+File: lispref.info, Node: Glyph Properties, Next: Glyph Convenience Functions, Prev: Creating Glyphs, Up: Glyph Functions
+
+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. 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).
+ 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: 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: Glyph Functions
+
+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, Prev: Glyph Convenience Functions, Up: Glyph Functions
+
+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: Images, Next: Glyph Types, Prev: Glyph Functions, Up: Glyphs
+
+Images
+======
+
+* Menu:
+
+* Image Specifiers:: Specifying how an image will appear.
+* 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'.
+* Image Instances:: What an image specifier gets instanced as.
+
+\1f