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J. Controlling the DisplaySince only part of a large buffer fits in the window, Emacs tries to show a part that is likely to be interesting. Display-control commands allow you to specify which part of the text you want to see, and how to display it.
J.1 Using Multiple TypefacesWhen using Emacs with a window system, you can set up multiple styles of displaying characters. Each style is called a face. Each face can specify various attributes, such as the height, weight and slant of the characters, the foreground and background color, and underlining. But it does not have to specify all of them. Emacs on a character terminal supports only part of face attributes. Which attributes are supported depends on your display type, but many displays support inverse video, bold, and underline attributes, and some support colors.
Features which rely on text in multiple faces (such as Font Lock mode)
will also work on non-windowed terminals that can display more than one
face, whether by colors or underlining and emboldening. This includes
the console on GNU/Linux, an
You control the appearance of a part of the text in the buffer by
specifying the face or faces to use for it. The style of display used
for any given character is determined by combining the attributes of
all the applicable faces specified for that character. Any attribute
that isn't specified by these faces is taken from the Enriched mode, the mode for editing formatted text, includes several commands and menus for specifying faces for text in the buffer. See section T.11.4 Faces in Formatted Text, for how to specify the font for text in the buffer. See section T.11.5 Colors in Formatted Text, for how to specify the foreground and background color.
To alter the appearance of a face, use the customization buffer.
See section AD.2.2.3 Customizing Faces. You can also use X resources to specify
attributes of particular faces (see section AE.13 X Resources). Alternatively,
you can change the foreground and background colors of a specific face
with M-x set-face-foreground and M-x set-face-background.
These commands prompt in the minibuffer for a face name and a color
name, with completion, and then set that face to use the specified
color. Changing the colors of the Emacs 21 can correctly display variable-width fonts, but Emacs commands that calculate width and indentation do not know how to calculate variable widths. This can sometimes lead to incorrect results when you use variable-width fonts. In particular, indentation commands can give inconsistent results, so we recommend you avoid variable-width fonts for editing program source code. Filling will sometimes make lines too long or too short. We plan to address these issues in future Emacs versions. To see what faces are currently defined, and what they look like, type M-x list-faces-display. It's possible for a given face to look different in different frames; this command shows the appearance in the frame in which you type it. Here's a list of the standard defined faces:
When Transient Mark mode is enabled, the text of the region is
highlighted when the mark is active. This uses the face named
One easy way to use faces is to turn on Font Lock mode. This minor mode, which is always local to a particular buffer, arranges to choose faces according to the syntax of the text you are editing. It can recognize comments and strings in most languages; in several languages, it can also recognize and properly highlight various other important constructs. See section J.2 Font Lock mode, for more information about Font Lock mode and syntactic highlighting.
You can print out the buffer with the highlighting that appears
on your screen using the command
J.2 Font Lock modeFont Lock mode is a minor mode, always local to a particular buffer, which highlights (or "fontifies") using various faces according to the syntax of the text you are editing. It can recognize comments and strings in most languages; in several languages, it can also recognize and properly highlight various other important constructs--for example, names of functions being defined or reserved keywords.
The command M-x font-lock-mode turns Font Lock mode on or off
according to the argument, and toggles the mode when it has no argument.
The function
To turn on Font Lock mode automatically in all modes which support
it, customize the user option
Font Lock mode uses several specifically named faces to do its job,
including To change the colors or the fonts used by Font Lock mode to fontify different parts of text, just change these faces. There are two ways to do it:
To get the full benefit of Font Lock mode, you need to choose a default font which has bold, italic, and bold-italic variants; or else you need to have a color or gray-scale screen.
The variable
Fontification can be too slow for large buffers, so you can suppress
it. The variable Comment and string fontification (or "syntactic" fontification) relies on analysis of the syntactic structure of the buffer text. For the sake of speed, some modes, including C mode and Lisp mode, rely on a special convention: an open-parenthesis or open-brace in the leftmost column always defines the beginning of a defun, and is thus always outside any string or comment. (See section U.2.1 Left Margin Convention.) If you don't follow this convention, Font Lock mode can misfontify the text that follows an open-parenthesis or open-brace in the leftmost column that is inside a string or comment.
The variable
Font Lock highlighting patterns already exist for many modes, but you
may want to fontify additional patterns. You can use the function
To remove keywords from the font-lock highlighting patterns, use the
function
J.3 Highlight Changes ModeUse M-x highlight-changes-mode to enable a minor mode that uses faces (colors, typically) to indicate which parts of the buffer were changed most recently.
J.4 Interactive Highlighting by MatchingIt is sometimes useful to highlight the strings that match a certain regular expression. For example, you might wish to see all the references to a certain variable in a program source file, or highlight certain parts in a voluminous output of some program, or make certain cliches stand out in an article. Use the M-x hi-lock-mode command to turn on a minor mode that allows you to specify regular expressions of the text to be highlighted. Hi-lock mode works like Font Lock (see section J.2 Font Lock mode), except that it lets you specify explicitly what parts of text to highlight. You control Hi-lock mode with these commands:
J.5 Trailing WhitespaceIt is easy to leave unnecessary spaces at the end of a line without realizing it. In most cases, this trailing whitespace has no effect, but there are special circumstances where it matters.
You can make trailing whitespace visible on the screen by setting the
buffer-local variable Trailing whitespace is defined as spaces or tabs at the end of a line. But trailing whitespace is not displayed specially if point is at the end of the line containing the whitespace. (Doing that looks ugly while you are typing in new text, and the location of point is enough in that case to show you that the spaces are present.) To delete all trailing whitespace within the current buffer's restriction (see section AC.22 Narrowing), type M-x delete-trailing-whitespace RET. (This command does not remove the form-feed characters.)
Emacs can indicate empty lines at the end of the buffer with a
special bitmap on the left fringe of the window. To enable this
feature, set the buffer-local variable
J.6 ScrollingIf a buffer contains text that is too large to fit entirely within a window that is displaying the buffer, Emacs shows a contiguous portion of the text. The portion shown always contains point. Scrolling means moving text up or down in the window so that different parts of the text are visible. Scrolling forward means that text moves up, and new text appears at the bottom. Scrolling backward moves text down and new text appears at the top. Scrolling happens automatically if you move point past the bottom or top of the window. You can also explicitly request scrolling with the commands in this section.
The most basic scrolling command is C-l (
To read the buffer a windowful at a time, use C-v
(
M-v ( The commands C-v and M-v with a numeric argument scroll the text in the selected window up or down a few lines. C-v with an argument moves the text and point up, together, that many lines; it brings the same number of new lines into view at the bottom of the window. M-v with numeric argument scrolls the text downward, bringing that many new lines into view at the top of the window. C-v with a negative argument is like M-v and vice versa.
The names of scroll commands are based on the direction that the
text moves in the window. Thus, the command to scroll forward is
called
Some users like the full-screen scroll commands to keep point at the
same screen line. To enable this behavior, set the variable
Another way to do scrolling is with C-l with a numeric argument. C-l does not clear the screen when given an argument; it only scrolls the selected window. With a positive argument n, it repositions text to put point n lines down from the top. An argument of zero puts point on the very top line. Point does not move with respect to the text; rather, the text and point move rigidly on the screen. C-l with a negative argument puts point that many lines from the bottom of the window. For example, C-u - 1 C-l puts point on the bottom line, and C-u - 5 C-l puts it five lines from the bottom. C-u C-l scrolls to put point at the center (vertically) of the selected window.
The C-M-l command (
Scrolling happens automatically when point moves out of the visible
portion of the text. Normally, automatic scrolling centers point
vertically within the window. However, if you set
When the window does scroll by a longer distance, you can control
how aggressively it scrolls, by setting the variables
Likewise,
The variable
J.7 Horizontal ScrollingHorizontal scrolling means shifting all the lines sideways within a window--so that some of the text near the left margin is not displayed at all. Emacs does this automatically in any window that uses line truncation rather than continuation: whenever point moves off the left or right edge of the screen, Emacs scrolls the buffer horizontally to make point visible. When a window has been scrolled horizontally, text lines are truncated rather than continued (see section D.8 Continuation Lines), with a `$' appearing in the first column when there is text truncated to the left, and in the last column when there is text truncated to the right. You can use these commands to do explicit horizontal scrolling.
The command C-x < (
C-x > (
If you scroll a window horizontally by hand, that sets a lower bound
for automatic horizontal scrolling. Automatic scrolling will continue
to scroll the window, but never farther to the right than the amount
you previously set by
To disable automatic horizontal scrolling, set the variable
J.8 Follow ModeFollow mode is a minor mode that makes two windows showing the same buffer scroll as one tall "virtual window." To use Follow mode, go to a frame with just one window, split it into two side-by-side windows using C-x 3, and then type M-x follow-mode. From then on, you can edit the buffer in either of the two windows, or scroll either one; the other window follows it. In Follow mode, if you move point outside the portion visible in one window and into the portion visible in the other window, that selects the other window--again, treating the two as if they were parts of one large window. To turn off Follow mode, type M-x follow-mode a second time.
J.9 Selective DisplayEmacs has the ability to hide lines indented more than a certain number of columns (you specify how many columns). You can use this to get an overview of a part of a program.
To hide lines, type C-x $ ( The commands C-n and C-p move across the hidden lines as if they were not there. The hidden lines are still present in the buffer, and most editing commands see them as usual, so you may find point in the middle of the hidden text. When this happens, the cursor appears at the end of the previous line, after the three dots. If point is at the end of the visible line, before the newline that ends it, the cursor appears before the three dots. To make all lines visible again, type C-x $ with no argument.
If you set the variable
J.10 Optional Mode Line FeaturesThe current line number of point appears in the mode line when Line Number mode is enabled. Use the command M-x line-number-mode to turn this mode on and off; normally it is on. The line number appears before the buffer percentage pos, with the letter `L' to indicate what it is. See section AD.1 Minor Modes, for more information about minor modes and about how to use this command. If you have narrowed the buffer (see section AC.22 Narrowing), the displayed line number is relative to the accessible portion of the buffer.
If the buffer is very large (larger than the value of
Line-number computation can also be slow if the lines in the buffer
are too long. For this reason, Emacs normally doesn't display line
numbers if the average width, in characters, of lines near point is
larger than the value of the variable
You can also display the current column number by turning on Column Number mode. It displays the current column number preceded by the letter `C'. Type M-x column-number-mode to toggle this mode.
Emacs can optionally display the time and system load in all mode
lines. To enable this feature, type M-x display-time or customize
the option
Here hh and mm are the hour and minute, followed always by
`am' or `pm'. l.ll is the average number of running
processes in the whole system recently. (Some fields may be missing if
your operating system cannot support them.) If you prefer time display
in 24-hour format, set the variable
The word `Mail' appears after the load level if there is mail
for you that you have not read yet. On a graphical display you can use
an icon instead of `Mail' by customizing
By default, the mode line is drawn on graphics displays with
3D-style highlighting, like that of a button when it is not being
pressed. If you don't like this effect, you can disable the 3D
highlighting of the mode line, by customizing the attributes of the
Alternatively, you can turn off the box attribute in your `.Xdefaults' file:
J.11 How Text Is DisplayedASCII printing characters (octal codes 040 through 0176) in Emacs buffers are displayed with their graphics, as are non-ASCII multibyte printing characters (octal codes above 0400). Some ASCII control characters are displayed in special ways. The newline character (octal code 012) is displayed by starting a new line. The tab character (octal code 011) is displayed by moving to the next tab stop column (normally every 8 columns). Other ASCII control characters are normally displayed as a caret (`^') followed by the non-control version of the character; thus, control-A is displayed as `^A'. Non-ASCII characters 0200 through 0237 (octal) are displayed with octal escape sequences; thus, character code 0230 (octal) is displayed as `\230'. The display of character codes 0240 through 0377 (octal) may be either as escape sequences or as graphics. They do not normally occur in multibyte buffers, but if they do, they are displayed as Latin-1 graphics. In unibyte mode, if you enable European display they are displayed using their graphics (assuming your terminal supports them), otherwise as escape sequences. See section Q.13 Single-byte Character Set Support.
J.12 Customization of DisplayThis section contains information for customization only. Beginning users should skip it.
The variable
If the variable
If the variable
When you reenter Emacs after suspending, Emacs normally clears the
screen and redraws the entire display. On some terminals with more than
one page of memory, it is possible to arrange the termcap entry so that
the `ti' and `te' strings (output to the terminal when Emacs
is entered and exited, respectively) switch between pages of memory so
as to use one page for Emacs and another page for other output. Then
you might want to set the variable
The variable
If the variable
Normally, a tab character in the buffer is displayed as whitespace which
extends to the next display tab stop position, and display tab stops come
at intervals equal to eight spaces. The number of spaces per tab is
controlled by the variable
If the variable
If the variable
The variable
On window-systems, You can customize the way any particular character code is displayed by means of a display table. See section `Display Tables' in The Emacs Lisp Reference Manual.
On a window system, Emacs can optionally display the mouse pointer
in a special shape to say that Emacs is busy. To turn this feature on
or off, customize the group
On some text-only terminals, bold face and inverse video together
result in text that is hard to read. Call the function
J.13 Displaying the CursorThere are a number of ways to customize the display of the cursor. M-x hl-line-mode enables or disables a minor mode which highlights the line containing point. On window systems, the command M-x blink-cursor-mode turns on or off the blinking of the cursor. (On terminals, the terminal itself blinks the cursor, and Emacs has no control over it.)
You can customize the cursor's color, and whether it blinks, using
the
When displaying on a window system, Emacs can optionally draw the
block cursor as wide as the character under the cursor--for example,
if the cursor is on a tab character, it would cover the full width
occupied by that tab character. To enable this feature, set the
variable
Normally, the cursor in non-selected windows is shown as a hollow box.
To turn off cursor display in non-selected windows, customize the option
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