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This chapter describes a number of features related to the display that Emacs presents to the user.
38.1 Refreshing the Screen Clearing the screen and redrawing everything on it. 38.2 Forcing Redisplay Forcing redisplay. 38.3 Truncation Folding or wrapping long text lines. 38.4 The Echo Area Where messages are displayed. 38.5 Invisible Text Hiding part of the buffer text. 38.6 Selective Display Hiding part of the buffer text (the old way). 38.7 The Overlay Arrow Display of an arrow to indicate position. 38.8 Temporary Displays Displays that go away automatically. 38.9 Overlays Use overlays to highlight parts of the buffer. 38.10 Width How wide a character or string is on the screen. 38.11 Faces A face defines a graphics style for text characters: font, colors, etc. 38.12 The displayPropertyEnabling special display features. 38.13 Images Displaying images in Emacs buffers. 38.14 Blinking Parentheses How Emacs shows the matching open parenthesis. 38.15 Inverse Video Specifying how the screen looks. 38.16 Usual Display Conventions The usual conventions for displaying nonprinting chars. 38.17 Display Tables How to specify other conventions. 38.18 Beeping Audible signal to the user. 38.19 Window Systems Which window system is being used.
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The function redraw-frame redisplays the entire contents of a
given frame (see section 29. Frames).
Even more powerful is redraw-display:
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 Emacs also refreshes the screen. Some terminal emulators record separate contents for display-oriented programs such as Emacs and for ordinary sequential display. If you are using such a terminal, you might want to inhibit the redisplay on resumption.
nil means there is no need
to redraw, nil means redrawing is needed. The default is nil.
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Emacs redisplay normally stops if input arrives, and does not happen
at all if input is available before it starts. Most of the time, this
is exactly what you want. However, you can prevent preemption by
binding redisplay-dont-pause to a non-nil value.
nil, pending input does not
prevent or halt redisplay; redisplay occurs, and finishes,
regardless of whether input is available. This feature is available
as of Emacs 21.
You can request a display update, but only if no input is pending,
with (sit-for 0). To force a display update even when input is
pending, do this:
(let ((redisplay-dont-pause t)) (sit-for 0)) |
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When a line of text extends beyond the right edge of a window, the line can either be continued on the next screen line, or truncated to one screen line. The additional screen lines used to display a long text line are called continuation lines. Normally, a `$' in the rightmost column of the window indicates truncation; a `\' on the rightmost column indicates a line that "wraps" onto the next line, which is also called continuing the line. (The display table can specify alternative indicators; see 38.17 Display Tables.)
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. See section 32.11 Filling.
nil, which
specifies continuation. If the value is non-nil, then these
lines are truncated.
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.
truncate-lines, for
buffers that do not have buffer-local values for it.
nil, these lines are truncated; otherwise,
truncate-lines says what to do with them.
When horizontal scrolling (see section 28.13 Horizontal Scrolling) is in use in a window, that forces truncation.
You can override the glyphs that indicate continuation or truncation using the display table; see 38.17 Display Tables.
If your buffer contains very long lines, and you use
continuation to display them, just thinking about them can make Emacs
redisplay slow. The column computation and indentation functions also
become slow. Then you might find it advisable to set
cache-long-line-scans to t.
nil, various indentation and motion
functions, and Emacs redisplay, cache the results of scanning the
buffer, and consult the cache to avoid rescanning regions of the buffer
unless they are modified.
Turning on the cache slows down processing of short lines somewhat.
This variable is automatically buffer-local in every buffer.
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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
GNU Emacs Manual specifies the rules for resolving conflicts
between the echo area and the minibuffer for use of that screen space
(see section `The Minibuffer' in The GNU Emacs Manual).
Error messages appear in the echo area; see 10.5.3 Errors.
You can write output in the echo area by using the Lisp printing
functions with t as the stream (see section 19.5 Output Functions), or as
follows:
printf control
string. See format in 4.6 Conversion of Characters and Strings, 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, or strings among the arguments, have face
text properties, these affect the way the message is displayed.
If string is nil, message clears the echo area; if
the echo area has been expanded automatically, this brings it back to
its normal size. If the minibuffer is active, this brings the
minibuffer contents back onto the screen immediately.
Normally, displaying a long message resizes the echo area to display
the entire message. But if the variable message-truncate-lines
is non-nil, the echo area does not resize, and the message is
truncated to fit it, as in Emacs 20 and before.
(message "Minibuffer depth is %d."
(minibuffer-depth))
-| Minibuffer depth is 0.
=> "Minibuffer depth is 0."
---------- Echo Area ----------
Minibuffer depth is 0.
---------- Echo Area ----------
|
To automatically display a message in the echo area or in a pop-buffer,
depending on its size, use display-message-or-buffer.
message, but may display it
in a dialog box instead of the echo area. If this function is called in
a command that was invoked using the mouse--more precisely, if
last-nonmenu-event (see section 21.4 Information from the Command Loop) is either
nil or a list--then it uses a dialog box or pop-up menu to
display the message. Otherwise, it uses the echo area. (This is the
same criterion that y-or-n-p uses to make a similar decision; see
20.6 Yes-or-No Queries.)
You can force use of the mouse or of the echo area by binding
last-nonmenu-event to a suitable value around the call.
message, but uses a dialog
box (or a pop-up menu) whenever that is possible. If it is impossible
to use a dialog box or pop-up menu, because the terminal does not
support them, then message-box uses the echo area, like
message.
max-mini-window-height, it is displayed
in the echo area, using message. Otherwise,
display-buffer is used to show it in a pop-up buffer.
Returns either the string shown in the echo area, or when a pop-up buffer is used, the window used to display it.
If message is a string, then the optional argument buffer-name is the name of the buffer used to display it when a pop-up buffer is used, defaulting to `*Message*'. In the case where message is a string and displayed in the echo area, it is not specified whether the contents are inserted into the buffer anyway.
The optional arguments not-this-window and frame are as for
display-buffer, and only used if a buffer is displayed.
nil if there is none.
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.
(message nil) or for any other reason.
Almost all the messages displayed in the echo area are also recorded in the `*Messages*' buffer.
t means there is no limit on how many lines to
keep. The value nil disables message logging entirely. Here's
how to display a message and prevent it from being logged:
(let (message-log-max) (message ...)) |
If the value is zero, then command input is not echoed.
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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 (see section 32.19 Text Properties) or a property of an overlay
(see section 38.9 Overlays).
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
invisible property works.
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
database. It permits the implementation of convenient filtering
commands to view just a part of the entries in the database. Setting
this variable is very fast, much faster than scanning all the text in
the buffer looking for properties to change.
invisible properties
actually make a character invisible.
t
invisible property is
non-nil. This is the default.
invisible property fits any one of these criteria,
the character is invisible. The list can have two kinds of elements:
atom
invisible property value
is atom or if it is a list with atom as a member.
(atom . t)
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.
Two functions are specifically provided for adding elements to
buffer-invisibility-spec and removing elements from it.
buffer-invisibility-spec
(if it is not already present in that list).
buffer-invisibility-spec.
This does nothing if element is not in the list.
One convention about the use of buffer-invisibility-spec is
that a major mode should use the mode's own name as an element of
buffer-invisibility-spec and as the value of the invisible
property:
;; If you want to display an ellipsis:
(add-to-invisibility-spec '(my-symbol . t))
;; If you don't want ellipsis:
(add-to-invisibility-spec 'my-symbol)
(overlay-put (make-overlay beginning end)
'invisible 'my-symbol)
;; When done with the overlays:
(remove-from-invisibility-spec '(my-symbol . t))
;; Or respectively:
(remove-from-invisibility-spec 'my-symbol)
|
Ordinarily, commands that operate on text or move point do not care
whether the text is invisible. The user-level line motion commands
explicitly ignore invisible newlines if
line-move-ignore-invisible is non-nil, but only because
they are explicitly programmed to do so.
Incremental search can make invisible overlays visible temporarily
and/or permanently when a match includes invisible text. To enable
this, the overlay should have a non-nil
isearch-open-invisible property. The property value should be a
function to be called with the overlay as an argument. This function
should make the overlay visible permanently; it is used when the match
overlaps the overlay on exit from the search.
During the search, such overlays are made temporarily visible by
temporarily modifying their invisible and intangible properties. If you
want this to be done differently for a certain overlay, give it an
isearch-open-invisible-temporary property which is a function.
The function is called with two arguments: the first is the overlay, and
the second is nil to make the overlay visible, or t to
make it invisible again.
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Selective display refers to a pair of related features for hiding certain lines on the screen.
The first variant, explicit selective display, is designed for use in a Lisp program: it controls which lines are hidden by altering the text. The invisible text feature (see section 38.5 Invisible Text) has partially replaced this feature.
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 Emacs.
selective-display is t, then the character
control-m marks the start of invisible text; the control-m, and the rest
of the line following it, are not displayed. This is explicit selective
display.
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 ----------
|
nil, then Emacs 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 (`...'). See section 38.17 Display Tables.
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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.
nil if the arrow feature is not in use.
On a graphical display the contents of the string are ignored; instead a
glyph is displayed in the fringe area to the left of the display area.
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 a similar job by creating an overlay with a
before-string property. See section 38.9.1 Overlay Properties.
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Temporary displays are used by Lisp programs to put output into a buffer and then present it to the user for perusal rather than for editing. Many help commands use this feature.
If the forms do not change the major mode in the output buffer, so
that it is still Help mode at the end of their execution, then
with-output-to-temp-buffer makes this buffer read-only at the
end, and also scans it for function and variable names to make them into
clickable cross-references.
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).
See section 19.5 Output Functions.
Several hooks are available for customizing the behavior of this construct; they are listed below.
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 ----------
|
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.
It is a good idea for this function to run temp-buffer-show-hook
just as with-output-to-temp-buffer normally would, inside of
save-selected-window and with the chosen window and buffer
selected.
with-output-to-temp-buffer before
evaluating body. When the hook runs, the help buffer is current.
This hook is normally set up with a function to put the buffer in Help
mode.
with-output-to-temp-buffer after
displaying the help buffer. When the hook runs, the help buffer is
current, and the window it was displayed in is selected. This hook is
normally set up with a function to make the buffer read only, and find
function names and variable names in it, provided the major mode is
still Help mode.
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.
If the string string does not contain control characters, you can
do the same job in a more general way by creating (and then subsequently
deleting) an overlay with a before-string property.
See section 38.9.1 Overlay 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 ---------- |
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You can use overlays to alter the appearance of a buffer's text on the screen, for the sake of presentation features. An overlay is an object that belongs to a particular buffer, and has a specified beginning and end. It also has properties that you can examine and set; these affect the display of the text within the overlay.
38.9.1 Overlay Properties How to read and set properties. What properties do to the screen display. 38.9.2 Managing Overlays Creating and moving overlays. 38.9.3 Searching for Overlays Searching for overlays.
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Overlay properties are like text properties in that the properties that alter how a character is displayed can come from either source. But in most respects they are different. Text properties are considered a part of the text; overlays are specifically considered not to be part of the text. Thus, copying text between various buffers and strings preserves text properties, but does not try to preserve overlays. Changing a buffer's text properties marks the buffer as modified, while moving an overlay or changing its properties does not. Unlike text property changes, overlay changes are not recorded in the buffer's undo list. See section 32.19 Text Properties, for comparison.
These functions are used for reading and writing the properties of an overlay:
category property which is a
symbol, that symbol's prop property is used. Otherwise, the value
is nil.
See also the function get-char-property which checks both
overlay properties and text properties for a given character.
See section 32.19.1 Examining Text Properties.
Many overlay properties have special meanings; here is a table of them:
priority
priority value is larger takes priority over the
other, and its face attributes override the face attributes of the lower
priority overlay.
Currently, all overlays take priority over text properties. Please avoid using negative priority values, as we have not yet decided just what they should mean.
window
window property is non-nil, then the overlay
applies only on that window.
category
category property, we call it the
category of the overlay. It should be a symbol. The properties
of the symbol serve as defaults for the properties of the overlay.
face
In the simplest case, the value is a face name. It can also be a list; then each element can be any of these possibilities:
(foreground-color . color-name) or
(background-color . color-name). These elements specify
just the foreground color or just the background color.
(foreground-color . color-name) is equivalent to
(:foreground color-name), and likewise for the background.
mouse-face
face when the mouse is within
the range of the overlay.
display
display Property.
help-echo
help-echo property, then when you move the
mouse onto the text in the overlay, Emacs displays a help string in the
echo area, or in the tooltip window. For details see Text help-echo. This feature is available starting in Emacs 21.
modification-hooks
The hook functions are called both before and after each change. If the functions save the information they receive, and compare notes between calls, they can determine exactly what change has been made in the buffer text.
When called before a change, each function receives four arguments: the
overlay, nil, and the beginning and end of the text range to be
modified.
When called after a change, each function receives five arguments: the
overlay, t, the beginning and end of the text range just
modified, and the length of the pre-change text replaced by that range.
(For an insertion, the pre-change length is zero; for a deletion, that
length is the number of characters deleted, and the post-change
beginning and end are equal.)
insert-in-front-hooks
modification-hooks functions.
insert-behind-hooks
modification-hooks functions.
invisible
invisible property can make the text in the overlay
invisible, which means that it does not appear on the screen.
See section 38.5 Invisible Text, for details.
intangible
intangible property on an overlay works just like the
intangible text property. See section 32.19.4 Properties with Special Meanings, for details.
isearch-open-invisible
isearch-open-invisible-temporary
before-string
after-string
evaporate
nil, the overlay is deleted automatically
if it ever becomes empty (i.e., if it spans no characters).
local-map
nil, it specifies a keymap for a portion
of the text. The property's value replaces the buffer's local map, when
the character after point is within the overlay. See section 22.6 Active Keymaps.
keymap
keymap property is similar to local-map but overrides the
buffer's local map (and the map specified by the local-map
property) rather than replacing it.
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This section describes the functions to create, delete and move overlays, and to examine their contents.
The arguments front-advance and rear-advance specify the insertion type for the start of the overlay and for the end of the overlay, respectively. See section 31.5 Marker Insertion Types.
A deleted overlay is not permanently disconnected. You can give it a
position in a buffer again by calling move-overlay.
If buffer is omitted, overlay stays in the same buffer it was already associated with; if overlay was deleted, it goes into the current buffer.
The return value is overlay.
This is the only valid way to change the endpoints of an overlay. Do not try modifying the markers in the overlay by hand, as that fails to update other vital data structures and can cause some overlays to be "lost".
Here are some examples:
;; Create an overlay.
(setq foo (make-overlay 1 10))
=> #<overlay from 1 to 10 in display.texi>
(overlay-start foo)
=> 1
(overlay-end foo)
=> 10
(overlay-buffer foo)
=> #<buffer display.texi>
;; Give it a property we can check later.
(overlay-put foo 'happy t)
=> t
;; Verify the property is present.
(overlay-get foo 'happy)
=> t
;; Move the overlay.
(move-overlay foo 5 20)
=> #<overlay from 5 to 20 in display.texi>
(overlay-start foo)
=> 5
(overlay-end foo)
=> 20
;; Delete the overlay.
(delete-overlay foo)
=> nil
;; Verify it is deleted.
foo
=> #<overlay in no buffer>
;; A deleted overlay has no position.
(overlay-start foo)
=> nil
(overlay-end foo)
=> nil
(overlay-buffer foo)
=> nil
;; Undelete the overlay.
(move-overlay foo 1 20)
=> #<overlay from 1 to 20 in display.texi>
;; Verify the results.
(overlay-start foo)
=> 1
(overlay-end foo)
=> 20
(overlay-buffer foo)
=> #<buffer display.texi>
;; Moving and deleting the overlay does not change its properties.
(overlay-get foo 'happy)
=> t
|
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To illustrate usage, here is a Lisp function that returns a list of the overlays that specify property prop for the character at point:
(defun find-overlays-specifying (prop)
(let ((overlays (overlays-at (point)))
found)
(while overlays
(let ((overlay (car overlays)))
(if (overlay-get overlay prop)
(setq found (cons overlay found))))
(setq overlays (cdr overlays)))
found))
|
Here's an easy way to use next-overlay-change to search for the
next character which gets a non-nil happy property from
either its overlays or its text properties (see section 32.19.3 Text Property Search Functions):
(defun find-overlay-prop (prop)
(save-excursion
(while (and (not (eobp))
(not (get-char-property (point) 'happy)))
(goto-char (min (next-overlay-change (point))
(next-single-property-change (point) 'happy))))
(point)))
|
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Since not all characters have the same width, these functions let you check the width of a character. See section 32.17.1 Indentation Primitives, and 30.2.5 Motion by Screen Lines, for related functions.
If string does not reach width, then the result ends where string ends. If one multi-column character in string extends across the column width, that character is not included in the result. Thus, the result can fall short of width but cannot go beyond it.
The optional argument start-column specifies the starting column.
If this is non-nil, then the first start-column columns of
the string are omitted from the value. If one multi-column character in
string extends across the column start-column, that
character is not included.
The optional argument padding, if non-nil, is a padding
character added at the beginning and end of the result string, to extend
it to exactly width columns. The padding character is used at the
end of the result if it falls short of width. It is also used at
the beginning of the result if one multi-column character in
string extends across the column start-column.
(truncate-string-to-width "\tab\t" 12 4)
=> "ab"
(truncate-string-to-width "\tab\t" 12 4 ?\ )
=> " ab "
|
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A face is a named collection of graphical attributes: font family, foreground color, background color, optional underlining, and many others. Faces are used in Emacs to control the style of display of particular parts of the text or the frame.
Each face has its own face number, which distinguishes faces at low levels within Emacs. However, for most purposes, you refer to faces in Lisp programs by their names.
t if object is a face name symbol (or
if it is a vector of the kind used internally to record face data). It
returns nil otherwise.
Each face name is meaningful for all frames, and by default it has the same meaning in all frames. But you can arrange to give a particular face name a special meaning in one frame if you wish.
38.11.1 Standard Faces The faces Emacs normally comes with. 38.11.2 Defining Faces How to define a face with defface.38.11.3 Face Attributes What is in a face? 38.11.4 Face Attribute Functions Functions to examine and set face attributes. 38.11.5 Merging Faces for Display How Emacs combines the faces specified for a character. 38.11.6 Font Selection Finding the best available font for a face. 38.11.7 Functions for Working with Faces How to define and examine faces. 38.11.8 Automatic Face Assignment Hook for automatic face assignment. 38.11.9 Looking Up Fonts Looking up the names of available fonts and information about them. 38.11.10 Fontsets A fontset is a collection of fonts that handle a range of character sets.
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This table lists all the standard faces and their uses. Most of them are used for displaying certain parts of the frames or certain kinds of text; you can control how those places look by customizing these faces.
default
mode-line
mode-line-inverse-video is
non-nil.
modeline
mode-line face, for compatibility with
old Emacs versions.
header-line
menu
fringe
scroll-bar
tool-bar
region
secondary-selection
highlight
trailing-whitespace
show-trailing-whitespace is non-nil.
In contrast, these faces are provided to change the appearance of text in specific ways. You can use them on specific text, when you want the effects they produce.
bold
italic
bold-italic
underline
fixed-pitch
variable-pitch
nil, Emacs uses the
trailing-whitespace face to display any spaces and tabs at the
end of a line.
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The way to define a new face is with defface. This creates a
kind of customization item (see section 14. Writing Customization Definitions) which the user can
customize using the Customization buffer (see section `Easy Customization' in The GNU Emacs Manual).
defface are the same ones that are meaningful in both
defgroup and defcustom (see section 14.1 Common Item Keywords).
When defface executes, it defines the face according to
spec, then uses any customizations that were read from the
init file (see section 40.1.2 The Init File, `.emacs') to override that specification.
The purpose of spec is to specify how the face should appear on
different kinds of terminals. It should be an alist whose elements have
the form (display atts). Each element's CAR,
display, specifies a class of terminals. The element's second element,
atts, is a list of face attributes and their values; it specifies
what the face should look like on that kind of terminal. The possible
attributes are defined in the value of custom-face-attributes.
The display part of an element of spec determines which frames the element applies to. If more than one element of spec matches a given frame, the first matching element is the only one used for that frame. There are two possibilities for display:
t
t is used in the last (or only) element of spec.
(characteristic value...). Here
characteristic specifies a way of classifying frames, and the
values are possible classifications which display should
apply to. Here are the possible values of characteristic:
type
graphic (any
graphics-capable display), x, pc (for the MS-DOS console),
w32 (for MS Windows 9X/NT), or tty (a non-graphics-capable
display).
class
color,
grayscale, or mono.
background
light or dark.
If an element of display specifies more than one value for a given characteristic, any of those values is acceptable. If display has more than one element, each element should specify a different characteristic; then each characteristic of the frame must match one of the values specified for it in display.
Here's how the standard face region is defined:
(defface region
`((((type tty) (class color))
(:background "blue" :foreground "white"))
(((type tty) (class mono))
(:inverse-video t))
(((class color) (background dark))
(:background "blue"))
(((class color) (background light))
(:background "lightblue"))
(t (:background "gray")))
"Basic face for highlighting the region."
:group 'basic-faces)
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Internally, defface uses the symbol property
face-defface-spec to record the face attributes specified in
defface, saved-face for the attributes saved by the user
with the customization buffer, and face-documentation for the
documentation string.
nil, specifies the background type to use for
interpreting face definitions. If it is dark, then Emacs treats
all frames as if they had a dark background, regardless of their actual
background colors. If it is light, then Emacs treats all frames
as if they had a light background.
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The effect of using a face is determined by a fixed set of face attributes. This table lists all the face attributes, and what they mean. Note that in general, more than one face can be specified for a given piece of text; when that happens, the attributes of all the faces are merged to specify how to display the text. See section 38.11.5 Merging Faces for Display.
In Emacs 21, any attribute in a face can have the value
unspecified. This means the face doesn't specify that attribute.
In face merging, when the first face fails to specify a particular
attribute, that means the next face gets a chance. However, the
default face must specify all attributes.
Some of these font attributes are meaningful only on certain kinds of
displays--if your display cannot handle a certain attribute, the
attribute is ignored. (The attributes :family, :width,
:height, :weight, and :slant correspond to parts of
an X Logical Font Descriptor.)
:family
:width
ultra-condensed,
extra-condensed, condensed, semi-condensed,
normal, semi-expanded, expanded,
extra-expanded, or ultra-expanded.
:height
:weight
ultra-bold, extra-bold, bold, semi-bold,
normal, semi-light, light, extra-light,
or ultra-light.
On a text-only terminal, any weight greater than normal is displayed as extra bright, and any weight less than normal is displayed as half-bright (provided the terminal supports the feature).
:slant
italic, oblique, normal,
reverse-italic, or reverse-oblique.
On a text-only terminal, slanted text is displayed as half-bright, if the terminal supports the feature.
:foreground
:background
:inverse-video
t (yes) or nil (no).
:stipple
The value can be a string; that should be the name of a file containing
external-format X bitmap data. The file is found in the directories
listed in the variable x-bitmap-file-path.
Alternatively, the value can specify the bitmap directly, with a list of
the form (width height data). Here,
width and height specify the size in pixels, and data
is a string containing the raw bits of the bitmap, row by row. Each row
occupies (width + 7) / 8 consecutie bytes in the string
(which should be a unibyte string for best results).
If the value is nil, that means use no stipple pattern.
Normally you do not need to set the stipple attribute, because it is used automatically to handle certain shades of gray.
:underline
t, underlining uses the foreground color of the
face. If the value is a string, underlining uses that color. The
value nil means do not underline.
:overline
:underline.
:strike-through
:underline.
:inherit
:box
Here are the possible values of the :box attribute, and what
they mean:
nil
t
(:line-width width :color color :style style)
The value color specifies the color to draw with. The default is the foreground color of the face for simple boxes, and the background color of the face for 3D boxes.
The value style specifies whether to draw a 3D box. If it is
released-button, the box looks like a 3D button that is not being
pressed. If it is pressed-button, the box looks like a 3D button
that is being pressed. If it is nil or omitted, a plain 2D box
is used.
The attributes :overline, :strike-through and
:box are new in Emacs 21. The attributes :family,
:height, :width, :weight, :slant are also
new; previous versions used the following attributes, now semi-obsolete,
to specify some of the same information:
:font
:bold
nil value specifies a bold font.
:italic
nil value specifies an italic font.
For compatibility, you can still set these "attributes" in Emacs 21, even though they are not real face attributes. Here is what that does:
:font
:family, :width, :height,
:weight, and :slant attributes according to the font name.
If the value is a pattern with wildcards, the first font that matches the pattern is used to set these attributes.
:bold
nil makes the face bold; nil makes it normal.
This actually works by setting the :weight attribute.
:italic
nil makes the face italic; nil makes it normal.
This actually works by setting the :slant attribute.
:stipple attribute.
t if object is a valid bitmap
specification, suitable for use with :stipple.
It returns nil otherwise.
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You can modify the attributes of an existing face with the following functions. If you specify frame, they affect just that frame; otherwise, they affect all frames as well as the defaults that apply to new frames.
nil, it sets
the attribute for all frames, and the defaults for new frames.
The extra arguments arguments specify the attributes to set, and
the values for them. They should consist of alternating attribute names
(such as :family or :underline) and corresponding values.
Thus,
(set-face-attribute 'foo nil
:width :extended
:weight :bold
:underline "red")
|
sets the attributes :width, :weight and :underline
to the corresponding values.
nil,
that means the selected frame (see section 29.9 Input Focus).
If frame is t, the value is the default for
face for new frames.
For example,
(face-attribute 'bold :weight)
=> bold
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The functions above did not exist before Emacs 21. For compatibility with older Emacs versions, you can use the following functions to set and examine the face attributes which existed in those versions.
Certain shades of gray are implemented by stipple patterns on black-and-white screens.
nil meaning don't use
stipple.
Normally there is no need to pay attention to stipple patterns, because they are used automatically to handle certain shades of gray.
In Emacs 21, this actually sets the attributes :family,
:width, :height, :weight, and :slant
according to the font name font.
In Emacs 20, this sets the font attribute. Once you set the font explicitly, the bold and italic attributes cease to have any effect, because the precise font that you specified is used.
nil, that means yes; nil means no.
In Emacs 21, this sets the :weight attribute.
In Emacs 20, it sets the :bold attribute.
nil, that means yes; nil means no.
In Emacs 21, this sets the :slant attribute.
In Emacs 20, it sets the :italic attribute.
nil means do underline; nil means don't.
:inverse-video attribute of face
face. If the attribute is nil, this function sets it to
t, and vice versa.
These functions examine the attributes of a face. If you don't
specify frame, they refer to the default data for new frames.
They return the symbol unspecified if the face doesn't define any
value for that attribute.
nil if it doesn't have one.
t if face is bold--that is, if it is
bolder than normal. It returns nil otherwise.
t if face is italic or oblique,
nil otherwise.
:underline attribute of face face.
:inverse-video attribute of face face.
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Here are the ways to specify which faces to use for display of text:
default face is used as the ultimate
default for all text. (In Emacs 19 and 20, the default
face is used only when no other face is specified.)
For a mode line or header line, the face modeline or
header-line is used just before default.
face property; if
so, the faces and face attributes specified there apply. See section 32.19.4 Properties with Special Meanings.
If the character has a mouse-face property, that is used instead
of the face property when the mouse is "near enough" to the
character.
face and mouse-face
properties too; they apply to all the text covered by the overlay.
region (see section 38.11.1 Standard Faces).
If these various sources together specify more than one face for a particular character, Emacs merges the attributes of the various faces specified. The attributes of the faces of special glyphs come first; then comes the face for region highlighting, if appropriate; then come attributes of faces from overlays, followed by those from text properties, and last the default face.
When multiple overlays cover one character, an overlay with higher priority overrides those with lower priority. See section 38.9 Overlays.
In Emacs 20, if an attribute such as the font or a color is not
specified in any of the above ways, the frame's own font or color is
used. In newer Emacs versions, this cannot happen, because the
default face specifies all attributes--in fact, the frame's own
font and colors are synonymous with those of the default face.
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Selecting a font means mapping the specified face attributes for a character to a font that is available on a particular display. The face attributes, as determined by face merging, specify most of the font choice, but not all. Part of the choice depends on what character it is.
For multibyte characters, typically each font covers only one
character set. So each character set (see section 33.5 Character Sets) specifies
a registry and encoding to use, with the character set's
x-charset-registry property. Its value is a string containing
the registry and the encoding, with a dash between them:
(plist-get (charset-plist 'latin-iso8859-1)
'x-charset-registry)
=> "ISO8859-1"
|
Unibyte text does not have character sets, so displaying a unibyte
character takes the registry and encoding from the variable
face-default-registry.
If the face specifies a fontset name, that fontset determines a pattern for fonts of the given charset. If the face specifies a font family, a font pattern is constructed.
Emacs tries to find an available font for the given face attributes and character's registry and encoding. If there is a font that matches exactly, it is used, of course. The hard case is when no available font exactly fits the specification. Then Emacs looks for one that is "close"---one attribute at a time. You can specify the order to consider the attributes. In the case where a specified font family is not available, you can specify a set of mappings for alternatives to try.
:width, :height, :weight, and :slant. The
value should be a list containing those four symbols, in order of
decreasing importance.
Font selection first finds the best available matches for the first attribute listed; then, among the fonts which are best in that way, it searches for the best matches in the second attribute, and so on.
The attributes :weight and :width have symbolic values in
a range centered around normal. Matches that are more extreme
(farther from normal) are somewhat preferred to matches that are
less extreme (closer to normal); this is designed to ensure that
non-normal faces contrast with normal ones, whenever possible.
The default is (:width :height :weight :slant), which means first
find the fonts closest to the specified :width, then--among the
fonts with that width--find a best match for the specified font height,
and so on.
One example of a case where this variable makes a difference is when the
default font has no italic equivalent. With the default ordering, the
italic face will use a non-italic font that is similar to the
default one. But if you put :slant before :height, the
italic face will use an italic font, even if its height is not
quite right.
(family alternate-families...) |
If family is specified but not available, Emacs will try the other families given in alternate-families, one by one, until it finds a family that does exist.
(registry alternate-registries...) |
If registry is specified but not available, Emacs will try the other registries given in alternate-registries, one by one, until it finds a registry that does exist.
Emacs can make use of scalable fonts, but by default it does not use them, since the use of too many or too big scalable fonts can crash XFree86 servers.
nil, the default, means do not use scalable fonts. t
means to use any scalable font that seems appropriate for the text.
Otherwise, the value must be a list of regular expressions. Then a scalable font is enabled for use if its name matches any regular expression in the list. For example,
(setq scalable-fonts-allowed '("muleindian-2$"))
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allows the use of scalable fonts with registry muleindian-2.
nil, that means to unload
all unused fonts as well.
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Here are additional functions for creating and working with faces.
nil. It does nothing if there is already a face named
name.
If the optional argument frame is given, this function applies only to that frame. Otherwise it applies to each frame individually, copying attributes from old-face in each frame to new-face in the same frame.
If the optional argument new-frame is given, then copy-face
copies the attributes of old-face in frame to new-name
in new-frame.
nil if none was specified for it.
t if the faces face1 and face2 have the
same attributes for display.
t if the face face displays differently from
the default face. A face is considered to be "the same" as the
default face if each attribute is either the same as that of the default
face, or unspecified (meaning to inherit from the default).
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Starting with Emacs 21, a hook is available for automatically assigning faces to text in the buffer. This hook is used for part of the implementation of Font-Lock mode.
The functions are called in the order listed, with one argument, a buffer position pos. Each function should attempt to assign faces to the text in the current buffer starting at pos.
Each function should record the faces they assign by setting the
face property. It should also add a non-nil
fontified property for all the text it has assigned faces to.
That property tells redisplay that faces have been assigned to that text
already.
It is probably a good idea for each function to do nothing if the
character after pos already has a non-nil fontified
property, but this is not required. If one function overrides the
assignments made by a previous one, the properties as they are
after the last function finishes are the ones that really matter.
For efficiency, we recommend writing these functions so that they usually assign faces to around 400 to 600 characters at each call.
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The argument pattern should be a string, perhaps with wildcard characters: the `*' character matches any substring, and the `?' character matches any single character. Pattern matching of font names ignores case.
If you specify face and frame, face should be a face name (a symbol) and frame should be a frame.
The optional argument maximum sets a limit on how many fonts to
return. If this is non-nil, then the return value is truncated
after the first maximum matching fonts. Specifying a small value
for maximum can make this function much faster, in cases where
many fonts match the pattern.
These additional functions are available starting in Emacs 21.
nil,
this list applies to all families, and therefore, it contains all
available fonts. Otherwise, family must be a string; it may
contain the wildcards `?' and `*'.
The list describes the display that frame is on; if frame is
omitted or nil, it applies to the selected frame's display
(see section 29.9 Input Focus).
The list contains a vector of the following form for each font:
[family width point-size weight slant fixed-p full registry-and-encoding] |
The first five elements correspond to face attributes; if you specify these attributes for a face, it will use this font.
The last three elements give additional information about the font. fixed-p is non-nil if the font is fixed-pitch. full is the full name of the font, and registry-and-encoding is a string giving the registry and encoding of the font.
The result list is sorted according to the current face font sort order.
nil, it
describes the selected frame's display (see section 29.9 Input Focus).
The value is a list of elements of this form:
(family . fixed-p) |
Here family is a font family, and fixed-p is
non-nil if fonts of that family are fixed-pitch.
x-family-fonts will not return more than
that many fonts, and font selection will consider only that many fonts
when searching a matching font for face attributes. The default is
currently 100.
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A fontset is a list of fonts, each assigned to a range of character codes. An individual font cannot display the whole range of characters that Emacs supports, but a fontset can. Fontsets have names, just as fonts do, and you can use a fontset name in place of a font name when you specify the "font" for a frame or a face. Here is information about defining a fontset under Lisp program control.
fontpattern, [charsetname:fontname]... |
Whitespace characters before and after the commas are ignored.
The first part of the string, fontpattern, should have the form of a standard X font name, except that the last two fields should be `fontset-alias'.
The new fontset has two names, one long and one short. The long name is
fontpattern in its entirety. The short name is
`fontset-alias'. You can refer to the fontset by either
name. If a fontset with the same name already exists, an error is
signaled, unless noerror is non-nil, in which case this
function does nothing.
If optional argument style-variant-p is non-nil, that says
to create bold, italic and bold-italic variants of the fontset as well.
These variant fontsets do not have a short name, only a long one, which
is made by altering fontpattern to indicate the bold or italic
status.
The specification string also says which fonts to use in the fontset. See below for the details.
The construct `charset:font' specifies which font to use (in this fontset) for one particular character set. Here, charset is the name of a character set, and font is the font to use for that character set. You can use this construct any number of times in the specification string.
For the remaining character sets, those that you don't specify explicitly, Emacs chooses a font based on fontpattern: it replaces `fontset-alias' with a value that names one character set. For the ASCII character set, `fontset-alias' is replaced with `ISO8859-1'.
In addition, when several consecutive fields are wildcards, Emacs collapses them into a single wildcard. This is to prevent use of auto-scaled fonts. Fonts made by scaling larger fonts are not usable for editing, and scaling a smaller font is not useful because it is better to use the smaller font in its own size, which Emacs does.
Thus if fontpattern is this,
-*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24 |
the font specification for ASCII characters would be this:
-*-fixed-medium-r-normal-*-24-*-ISO8859-1 |
and the font specification for Chinese GB2312 characters would be this:
-*-fixed-medium-r-normal-*-24-*-gb2312*-* |
You may not have any Chinese font matching the above font specification. Most X distributions include only Chinese fonts that have `song ti' or `fangsong ti' in the family field. In such a case, `Fontset-n' can be specified as below:
Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
|
Then, the font specifications for all but Chinese GB2312 characters have `fixed' in the family field, and the font specification for Chinese GB2312 characters has a wild card `*' in the family field.
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display Property
The display text property (or overlay property) is used to
insert images into text, and also control other aspects of how text
displays. These features are available starting in Emacs 21. The value
of the display property should be a display specification, or a
list or vector containing several display specifications. The rest of
this section describes several kinds of display specifications and what
they mean.
38.12.1 Specified Spaces Displaying one space with a specified width. 38.12.2 Other Display Specifications Displaying an image; magnifying text; moving it up or down on the page; adjusting the width of spaces within text. 38.12.3 Displaying in the Margins Displaying text or images to the side of the main text. 38.12.4 Conditional Display Specifications Making any of the above features conditional depending on some Lisp expression.
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To display a space of specified width and/or height, use a display
specification of the form (space . props), where
props is a property list (a list of alternating properties and
values). You can put this property on one or more consecutive
characters; a space of the specified height and width is displayed in
place of all of those characters. These are the properties you
can use to specify the weight of the space:
:width width
:relative-width factor
display property. The space width is the width of that
character, multiplied by factor.
:align-to hpos
Exactly one of the above properties should be used. You can also specify the height of the space, with other properties:
:height height
:relative-height factor
:ascent ascent
You should not use both :height and :relative-height
together.
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(image . image-props)
((margin nil) string)
string
Recursive display specifications are not supported, i.e. string display specifications that have a display specification property themselves.
(space-width factor)
(height height)
(+ n)
(- n)
height bound to the current specified font height.
(raise factor)
factor must be a number, which is interpreted as a multiple of the height of the affected text. If it is positive, that means to display the characters raised. If it is negative, that means to display them lower down.
If the text also has a height display specification, that does
not affect the amount of raising or lowering, which is based on the
faces used for the text.
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A buffer can have blank areas called display margins on the left
and on the right. Ordinary text never appears in these areas, but you
can put things into the display margins using the display
property.
To put text in the left or right display margin of the window, use a
display specification of the form (margin right-margin) or
(margin left-margin) on it. To put an image in a display margin,
use that display specification along with the display specification for
the image.
Before the display margins can display anything, you must give them a nonzero width. The usual way to do that is to set these variables:
Setting these variables does not immediately affect the window. These
variables are checked when a new buffer is displayed in the window.
Thus, you can make changes take effect by calling
set-window-buffer.
You can also set the margin widths immediately.
0).
(left . right).
If window is nil, the selected window is used.
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You can make any display specification conditional. To do that,
package it in another list of the form (when condition .
spec). Then the specification spec applies only when
condition evaluates to a non-nil value. During the
evaluation, object is bound to the string or buffer having the
conditional display property. position and
buffer-position are bound to the position within object
and the buffer position where the display property was found,
respectively. Both positions can be different when object is a
string.
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To display an image in an Emacs buffer, you must first create an image
descriptor, then use it as a display specifier in the display
property of text that is displayed (see section 38.12 The display Property). Like the
display property, this feature is available starting in Emacs 21.
Emacs can display a number of different image formats; some of them
are supported only if particular support libraries are installed on your
machine. The supported image formats include XBM, XPM (needing the
libraries libXpm version 3.4k and libz), GIF (needing
libungif 4.1.0), Postscript, PBM, JPEG (needing the
libjpeg library version v6a), TIFF (needing libtiff v3.4),
and PNG (needing libpng 1.0.2).
You specify one of these formats with an image type symbol. The image
type symbols are xbm, xpm, gif, postscript,
pbm, jpeg, tiff, and png.
38.13.1 Image Descriptors How to specify an image for use in :display.38.13.2 XBM Images Special features for XBM format. 38.13.3 XPM Images Special features for XPM format. 38.13.4 GIF Images Special features for GIF format. 38.13.5 Postscript Images Special features for Postscript format. 38.13.6 Other Image Types Various other formats are supported. 38.13.7 Defining Images Convenient ways to define an image for later use. 38.13.8 Showing Images Convenient ways to display an image once it is defined. 38.13.9 Image Cache Internal mechanisms of image display.
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An image description is a list of the form (image
. props), where props is a property list containing
alternating keyword symbols (symbols whose names start with a colon) and
their values. You can use any Lisp object as a property, but the only
properties that have any special meaning are certain symbols, all of
them keywords.
Every image descriptor must contain the property :type
type to specify the format of the image. The value of type
should be an image type symbol; for example, xpm for an image in
XPM format.
Here is a list of other properties that are meaningful for all image types:
:file file
:file property specifies to load the image from file
file. If file is not an absolute file name, it is expanded
in data-directory.
:data data
:data property specifies the actual contents of the image.
Each image must use either :data or :file, but not both.
For most image types, the value of the :data property should be a
string containing the image data; we recommend using a unibyte string.
Before using :data, look for further information in the section
below describing the specific image format. For some image types,
:data may not be supported; for some, it allows other data types;
for some, :data alone is not enough, so you need to use other
image properties along with :data.
:margin margin
:margin property specifies how many pixels to add as an
extra margin around the image. The value, margin, must be a a
non-negative number, or a pair (x . y) of such
numbers. If it is a pair, x specifies how many pixels to add
horizontally, and y specifies how many pixels to add vertically.
If :margin is not specified, the default is zero.
:ascent ascent
:ascent property specifies the amount of the image's
height to use for its ascent--that is, the part above the baseline.
The value, ascent, must be a number in the range 0 to 100, or
the symbol center.
If ascent is a number, that percentage of the image's height is used for its ascent.
If ascent is center, the image is vertically centered
around a centerline which would be the vertical centerline of text drawn
at the position of the image, in the manner specified by the text
properties and overlays that apply to the image.
If this property is omitted, it defaults to 50.
:relief relief
:relief property, if non-nil, adds a shadow rectangle
around the image. The value, relief, specifies the width of the
shadow lines, in pixels. If relief is negative, shadows are drawn
so that the image appears as a pressed button; otherwise, it appears as
an unpressed button.
:conversion algorithm
:conversion property, if non-nil, specifies a
conversion algorithm that should be applied to the image before it is
displayed; the value, algorithm, specifies which algorithm.
laplace
emboss
(edge-detection :matrix matrix :color-adjust adjust)
(x-1/y-1 x/y-1 x+1/y-1 x-1/y x/y x+1/y x-1/y+1 x/y+1 x+1/y+1) |
The resulting pixel is computed from the color intensity of the color resulting from summing up the RGB values of surrounding pixels, multiplied by the specified factors, and dividing that sum by the sum of the factors' absolute values.
Laplace edge-detection currently uses a matrix of
(1 0 0 0 0 0 9 9 -1) |
Emboss edge-detection uses a matrix of
( 2 -1 0
-1 0 1
0 1 -2)
|
disabled
:mask mask
heuristic or (heuristic bg), build
a clipping mask for the image, so that the background of a frame is
visible behind the image. If bg is not specified, or if bg
is t, determine the background color of the image by looking at
the four corners of the image, assuming the most frequently occurring
color from the corners is the background color of the image. Otherwise,
bg must be a list (red green blue)
specifying the color to assume for the background of the image.
If mask is nil, remove a mask from the image, if it has one. Images
in some formats include a mask which can be removed by specifying
:mask nil.
t if image spec has a mask bitmap.
frame is the frame on which the image will be displayed.
frame nil or omitted means to use the selected frame
(see section 29.9 Input Focus).
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To use XBM format, specify xbm as the image type. This image
format doesn't require an external library, so images of this type are
always supported.
Additional image properties supported for the xbm image type are:
:foreground foreground
nil for the default color. This color is
used for each pixel in the XBM that is 1. The default is the frame's
foreground color.
:background background
nil for the default color. This color is
used for each pixel in the XBM that is 0. The default is the frame's
background color.
If you specify an XBM image using data within Emacs instead of an external file, use the following three properties:
:data data
:height and :width.
:height and :width in this case,
because omitting them is what indicates the data has the format of an
XBM file. The file contents specify the height and width of the image.
height bits. In this case, you must specify
:height and :width, both to indicate that the string
contains just the bits rather than a whole XBM file, and to specify the
size of the image.
:width width
:height height
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To use XPM format, specify xpm as the image type. The
additional image property :color-symbols is also meaningful with
the xpm image type:
:color-symbols symbols
(name . color). In each element, name is
the name of a color as it appears in the image file, and color
specifies the actual color to use for displaying that name.
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For GIF images, specify image type gif. Because of the patents
in the US covering the LZW algorithm, the continued use of GIF format is
a problem for the whole Internet; to end this problem, it is a good idea
for everyone, even outside the US, to stop using GIFS right away
(http://www.burnallgifs.org/). But if you still want to use
them, Emacs can display them.
:index index
:index to specify one image from a GIF file that
contains more than one image. This property specifies use of image
number index from the file. An error is signaled if the GIF file
doesn't contain an image with index index.
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To use Postscript for an image, specify image type postscript.
This works only if you have Ghostscript installed. You must always use
these three properties:
:pt-width width
:pt-height height
:bounding-box box
%%BoundingBox: 22 171 567 738 |
Displaying Postscript images from Lisp data is not currently implemented, but it may be implemented by the time you read this. See the `etc/NEWS' file to make sure.
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For PBM images, specify image type pbm. Color, gray-scale and
monochromatic images are supported. For mono PBM images, two additional
image properties are supported.
:foreground foreground
nil for the default color. This color is
used for each pixel in the XBM that is 1. The default is the frame's
foreground color.
:background background
nil for the default color. This color is
used for each pixel in the XBM that is 0. The default is the frame's
background color.
For JPEG images, specify image type jpeg.
For TIFF images, specify image type tiff.
For PNG images, specify image type png.
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The functions create-image, defimage and
find-image provide convenient ways to create image descriptors.
The optional argument type is a symbol specifying the image type.
If type is omitted or nil, create-image tries to
determine the image type from the file's first few bytes, or else
from the file's name.
The remaining arguments, props, specify additional image properties--for example,
(create-image "foo.xpm" 'xpm :heuristic-mask t) |
The function returns nil if images of this type are not
supported. Otherwise it returns an image descriptor.
Each argument in specs has the form of a property list, and each
one should specify at least the :type property and the
:file property. Here is an example:
(defimage test-image
'((:type xpm :file "~/test1.xpm")
(:type xbm :file "~/test1.xbm")))
|
defimage tests each argument, one by one, to see if it is
usable--that is, if the type is supported and the file exists. The
first usable argument is used to make an image descriptor which is
stored in the variable variable.
If none of the alternatives will work, then variable is defined
as nil.
Each specification in specs is a property list with contents
depending on image type. All specifications must at least contain the
properties :type type and either :file file
or :data DATA, where type is a symbol specifying
the image type, e.g. xbm, file is the file to load the
image from, and data is a string containing the actual image data.
The first specification in the list whose type is supported, and
file exists, is used to construct the image specification to be
returned. If no specification is satisfied, nil is returned.
The image is looked for first on load-path and then in
data-directory.
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You can use an image descriptor by setting up the display
property yourself, but it is easier to use the functions in this
section.
create-image, or the value of a symbol defined with
defimage. The argument string specifies the text to put in
the buffer to hold the image.
The argument area specifies whether to put the image in a margin.
If it is left-margin, the image appears in the left margin;
right-margin specifies the right margin. If area is
nil or omitted, the image is displayed at point within the
buffer's text.
Internally, this function inserts string in the buffer, and gives
it a display property which specifies image. See section 38.12 The display Property.
The argument image must be an image descriptor, perhaps returned
by create-image or stored by defimage.
The argument area specifies whether to put the image in a margin.
If it is left-margin, the image appears in the left margin;
right-margin specifies the right margin. If area is
nil or omitted, the image is displayed at point within the
buffer's text.
Internally, this function creates an overlay, and gives it a
before-string property containing text that has a display
property whose value is the image. (Whew!)
nil,
images are removed from the current buffer.
This removes only images that were put into buffer the way
put-image does it, not images that were inserted with
insert-image or in other ways.
(width . height). spec is an image
specification. pixels non-nil means return sizes measured in
pixels, otherwise return sizes measured in canonical character units
(fractions of the width/height of the frame's default font).
frame is the frame on which the image will be displayed.
frame null or omitted means use the selected frame (see section 29.9 Input Focus).
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Emacs stores images in an image cache when it displays them, so it can display them again more efficiently. It removes an image from the cache when it hasn't been displayed for a specified period of time.
When an image is looked up in the cache, its specification is compared
with cached image specifications using equal. This means that
all images with equal specifications share the same image in the cache.
If the value is nil, Emacs does not remove images from the cache
except when you explicitly clear it. This mode can be useful for
debugging.
nil,
only the cache for that frame is cleared. Otherwise all frames' caches
are cleared.
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This section describes the mechanism by which Emacs shows a matching open parenthesis when the user inserts a close parenthesis.
blink-paren-function may be nil, in which
case nothing is done.
nil, then blink-matching-open does
nothing.
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)))
|
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nil means yes, nil means no. The
default is nil.
nil, then these lines are displayed in
inverse video. Otherwise, these lines are displayed normally, just like
other text. The default is t.
For window frames, this feature actually applies the face named
mode-line; that face is normally set up as the inverse of the
default face, unless you change it.
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The usual display conventions define how to display each character code. You can override these conventions by setting up a display table (see section 38.17 Display Tables). Here are the usual display conventions:
tab-width.
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.
On MS-DOS terminals, Emacs arranges by default for the character code 127 to be mapped to the glyph code 127, which normally displays as an empty polygon. This glyph is used to display non-ASCII characters that the MS-DOS terminal doesn't support. See section `MS-DOS and MULE' in The GNU Emacs Manual.
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 special behavior.
These display rules apply to carriage return (character code 13), when it appears in the buffer. But that character may not appear in the buffer where you expect it, if it was eliminated as part of end-of-line conversion (see section 33.10.1 Basic Concepts of Coding Systems).
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. These variables also affect
how the mode line is displayed; if you want to force redisplay of the
mode line using the new values, call the function
force-mode-line-update (see section 23.3 Mode Line Format).
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'.
ctl-arrow in
buffers that do not override it. See section 11.10.3 The Default Value of a Buffer-Local Variable.
nil, Emacs displays a special glyph in
each empty line at the end of the buffer, on terminals that
support it (window systems).
tab-to-tab-stop. See section 32.17.5 Adjustable "Tab Stops".
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You can use the display table feature to control how all 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 glyphs, each glyph being a graphic that takes up one character position on the screen. You can also define how to display each glyph on your terminal, using the glyph table.
Display tables affect how the mode line is displayed; if you want to
force redisplay of the mode line using a new display table, call
force-mode-line-update (see section 23.3 Mode Line Format).
38.17.1 Display Table Format What a display table consists of. 38.17.2 Active Display Table How Emacs selects a display table to use. 38.17.3 Glyphs How to define a glyph, and what glyphs mean.
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A display table is actually a char-table (see section 6.6 Char-Tables) with
display-table as its subtype.
nil in all elements.
The ordinary elements of the display table are indexed by character
codes; the element at index c says how to display the character
code c. The value should be nil or a vector of glyph
values (see section 38.17.3 Glyphs). If an element is nil, it says to
display that character according to the usual display conventions
(see section 38.16 Usual Display Conventions).
If you use the display table to change the display of newline characters, the whole buffer will be displayed as one long "line."
The display table also has six "extra slots" which serve special
purposes. Here is a table of their meanings; nil in any slot
means to use the default for that slot, as stated below.
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 (vector ?^ (+ i 64))))
(setq i (1+ i)))
(aset disptab 127 (vector ?^ ??)))
|
truncation, wrap, escape, control,
selective-display, and vertical-border.
truncation, wrap, escape, control,
selective-display, and vertical-border.
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Each window can specify a display table, and so can each buffer. When a buffer b is displayed in window w, display uses the display table for window w if it has one; otherwise, the display table for buffer b if it has one; otherwise, the standard display table if any. The display table chosen is called the active display table.
nil
if window does not have an assigned display table.
nil.
nil, that means the buffer does not have an assigned display
table.
nil by default.
If there is no display table to use for a particular window--that is,
if the window specifies none, its buffer specifies none, and
standard-display-table is nil---then Emacs uses the usual
display conventions for all character codes in that window. See section 38.16 Usual Display Conventions.
A number of functions for changing the standard display table are defined in the library `disp-table'.
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A glyph is a generalization of a character; it stands for an image that takes up a single character position on the screen. Glyphs are represented in Lisp as integers, just as characters are.
The meaning of each integer, as a glyph, is defined by the glyph
table, which is the value of the variable glyph-table.
nil instead of a vector, then all glyphs are simple (see
below). The glyph table is not used on windowed displays.
Here are the possible types of elements in the glyph table:
nil
If a glyph code is greater than or equal to the length of the glyph table, that code is automatically simple.
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This section describes how to make Emacs ring the bell (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 just beeping when signaling an error is more appropriate. (See section 10.5.3 Errors.)
visible-bell below).
It also terminates any keyboard macro currently executing unless
do-not-terminate is non-nil.
ding.
nil means yes, nil means no. This
is effective on a window system, and on a character-only terminal
provided the terminal's Termcap entry defines the visible bell
capability (`vb').
nil, it specifies how Emacs should "ring the
bell." Its value should be a function of no arguments. If this is
non-nil, it takes precedence over the visible-bell
variable.
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Emacs works with several window systems, most notably the X Window System. Both Emacs and X use the term "window", but use it differently. An Emacs frame is a single window as far as X is concerned; the individual Emacs windows are not known to X at all.
x
pc
w32
mac
nil
term-setup-hook.
This hook is used for internal purposes: setting up communication with the window system, and creating the initial window. Users should not interfere with it.
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