argument COMMAND is a shell
     command name, and COMMAND-ARGS are the arguments for the shell
     command.

 -- Variable: process-connection-type
     This variable controls the type of device used to communicate with
     asynchronous subprocesses.  If it is non-`nil', then PTYs are
     used, when available.  Otherwise, pipes are used.

     PTYs are usually preferable for processes visible to the user, as
     in Shell mode, because they allow job control (`C-c', `C-z', etc.)
     to work between the process and its children whereas pipes do not.
     For subprocesses used for internal purposes by programs, it is
     often better to use a pipe, because they are more efficient.  In
     addition, the total number of PTYs is limited on many systems and
     it is good not to waste them.  A rule of thumb is to use ptys for
     processes the user interacts with directly, and pipes for
     processes that are hidden from the user.

     The value `process-connection-type' is used when `start-process'
     is called.  So you can specify how to communicate with one
     subprocess by binding the variable around the call to
     `start-process'.

          (let ((process-connection-type nil))  ; Use a pipe.
            (start-process ...))

     To determine whether a given subprocess actually got a pipe or a
     PTY, use the function `process-tty-name' (*note Process
     Information::).

   Lisp functions that manipulate processes usually accept a PROCESS
argument.  Besides using an actual process object for this argument, you
can use a process name, a buffer object, the name of a buffer, or
`nil'.  Specifying a buffer or buffer name for the PROCESS argument
means use the process associated with the buffer (or the most recent
one, if there is more than one).  `nil' means use the process
associated with the current buffer.  *Note Process Information::.
*Note Process Buffers::.

\1f
File: lispref.info,  Node: Deleting Processes,  Next: Process Information,  Prev: Asynchronous Processes,  Up: Processes

56.5 Deleting Processes
=======================

"Deleting a process" disconnects XEmacs immediately from the
subprocess, and removes it from the list of active processes.  It sends
a signal to the subprocess to make the subprocess terminate, but this is
not guaranteed to happen immediately.  The process object itself
continues to exist as long as other Lisp objects point to it.

   You can delete a process explicitly at any time.  Processes are
deleted automatically after they terminate, but not necessarily right
away.  If you delete a terminated process explicitly before it is
deleted automatically, no harm results.

 -- Variable: delete-exited-processes
     This variable controls automatic deletion of processes that have
     terminated (due to calling `exit' or to a signal).  If it is
     `nil', then they continue to exist until the user runs
     `list-processes'.  Otherwise, they are deleted immediately after
     they exit.

 -- Function: delete-process name
     This function deletes the process associated with NAME, killing it
     with a `SIGHUP' signal.  The argument NAME may be a process, the
     name of a process, a buffer, or the name of a buffer.

          (delete-process "*shell*")
               => nil

 -- Function: process-kill-without-query process &optional
          require-query-p
     This function declares that XEmacs need not query the user if
     PROCESS is still running when XEmacs is exited.  The process will
     be deleted silently.  If REQUIRE-QUERY-P is non-`nil', then XEmacs
     _will_ query the user (this is the default).  The return value is
     `t' if a query was formerly required, and `nil' otherwise.

          (process-kill-without-query (get-process "shell"))
               => t

\1f
File: lispref.info,  Node: Process Information,  Next: Input to Processes,  Prev: Deleting Processes,  Up: Processes

56.6 Process Information
========================

Several functions return information about processes.  `list-processes'
is provided for interactive use.

 -- Command: list-processes
     This command displays a listing of all living processes.  In
     addition, it finally deletes any process whose status was `Exited'
     or `Signaled'.  It returns `nil'.

 -- Function: process-list
     This function returns a list of all processes that have not been
     deleted.

          (process-list)
               => (#<process display-time> #<process shell>)

 -- Function: get-process process-name
     This function returns the process named PROCESS-NAME.  If
     PROCESS-NAME is a string and there is no process with that name,
     the value is `nil'.  If PROCESS-NAME is actually a process, it is
     returned as given.  (That is not very useful, so the argument is
     usually a name.) For example:

          (get-process "shell")
               => #<process shell>

 -- Function: process-command process
     This function returns the command that was executed to start
     PROCESS.  This is a list of strings, the first string being the
     program executed and the rest of the strings being the arguments
     that were given to the program.

          (process-command (get-process "shell"))
               => ("/bin/csh" "-i")

 -- Function: process-id process
     This function returns the PID of PROCESS.  This is an integer that
     distinguishes the process PROCESS from all other processes running
     on the same computer at the current time.  The PID of a process is
     chosen by the operating system kernel when the process is started
     and remains constant as long as the process exists.

 -- Function: process-name process
     This function returns the name of PROCESS.

 -- Function: process-status process
     This function returns the status of PROCESS as a symbol.  The
     argument PROCESS must be a process, a buffer, a process name
     (string) or a buffer name (string).

     The possible values for an actual subprocess are:

    `run'
          for a process that is running.

    `stop'
          for a process that is stopped but continuable.

    `exit'
          for a process that has exited.

    `signal'
          for a process that has received a fatal signal.

    `open'
          for a network connection that is open.

    `closed'
          for a network connection that is closed.  Once a connection
          is closed, you cannot reopen it, though you might be able to
          open a new connection to the same place.

    `nil'
          if PROCESS does not identify an existing process.

          (process-status "shell")
               => run
          (process-status (get-buffer "*shell*"))
               => run
          x
               => #<process xx<1>>
          (process-status x)
               => exit

     For a network connection, `process-status' returns one of the
     symbols `open' or `closed'.  The latter means that the other side
     closed the connection, or XEmacs did `delete-process'.

     In earlier Emacs versions (prior to version 19), the status of a
     network connection was `run' if open, and `exit' if closed.

 -- Function: process-kill-without-query-p process
     This function returns whether PROCESS will be killed without
     querying the user, if it is running when XEmacs is exited.  The
     default value is `nil'.

 -- Function: process-exit-status process
     This function returns the exit status of PROCESS or the signal
     number that killed it.  (Use the result of `process-status' to
     determine which of those it is.)  If PROCESS has not yet
     terminated, the value is 0.

 -- Function: process-tty-name process
     This function returns the terminal name that PROCESS is using for
     its communication with Emacs--or `nil' if it is using pipes
     instead of a terminal (see `process-connection-type' in *Note
     Asynchronous Processes::).

\1f
File: lispref.info,  Node: Input to Processes,  Next: Signals to Processes,  Prev: Process Information,  Up: Processes

56.7 Sending Input to Processes
===============================

Asynchronous subprocesses receive input when it is sent to them by
XEmacs, which is done with the functions in this section.  You must
specify the process to send input to, and the input data to send.  The
data appears on the "standard input" of the subprocess.

   Some operating systems have limited space for buffered input in a
PTY.  On these systems, XEmacs sends long input in chunks, with EOF
characters added amidst the other characters, to force the operating
system to periodically drain the input buffer.  For most programs,
these EOFs do no harm.

 -- Function: process-send-string process string &optional start end
     This function sends PROCESS the contents of STRING as standard
     input.

     The argument PROCESS may be a process or the name of a process, or
     a buffer or the name of a buffer, in which case the buffer's
     process is used.  If it is `nil', the current buffer's process is
     used.

     Optional arguments START and END specify part of STRING; see
     `substring'.

     The function returns `nil'.

          (process-send-string "shell<1>" "ls\n")
               => nil


          ---------- Buffer: *shell* ----------
          ...
          introduction.texi               syntax-tables.texi~
          introduction.texi~              text.texi
          introduction.txt                text.texi~
          ...
          ---------- Buffer: *shell* ----------

 -- Function: process-send-region process start end &optional buffer
     This function sends the text in the region defined by START and
     END as standard input to PROCESS.

     The argument PROCESS may be a process or the name of a process, or
     a buffer or the name of a buffer, in which case the buffer's
     process is used.  If it is `nil', the current buffer's process is
     used.

     An error is signaled unless both START and END are integers or
     markers that indicate positions in the current buffer.  (It is
     unimportant which number is larger.)

 -- Function: process-send-eof &optional process
     This function makes PROCESS see an end-of-file in its input.  The
     EOF comes after any text already sent to it.

     PROCESS may be a process, a buffer, the name of a process or
     buffer, or `nil', indicating the current buffer's process.  An
     error is signaled if PROCESS does not identify any process.

     The function returns the process object identified by PROCESS.

          (process-send-eof "shell")
               => "shell"

\1f
File: lispref.info,  Node: Signals to Processes,  Next: Output from Processes,  Prev: Input to Processes,  Up: Processes

56.8 Sending Signals to Processes
=================================

"Sending a signal" to a subprocess is a way of interrupting its
activities.  There are several different signals, each with its own
meaning.  The set of signals and their names is defined by the operating
system.  For example, the signal `SIGINT' means that the user has typed
`C-c', or that some analogous thing has happened.

   Each signal has a standard effect on the subprocess.  Most signals
kill the subprocess, but some stop or resume execution instead.  Most
signals can optionally be handled by programs; if the program handles
the signal, then we can say nothing in general about its effects.

   The set of signals and their names is defined by the operating
system; XEmacs has facilities for sending only a few of the signals
that are defined.  XEmacs can send signals only to its own subprocesses.

   You can send signals explicitly by calling the functions in this
section.  XEmacs also sends signals automatically at certain times:
killing a buffer sends a `SIGHUP' signal to all its associated
processes; killing XEmacs sends a `SIGHUP' signal to all remaining
processes.  (`SIGHUP' is a signal that indicates that the connection
between the user and the process is broken, for example if a connection
via a telephone line is hung up.)

   Each of the signal-sending functions takes two optional arguments:
PROCESS and CURRENT-GROUP.

   The argument PROCESS must be either a process or a buffer, the name
of one, or `nil'.  If it is `nil', the process defaults to the process
associated with the current buffer.  An error is signaled if PROCESS
does not identify a process.

   The argument CURRENT-GROUP is a flag that makes a difference when
you are running a job-control shell as an XEmacs subprocess.  If it is
non-`nil', then the signal is sent to the current foreground process
group of the terminal that XEmacs uses to communicate with the
subprocess.  If the process is a job-control shell, this means the
shell's current subjob.  If it is `nil', the signal is sent to the
process group of the immediate subprocess of XEmacs.  If the subprocess
is a job-control shell, this is the shell itself.

   The flag CURRENT-GROUP has no effect when a pipe is used to
communicate with the subprocess, because the operating system does not
support the distinction in the case of pipes.  For the same reason,
job-control shells won't work when a pipe is used.  See
`process-connection-type' in *Note Asynchronous Processes::.

   Some of the functions below take a SIGNAL argument, which identifies
a signal to be sent.  It must be either an integer or a symbol which
names the signal, like `SIGSEGV'.

 -- Function: process-send-signal signal &optional process current-group
     This function sends the signal SIGNAL to the process PROCESS.  The
     following functions can be implemented in terms of
     `process-send-signal'.

 -- Function: interrupt-process &optional process current-group
     This function interrupts the process PROCESS by sending the signal
     `SIGINT'.  Outside of XEmacs, typing the "interrupt character"
     (normally `C-c') sends this signal.  When the argument
     CURRENT-GROUP is non-`nil', you can think of this function as
     "typing `C-c'" on the terminal by which XEmacs talks to the
     subprocess.

 -- Function: kill-process &optional process current-group
     This function kills the process PROCESS by sending the signal
     `SIGKILL'.  This signal kills the subprocess immediately, and
     cannot be handled by the subprocess.

 -- Function: quit-process &optional process current-group
     This function sends the signal `SIGQUIT' to the process PROCESS.
     This signal is the one sent by the "quit character" (usually
     `C-\') when you are not inside XEmacs.

 -- Function: stop-process &optional process current-group
     This function stops the process PROCESS by sending the signal
     `SIGTSTP'.  Use `continue-process' to resume its execution.

     On systems with job control, the "stop character" (usually `C-z')
     sends this signal (outside of XEmacs).  When CURRENT-GROUP is
     non-`nil', you can think of this function as "typing `C-z'" on the
     terminal XEmacs uses to communicate with the subprocess.

 -- Function: continue-process &optional process current-group
     This function resumes execution of the process PROCESS by sending
     it the signal `SIGCONT'.  This presumes that PROCESS was stopped
     previously.

 -- Command: signal-process pid signal
     This function sends a signal to the process with process id PID,
     which need not be a child of XEmacs.  The argument SIGNAL
     specifies which signal to send.

\1f
File: lispref.info,  Node: Output from Processes,  Next: Sentinels,  Prev: Signals to Processes,  Up: Processes

56.9 Receiving Output from Processes
====================================

There are two ways to receive the output that a subprocess writes to
its standard output stream.  The output can be inserted in a buffer,
which is called the associated buffer of the process, or a function
called the "filter function" can be called to act on the output.  If
the process has no buffer and no filter function, its output is
discarded.

* Menu:

* Process Buffers::       If no filter, output is put in a buffer.
* Filter Functions::      Filter functions accept output from the process.
* Accepting Output::      Explicitly permitting subprocess output.
                            Waiting for subprocess output.

\1f
File: lispref.info,  Node: Process Buffers,  Next: Filter Functions,  Up: Output from Processes

56.9.1 Process Buffers
----------------------

A process can (and usually does) have an "associated buffer", which is
an ordinary Emacs buffer that is used for two purposes: storing the
output from the process, and deciding when to kill the process.  You
can also use the buffer to identify a process to operate on, since in
normal practice only one process is associated with any given buffer.
Many applications of processes also use the buffer for editing input to
be sent to the process, but this is not built into XEmacs Lisp.

   Unless the process has a filter function (*note Filter Functions::),
its output is inserted in the associated buffer.  The position to insert
the output is determined by the `process-mark', which is then updated
to point to the end of the text just inserted.  Usually, but not
always, the `process-mark' is at the end of the buffer.

 -- Function: process-buffer process
     This function returns the associated buffer of the process PROCESS.

          (process-buffer (get-process "shell"))
               => #<buffer *shell*>

 -- Function: process-mark process
     This function returns the process marker for PROCESS, which is the
     marker that says where to insert output from the process.

     If PROCESS does not have a buffer, `process-mark' returns a marker
     that points nowhere.

     Insertion of process output in a buffer uses this marker to decide
     where to insert, and updates it to point after the inserted text.
     That is why successive batches of output are inserted
     consecutively.

     Filter functions normally should use this marker in the same
     fashion as is done by direct insertion of output in the buffer.  A
     good example of a filter function that uses `process-mark' is
     found at the end of the following section.

     When the user is expected to enter input in the process buffer for
     transmission to the process, the process marker is useful for
     distinguishing the new input from previous output.

 -- Function: set-process-buffer process buffer
     This function sets the buffer associated with PROCESS to BUFFER.
     If BUFFER is `nil', the process becomes associated with no buffer.

 -- Function: get-buffer-process buffer-or-name
     This function returns the process associated with BUFFER-OR-NAME.
     If there are several processes associated with BUFFER-OR-NAME,
     then one is chosen.  (Presently, the one chosen is the one most
     recently created.)  It is usually a bad idea to have more than one
     process associated with the same buffer.

          (get-buffer-process "*shell*")
               => #<process shell>

     Killing the process's buffer deletes the process, which kills the
     subprocess with a `SIGHUP' signal (*note Signals to Processes::).

\1f
File: lispref.info,  Node: Filter Functions,  Next: Accepting Output,  Prev: Process Buffers,  Up: Output from Processes

56.9.2 Process Filter Functions
-------------------------------

A process "filter function" is a function that receives the standard
output from the associated process.  If a process has a filter, then
_all_ output from that process is passed to the filter.  The process
buffer is used directly for output from the process only when there is
no filter.

   A filter function must accept two arguments: the associated process
and a string, which is the output.  The function is then free to do
whatever it chooses with the output.

   A filter function runs only while XEmacs is waiting (e.g., for
terminal input, or for time to elapse, or for process output).  This
avoids the timing errors that could result from running filters at
random places in the middle of other Lisp programs.  You may explicitly
cause Emacs to wait, so that filter functions will run, by calling
`sit-for' or `sleep-for' (*note Waiting::), or `accept-process-output'
(*note Accepting Output::).  Emacs is also waiting when the command loop
is reading input.

   Quitting is normally inhibited within a filter function--otherwise,
the effect of typing `C-g' at command level or to quit a user command
would be unpredictable.  If you want to permit quitting inside a filter
function, bind `inhibit-quit' to `nil'.  *Note Quitting::.

   If an error happens during execution of a filter function, it is
caught automatically, so that it doesn't stop the execution of whatever
program was running when the filter function was started.  However, if
`debug-on-error' is non-`nil', the error-catching is turned off.  This
makes it possible to use the Lisp debugger to debug the filter
function.  *Note Debugger::.

   Many filter functions sometimes or always insert the text in the
process's buffer, mimicking the actions of XEmacs when there is no
filter.  Such filter functions need to use `set-buffer' in order to be
sure to insert in that buffer.  To avoid setting the current buffer
semipermanently, these filter functions must use `unwind-protect' to
make sure to restore the previous current buffer.  They should also
update the process marker, and in some cases update the value of point.
Here is how to do these things:

     (defun ordinary-insertion-filter (process string)
       (let ((old-buffer (current-buffer)))
         (unwind-protect
             (let (moving)
               (set-buffer (process-buffer process))
               (setq moving (= (point) (process-mark process)))
               (save-excursion
                 ;; Insert the text, moving the process-marker.
                 (goto-char (process-mark process))
                 (insert string)
                 (set-marker (process-mark process) (point)))
               (if moving (goto-char (process-mark process))))
           (set-buffer old-buffer))))

The reason to use an explicit `unwind-protect' rather than letting
`save-excursion' restore the current buffer is so as to preserve the
change in point made by `goto-char'.

   To make the filter force the process buffer to be visible whenever
new text arrives, insert the following line just before the
`unwind-protect':

     (display-buffer (process-buffer process))

   To force point to move to the end of the new output no matter where
it was previously, eliminate the variable `moving' and call `goto-char'
unconditionally.

   In earlier Emacs versions, every filter function that did regexp
searching or matching had to explicitly save and restore the match data.
Now Emacs does this automatically; filter functions never need to do it
explicitly.  *Note Match Data::.

   A filter function that writes the output into the buffer of the
process should check whether the buffer is still alive.  If it tries to
insert into a dead buffer, it will get an error.  If the buffer is dead,
`(buffer-name (process-buffer PROCESS))' returns `nil'.

   The output to the function may come in chunks of any size.  A program
that produces the same output twice in a row may send it as one batch
of 200 characters one time, and five batches of 40 characters the next.

 -- Function: set-process-filter process filter
     This function gives PROCESS the filter function FILTER.  If FILTER
     is `nil', then the process will have no filter.  If FILTER is `t',
     then no output from the process will be accepted until the filter
     is changed. (Output received during this time is not discarded,
     but is queued, and will be processed as soon as the filter is
     changed.)

 -- Function: process-filter process
     This function returns the filter function of PROCESS, or `nil' if
     it has none.  `t' means that output processing has been stopped.

   Here is an example of use of a filter function:

     (defun keep-output (process output)
        (setq kept (cons output kept)))
          => keep-output
     (setq kept nil)
          => nil
     (set-process-filter (get-process "shell") 'keep-output)
          => keep-output
     (process-send-string "shell" "ls ~/other\n")
          => nil
     kept
          => ("lewis@slug[8] % "
     "FINAL-W87-SHORT.MSS    backup.otl              kolstad.mss~
     address.txt             backup.psf              kolstad.psf
     backup.bib~             david.mss               resume-Dec-86.mss~
     backup.err              david.psf               resume-Dec.psf
     backup.mss              dland                   syllabus.mss
     "
     "#backups.mss#          backup.mss~             kolstad.mss
     ")

\1f
File: lispref.info,  Node: Accepting Output,  Prev: Filter Functions,  Up: Output from Processes

56.9.3 Accepting Output from Processes
--------------------------------------

Output from asynchronous subprocesses normally arrives only while
XEmacs is waiting for some sort of external event, such as elapsed time
or terminal input.  Occasionally it is useful in a Lisp program to
explicitly permit output to arrive at a specific point, or even to wait
until output arrives from a process.

 -- Function: accept-process-output &optional process seconds millisec
     This function allows XEmacs to read pending output from processes.
     The output is inserted in the associated buffers or given to
     their filter functions.  If PROCESS is non-`nil' then this
     function does not return until some output has been received from
     PROCESS.

     The arguments SECONDS and MILLISEC let you specify timeout
     periods.  The former specifies a period measured in seconds and the
     latter specifies one measured in milliseconds.  The two time
     periods thus specified are added together, and
     `accept-process-output' returns after that much time whether or
     not there has been any subprocess output.  Note that SECONDS is
     allowed to be a floating-point number; thus, there is no need to
     ever use MILLISEC. (It is retained for compatibility purposes.)

     The function `accept-process-output' returns non-`nil' if it did
     get some output, or `nil' if the timeout expired before output
     arrived.

\1f
File: lispref.info,  Node: Sentinels,  Next: Process Window Size,  Prev: Output from Processes,  Up: Processes

56.10 Sentinels: Detecting Process Status Changes
=================================================

A "process sentinel" is a function that is called whenever the
associated process changes status for any reason, including signals
(whether sent by XEmacs or caused by the process's own actions) that
terminate, stop, or continue the process.  The process sentinel is also
called if the process exits.  The sentinel receives two arguments: the
process for which the event occurred, and a string describing the type
of event.

   The string describing the event looks like one of the following:

   * `"finished\n"'.

   * `"exited abnormally with code EXITCODE\n"'.

   * `"NAME-OF-SIGNAL\n"'.

   * `"NAME-OF-SIGNAL (core dumped)\n"'.

   A sentinel runs only while XEmacs is waiting (e.g., for terminal
input, or for time to elapse, or for process output).  This avoids the
timing errors that could result from running them at random places in
the middle of other Lisp programs.  A program can wait, so that
sentinels will run, by calling `sit-for' or `sleep-for' (*note
Waiting::), or `accept-process-output' (*note Accepting Output::).
Emacs is also waiting when the command loop is reading input.

   Quitting is normally inhibited within a sentinel--otherwise, the
effect of typing `C-g' at command level or to quit a user command would
be unpredictable.  If you want to permit quitting inside a sentinel,
bind `inhibit-quit' to `nil'.  *Note Quitting::.

   A sentinel that writes the output into the buffer of the process
should check whether the buffer is still alive.  If it tries to insert
into a dead buffer, it will get an error.  If the buffer is dead,
`(buffer-name (process-buffer PROCESS))' returns `nil'.

   If an error happens during execution of a sentinel, it is caught
automatically, so that it doesn't stop the execution of whatever
programs was running when the sentinel was started.  However, if
`debug-on-error' is non-`nil', the error-catching is turned off.  This
makes it possible to use the Lisp debugger to debug the sentinel.
*Note Debugger::.

   In earlier Emacs versions, every sentinel that did regexp searching
or matching had to explicitly save and restore the match data.  Now
Emacs does this automatically; sentinels never need to do it explicitly.
*Note Match Data::.

 -- Function: set-process-sentinel process sentinel
     This function associates SENTINEL with PROCESS.  If SENTINEL is
     `nil', then the process will have no sentinel.  The default
     behavior when there is no sentinel is to insert a message in the
     process's buffer when the process status changes.

          (defun msg-me (process event)
             (princ
               (format "Process: %s had the event `%s'" process event)))
          (set-process-sentinel (get-process "shell") 'msg-me)
               => msg-me
          (kill-process (get-process "shell"))
               -| Process: #<process shell> had the event `killed'
               => #<process shell>

 -- Function: process-sentinel process
     This function returns the sentinel of PROCESS, or `nil' if it has
     none.

 -- Function: waiting-for-user-input-p
     While a sentinel or filter function is running, this function
     returns non-`nil' if XEmacs was waiting for keyboard input from
     the user at the time the sentinel or filter function was called,
     `nil' if it was not.

\1f
File: lispref.info,  Node: Process Window Size,  Next: Transaction Queues,  Prev: Sentinels,  Up: Processes

56.11 Process Window Size
=========================

 -- Function: set-process-window-size process height width
     This function tells PROCESS that its logical window size is HEIGHT
     by WIDTH characters.  This is principally useful with pty's.

\1f
File: lispref.info,  Node: Transaction Queues,  Next: Network,  Prev: Process Window Size,  Up: Processes

56.12 Transaction Queues
========================

You can use a "transaction queue" for more convenient communication
with subprocesses using transactions.  First use `tq-create' to create
a transaction queue communicating with a specified process.  Then you
can call `tq-enqueue' to send a transaction.

 -- Function: tq-create process
     This function creates and returns a transaction queue
     communicating with PROCESS.  The argument PROCESS should be a
     subprocess capable of sending and receiving streams of bytes.  It
     may be a child process, or it may be a TCP connection to a server,
     possibly on another machine.

 -- Function: tq-enqueue queue question regexp closure fn
     This function sends a transaction to queue QUEUE.  Specifying the
     queue has the effect of specifying the subprocess to talk to.

     The argument QUESTION is the outgoing message that starts the
     transaction.  The argument FN is the function to call when the
     corresponding answer comes back; it is called with two arguments:
     CLOSURE, and the answer received.

     The argument REGEXP is a regular expression that should match the
     entire answer, but nothing less; that's how `tq-enqueue' determines
     where the answer ends.

     The return value of `tq-enqueue' itself is not meaningful.

 -- Function: tq-close queue
     Shut down transaction queue QUEUE, waiting for all pending
     transactions to complete, and then terminate the connection or
     child process.

   Transaction queues are implemented by means of a filter function.
*Note Filter Functions::.

\1f
File: lispref.info,  Node: Network,  Prev: Transaction Queues,  Up: Processes

56.13 Network Connections
=========================

XEmacs Lisp programs can open TCP network connections to other
processes on the same machine or other machines.  A network connection
is handled by Lisp much like a subprocess, and is represented by a
process object.  However, the process you are communicating with is not
a child of the XEmacs process, so you can't kill it or send it signals.
All you can do is send and receive data.  `delete-process' closes the
connection, but does not kill the process at the other end; that
process must decide what to do about closure of the connection.

   You can distinguish process objects representing network connections
from those representing subprocesses with the `process-status'
function.  It always returns either `open' or `closed' for a network
connection, and it never returns either of those values for a real
subprocess.  *Note Process Information::.

 -- Function: open-network-stream name buffer-or-name host service
          &optional protocol
     This function opens a TCP connection for a service to a host.  It
     returns a process object to represent the connection.

     Input and output work as for other process objects.
     `delete-process' closes the connection.

     The NAME argument specifies the name for the process object.  It
     is modified as necessary to make it unique.

     The BUFFER-OR-NAME argument is the buffer to associate with the
     connection.  It can be a buffer or the name of one.  Output from
     the connection is inserted in the buffer, unless you specify a
     filter function to handle the output.  If BUFFER-OR-NAME is `nil',
     it means that the connection is not associated with any buffer.

     The arguments HOST and SERVICE specify where to connect to; HOST
     is the host name or IP address (a string), and SERVICE is the name
     of a defined network service (a string) or a port number (an
     integer).

     Optional fifth arg PROTOCOL is the network protocol to use.
     Currently only `tcp' (Transmission Control Protocol) and `udp'
     (User Datagram Protocol) are supported.  When omitted, `tcp' is
     assumed.

     Output via `process-send-string' and input via buffer or filter
     (see `set-process-filter') are stream-oriented.  That means UDP
     datagrams are not guaranteed to be sent and received in discrete
     packets. (But small datagrams around 500 bytes that are not
     truncated by `process-send-string' are usually fine.)  Note further
     that the UDP protocol does not guard against lost packets.

\1f
File: lispref.info,  Node: System Interface,  Next: X-Windows,  Prev: Processes,  Up: Top

57 Operating System Interface
*****************************

This chapter is about starting and getting out of Emacs, access to
values in the operating system environment, and terminal input, output,
and flow control.

   *Note Building XEmacs::, for related information.  See also *Note
Display::, for additional operating system status information
pertaining to the terminal and the screen.

* Menu:

* Starting Up::         Customizing XEmacs start-up processing.
* Getting Out::         How exiting works (permanent or temporary).
* System Environment::  Distinguish the name and kind of system.
* User Identification:: Finding the name and user id of the user.
* Time of Day::         Getting the current time.
* Time Conversion::     Converting a time from numeric form to a string, or
                          to calendrical data (or vice versa).
* Timers::              Setting a timer to call a function at a certain time.
* Terminal Input::      Recording terminal input for debugging.
* Terminal Output::     Recording terminal output for debugging.
* Flow Control::        How to turn output flow control on or off.
* Batch Mode::          Running XEmacs without terminal interaction.

\1f
File: lispref.info,  Node: Starting Up,  Next: Getting Out,  Up: System Interface

57.1 Starting Up XEmacs
=======================

This section describes what XEmacs does when it is started, and how you
can customize these actions.

* Menu:

* Start-up Summary::        Sequence of actions XEmacs performs at start-up.
* Init File::               Details on reading the init file (`.emacs').
* Terminal-Specific::       How the terminal-specific Lisp file is read.
* Command Line Arguments::  How command line arguments are processed,
                              and how you can customize them.

\1f
File: lispref.info,  Node: Start-up Summary,  Next: Init File,  Up: Starting Up

57.1.1 Summary: Sequence of Actions at Start Up
-----------------------------------------------

The order of operations performed (in `startup.el') by XEmacs when it
is started up is as follows:

  1. It loads the initialization library for the window system, if you
     are using a window system.  This library's name is
     `term/WINDOWSYSTEM-win.el'.

  2. It processes the initial options.  (Some of them are handled even
     earlier than this.)

  3. It initializes the X window frame and faces, if appropriate.

  4. It runs the normal hook `before-init-hook'.

  5. It loads the library `site-start', unless the option
     `-no-site-file' was specified.  The library's file name is usually
     `site-start.el'.  

  6. It loads the file `~/.emacs' unless `-q' was specified on the
     command line.  (This is not done in `-batch' mode.)  The `-u'
     option can specify the user name whose home directory should be
     used instead of `~'.

  7. It loads the library `default' unless `inhibit-default-init' is
     non-`nil'.  (This is not done in `-batch' mode or if `-q' was
     specified on the command line.)  The library's file name is
     usually `default.el'.  

  8. It runs the normal hook `after-init-hook'.

  9. It sets the major mode according to `initial-major-mode', provided
     the buffer `*scratch*' is still current and still in Fundamental
     mode.

 10. It loads the terminal-specific Lisp file, if any, except when in
     batch mode or using a window system.

 11. It displays the initial echo area message, unless you have
     suppressed that with `inhibit-startup-echo-area-message'.

 12. It processes the action arguments from the command line.

 13. It runs `term-setup-hook'.

 14. It calls `frame-notice-user-settings', which modifies the
     parameters of the selected frame according to whatever the init
     files specify.

 15. It runs `window-setup-hook'.  *Note Terminal-Specific::.

 16. It displays copyleft, nonwarranty, and basic use information,
     provided there were no remaining command line arguments (a few
     steps above) and the value of `inhibit-startup-message' is `nil'.

 -- User Option: inhibit-startup-message
     This variable inhibits the initial startup messages (the
     nonwarranty, etc.).  If it is non-`nil', then the messages are not
     printed.

     This variable exists so you can set it in your personal init file,
     once you are familiar with the contents of the startup message.
     Do not set this variable in the init file of a new user, or in a
     way that affects more than one user, because that would prevent
     new users from receiving the information they are supposed to see.

 -- User Option: inhibit-startup-echo-area-message
     This variable controls the display of the startup echo area
     message.  You can suppress the startup echo area message by adding
     text with this form to your `.emacs' file:

          (setq inhibit-startup-echo-area-message
                "YOUR-LOGIN-NAME")

     Simply setting `inhibit-startup-echo-area-message' to your login
     name is not sufficient to inhibit the message; Emacs explicitly
     checks whether `.emacs' contains an expression as shown above.
     Your login name must appear in the expression as a Lisp string
     constant.

     This way, you can easily inhibit the message for yourself if you
     wish, but thoughtless copying of your `.emacs' file will not
     inhibit the message for someone else.

\1f
File: lispref.info,  Node: Init File,  Next: Terminal-Specific,  Prev: Start-up Summary,  Up: Starting Up

57.1.2 The Init File: `.emacs'
------------------------------

When you start XEmacs, it normally attempts to load the file `.emacs'
from your home directory.  This file, if it exists, must contain Lisp
code.  It is called your "init file".  The command line switches `-q'
and `-u' affect the use of the init file; `-q' says not to load an init
file, and `-u' says to load a specified user's init file instead of
yours.  *Note Entering XEmacs: (xemacs)Entering XEmacs.

   A site may have a "default init file", which is the library named
`default.el'.  XEmacs finds the `default.el' file through the standard
search path for libraries (*note How Programs Do Loading::).  The
XEmacs distribution does not come with this file; sites may provide one
for local customizations.  If the default init file exists, it is
loaded whenever you start Emacs, except in batch mode or if `-q' is
specified.  But your own personal init file, if any, is loaded first; if
it sets `inhibit-default-init' to a non-`nil' value, then XEmacs does
not subsequently load the `default.el' file.

   Another file for site-customization is `site-start.el'.  Emacs loads
this _before_ the user's init file.  You can inhibit the loading of
this file with the option `-no-site-file'.

 -- Variable: site-run-file
     This variable specifies the site-customization file to load before
     the user's init file.  Its normal value is `"site-start"'.

   If there is a great deal of code in your `.emacs' file, you should
move it into another file named `SOMETHING.el', byte-compile it (*note
Byte Compilation::), and make your `.emacs' file load the other file
using `load' (*note Loading::).

   *Note Init File Examples: (xemacs)Init File Examples, for examples
of how to make various commonly desired customizations in your `.emacs'
file.

 -- User Option: inhibit-default-init
     This variable prevents XEmacs from loading the default
     initialization library file for your session of XEmacs.  If its
     value is non-`nil', then the default library is not loaded.  The
     default value is `nil'.

 -- Variable: before-init-hook
 -- Variable: after-init-hook
     These two normal hooks are run just before, and just after,
     loading of the user's init file, `default.el', and/or
     `site-start.el'.

\1f
File: lispref.info,  Node: Terminal-Specific,  Next: Command Line Arguments,  Prev: Init File,  Up: Starting Up

57.1.3 Terminal-Specific Initialization
---------------------------------------

Each terminal type can have its own Lisp library that XEmacs loads when
run on that type of terminal.  For a terminal type named TERMTYPE, the
library is called `term/TERMTYPE'.  XEmacs finds the file by searching
the `load-path' directories as it does for other files, and trying the
`.elc' and `.el' suffixes.  Normally, terminal-specific Lisp library is
located in `emacs/lisp/term', a subdirectory of the `emacs/lisp'
directory in which most XEmacs Lisp libraries are kept.

   The library's name is constructed by concatenating the value of the
variable `term-file-prefix' and the terminal type.  Normally,
`term-file-prefix' has the value `"term/"'; changing this is not
recommended.

   The usual function of a terminal-specific library is to enable
special keys to send sequences that XEmacs can recognize.  It may also
need to set or add to `function-key-map' if the Termcap entry does not
specify all the terminal's function keys.  *Note Terminal Input::.

   When the name of the terminal type contains a hyphen, only the part
of the name before the first hyphen is significant in choosing the
library name.  Thus, terminal types `aaa-48' and `aaa-30-rv' both use
the `term/aaa' library.  If necessary, the library can evaluate
`(getenv "TERM")' to find the full name of the terminal type.

   Your `.emacs' file can prevent the loading of the terminal-specific
library by setting the variable `term-file-prefix' to `nil'.  This
feature is useful when experimenting with your own peculiar
customizations.

   You can also arrange to override some of the actions of the
terminal-specific library by setting the variable `term-setup-hook'.
This is a normal hook which XEmacs runs using `run-hooks' at the end of
XEmacs initialization, after loading both your `.emacs' file and any
terminal-specific libraries.  You can use this variable to define
initializations for terminals that do not have their own libraries.
*Note Hooks::.

 -- Variable: term-file-prefix
     If the `term-file-prefix' variable is non-`nil', XEmacs loads a
     terminal-specific initialization file as follows:

          (load (concat term-file-prefix (getenv "TERM")))

     You may set the `term-file-prefix' variable to `nil' in your
     `.emacs' file if you do not wish to load the
     terminal-initialization file.  To do this, put the following in
     your `.emacs' file: `(setq term-file-prefix nil)'.

 -- Variable: term-setup-hook
     This variable is a normal hook that XEmacs runs after loading your
     `.emacs' file, the default initialization file (if any) and the
     terminal-specific Lisp file.

     You can use `term-setup-hook' to override the definitions made by a
     terminal-specific file.

 -- Variable: window-setup-hook
     This variable is a normal hook which XEmacs runs after loading your
     `.emacs' file and the default initialization file (if any), after
     loading terminal-specific Lisp code, and after running the hook
     `term-setup-hook'.

\1f
File: lispref.info,  Node: Command Line Arguments,  Prev: Terminal-Specific,  Up: Starting Up

57.1.4 Command Line Arguments
-----------------------------

You can use command line arguments to request various actions when you
start XEmacs.  Since you do not need to start XEmacs more than once per
day, and will often leave your XEmacs session running longer than that,
command line arguments are hardly ever used.  As a practical matter, it
is best to avoid making the habit of using them, since this habit would
encourage you to kill and restart XEmacs unnecessarily often.  These
options exist for two reasons: to be compatible with other editors (for
invocation by other programs) and to enable shell scripts to run
specific Lisp programs.

   This section describes how Emacs processes command line arguments,
and how you can customize them.

 -- Function: command-line
     This function parses the command line that XEmacs was called with,
     processes it, loads the user's `.emacs' file and displays the
     startup messages.

 -- Variable: command-line-processed
     The value of this variable is `t' once the command line has been
     processed.

     If you redump XEmacs by calling `dump-emacs', you may wish to set
     this variable to `nil' first in order to cause the new dumped
     XEmacs to process its new command line arguments.

 -- Variable: command-switch-alist
     The value of this variable is an alist of user-defined command-line
     options and associated handler functions.  This variable exists so
     you can add elements to it.

     A "command line option" is an argument on the command line of the
     form:

          -OPTION

     The elements of the `command-switch-alist' look like this:

          (OPTION . HANDLER-FUNCTION)

     The HANDLER-FUNCTION is called to handle OPTION and receives the
     option name as its sole argument.

     In some cases, the option is followed in the command line by an
     argument.  In these cases, the HANDLER-FUNCTION can find all the
     remaining command-line arguments in the variable
     `command-line-args-left'.  (The entire list of command-line
     arguments is in `command-line-args'.)

     The command line arguments are parsed by the `command-line-1'
     function in the `startup.el' file.  See also *Note Command Line
     Switches and Arguments: (xemacs)Command Switches.

 -- Variable: command-line-args
     The value of this variable is the list of command line arguments
     passed to XEmacs.

 -- Variable: command-line-functions
     This variable's value is a list of functions for handling an
     unrecognized command-line argument.  Each time the next argument
     to be processed has no special meaning, the functions in this list
     are called, in order of appearance, until one of them returns a
     non-`nil' value.

     These functions are called with no arguments.  They can access the
     command-line argument under consideration through the variable
     `argi'.  The remaining arguments (not including the current one)
     are in the variable `command-line-args-left'.

     When a function recognizes and processes the argument in `argi', it
     should return a non-`nil' value to say it has dealt with that
     argument.  If it has also dealt with some of the following
     arguments, it can indicate that by deleting them from
     `command-line-args-left'.

     If all of these functions return `nil', then the argument is used
     as a file name to visit.

\1f
File: lispref.info,  Node: Getting Out,  Next: System Environment,  Prev: Starting Up,  Up: System Interface

57.2 Getting out of XEmacs
==========================

There are two ways to get out of XEmacs: you can kill the XEmacs job,
which exits permanently, or you can suspend it, which permits you to
reenter the XEmacs process later.  As a practical matter, you seldom
kill XEmacs--only when you are about to log out.  Suspending is much
more common.

* Menu:

* Killing XEmacs::        Exiting XEmacs irreversibly.
* Suspending XEmacs::     Exiting XEmacs reversibly.

\1f
File: lispref.info,  Node: Killing XEmacs,  Next: Suspending XEmacs,  Up: Getting Out

57.2.1 Killing XEmacs
---------------------

Killing XEmacs means ending the execution of the XEmacs process.  The
parent process normally resumes control.  The low-level primitive for
killing XEmacs is `kill-emacs'.

 -- Command: kill-emacs &optional exit-data
     This function exits the XEmacs process and kills it.

     If EXIT-DATA is an integer, then it is used as the exit status of
     the XEmacs process.  (This is useful primarily in batch operation;
     see *Note Batch Mode::.)

     If EXIT-DATA is a string, its contents are stuffed into the
     terminal input buffer so that the shell (or whatever program next
     reads input) can read them.

   All the information in the XEmacs process, aside from files that have
been saved, is lost when the XEmacs is killed.  Because killing XEmacs
inadvertently can lose a lot of work, XEmacs queries for confirmation
before actually terminating if you have buffers that need saving or
subprocesses that are running.  This is done in the function
`save-buffers-kill-emacs'.

 -- Variable: kill-emacs-query-functions
     After asking the standard questions, `save-buffers-kill-emacs'
     calls the functions in the list `kill-buffer-query-functions', in
     order of appearance, with no arguments.  These functions can ask
     for additional confirmation from the user.  If any of them returns
     non-`nil', XEmacs is not killed.

 -- Variable: kill-emacs-hook
     This variable is a normal hook; once `save-buffers-kill-emacs' is
     finished with all file saving and confirmation, it runs the
     functions in this hook.

\1f
File: lispref.info,  Node: Suspending XEmacs,  Prev: Killing XEmacs,  Up: Getting Out

57.2.2 Suspending XEmacs
------------------------

"Suspending XEmacs" means stopping XEmacs temporarily and returning
control to its superior process, which is usually the shell.  This
allows you to resume editing later in the same XEmacs process, with the
same buffers, the same kill ring, the same undo history, and so on.  To
resume XEmacs, use the appropriate command in the parent shell--most
likely `fg'.

   Some operating systems do not support suspension of jobs; on these
systems, "suspension" actually creates a new shell temporarily as a
subprocess of XEmacs.  Then you would exit the shell to return to
XEmacs.

   Suspension is not useful with window systems such as X, because the
XEmacs job may not have a parent that can resume it again, and in any
case you can give input to some other job such as a shell merely by
moving to a different window.  Therefore, suspending is not allowed
when XEmacs is an X client.

 -- Command: suspend-emacs &optional stuffstring
     This function stops XEmacs and returns control to the superior
     process.  If and when the superior process resumes XEmacs,
     `suspend-emacs' returns `nil' to its caller in Lisp.

     If optional arg STUFFSTRING is non-`nil', its characters are sent
     to be read as terminal input by XEmacs's superior shell.  The
     characters in STUFFSTRING are not echoed by the superior shell;
     only the results appear.

     Before suspending, `suspend-emacs' runs the normal hook
     `suspend-hook'.  In Emacs version 18, `suspend-hook' was not a
     normal hook; its value was a single function, and if its value was
     non-`nil', then `suspend-emacs' returned immediately without
     actually suspending anything.

     After the user resumes XEmacs, `suspend-emacs' runs the normal hook
     `suspend-resume-hook'.  *Note Hooks::.

     The next redisplay after resumption will redraw the entire screen,
     unless the variable `no-redraw-on-reenter' is non-`nil' (*note
     Refresh Screen::).

     In the following example, note that `pwd' is not echoed after
     XEmacs is suspended.  But it is read and executed by the shell.

          (suspend-emacs)
               => nil

          (add-hook 'suspend-hook
                    (function (lambda ()
                                (or (y-or-n-p
                                      "Really suspend? ")
                                    (error "Suspend cancelled")))))
               => (lambda nil
                    (or (y-or-n-p "Really suspend? ")
                        (error "Suspend cancelled")))
          (add-hook 'suspend-resume-hook
                    (function (lambda () (message "Resumed!"))))
               => (lambda nil (message "Resumed!"))
          (suspend-emacs "pwd")
               => nil
          ---------- Buffer: Minibuffer ----------
          Really suspend? y
          ---------- Buffer: Minibuffer ----------

          ---------- Parent Shell ----------
          lewis@slug[23] % /user/lewis/manual
          lewis@slug[24] % fg

          ---------- Echo Area ----------
          Resumed!

 -- Variable: suspend-hook
     This variable is a normal hook run before suspending.

 -- Variable: suspend-resume-hook
     This variable is a normal hook run after suspending.

\1f
File: lispref.info,  Node: System Environment,  Next: User Identification,  Prev: Getting Out,  Up: System Interface

57.3 Operating System Environment
=================================

XEmacs provides access to variables in the operating system environment
through various functions.  These variables include the name of the
system, the user's UID, and so on.

 -- Variable: system-type
     The value of this variable is a symbol indicating the type of
     operating system XEmacs is operating on.  Here is a table of the
     possible values:

    `aix-v3'
          AIX.

    `berkeley-unix'
          Berkeley BSD.

    `dgux'
          Data General DGUX operating system.

    `gnu'
          A GNU system using the GNU HURD and Mach.

    `hpux'
          Hewlett-Packard HPUX operating system.

    `irix'
          Silicon Graphics Irix system.

    `linux'
          A GNU system using the Linux kernel.

    `ms-dos'
          Microsoft MS-DOS "operating system."

    `next-mach'
          NeXT Mach-based system.

    `rtu'
          Masscomp RTU, UCB universe.

    `unisoft-unix'
          UniSoft UniPlus.

    `usg-unix-v'
          AT&T System V.

    `windows-nt'
          Microsoft windows NT.

    `xenix'
          SCO Xenix 386.

     We do not wish to add new symbols to make finer distinctions
     unless it is absolutely necessary!  In fact, we hope to eliminate
     some of these alternatives in the future.  We recommend using
     `system-configuration' to distinguish between different operating
     systems.

 -- Variable: system-configuration
     This variable holds the three-part configuration name for the
     hardware/software configuration of your system, as a string.  The
     convenient way to test parts of this string is with `string-match'.

 -- Function: system-name
     This function returns the name of the machine you are running on.
          (system-name)
               => "prep.ai.mit.edu"

   The symbol `system-name' is a variable as well as a function.  In
fact, the function returns whatever value the variable `system-name'
currently holds.  Thus, you can set the variable `system-name' in case
Emacs is confused about the name of your system.  The variable is also
useful for constructing frame titles (*note Frame Titles::).

 -- Variable: mail-host-address
     If this variable is non-`nil', it is used instead of `system-name'
     for purposes of generating email addresses.  For example, it is
     used when constructing the default value of `user-mail-address'.
     *Note User Identification::.  (Since this is done when XEmacs
     starts up, the value actually used is the one saved when XEmacs
     was dumped.  *Note Building XEmacs::.)

 -- Command: getenv var &optional interactivep
     This function returns the value of the environment variable VAR,
     as a string.  Within XEmacs, the environment variable values are
     kept in the Lisp variable `process-environment'.

     When invoked interactively, `getenv' prints the value in the echo
     area.

          (getenv "USER")
               => "lewis"

          lewis@slug[10] % printenv
          PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin
          USER=lewis
          TERM=ibmapa16
          SHELL=/bin/csh
          HOME=/user/lewis

 -- Command: setenv variable &optional value unset
     This command sets the value of the environment variable named
     VARIABLE to VALUE.  Both arguments should be strings.  This
     function works by modifying `process-environment'; binding that
     variable with `let' is also reasonable practice.

 -- Variable: process-environment
     This variable is a list of strings, each describing one environment
     variable.  The functions `getenv' and `setenv' work by
     manipulating this variable.

          process-environment
          => ("l=/usr/stanford/lib/gnuemacs/lisp"
              "PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin"
              "USER=lewis"
              "TERM=ibmapa16"
              "SHELL=/bin/csh"
              "HOME=/user/lewis")

 -- Variable: path-separator
     This variable holds a string which says which character separates
     directories in a search path (as found in an environment
     variable).  Its value is `":"' for Unix and GNU systems, and `";"'
     for MS-DOS and Windows NT.

 -- Variable: invocation-name
     This variable holds the program name under which Emacs was
     invoked.  The value is a string, and does not include a directory
     name.

 -- Variable: invocation-directory
     This variable holds the directory from which the Emacs executable
     was invoked, or perhaps `nil' if that directory cannot be
     determined.

 -- Variable: installation-directory
     If non-`nil', this is a directory within which to look for the
     `lib-src' and `etc' subdirectories.  This is non-`nil' when Emacs
     can't find those directories in their standard installed
     locations, but can find them in a directory related somehow to the
     one containing the Emacs executable.

 -- Function: load-average &optional use-floats
     This function returns a list of the current 1-minute, 5-minute and
     15-minute load averages.  The values are integers that are 100
     times the system load averages.  (The load averages indicate the
     number of processes trying to run.)

     When USE-FLOATS is non-`nil', floats will be returned instead of
     integers.  These floats are not multiplied by 100.

          (load-average)
               => (169 158 164)
          (load-average t)
               => (1.69921875 1.58984375 1.640625)

          lewis@rocky[5] % uptime
            8:06pm  up 16 day(s), 21:57,  40 users,
           load average: 1.68, 1.59, 1.64

     If the 5-minute or 15-minute load averages are not available,
     return a shortened list, containing only those averages which are
     available.

     On some systems, this function may require special privileges to
     run, or it may be unimplemented for the particular system type.
     In that case, the function will signal an error.

 -- Function: emacs-pid
     This function returns the process ID of the Emacs process.

\1f
File: lispref.info,  Node: User Identification,  Next: Time of Day,  Prev: System Environment,  Up: System Interface

57.4 User Identification
========================

 -- Variable: user-mail-address
     This holds the nominal email address of the user who is using
     Emacs.  When Emacs starts up, it computes a default value that is
     usually right, but users often set this themselves when the
     default value is not right.

 -- Function: user-login-name &optional uid
     If you don't specify UID, this function returns the name under
     which the user is logged in.  If the environment variable `LOGNAME'
     is set, that value is used.  Otherwise, if the environment variable
     `USER' is set, that value is used.  Otherwise, the value is based
     on the effective UID, not the real UID.

     If you specify UID, the value is the user name that corresponds to
     UID (which should be an integer).

          (user-login-name)
               => "lewis"

 -- Function: user-real-login-name
     This function returns the user name corresponding to Emacs's real
     UID.  This ignores the effective UID and ignores the environment
     variables `LOGNAME' and `USER'.

 -- Variable: user-full-name
     This variable holds the name of the user running this Emacs.  It is
     initialized at startup time from the value of `NAME' environment
     variable.  You can change the value of this variable to alter the
     result of the `user-full-name' function.

 -- Function: user-full-name &optional user
     This function returns the full name of USER.  If USER is `nil', it
     defaults to the user running this Emacs.  In that case, the value
     of `user-full-name' variable, if non-`nil', will be used.

     If USER is specified explicitly, `user-full-name' variable is
     ignored.

          (user-full-name)
               => "Hrvoje Niksic"
          (setq user-full-name "Hrvoje \"Niksa\" Niksic")
          (user-full-name)
               => "Hrvoje \"Niksa\" Niksic"
          (user-full-name "hniksic")
               => "Hrvoje Niksic"

   The symbols `user-login-name', `user-real-login-name' and
`user-full-name' are variables as well as functions.  The functions
return the same values that the variables hold.  These variables allow
you to "fake out" Emacs by telling the functions what to return.  The
variables are also useful for constructing frame titles (*note Frame
Titles::).

 -- Function: user-real-uid
     This function returns the real UID of the user.

          (user-real-uid)
               => 19

 -- Function: user-uid
     This function returns the effective UID of the user.

 -- Function: user-home-directory
     This function returns the "`HOME'" directory of the user, and is
     intended to replace occurrences of "`(getenv "HOME")'".  Under
     Unix systems, the following is done:

       1. Return the value of "`(getenv "HOME")'", if set.

       2. Return "/", as a fallback, but issue a warning.  (Future
          versions of XEmacs will also attempt to lookup the `HOME'
          directory via `getpwent()', but this has not yet been
          implemented.)

     Under MS Windows, this is done:

       1. Return the value of "`(getenv "HOME")'", if set.

       2. If the environment variables `HOMEDRIVE' and `HOMEDIR' are
          both set, return the concatenation (the following description
          uses MS Windows environment variable substitution syntax):
          `%HOMEDRIVE%%HOMEDIR%'.

       3. Return "C:\", as a fallback, but issue a warning.

\1f
File: lispref.info,  Node: Time of Day,  Next: Time Conversion,  Prev: User Identification,  Up: System Interface

57.5 Time of Day
================

This section explains how to determine the current time and the time
zone.

 -- Function: current-time-string &optional time-value
     This function returns the current time and date as a
     humanly-readable string.  The format of the string is unvarying;
     the number of characters used for each part is always the same, so
     you can reliably use `substring' to extract pieces of it.  It is
     wise to count the characters from the beginning of the string
     rather than from the end, as additional information may be added
     at the end.

     The argument TIME-VALUE, if given, specifies a time to format
     instead of the current time.  The argument should be a list whose
     first two elements are integers.  Thus, you can use times obtained
     from `current-time' (see below) and from `file-attributes' (*note
     File Attributes::).

          (current-time-string)
               => "Wed Oct 14 22:21:05 1987"

 -- Function: current-time
     This function returns the system's time value as a list of three
     integers: `(HIGH LOW MICROSEC)'.  The integers HIGH and LOW
     combine to give the number of seconds since 0:00 January 1, 1970,
     which is HIGH * 2**16 + LOW.

     The third element, MICROSEC, gives the microseconds since the
     start of the current second (or 0 for systems that return time
     only on the resolution of a second).

     The first two elements can be compared with file time values such
     as you get with the function `file-attributes'.  *Note File
     Attributes::.

 -- Function: current-time-zone &optional time-value
     This function returns a list describing the time zone that the
     user is in.

     The value has the form `(OFFSET NAME)'.  Here OFFSET is an integer
     giving the number of seconds ahead of UTC (east of Greenwich).  A
     negative value means west of Greenwich.  The second element, NAME
     is a string giving the name of the time zone.  Both elements
     change when daylight savings time begins or ends; if the user has
     specified a time zone that does not use a seasonal time
     adjustment, then the value is constant through time.

     If the operating system doesn't supply all the information
     necessary to compute the value, both elements of the list are
     `nil'.

     The argument TIME-VALUE, if given, specifies a time to analyze
     instead of the current time.  The argument should be a cons cell
     containing two integers, or a list whose first two elements are
     integers.  Thus, you can use times obtained from `current-time'
     (see above) and from `file-attributes' (*note File Attributes::).

\1f
File: lispref.info,  Node: Time Conversion,  Next: Timers,  Prev: Time of Day,  Up: System Interface

57.6 Time Conversion
====================

These functions convert time values (lists of two or three integers) to
strings or to calendrical information.  There is also a function to
convert calendrical information to a time value.  You can get time
values from the functions `current-time' (*note Time of Day::) and
`file-attributes' (*note File Attributes::).

 -- Function: format-time-string format-string &optional time
     This function converts TIME to a string according to
     FORMAT-STRING.  If TIME is omitted, it defaults to the current
     time.  The argument FORMAT-STRING may contain `%'-sequences which
     say to substitute parts of the time.  Here is a table of what the
     `%'-sequences mean:

    `%a'
          This stands for the abbreviated name of the day of week.

    `%A'
          This stands for the full name of the day of week.

    `%b'
          This stands for the abbreviated name of the month.

    `%B'
          This stands for the full name of the month.

    `%c'
          This is a synonym for `%x %X'.

    `%C'
          This has a locale-specific meaning.  In the default locale
          (named C), it is equivalent to `%A, %B %e, %Y'.

    `%d'
          This stands for the day of month, zero-padded.

    `%D'
          This is a synonym for `%m/%d/%y'.

    `%e'
          This stands for the day of month, blank-padded.

    `%h'
          This is a synonym for `%b'.

    `%H'
          This stands for the hour (00-23).

    `%I'
          This stands for the hour (00-12).

    `%j'
          This stands for the day of the year (001-366).

    `%k'
          This stands for the hour (0-23), blank padded.

    `%l'
          This stands for the hour (1-12), blank padded.

    `%m'
          This stands for the month (01-12).

    `%M'
          This stands for the minute (00-59).

    `%n'
          This stands for a newline.

    `%p'
          This stands for `AM' or `PM', as appropriate.

    `%r'
          This is a synonym for `%I:%M:%S %p'.

    `%R'
          This is a synonym for `%H:%M'.

    `%S'
          This stands for the seconds (00-60).

    `%t'
          This stands for a tab character.

    `%T'
          This is a synonym for `%H:%M:%S'.

    `%U'
          This stands for the week of the year (01-52), assuming that
          weeks start on Sunday.

    `%w'
          This stands for the numeric day of week (0-6).  Sunday is day
          0.

    `%W'
          This stands for the week of the year (01-52), assuming that
          weeks start on Monday.

    `%x'
          This has a locale-specific meaning.  In the default locale
          (named C), it is equivalent to `%D'.

    `%X'
          This has a locale-specific meaning.  In the default locale
          (named C), it is equivalent to `%T'.

    `%y'
          This stands for the year without century (00-99).

    `%Y'
          This stands for the year with century.

    `%Z'
          This stands for the time zone abbreviation.

 -- Function: decode-time &optional specified-time
     This function converts a time value into calendrical information.
     The optional SPECIFIED-TIME should be a list of (HIGH LOW .
     IGNORED) or (HIGH . LOW), as from `current-time' and
     `file-attributes', or `nil' to use the current time.

     The return value is a list of nine elements, as follows:

          (SECONDS MINUTES HOUR DAY MONTH YEAR DOW DST ZONE)

     Here is what the elements mean:

    SEC
          The number of seconds past the minute, as an integer between
          0 and 59.

    MINUTE
          The number of minutes past the hour, as an integer between 0
          and 59.

    HOUR
          The hour of the day, as an integer between 0 and 23.

    DAY
          The day of the month, as an integer between 1 and 31.

    MONTH
          The month of the year, as an integer between 1 and 12.

    YEAR
          The year, an integer typically greater than 1900.

    DOW
          The day of week, as an integer between 0 and 6, where 0
          stands for Sunday.

    DST
          `t' if daylight savings time is effect, otherwise `nil'.

    ZONE
          An integer indicating the time zone, as the number of seconds
          east of Greenwich.

     Note that Common Lisp has different meanings for DOW and ZONE.

 -- Function: encode-time seconds minutes hour day month year &optional
          zone
     This function is the inverse of `decode-time'.  It converts seven
     items of calendrical data into a time value.  For the meanings of
     the arguments, see the table above under `decode-time'.

     Year numbers less than 100 are treated just like other year
     numbers.  If you want them to stand for years above 1900, you must
     alter them yourself before you call `encode-time'.

     The optional argument ZONE defaults to the current time zone and
     its daylight savings time rules.  If specified, it can be either a
     list (as you would get from `current-time-zone') or an integer (as
     you would get from `decode-time').  The specified zone is used
     without any further alteration for daylight savings time.

\1f
File: lispref.info,  Node: Timers,  Next: Terminal Input,  Prev: Time Conversion,  Up: System Interface

57.7 Timers for Delayed Execution
=================================

You can set up a timer to call a function at a specified future time.

 -- Function: add-timeout secs function object &optional resignal
     This function adds a timeout, to be signaled after the timeout
     period has elapsed.  SECS is a number of seconds, expressed as an
     integer or a float.  FUNCTION will be called after that many
     seconds have elapsed, with one argument, the given OBJECT.  If the
     optional RESIGNAL argument is provided, then after this timeout
     expires, `add-timeout' will automatically be called again with
     RESIGNAL as the first argument.

     This function returns an object which is the "id" of this
     particular timeout.  You can pass that object to `disable-timeout'
     to turn off the timeout before it has been signalled.

     The number of seconds may be expressed as a floating-point number,
     in which case some fractional part of a second will be used.
     Caveat: the usable timeout granularity will vary from system to
     system.

     Adding a timeout causes a timeout event to be returned by
     `next-event', and the function will be invoked by
     `dispatch-event', so if XEmacs is in a tight loop, the function
     will not be invoked until the next call to sit-for or until the
     return to top-level (the same is true of process filters).

     WARNING: if you are thinking of calling add-timeout from inside of
     a callback function as a way of resignalling a timeout, think
     again.  There is a race condition.  That's why the RESIGNAL
     argument exists.

     (NOTE: In FSF Emacs, this function is called `run-at-time' and has
     different semantics.)

 -- Function: disable-timeout id
     Cancel the requested action for ID, which should be a value
     previously returned by `add-timeout'.  This cancels the effect of
     that call to `add-timeout'; the arrival of the specified time will
     not cause anything special to happen.  (NOTE: In FSF Emacs, this
     function is called `cancel-timer'.)

\1f
File: lispref.info,  Node: Terminal Input,  Next: Terminal Output,  Prev: Timers,  Up: System Interface

57.8 Terminal Input
===================

This section describes functions and variables for recording or
manipulating terminal input.  See *Note Display::, for related
functions.

* Menu:

* Input Modes::         Options for how input is processed.
* Translating Input::   Low level conversion of some characters or events
                          into others.
* Recording Input::     Saving histories of recent or all input events.

\1f
File: lispref.info,  Node: Input Modes,  Next: Translating Input,  Up: Terminal Input

57.8.1 Input Modes
------------------

 -- Function: set-input-mode interrupt flow meta &optional quit-char
          console
     This function sets the mode for reading keyboard input.  If
     INTERRUPT is non-null, then XEmacs uses input interrupts.  If it is
     `nil', then it uses CBREAK mode.  When XEmacs communicates
     directly with X, it ignores this argument and uses interrupts if
     that is the way it knows how to communicate.

     If FLOW is non-`nil', then XEmacs uses XON/XOFF (`C-q', `C-s')
     flow control for output to the terminal.  This has no effect except
     in CBREAK mode.  *Note Flow Control::.

     The default setting is system dependent.  Some systems always use
     CBREAK mode regardless of what is specified.

     The argument META controls support for input character codes above
     127.  If META is `t', XEmacs converts characters with the 8th bit
     set into Meta characters.  If META is `nil', XEmacs disregards the
     8th bit; this is necessary when the terminal uses it as a parity
     bit.  If META is neither `t' nor `nil', XEmacs uses all 8 bits of
     input unchanged.  This is good for terminals using European 8-bit
     character sets.

     If QUIT-CHAR is non-`nil', it specifies the character to use for
     quitting.  Normally this character is `C-g'.  *Note Quitting::.

   The `current-input-mode' function returns the input mode settings
XEmacs is currently using.

 -- Function: current-input-mode &optional console
     This function returns current mode for reading keyboard input.  It
     returns a list, corresponding to the arguments of `set-input-mode',
     of the form `(INTERRUPT FLOW META QUIT)' in which:
    INTERRUPT
          is non-`nil' when XEmacs is using interrupt-driven input.  If
          `nil', Emacs is using CBREAK mode.

    FLOW
          is non-`nil' if XEmacs uses XON/XOFF (`C-q', `C-s') flow
          control for output to the terminal.  This value has no effect
          unless INTERRUPT is non-`nil'.

    META
          is `t' if XEmacs treats the eighth bit of input characters as
          the meta bit; `nil' means XEmacs clears the eighth bit of
          every input character; any other value means XEmacs uses all
          eight bits as the basic character code.

    QUIT
          is the character XEmacs currently uses for quitting, usually
          `C-g'.

\1f
File: lispref.info,  Node: Translating Input,  Next: Recording Input,  Prev: Input Modes,  Up: Terminal Input

57.8.2 Translating Input Events
-------------------------------

This section describes features for translating input events into other
input events before they become part of key sequences.

 -- Variable: function-key-map
     This variable holds a keymap that describes the character sequences
     sent by function keys on an ordinary character terminal.  This
     keymap uses the same data structure as other keymaps, but is used
     differently: it specifies translations to make while reading
     events.

     If `function-key-map' "binds" a key sequence K to a vector V, then
     when K appears as a subsequence _anywhere_ in a key sequence, it
     is replaced with the events in V.

     For example, VT100 terminals send `<ESC> O P' when the keypad PF1
     key is pressed.  Therefore, we want XEmacs to translate that
     sequence of events into the single event `pf1'.  We accomplish
     this by "binding" `<ESC> O P' to `[pf1]' in `function-key-map',
     when using a VT100.

     Thus, typing `C-c <PF1>' sends the character sequence `C-c <ESC> O
     P'; later the function `read-key-sequence' translates this back
     into `C-c <PF1>', which it returns as the vector `[?\C-c pf1]'.

     Entries in `function-key-map' are ignored if they conflict with
     bindings made in the minor mode, local, or global keymaps.  The
     intent is that the character sequences that function keys send
     should not have command bindings in their own right.

     The value of `function-key-map' is usually set up automatically
     according to the terminal's Terminfo or Termcap entry, but
     sometimes those need help from terminal-specific Lisp files.
     XEmacs comes with terminal-specific files for many common
     terminals; their main purpose is to make entries in
     `function-key-map' beyond those that can be deduced from Termcap
     and Terminfo.  *Note Terminal-Specific::.

     Emacs versions 18 and earlier used totally different means of
     detecting the character sequences that represent function keys.

 -- Variable: key-translation-map
     This variable is another keymap used just like `function-key-map'
     to translate input events into other events.  It differs from
     `function-key-map' in two ways:

        * `key-translation-map' goes to work after `function-key-map' is
          finished; it receives the results of translation by
          `function-key-map'.

        * `key-translation-map' overrides actual key bindings.

     The intent of `key-translation-map' is for users to map one
     character set to another, including ordinary characters normally
     bound to `self-insert-command'.

   You can use `function-key-map' or `key-translation-map' for more
than simple aliases, by using a function, instead of a key sequence, as
the "translation" of a key.  Then this function is called to compute
the translation of that key.

   The key translation function receives one argument, which is the
prompt that was specified in `read-key-sequence'--or `nil' if the key
sequence is being read by the editor command loop.  In most cases you
can ignore the prompt value.

   If the function reads input itself, it can have the effect of
altering the event that follows.  For example, here's how to define
`C-c h' to turn the character that follows into a Hyper character:

     (defun hyperify (prompt)
       (let ((e (read-event)))
         (vector (if (numberp e)
                     (logior (lsh 1 20) e)
                   (if (memq 'hyper (event-modifiers e))
                       e
                     (add-event-modifier "H-" e))))))

     (defun add-event-modifier (string e)
       (let ((symbol (if (symbolp e) e (car e))))
         (setq symbol (intern (concat string
                                      (symbol-name symbol))))
         (if (symbolp e)
             symbol
           (cons symbol (cdr e)))))

     (define-key function-key-map "\C-ch" 'hyperify)

   The `iso-transl' library uses this feature to provide a way of
inputting non-ASCII Latin-1 characters.

\1f
File: lispref.info,  Node: Recording Input,  Prev: Translating Input,  Up: Terminal Input

57.8.3 Recording Input
----------------------

 -- Function: recent-keys &optional number
     This function returns a vector containing recent input events from
     the keyboard or mouse.  By default, 100 events are recorded, which
     is how many `recent-keys' returns.

     All input events are included, whether or not they were used as
     parts of key sequences.  Thus, you always get the last 100 inputs,
     not counting keyboard macros.  (Events from keyboard macros are
     excluded because they are less interesting for debugging; it
     should be enough to see the events that invoked the macros.)

     If NUMBER is specified, not more than NUMBER events will be
     returned.  You may change the number of stored events using
     `set-recent-keys-ring-size'.

 -- Function: recent-keys-ring-size
     This function returns the number of recent events stored
     internally.  This is also the maximum number of events
     `recent-keys' can return.  By default, 100 events are stored.

 -- Function: set-recent-keys-ring-size size
     This function changes the number of events stored by XEmacs and
     returned by `recent-keys'.

     For example, `(set-recent-keys-ring-size 250)' will make XEmacs
     remember last 250 events and will make `recent-keys' return last
     250 events by default.

 -- Command: open-dribble-file filename
     This function opens a "dribble file" named FILENAME.  When a
     dribble file is open, each input event from the keyboard or mouse
     (but not those from keyboard macros) is written in that file.  A
     non-character event is expressed using its printed representation
     surrounded by `<...>'.

     You close the dribble file by calling this function with an
     argument of `nil'.

     This function is normally used to record the input necessary to
     trigger an XEmacs bug, for the sake of a bug report.

          (open-dribble-file "~/dribble")
               => nil

   See also the `open-termscript' function (*note Terminal Output::).

\1f
File: lispref.info,  Node: Terminal Output,  Next: Flow Control,  Prev: Terminal Input,  Up: System Interface

57.9 Terminal Output
====================

The terminal output functions send output to the terminal or keep track
of output sent to the terminal.  The function `device-baud-rate' tells
you what XEmacs thinks is the output speed of the terminal.

 -- Function: device-baud-rate &optional device
     This function's value is the output speed of the terminal
     associated with DEVICE, as far as XEmacs knows.  DEVICE defaults
     to the selected device (usually the only device) if omitted.
     Changing this value does not change the speed of actual data
     transmission, but the value is used for calculations such as
     padding.  This value has no effect for window-system devices.
     (This is different in FSF Emacs, where the baud rate also affects
     decisions about whether to scroll part of the screen or repaint,
     even when using a window system.)

     The value is measured in bits per second.

   XEmacs attempts to automatically initialize the baud rate by querying
the terminal.  If you are running across a network, however, and
different parts of the network work are at different baud rates, the
value returned by XEmacs may be different from the value used by your
local terminal.  Some network protocols communicate the local terminal
speed to the remote machine, so that XEmacs and other programs can get
the proper value, but others do not.  If XEmacs has the wrong value, it
makes decisions that are less than optimal.  To fix the problem, use
`set-device-baud-rate'.

 -- Function: set-device-baud-rate device baud-rate
     This function sets the output speed of DEVICE.  See
     `device-baud-rate'.  DEVICE defaults to the selected device
     (usually the only device) if `nil'.

 -- Function: send-string-to-terminal char-or-string &optional stdout-p
          device
     This function sends CHAR-OR-STRING to the terminal without
     alteration.  Control characters in CHAR-OR-STRING have
     terminal-dependent effects.

     If DEVICE is `nil', this function writes to XEmacs's stderr, or to
     stdout if STDOUT-P is non-`nil'.  Otherwise, DEVICE should be a
     tty or stream device, and the function writes to the device's
     normal or error output, according to STDOUT-P.

     One use of this function is to define function keys on terminals
     that have downloadable function key definitions.  For example,
     this is how on certain terminals to define function key 4 to move
     forward four characters (by transmitting the characters `C-u C-f'
     to the computer):

          (send-string-to-terminal "\eF4\^U\^F")
               => nil

 -- Command: open-termscript filename
     This function is used to open a "termscript file" that will record
     all the characters sent by XEmacs to the terminal. (If there are
     multiple tty or stream devices, all characters sent to all such
     devices are recorded.) The function returns `nil'.  Termscript
     files are useful for investigating problems where XEmacs garbles
     the screen, problems that are due to incorrect Termcap entries or
     to undesirable settings of terminal options more often than to
     actual XEmacs bugs.  Once you are certain which characters were
     actually output, you can determine reliably whether they
     correspond to the Termcap specifications in use.

     A `nil' value for FILENAME stops recording terminal output.

     See also `open-dribble-file' in *Note Terminal Input::.

          (open-termscript "../junk/termscript")
               => nil