Gutter
******

A gutter is a rectangle displayed along one edge of a frame.  It can contain arbitrary text or graphics.

Gutter Intro
============

A gutter is a rectangle displayed along one edge of a frame.  It can contain arbitrary text or graphics.  It could be considered a generalization of a toolbar, although toolbars are not currently implemented using gutters.

In XEmacs, a gutter can be displayed along any of the four edges of the frame, and two or more different edges can be displaying gutters simultaneously.  The contents, thickness, and visibility of the gutters can be controlled separately, and the values can be per-buffer, per-frame, etc., using specifiers (see Specifiers).

Normally, there is one gutter displayed in a frame.  Usually, this is the default gutter, containing buffer tabs, but modes cab override this and substitute their own gutter.  This default gutter is usually positioned along the top of the frame, but this can be changed using set-default-gutter-position.

Note that, for each of the gutter properties (contents, thickness, and visibility), there is a separate specifier for each of the four gutter positions (top, bottom, left, and right), and an additional specifier for the ``default'' gutter, i.e. the gutter whose position is controlled by set-default-gutter-position.  The way this works is that set-default-gutter-position arranges things so that the appropriate position-specific specifiers for the default position inherit from the corresponding default specifiers. That way, if the position-specific specifier does not give a value (which it usually doesn't), then the value from the default specifier applies.  If you want to control the default gutter, you just change the default specifiers, and everything works.  A package such as VM that wants to put its own gutter in a different location from the default just sets the position-specific specifiers, and if the user sets the default gutter to the same position, it will just not be visible.

Creating Gutter
===============

 -- Function: make-gutter-specifier spec-list

     Return a new gutter 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.  See Specifiers, for more information about specifiers.

     Gutter specifiers are used to specify the format of a gutter.  The values of the variables default-gutter, top-gutter, left-gutter, right-gutter, and bottom-gutter are always gutter specifiers.

     Valid gutter instantiators are called "gutter descriptors" and are either strings or property-lists of strings.  See default-gutter for a description of the exact format.

 -- Function: make-gutter-size-specifier spec-list

     Return a new gutter-size 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.  See Specifiers, for more information about specifiers.

     Gutter-size specifiers are used to specify the size of a gutter.  The values of the variables default-gutter-size, top-gutter-size, left-gutter-size, right-gutter-size, and bottom-gutter-size are always gutter-size specifiers.

     Valid gutter-size instantiators are either integers or the special symbol autodetect. If a gutter-size is set to autodetect them the size of the gutter will be adjusted to just accomodate the gutters contents. autodetect only works for top and bottom gutters.

 -- Function: make-gutter-visible-specifier spec-list

     Return a new gutter-visible 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.  See Specifiers, for more information about specifiers.

     Gutter-visible specifiers are used to specify the visibility of a gutter.  The values of the variables default-gutter-visible-p, top-gutter-visible-p, left-gutter-visible-p, right-gutter-visible-p, and bottom-gutter-visible-p are always gutter-visible specifiers.

     Valid gutter-visible instantiators are t, nil or a list of symbols.  If a gutter-visible instantiator is set to a list of symbols, and the correspondong gutter specification is a property-list strings, then elements of the gutter specification will only be visible if the corresponding symbol occurs in the gutter-visible instantiator.

Gutter Descriptor Format
========================

The contents of a gutter are specified using a gutter descriptor. The format of a gutter descriptor is a list of gutter button descriptors.  Each gutter button descriptor is a vector in one of the following formats:

  * [GLYPH-LIST FUNCTION ENABLED-P HELP]

  * [:style 2D-OR-3D]

  * [:style 2D-OR-3D :size WIDTH-OR-HEIGHT]

  * [:size WIDTH-OR-HEIGHT :style 2D-OR-3D]

Optionally, one of the gutter button descriptors may be nil instead of a vector; this signifies the division between the gutter buttons that are to be displayed flush-left, and the buttons to be displayed flush-right.

The first vector format above specifies a normal gutter button; the others specify blank areas in the gutter.

For the first vector format:

  * GLYPH-LIST should be a list of one to six glyphs (as created by make-glyph) or a symbol whose value is such a list.  The first glyph, which must be provided, is the glyph used to display the gutter button when it is in the ``up'' (not pressed) state.  The optional second glyph is for displaying the button when it is in the ``down'' (pressed) state.  The optional third glyph is for when the button is disabled.  The last three glyphs are for displaying the button in the ``up'', ``down'', and ``disabled'' states, respectively, but are used when the user has called for captioned gutter buttons (using gutter-buttons-captioned-p).  The function gutter-make-button-list is useful in creating these glyph lists.

  * Even if you do not provide separate down-state and disabled-state glyphs, the user will still get visual feedback to indicate which state the button is in.  Buttons in the up-state are displayed with a shadowed border that gives a raised appearance to the button.  Buttons in the down-state are displayed with shadows that give a recessed appearance.  Buttons in the disabled state are displayed with no shadows, giving a 2-d effect.

  * If some of the gutter glyphs are not provided, they inherit as follows:

               UP:                up
               DOWN:              down -> up
               DISABLED:          disabled -> up
               CAP-UP:            cap-up -> up
               CAP-DOWN:          cap-down -> cap-up -> down -> up
               CAP-DISABLED:      cap-disabled -> cap-up -> disabled -> up

  * The second element FUNCTION is a function to be called when the gutter button is activated (i.e. when the mouse is released over the gutter button, if the press occurred in the gutter).  It can be any form accepted by call-interactively, since this is how it is invoked.

  * The third element ENABLED-P specifies whether the gutter button is enabled (disabled buttons do nothing when they are activated, and are displayed differently; see above).  It should be either a boolean or a form that evaluates to a boolean.

  * The fourth element HELP, if non-nil, should be a string. This string is displayed in the echo area when the mouse passes over the gutter button.

For the other vector formats (specifying blank areas of the gutter):

  * 2D-OR-3D should be one of the symbols 2d or 3d, indicating whether the area is displayed with shadows (giving it a raised, 3-d appearance) or without shadows (giving it a flat appearance).

  * WIDTH-OR-HEIGHT specifies the length, in pixels, of the blank area.  If omitted, it defaults to a device-specific value (8 pixels for X devices).

 -- Function: gutter-make-button-list up &optional down disabled cap-up cap-down cap-disabled
     This function calls make-glyph on each arg and returns a list of the results.  This is useful for setting the first argument of a gutter button descriptor (typically, the result of this function is assigned to a symbol, which is specified as the first argument of the gutter button descriptor).

 -- Function: check-gutter-button-syntax button &optional noerror
     Verify the syntax of entry BUTTON in a gutter description list. If you want to verify the syntax of a gutter description list as a whole, use check-valid-instantiator with a specifier type of gutter.

Specifying a Gutter
===================

In order to specify the contents of a gutter, set one of the specifier variables default-gutter, top-gutter, bottom-gutter, left-gutter, or right-gutter. These are specifiers, which means you set them with set-specifier and query them with specifier-specs or specifier-instance. You will get an error if you try to set them using setq.  The valid instantiators for these specifiers are gutter descriptors, as described above.  See Specifiers, for more information.

Most of the time, you will set default-gutter, which allows the user to choose where the gutter should go.

 -- Specifier: default-gutter
     The position of this gutter is specified in the function default-gutter-position.  If the corresponding position-specific gutter (e.g. top-gutter if default-gutter-position is top) does not specify a gutter in a particular domain, then the value of default-gutter in that domain, of any, will be used instead.

Note that the gutter at any particular position will not be displayed unless its thickness (width or height, depending on orientation) is non-zero and its visibility status is true.  The thickness is controlled by the specifiers top-gutter-height, bottom-gutter-height, left-gutter-width, and right-gutter-width, and the visibility status is controlled by the specifiers top-gutter-visible-p, bottom-gutter-visible-p, left-gutter-visible-p, and right-gutter-visible-p (see Other Gutter Variables).

 -- Function: set-default-gutter-position position
     This function sets the position that the default-gutter will be displayed at.  Valid positions are the symbols top, bottom, left and right.  What this actually does is set the fallback specifier for the position-specific specifier corresponding to the given position to default-gutter, and set the fallbacks for the other position-specific specifiers to nil. It also does the same thing for the position-specific thickness and visibility specifiers, which inherit from one of default-gutter-height or default-gutter-width, and from default-gutter-visible-p, respectively (see Other Gutter Variables).

 -- Function: default-gutter-position
     This function returns the position that the default-gutter will be displayed at.

You can also explicitly set a gutter at a particular position.  When redisplay determines what to display at a particular position in a particular domain (i.e. window), it first consults the position-specific gutter.  If that does not yield a gutter descriptor, the default-gutter is consulted if default-gutter-position indicates this position.

 -- Specifier: top-gutter
     Specifier for the gutter at the top of the frame.

 -- Specifier: bottom-gutter
     Specifier for the gutter at the bottom of the frame.

 -- Specifier: left-gutter
     Specifier for the gutter at the left edge of the frame.

 -- Specifier: right-gutter
     Specifier for the gutter at the right edge of the frame.

 -- Function: gutter-specifier-p object
     This function returns non-nil if OBJECT is a gutter specifier. Gutter specifiers are the actual objects contained in the gutter variables described above, and their valid instantiators are gutter descriptors (see Gutter Descriptor Format).

Other Gutter Variables
======================

The variables to control the gutter thickness, visibility status, and captioned status are all specifiers.  See Specifiers.

 -- Specifier: default-gutter-height
     This specifies the height of the default gutter, if it's oriented horizontally.  The position of the default gutter is specified by the function set-default-gutter-position.  If the corresponding position-specific gutter thickness specifier (e.g. top-gutter-height if default-gutter-position is top) does not specify a thickness in a particular domain (a window or a frame), then the value of default-gutter-height or default-gutter-width (depending on the gutter orientation) in that domain, if any, will be used instead.

 -- Specifier: default-gutter-width
     This specifies the width of the default gutter, if it's oriented vertically.  This behaves like default-gutter-height.

Note that default-gutter-height is only used when default-gutter-position is top or bottom, and default-gutter-width is only used when default-gutter-position is left or right.

 -- Specifier: top-gutter-height
     This specifies the height of the top gutter.

 -- Specifier: bottom-gutter-height
     This specifies the height of the bottom gutter.

 -- Specifier: left-gutter-width
     This specifies the width of the left gutter.

 -- Specifier: right-gutter-width
     This specifies the width of the right gutter.

Note that all of the position-specific gutter thickness specifiers have a fallback value of zero when they do not correspond to the default gutter.  Therefore, you will have to set a non-zero thickness value if you want a position-specific gutter to be displayed.

 -- Specifier: default-gutter-visible-p
     This specifies whether the default gutter is visible.  The position of the default gutter is specified by the function set-default-gutter-position.  If the corresponding position-specific gutter visibility specifier (e.g. top-gutter-visible-p if default-gutter-position is top) does not specify a visible-p value in a particular domain (a window or a frame), then the value of default-gutter-visible-p in that domain, if any, will be used instead.

 -- Specifier: top-gutter-visible-p
     This specifies whether the top gutter is visible.

 -- Specifier: bottom-gutter-visible-p
     This specifies whether the bottom gutter is visible.

 -- Specifier: left-gutter-visible-p
     This specifies whether the left gutter is visible.

 -- Specifier: right-gutter-visible-p
     This specifies whether the right gutter is visible.

default-gutter-visible-p and all of the position-specific gutter visibility specifiers have a fallback value of true.

Internally, gutter thickness and visibility specifiers are instantiated in both window and frame domains, for different purposes.  The value in the domain of a frame's selected window specifies the actual gutter thickness or visibility that you will see in that frame.  The value in the domain of a frame itself specifies the gutter thickness or visibility that is used in frame geometry calculations.

Thus, for example, if you set the frame width to 80 characters and the left gutter width for that frame to 68 pixels, then the frame will be sized to fit 80 characters plus a 68-pixel left gutter.  If you then set the left gutter width to 0 for a particular buffer (or if that buffer does not specify a left gutter or has a nil value specified for left-gutter-visible-p), you will find that, when that buffer is displayed in the selected window, the window will have a width of 86 or 87 characters -- the frame is sized for a 68-pixel left gutter but the selected window specifies that the left gutter is not visible, so it is expanded to take up the slack.

 -- Specifier: gutter-buttons-captioned-p
     Whether gutter buttons are captioned.  This affects which glyphs from a gutter button descriptor are chosen.  See Gutter Descriptor Format.

You can also reset the gutter to what it was when XEmacs started up.

 -- Constant: initial-gutter-spec
     The gutter descriptor used to initialize default-gutter at startup.

Common Gutter Widgets
=====================

A gutter can contain arbitrary text.  So, for example, in an Info buffer you could put the title of the current node in the top gutter, and it would not scroll out of view in a long node.  (This is an artificial example, since usually the node name is sufficiently descriptive, and Info puts that in the mode line.)

A more common use for the gutter is to hold some kind of active widget.  The buffer-tab facility, available in all XEmacs frames, creates an array of file-folder-like tabs, which the user can click with the mouse to switch buffers.  W3 uses a progress-bar widget in the bottom gutter to give a visual indication of the progress of time-consuming operations like downloading.

Buffer Tabs
-----------

Not documented yet.

Progress Bars
-------------

Not documented yet.