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398 lines
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398 lines
18 KiB
Plaintext
@c This is part of the Emacs manual.
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@c Copyright (C) 1985, 86, 87, 93, 94, 95, 1997 Free Software Foundation, Inc.
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@c See file emacs.texi for copying conditions.
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@node Display, Search, Registers, Top
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@chapter Controlling the Display
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Since only part of a large buffer fits in the window, Emacs tries to
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show a part that is likely to be interesting. Display-control commands
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allow you to specify which part of the text you want to see, and how to
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display it.
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@menu
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* Scrolling:: Moving text up and down in a window.
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* Horizontal Scrolling:: Moving text left and right in a window.
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* Follow Mode:: Follow mode lets two windows scroll as one.
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* Selective Display:: Hiding lines with lots of indentation.
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* Optional Mode Line:: Optional mode line display features.
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* Text Display:: How text characters are normally displayed.
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* Display Vars:: Information on variables for customizing display.
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@end menu
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@node Scrolling
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@section Scrolling
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If a buffer contains text that is too large to fit entirely within a
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window that is displaying the buffer, Emacs shows a contiguous portion of
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the text. The portion shown always contains point.
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@cindex scrolling
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@dfn{Scrolling} means moving text up or down in the window so that
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different parts of the text are visible. Scrolling forward means that text
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moves up, and new text appears at the bottom. Scrolling backward moves
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text down and new text appears at the top.
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Scrolling happens automatically if you move point past the bottom or top
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of the window. You can also explicitly request scrolling with the commands
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in this section.
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@table @kbd
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@item C-l
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Clear screen and redisplay, scrolling the selected window to center
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point vertically within it (@code{recenter}).
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@item C-v
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Scroll forward (a windowful or a specified number of lines) (@code{scroll-up}).
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@item @key{NEXT}
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Likewise, scroll forward.
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@item M-v
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Scroll backward (@code{scroll-down}).
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@item @key{PRIOR}
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Likewise, scroll backward.
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@item @var{arg} C-l
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Scroll so point is on line @var{arg} (@code{recenter}).
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@item C-M-l
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Scroll heuristically to bring useful information onto the screen
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(@code{reposition-window}).
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@end table
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@kindex C-l
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@findex recenter
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The most basic scrolling command is @kbd{C-l} (@code{recenter}) with
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no argument. It clears the entire screen and redisplays all windows.
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In addition, it scrolls the selected window so that point is halfway
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down from the top of the window.
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@kindex C-v
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@kindex M-v
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@kindex NEXT
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@kindex PRIOR
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@findex scroll-up
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@findex scroll-down
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The scrolling commands @kbd{C-v} and @kbd{M-v} let you move all the text
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in the window up or down a few lines. @kbd{C-v} (@code{scroll-up}) with an
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argument shows you that many more lines at the bottom of the window, moving
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the text and point up together as @kbd{C-l} might. @kbd{C-v} with a
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negative argument shows you more lines at the top of the window.
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@kbd{M-v} (@code{scroll-down}) is like @kbd{C-v}, but moves in the
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opposite direction. The function keys @key{NEXT} and @key{PRIOR} are
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equivalent to @kbd{C-v} and @kbd{M-v}.
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The names of scroll commands are based on the direction that the text
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moves in the window. Thus, the command to scroll forward is called
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@code{scroll-up} because it moves the text upward on the screen.
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@vindex next-screen-context-lines
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To read the buffer a windowful at a time, use @kbd{C-v} with no argument.
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It takes the last two lines at the bottom of the window and puts them at
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the top, followed by nearly a whole windowful of lines not previously
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visible. If point was in the text scrolled off the top, it moves to the
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new top of the window. @kbd{M-v} with no argument moves backward with
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overlap similarly. The number of lines of overlap across a @kbd{C-v} or
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@kbd{M-v} is controlled by the variable @code{next-screen-context-lines}; by
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default, it is 2.
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@vindex scroll-preserve-screen-position
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Some users like the full-screen scroll commands to keep point at the
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same screen line. To enable this behavior, set the variable
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@code{scroll-preserve-screen-position} to a non-@code{nil} value. This
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mode is convenient for browsing through a file by scrolling by
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screenfuls; if you come back to the screen where you started, point goes
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back to the line where it started. However, this mode is inconvenient
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when you move to the next screen in order to move point to the text
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there.
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Another way to do scrolling is with @kbd{C-l} with a numeric argument.
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@kbd{C-l} does not clear the screen when given an argument; it only scrolls
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the selected window. With a positive argument @var{n}, it repositions text
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to put point @var{n} lines down from the top. An argument of zero puts
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point on the very top line. Point does not move with respect to the text;
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rather, the text and point move rigidly on the screen. @kbd{C-l} with a
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negative argument puts point that many lines from the bottom of the window.
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For example, @kbd{C-u - 1 C-l} puts point on the bottom line, and @kbd{C-u
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- 5 C-l} puts it five lines from the bottom. Just @kbd{C-u} as argument,
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as in @kbd{C-u C-l}, scrolls point to the center of the selected window.
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@kindex C-M-l
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@findex reposition-window
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The @kbd{C-M-l} command (@code{reposition-window}) scrolls the current
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window heuristically in a way designed to get useful information onto
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the screen. For example, in a Lisp file, this command tries to get the
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entire current defun onto the screen if possible.
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@vindex scroll-conservatively
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Scrolling happens automatically if point has moved out of the visible
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portion of the text when it is time to display. Normally, automatic
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scrolling centers point vertically within the window. However, if you
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set @code{scroll-conservatively} to a small number @var{n}, then if you
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move point just a little off the screen---less than @var{n} lines---then
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Emacs scrolls the text just far enough to bring point back on screen.
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By default, @code{scroll-conservatively} is 0.
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@vindex scroll-margin
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The variable @code{scroll-margin} restricts how close point can come
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to the top or bottom of a window. Its value is a number of screen
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lines; if point comes within that many lines of the top or bottom of the
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window, Emacs recenters the window. By default, @code{scroll-margin} is
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0.
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@node Horizontal Scrolling
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@section Horizontal Scrolling
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@cindex horizontal scrolling
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@dfn{Horizontal scrolling} means shifting all the lines sideways
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within a window---so that some of the text near the left margin
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is not displayed at all.
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@table @kbd
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@item C-x <
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Scroll text in current window to the left (@code{scroll-left}).
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@item C-x >
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Scroll to the right (@code{scroll-right}).
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@end table
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When a window has been scrolled horizontally, text lines are truncated
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rather than continued (@pxref{Continuation Lines}), with a @samp{$}
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appearing in the first column when there is text truncated to the left,
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and in the last column when there is text truncated to the right.
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@kindex C-x <
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@kindex C-x >
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@findex scroll-left
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@findex scroll-right
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The command @kbd{C-x <} (@code{scroll-left}) scrolls the selected
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window to the left by @var{n} columns with argument @var{n}. This moves
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part of the beginning of each line off the left edge of the window.
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With no argument, it scrolls by almost the full width of the window (two
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columns less, to be precise).
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@kbd{C-x >} (@code{scroll-right}) scrolls similarly to the right. The
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window cannot be scrolled any farther to the right once it is displayed
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normally (with each line starting at the window's left margin);
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attempting to do so has no effect. This means that you don't have to
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calculate the argument precisely for @w{@kbd{C-x >}}; any sufficiently large
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argument will restore the normal display.
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@cindex Hscroll mode
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@cindex mode, Hscroll
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@findex hscroll-mode
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You can request automatic horizontal scrolling by enabling Hscroll
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mode. When this mode is enabled, Emacs scrolls a window horizontally
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whenever that is necessary to keep point visible and not too far from
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the left or right edge. The command to enable or disable this mode is
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@kbd{M-x hscroll-mode}.
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@node Follow Mode
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@section Follow Mode
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@cindex Follow mode
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@cindex mode, Follow
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@dfn{Follow mode} is a minor mode that makes two windows showing the
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same buffer scroll as one tall ``virtual window.'' To use Follow mode,
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go to a frame with just one window, split it into two side-by-side
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windows using @kbd{C-x 3}, and then type @kbd{M-x follow-mode}. From
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then on, you can edit the buffer in either of the two windows, or scroll
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either one; the other window follows it.
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To turn off Follow mode, type @kbd{M-x follow-mode} a second time.
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@node Selective Display
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@section Selective Display
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@findex set-selective-display
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@kindex C-x $
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Emacs has the ability to hide lines indented more than a certain number
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of columns (you specify how many columns). You can use this to get an
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overview of a part of a program.
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To hide lines, type @kbd{C-x $} (@code{set-selective-display}) with a
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numeric argument @var{n}. Then lines with at least @var{n} columns of
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indentation disappear from the screen. The only indication of their
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presence is that three dots (@samp{@dots{}}) appear at the end of each
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visible line that is followed by one or more hidden ones.
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The commands @kbd{C-n} and @kbd{C-p} move across the hidden lines as
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if they were not there.
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The hidden lines are still present in the buffer, and most editing
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commands see them as usual, so you may find point in the middle of the
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hidden text. When this happens, the cursor appears at the end of the
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previous line, after the three dots. If point is at the end of the
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visible line, before the newline that ends it, the cursor appears before
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the three dots.
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To make all lines visible again, type @kbd{C-x $} with no argument.
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@vindex selective-display-ellipses
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If you set the variable @code{selective-display-ellipses} to
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@code{nil}, the three dots do not appear at the end of a line that
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precedes hidden lines. Then there is no visible indication of the
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hidden lines. This variable becomes local automatically when set.
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@node Optional Mode Line
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@section Optional Mode Line Features
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@cindex Line Number mode
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@cindex mode, Line Number
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@findex line-number-mode
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The current line number of point appears in the mode line when Line
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Number mode is enabled. Use the command @kbd{M-x line-number-mode} to
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turn this mode on and off; normally it is on. The line number appears
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before the buffer percentage @var{pos}, with the letter @samp{L} to
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indicate what it is. @xref{Minor Modes}, for more information about
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minor modes and about how to use this command.
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@vindex line-number-display-limit
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If the buffer is very large (larger than the value of
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@code{line-number-display-limit}), then the line number doesn't appear.
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Emacs doesn't compute the line number when the buffer is large, because
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that would be too slow. If you have narrowed the buffer
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(@pxref{Narrowing}), the displayed line number is relative to the
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accessible portion of the buffer.
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@cindex Column Number mode
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@cindex mode, Column Number
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@findex column-number-mode
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You can also display the current column number by turning on Column
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Number mode. It displays the current column number preceded by the
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letter @samp{C}. Type @kbd{M-x column-number-mode} to toggle this mode.
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@findex display-time
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@cindex time (on mode line)
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Emacs can optionally display the time and system load in all mode
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lines. To enable this feature, type @kbd{M-x display-time}. The
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information added to the mode line usually appears after the buffer
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name, before the mode names and their parentheses. It looks like this:
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@example
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@var{hh}:@var{mm}pm @var{l.ll}
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@end example
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@noindent
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@vindex display-time-24hr-format
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Here @var{hh} and @var{mm} are the hour and minute, followed always by
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@samp{am} or @samp{pm}. @var{l.ll} is the average number of running
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processes in the whole system recently. (Some fields may be missing if
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your operating system cannot support them.) If you prefer time display
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in 24-hour format, set the variable @code{display-time-24hr-format}
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to @code{t}.
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@cindex mail (on mode line)
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The word @samp{Mail} appears after the load level if there is mail
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for you that you have not read yet.
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@node Text Display
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@section How Text Is Displayed
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@cindex characters (in text)
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ASCII printing characters (octal codes 040 through 0176) in Emacs
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buffers are displayed with their graphics. So are non-ASCII multibyte
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printing characters (octal codes above 0400).
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Some ASCII control characters are displayed in special ways. The
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newline character (octal code 012) is displayed by starting a new line.
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The tab character (octal code 011) is displayed by moving to the next
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tab stop column (normally every 8 columns).
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Other ASCII control characters are normally displayed as a caret
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(@samp{^}) followed by the non-control version of the character; thus,
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control-A is displayed as @samp{^A}.
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Non-ASCII characters 0200 through 0377 are displayed with octal escape
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sequences; thus, character code 0243 (octal) is displayed as
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@samp{\243}. However, if you enable European display, most of these
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characters become non-ASCII printing characters, and are displayed using
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their graphics (assuming your terminal supports them).
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@xref{Single-Byte European Support}.
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@node Display Vars
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@section Variables Controlling Display
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This section contains information for customization only. Beginning
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users should skip it.
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@vindex mode-line-inverse-video
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The variable @code{mode-line-inverse-video} controls whether the mode
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line is displayed in inverse video (assuming the terminal supports it);
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@code{nil} means don't do so. @xref{Mode Line}. If you specify the
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foreground color for the @code{modeline} face, and
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@code{mode-line-inverse-video} is non-@code{nil}, then the default
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background color for that face is the usual foreground color.
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@xref{Faces}.
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@vindex inverse-video
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If the variable @code{inverse-video} is non-@code{nil}, Emacs attempts
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to invert all the lines of the display from what they normally are.
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@vindex visible-bell
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If the variable @code{visible-bell} is non-@code{nil}, Emacs attempts
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to make the whole screen blink when it would normally make an audible bell
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sound. This variable has no effect if your terminal does not have a way
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to make the screen blink.@refill
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@vindex no-redraw-on-reenter
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When you reenter Emacs after suspending, Emacs normally clears the
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screen and redraws the entire display. On some terminals with more than
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one page of memory, it is possible to arrange the termcap entry so that
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the @samp{ti} and @samp{te} strings (output to the terminal when Emacs
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is entered and exited, respectively) switch between pages of memory so
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as to use one page for Emacs and another page for other output. Then
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you might want to set the variable @code{no-redraw-on-reenter}
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non-@code{nil}; this tells Emacs to assume, when resumed, that the
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screen page it is using still contains what Emacs last wrote there.
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@vindex echo-keystrokes
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The variable @code{echo-keystrokes} controls the echoing of multi-character
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keys; its value is the number of seconds of pause required to cause echoing
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to start, or zero meaning don't echo at all. @xref{Echo Area}.
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@vindex ctl-arrow
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If the variable @code{ctl-arrow} is @code{nil}, control characters in
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the buffer are displayed with octal escape sequences, except for newline
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and tab. Altering the value of @code{ctl-arrow} makes it local to the
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current buffer; until that time, the default value is in effect. The
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default is initially @code{t}. @xref{Display Tables,, Display Tables,
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elisp, The Emacs Lisp Reference Manual}.
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@vindex tab-width
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Normally, a tab character in the buffer is displayed as whitespace which
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extends to the next display tab stop position, and display tab stops come
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at intervals equal to eight spaces. The number of spaces per tab is
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controlled by the variable @code{tab-width}, which is made local by
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changing it, just like @code{ctl-arrow}. Note that how the tab character
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in the buffer is displayed has nothing to do with the definition of
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@key{TAB} as a command. The variable @code{tab-width} must have an
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integer value between 1 and 1000, inclusive.
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@c @vindex truncate-lines @c No index entry here, because we have one
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@c in the continuation section.
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If the variable @code{truncate-lines} is non-@code{nil}, then each
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line of text gets just one screen line for display; if the text line is
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too long, display shows only the part that fits. If
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@code{truncate-lines} is @code{nil}, then long text lines display as
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more than one screen line, enough to show the whole text of the line.
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@xref{Continuation Lines}. Altering the value of @code{truncate-lines}
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makes it local to the current buffer; until that time, the default value
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is in effect. The default is initially @code{nil}.
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@c @vindex truncate-partial-width-windows @c Idx entry is in Split Windows.
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If the variable @code{truncate-partial-width-windows} is
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non-@code{nil}, it forces truncation rather than continuation in any
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window less than the full width of the screen or frame, regardless of
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the value of @code{truncate-lines}. For information about side-by-side
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windows, see @ref{Split Window}. See also @ref{Display,, Display,
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elisp, The Emacs Lisp Reference Manual}.
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@vindex baud-rate
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The variable @code{baud-rate} holds the output speed of the
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terminal, as far as Emacs knows. Setting this variable does not change
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the speed of actual data transmission, but the value is used for
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calculations such as padding. It also affects decisions about whether
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to scroll part of the screen or redraw it instead---even when using a
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window system. (We designed it this way, despite the fact that a window
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system has no true ``output speed,'' to give you a way to tune these
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decisions.)
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You can customize the way any particular character code is displayed
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by means of a display table. @xref{Display Tables,, Display Tables,
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elisp, The Emacs Lisp Reference Manual}.
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