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1 | @c This is part of the Emacs manual. |
2 | @c Copyright (C) 1985, 86, 87, 93, 94, 95, 1997 Free Software Foundation, Inc. | |
3 | @c See file emacs.texi for copying conditions. | |
4 | @node Display, Search, Registers, Top | |
5 | @chapter Controlling the Display | |
6 | ||
7 | Since only part of a large buffer fits in the window, Emacs tries to | |
8 | show a part that is likely to be interesting. Display-control commands | |
9 | allow you to specify which part of the text you want to see, and how to | |
10 | display it. | |
11 | ||
12 | @menu | |
13 | * Scrolling:: Moving text up and down in a window. | |
14 | * Horizontal Scrolling:: Moving text left and right in a window. | |
15 | * Follow Mode:: Follow mode lets two windows scroll as one. | |
16 | * Selective Display:: Hiding lines with lots of indentation. | |
17 | * Optional Mode Line:: Optional mode line display features. | |
18 | * Text Display:: How text characters are normally displayed. | |
19 | * Display Vars:: Information on variables for customizing display. | |
20 | @end menu | |
21 | ||
22 | @node Scrolling | |
23 | @section Scrolling | |
24 | ||
25 | If a buffer contains text that is too large to fit entirely within a | |
26 | window that is displaying the buffer, Emacs shows a contiguous portion of | |
27 | the text. The portion shown always contains point. | |
28 | ||
29 | @cindex scrolling | |
30 | @dfn{Scrolling} means moving text up or down in the window so that | |
31 | different parts of the text are visible. Scrolling forward means that text | |
32 | moves up, and new text appears at the bottom. Scrolling backward moves | |
33 | text down and new text appears at the top. | |
34 | ||
35 | Scrolling happens automatically if you move point past the bottom or top | |
36 | of the window. You can also explicitly request scrolling with the commands | |
37 | in this section. | |
38 | ||
39 | @table @kbd | |
40 | @item C-l | |
41 | Clear screen and redisplay, scrolling the selected window to center | |
42 | point vertically within it (@code{recenter}). | |
43 | @item C-v | |
44 | Scroll forward (a windowful or a specified number of lines) (@code{scroll-up}). | |
45 | @item @key{NEXT} | |
46 | Likewise, scroll forward. | |
47 | @item M-v | |
48 | Scroll backward (@code{scroll-down}). | |
49 | @item @key{PRIOR} | |
50 | Likewise, scroll backward. | |
51 | @item @var{arg} C-l | |
52 | Scroll so point is on line @var{arg} (@code{recenter}). | |
53 | @item C-M-l | |
54 | Scroll heuristically to bring useful information onto the screen | |
55 | (@code{reposition-window}). | |
56 | @end table | |
57 | ||
58 | @kindex C-l | |
59 | @findex recenter | |
60 | The most basic scrolling command is @kbd{C-l} (@code{recenter}) with | |
61 | no argument. It clears the entire screen and redisplays all windows. | |
62 | In addition, it scrolls the selected window so that point is halfway | |
63 | down from the top of the window. | |
64 | ||
65 | @kindex C-v | |
66 | @kindex M-v | |
67 | @kindex NEXT | |
68 | @kindex PRIOR | |
69 | @findex scroll-up | |
70 | @findex scroll-down | |
71 | The scrolling commands @kbd{C-v} and @kbd{M-v} let you move all the text | |
72 | in the window up or down a few lines. @kbd{C-v} (@code{scroll-up}) with an | |
73 | argument shows you that many more lines at the bottom of the window, moving | |
74 | the text and point up together as @kbd{C-l} might. @kbd{C-v} with a | |
75 | negative argument shows you more lines at the top of the window. | |
76 | @kbd{M-v} (@code{scroll-down}) is like @kbd{C-v}, but moves in the | |
77 | opposite direction. The function keys @key{NEXT} and @key{PRIOR} are | |
78 | equivalent to @kbd{C-v} and @kbd{M-v}. | |
79 | ||
80 | The names of scroll commands are based on the direction that the text | |
81 | moves in the window. Thus, the command to scroll forward is called | |
82 | @code{scroll-up} because it moves the text upward on the screen. | |
83 | ||
84 | @vindex next-screen-context-lines | |
85 | To read the buffer a windowful at a time, use @kbd{C-v} with no argument. | |
86 | It takes the last two lines at the bottom of the window and puts them at | |
87 | the top, followed by nearly a whole windowful of lines not previously | |
88 | visible. If point was in the text scrolled off the top, it moves to the | |
89 | new top of the window. @kbd{M-v} with no argument moves backward with | |
90 | overlap similarly. The number of lines of overlap across a @kbd{C-v} or | |
91 | @kbd{M-v} is controlled by the variable @code{next-screen-context-lines}; by | |
92 | default, it is 2. | |
93 | ||
94 | @vindex scroll-preserve-screen-position | |
95 | Some users like the full-screen scroll commands to keep point at the | |
96 | same screen line. To enable this behavior, set the variable | |
97 | @code{scroll-preserve-screen-position} to a non-@code{nil} value. This | |
98 | mode is convenient for browsing through a file by scrolling by | |
99 | screenfuls; if you come back to the screen where you started, point goes | |
100 | back to the line where it started. However, this mode is inconvenient | |
101 | when you move to the next screen in order to move point to the text | |
102 | there. | |
103 | ||
104 | Another way to do scrolling is with @kbd{C-l} with a numeric argument. | |
105 | @kbd{C-l} does not clear the screen when given an argument; it only scrolls | |
106 | the selected window. With a positive argument @var{n}, it repositions text | |
107 | to put point @var{n} lines down from the top. An argument of zero puts | |
108 | point on the very top line. Point does not move with respect to the text; | |
109 | rather, the text and point move rigidly on the screen. @kbd{C-l} with a | |
110 | negative argument puts point that many lines from the bottom of the window. | |
111 | For example, @kbd{C-u - 1 C-l} puts point on the bottom line, and @kbd{C-u | |
112 | - 5 C-l} puts it five lines from the bottom. Just @kbd{C-u} as argument, | |
113 | as in @kbd{C-u C-l}, scrolls point to the center of the selected window. | |
114 | ||
115 | @kindex C-M-l | |
116 | @findex reposition-window | |
117 | The @kbd{C-M-l} command (@code{reposition-window}) scrolls the current | |
118 | window heuristically in a way designed to get useful information onto | |
119 | the screen. For example, in a Lisp file, this command tries to get the | |
120 | entire current defun onto the screen if possible. | |
121 | ||
122 | @vindex scroll-conservatively | |
123 | Scrolling happens automatically if point has moved out of the visible | |
124 | portion of the text when it is time to display. Normally, automatic | |
125 | scrolling centers point vertically within the window. However, if you | |
126 | set @code{scroll-conservatively} to a small number @var{n}, then if you | |
127 | move point just a little off the screen---less than @var{n} lines---then | |
128 | Emacs scrolls the text just far enough to bring point back on screen. | |
129 | By default, @code{scroll-conservatively} is 0. | |
130 | ||
131 | @vindex scroll-margin | |
132 | The variable @code{scroll-margin} restricts how close point can come | |
133 | to the top or bottom of a window. Its value is a number of screen | |
134 | lines; if point comes within that many lines of the top or bottom of the | |
135 | window, Emacs recenters the window. By default, @code{scroll-margin} is | |
136 | 0. | |
137 | ||
138 | @node Horizontal Scrolling | |
139 | @section Horizontal Scrolling | |
140 | @cindex horizontal scrolling | |
141 | ||
142 | @dfn{Horizontal scrolling} means shifting all the lines sideways | |
143 | within a window---so that some of the text near the left margin | |
144 | is not displayed at all. | |
145 | ||
146 | @table @kbd | |
147 | @item C-x < | |
148 | Scroll text in current window to the left (@code{scroll-left}). | |
149 | @item C-x > | |
150 | Scroll to the right (@code{scroll-right}). | |
151 | @end table | |
152 | ||
153 | When a window has been scrolled horizontally, text lines are truncated | |
154 | rather than continued (@pxref{Continuation Lines}), with a @samp{$} | |
155 | appearing in the first column when there is text truncated to the left, | |
156 | and in the last column when there is text truncated to the right. | |
157 | ||
158 | @kindex C-x < | |
159 | @kindex C-x > | |
160 | @findex scroll-left | |
161 | @findex scroll-right | |
162 | The command @kbd{C-x <} (@code{scroll-left}) scrolls the selected | |
163 | window to the left by @var{n} columns with argument @var{n}. This moves | |
164 | part of the beginning of each line off the left edge of the window. | |
165 | With no argument, it scrolls by almost the full width of the window (two | |
166 | columns less, to be precise). | |
167 | ||
168 | @kbd{C-x >} (@code{scroll-right}) scrolls similarly to the right. The | |
169 | window cannot be scrolled any farther to the right once it is displayed | |
170 | normally (with each line starting at the window's left margin); | |
171 | attempting to do so has no effect. This means that you don't have to | |
172 | calculate the argument precisely for @w{@kbd{C-x >}}; any sufficiently large | |
173 | argument will restore the normal display. | |
174 | ||
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175 | @cindex horizontal scrolling |
176 | @vindex automatic-hscrolling | |
177 | Emacs automatically scrolls a window horizontally whenever that is | |
178 | necessary to keep point visible and not too far from the left or right | |
179 | edge. If you don't want this, customize the variable | |
180 | @code{automatic-hscrolling} and set it to nil. | |
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181 | |
182 | @node Follow Mode | |
183 | @section Follow Mode | |
184 | @cindex Follow mode | |
185 | @cindex mode, Follow | |
186 | ||
187 | @dfn{Follow mode} is a minor mode that makes two windows showing the | |
188 | same buffer scroll as one tall ``virtual window.'' To use Follow mode, | |
189 | go to a frame with just one window, split it into two side-by-side | |
190 | windows using @kbd{C-x 3}, and then type @kbd{M-x follow-mode}. From | |
191 | then on, you can edit the buffer in either of the two windows, or scroll | |
192 | either one; the other window follows it. | |
193 | ||
194 | To turn off Follow mode, type @kbd{M-x follow-mode} a second time. | |
195 | ||
196 | @node Selective Display | |
197 | @section Selective Display | |
198 | @findex set-selective-display | |
199 | @kindex C-x $ | |
200 | ||
201 | Emacs has the ability to hide lines indented more than a certain number | |
202 | of columns (you specify how many columns). You can use this to get an | |
203 | overview of a part of a program. | |
204 | ||
205 | To hide lines, type @kbd{C-x $} (@code{set-selective-display}) with a | |
206 | numeric argument @var{n}. Then lines with at least @var{n} columns of | |
207 | indentation disappear from the screen. The only indication of their | |
208 | presence is that three dots (@samp{@dots{}}) appear at the end of each | |
209 | visible line that is followed by one or more hidden ones. | |
210 | ||
211 | The commands @kbd{C-n} and @kbd{C-p} move across the hidden lines as | |
212 | if they were not there. | |
213 | ||
214 | The hidden lines are still present in the buffer, and most editing | |
215 | commands see them as usual, so you may find point in the middle of the | |
216 | hidden text. When this happens, the cursor appears at the end of the | |
217 | previous line, after the three dots. If point is at the end of the | |
218 | visible line, before the newline that ends it, the cursor appears before | |
219 | the three dots. | |
220 | ||
221 | To make all lines visible again, type @kbd{C-x $} with no argument. | |
222 | ||
223 | @vindex selective-display-ellipses | |
224 | If you set the variable @code{selective-display-ellipses} to | |
225 | @code{nil}, the three dots do not appear at the end of a line that | |
226 | precedes hidden lines. Then there is no visible indication of the | |
227 | hidden lines. This variable becomes local automatically when set. | |
228 | ||
229 | @node Optional Mode Line | |
230 | @section Optional Mode Line Features | |
231 | ||
232 | @cindex Line Number mode | |
233 | @cindex mode, Line Number | |
234 | @findex line-number-mode | |
235 | The current line number of point appears in the mode line when Line | |
236 | Number mode is enabled. Use the command @kbd{M-x line-number-mode} to | |
237 | turn this mode on and off; normally it is on. The line number appears | |
238 | before the buffer percentage @var{pos}, with the letter @samp{L} to | |
239 | indicate what it is. @xref{Minor Modes}, for more information about | |
240 | minor modes and about how to use this command. | |
241 | ||
242 | @vindex line-number-display-limit | |
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244 | If the buffer is very large (larger than the value of |
245 | @code{line-number-display-limit}), then the line number doesn't appear. | |
246 | Emacs doesn't compute the line number when the buffer is large, because | |
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247 | that would be too slow. Set it to @code{nil} to remove the limit. If |
248 | you have narrowed the buffer (@pxref{Narrowing}), the displayed line | |
249 | number is relative to the accessible portion of the buffer. | |
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250 | |
251 | @cindex Column Number mode | |
252 | @cindex mode, Column Number | |
253 | @findex column-number-mode | |
254 | You can also display the current column number by turning on Column | |
255 | Number mode. It displays the current column number preceded by the | |
256 | letter @samp{C}. Type @kbd{M-x column-number-mode} to toggle this mode. | |
257 | ||
258 | @findex display-time | |
259 | @cindex time (on mode line) | |
260 | Emacs can optionally display the time and system load in all mode | |
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261 | lines. To enable this feature, type @kbd{M-x display-time} or customize |
262 | the option @code{display-time-mode}. The information added to the mode | |
263 | line usually appears after the buffer name, before the mode names and | |
264 | their parentheses. It looks like this: | |
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265 | |
266 | @example | |
267 | @var{hh}:@var{mm}pm @var{l.ll} | |
268 | @end example | |
269 | ||
270 | @noindent | |
271 | @vindex display-time-24hr-format | |
272 | Here @var{hh} and @var{mm} are the hour and minute, followed always by | |
273 | @samp{am} or @samp{pm}. @var{l.ll} is the average number of running | |
274 | processes in the whole system recently. (Some fields may be missing if | |
275 | your operating system cannot support them.) If you prefer time display | |
276 | in 24-hour format, set the variable @code{display-time-24hr-format} | |
277 | to @code{t}. | |
278 | ||
279 | @cindex mail (on mode line) | |
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280 | @vindex display-time-use-mail-icon |
281 | @vindex display-time-mail-face | |
6bf7aab6 | 282 | The word @samp{Mail} appears after the load level if there is mail |
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283 | for you that you have not read yet. On a graphical display you can use |
284 | an icon instead of @samp{Mail} by customizing | |
285 | @code{display-time-use-mail-icon}; this may save some space on the mode | |
286 | line. You can customize @code{display-time-mail-face} to make the mail | |
287 | indicator prominent. | |
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288 | |
289 | @node Text Display | |
290 | @section How Text Is Displayed | |
291 | @cindex characters (in text) | |
292 | ||
293 | ASCII printing characters (octal codes 040 through 0176) in Emacs | |
294 | buffers are displayed with their graphics. So are non-ASCII multibyte | |
295 | printing characters (octal codes above 0400). | |
296 | ||
297 | Some ASCII control characters are displayed in special ways. The | |
298 | newline character (octal code 012) is displayed by starting a new line. | |
299 | The tab character (octal code 011) is displayed by moving to the next | |
300 | tab stop column (normally every 8 columns). | |
301 | ||
302 | Other ASCII control characters are normally displayed as a caret | |
303 | (@samp{^}) followed by the non-control version of the character; thus, | |
304 | control-A is displayed as @samp{^A}. | |
305 | ||
306 | Non-ASCII characters 0200 through 0377 are displayed with octal escape | |
307 | sequences; thus, character code 0243 (octal) is displayed as | |
308 | @samp{\243}. However, if you enable European display, most of these | |
309 | characters become non-ASCII printing characters, and are displayed using | |
310 | their graphics (assuming your terminal supports them). | |
a3ddb43a | 311 | @xref{Single-Byte Character Support}. |
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312 | |
313 | @node Display Vars | |
314 | @section Variables Controlling Display | |
315 | ||
316 | This section contains information for customization only. Beginning | |
317 | users should skip it. | |
318 | ||
319 | @vindex mode-line-inverse-video | |
320 | The variable @code{mode-line-inverse-video} controls whether the mode | |
321 | line is displayed in inverse video (assuming the terminal supports it); | |
322 | @code{nil} means don't do so. @xref{Mode Line}. If you specify the | |
323 | foreground color for the @code{modeline} face, and | |
324 | @code{mode-line-inverse-video} is non-@code{nil}, then the default | |
325 | background color for that face is the usual foreground color. | |
326 | @xref{Faces}. | |
327 | ||
328 | @vindex inverse-video | |
329 | If the variable @code{inverse-video} is non-@code{nil}, Emacs attempts | |
330 | to invert all the lines of the display from what they normally are. | |
331 | ||
332 | @vindex visible-bell | |
333 | If the variable @code{visible-bell} is non-@code{nil}, Emacs attempts | |
334 | to make the whole screen blink when it would normally make an audible bell | |
335 | sound. This variable has no effect if your terminal does not have a way | |
336 | to make the screen blink.@refill | |
337 | ||
338 | @vindex no-redraw-on-reenter | |
339 | When you reenter Emacs after suspending, Emacs normally clears the | |
340 | screen and redraws the entire display. On some terminals with more than | |
341 | one page of memory, it is possible to arrange the termcap entry so that | |
342 | the @samp{ti} and @samp{te} strings (output to the terminal when Emacs | |
343 | is entered and exited, respectively) switch between pages of memory so | |
344 | as to use one page for Emacs and another page for other output. Then | |
345 | you might want to set the variable @code{no-redraw-on-reenter} | |
346 | non-@code{nil}; this tells Emacs to assume, when resumed, that the | |
347 | screen page it is using still contains what Emacs last wrote there. | |
348 | ||
349 | @vindex echo-keystrokes | |
350 | The variable @code{echo-keystrokes} controls the echoing of multi-character | |
351 | keys; its value is the number of seconds of pause required to cause echoing | |
352 | to start, or zero meaning don't echo at all. @xref{Echo Area}. | |
353 | ||
354 | @vindex ctl-arrow | |
355 | If the variable @code{ctl-arrow} is @code{nil}, control characters in | |
356 | the buffer are displayed with octal escape sequences, except for newline | |
357 | and tab. Altering the value of @code{ctl-arrow} makes it local to the | |
358 | current buffer; until that time, the default value is in effect. The | |
359 | default is initially @code{t}. @xref{Display Tables,, Display Tables, | |
360 | elisp, The Emacs Lisp Reference Manual}. | |
361 | ||
362 | @vindex tab-width | |
363 | Normally, a tab character in the buffer is displayed as whitespace which | |
364 | extends to the next display tab stop position, and display tab stops come | |
365 | at intervals equal to eight spaces. The number of spaces per tab is | |
366 | controlled by the variable @code{tab-width}, which is made local by | |
367 | changing it, just like @code{ctl-arrow}. Note that how the tab character | |
368 | in the buffer is displayed has nothing to do with the definition of | |
369 | @key{TAB} as a command. The variable @code{tab-width} must have an | |
370 | integer value between 1 and 1000, inclusive. | |
371 | ||
372 | @c @vindex truncate-lines @c No index entry here, because we have one | |
373 | @c in the continuation section. | |
374 | If the variable @code{truncate-lines} is non-@code{nil}, then each | |
375 | line of text gets just one screen line for display; if the text line is | |
376 | too long, display shows only the part that fits. If | |
377 | @code{truncate-lines} is @code{nil}, then long text lines display as | |
378 | more than one screen line, enough to show the whole text of the line. | |
379 | @xref{Continuation Lines}. Altering the value of @code{truncate-lines} | |
380 | makes it local to the current buffer; until that time, the default value | |
381 | is in effect. The default is initially @code{nil}. | |
382 | ||
383 | @c @vindex truncate-partial-width-windows @c Idx entry is in Split Windows. | |
384 | If the variable @code{truncate-partial-width-windows} is | |
385 | non-@code{nil}, it forces truncation rather than continuation in any | |
386 | window less than the full width of the screen or frame, regardless of | |
387 | the value of @code{truncate-lines}. For information about side-by-side | |
388 | windows, see @ref{Split Window}. See also @ref{Display,, Display, | |
389 | elisp, The Emacs Lisp Reference Manual}. | |
390 | ||
391 | @vindex baud-rate | |
392 | The variable @code{baud-rate} holds the output speed of the | |
393 | terminal, as far as Emacs knows. Setting this variable does not change | |
394 | the speed of actual data transmission, but the value is used for | |
395 | calculations such as padding. It also affects decisions about whether | |
396 | to scroll part of the screen or redraw it instead---even when using a | |
397 | window system. (We designed it this way, despite the fact that a window | |
398 | system has no true ``output speed,'' to give you a way to tune these | |
399 | decisions.) | |
400 | ||
401 | You can customize the way any particular character code is displayed | |
402 | by means of a display table. @xref{Display Tables,, Display Tables, | |
403 | elisp, The Emacs Lisp Reference Manual}. |