@c This is part of the Emacs manual.
@c Copyright (C) 1985, 1986, 1987, 1993 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Display, Search, Registers, Top
@chapter Controlling the Display

  Since only part of a large buffer fits in the window, Emacs tries to show
the part that is likely to be interesting.  The display control commands
allow you to specify which part of the text you want to see.

@table @kbd
@item C-l
Clear screen and redisplay, scrolling the selected window to center
point vertically within it (@code{recenter}).
@item C-v
Scroll forward (a windowful or a specified number of lines) (@code{scroll-up}).
@item @key{NEXT}
Likewise, scroll forward.
@item M-v
Scroll backward (@code{scroll-down}).
@item @key{PRIOR}
Likewise, scroll backward.
@item @var{arg} C-l
Scroll so point is on line @var{arg} (@code{recenter}).
@item C-x <
Scroll text in current window to the left (@code{scroll-left}).
@item C-x >
Scroll to the right (@code{scroll-right}).
@item C-x $
Make deeply indented lines invisible (@code{set-selective-display}).
@end table

  The names of all scroll commands are based on the direction that the text
moves in the window.  Thus, the command to scrolling forward is called
@code{scroll-up}, since the text moves up.

@menu
* Scrolling::	           Moving text up and down in a window.
* Horizontal Scrolling::   Moving text left and right in a window.
* Selective Display::      Hiding lines with lots of indentation.
* Optional Display::       Optional display features.
* European Display::	   Displaying (and inputting) European characters.
* Display Vars::           Information on variables for customizing display.
@end menu

@node Scrolling
@section Scrolling

  If 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.

@cindex scrolling
  @dfn{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.

@ifinfo
@table @kbd
@item C-l
Clear screen and redisplay, scrolling the selected window to center
point vertically within it (@code{recenter}).
@item C-v
Scroll forward (a windowful or a specified number of lines) (@code{scroll-up}).
@item @key{NEXT}
Likewise, scroll forward.
@item M-v
Scroll backward (@code{scroll-down}).
@item @key{PRIOR}
Likewise, scroll backward.
@item @var{arg} C-l
Scroll so point is on line @var{arg} (@code{recenter}).
@item C-M-l
Scroll heuristically to bring useful information onto the screen
(@code{reposition-window}).
@end table
@end ifinfo

@kindex C-l
@findex recenter
  The most basic scrolling command is @kbd{C-l} (@code{recenter}) with
no argument.  It clears the entire screen and redisplays all windows.
In addition, it scrolls the selected window so that point is halfway
down from the top of the window.

@kindex C-v
@kindex M-v
@kindex @key{NEXT}
@kindex @key{PRIOR}
@findex scroll-up
@findex scroll-down
  The scrolling commands @kbd{C-v} and @kbd{M-v} let you move all the text
in the window up or down a few lines.  @kbd{C-v} (@code{scroll-up}) with an
argument shows you that many more lines at the bottom of the window, moving
the text and point up together as @kbd{C-l} might.  @kbd{C-v} with a
negative argument shows you more lines at the top of the window.
@kbd{M-v} (@code{scroll-down}) is like @kbd{C-v}, but moves in the
opposite direction.  The function keys @key{NEXT} and @key{PRIOR} are
equivalent to @kbd{C-v} and @kbd{M-v}.

@vindex next-screen-context-lines
  To read the buffer a windowful at a time, use @kbd{C-v} with no argument.
It takes the last two lines at the bottom of the window and puts them at
the top, followed by nearly a whole windowful of lines not previously
visible.  If point was in the text scrolled off the top, it moves to the
new top of the window.  @kbd{M-v} with no argument moves backward with
overlap similarly.  The number of lines of overlap across a @kbd{C-v} or
@kbd{M-v} is controlled by the variable @code{next-screen-context-lines}; by
default, it is two.

  Another way to do scrolling is with @kbd{C-l} with a numeric argument.
@kbd{C-l} does not clear the screen when given an argument; it only scrolls
the selected window.  With a positive argument @var{n}, it repositions text
to put point @var{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.  @kbd{C-l} with a
negative argument puts point that many lines from the bottom of the window.
For example, @kbd{C-u - 1 C-l} puts point on the bottom line, and @kbd{C-u
- 5 C-l} puts it five lines from the bottom.  Just @kbd{C-u} as argument,
as in @kbd{C-u C-l}, scrolls point to the center of the screen.

@kindex C-M-l
@findex reposition-window
  The @kbd{C-M-l} command (@code{reposition-window}) scrolls the current
window heuristically in a way designed to get useful information onto
the screen.  For example, in a Lisp file, this command tries to get the
entire current defun onto the screen if possible.

@vindex scroll-step
  Scrolling happens automatically if point has moved out of the visible
portion of the text when it is time to display.  Usually the scrolling is
done so as to put point vertically centered within the window.  However, if
the variable @code{scroll-step} has a nonzero value, an attempt is made to
scroll the buffer by that many lines; if that is enough to bring point back
into visibility, that is what is done.

@node Horizontal Scrolling
@section Horizontal Scrolling

@ifinfo
@table @kbd
@item C-x <
Scroll text in current window to the left (@code{scroll-left}).
@item C-x >
Scroll to the right (@code{scroll-right}).
@end table
@end ifinfo

@kindex C-x <
@kindex C-x >
@findex scroll-left
@findex scroll-right
@cindex horizontal scrolling
  The text in a window can also be scrolled horizontally.  This means that
each line of text is shifted sideways in the window, and one or more
characters at the beginning of each line are not displayed at all.  When a
window has been scrolled horizontally in this way, text lines are truncated
rather than continued (@pxref{Continuation Lines}), with a @samp{$} 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.

  The command @kbd{C-x <} (@code{scroll-left}) scrolls the selected
window to the left by @var{n} columns with argument @var{n}.  This moves
part of the beginning of each line off the left edge of the window.
With no argument, it scrolls by almost the full width of the window (two
columns less, to be precise).

  @kbd{C-x >} (@code{scroll-right}) scrolls similarly to the right.  The
window cannot be scrolled any farther to the right once it is displaying
normally (with each line starting at the window's left margin);
attempting to do so has no effect.  This means that you don't have to
calculate the argument precisely for @kbd{C-x >}; any sufficiently large
argument will restore normally display.

@node Selective Display
@section Selective Display
@findex set-selective-display
@kindex C-x $

  Emacs 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 @kbd{C-x $} (@code{set-selective-display}) with a
numeric argument @var{n}.  Then lines with at least @var{n} columns of
indentation disappear from the screen.  The only indication of their
presence is that three dots (@samp{@dots{}}) appear at the end of each
visible line that is followed by one or more invisible ones.

  The commands @kbd{C-n} and @kbd{C-p} move across the invisible lines
as if they were not there.

  The invisible lines are still present in the buffer, and most editing
commands see them as usual, so you may find point in the middle of
invisible 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 everything visible again, type @kbd{C-x $} with no argument.

@node European Display
@section European Character Set Display

@cindex European character set
@cindex accented characters
@cindex ISO Latin-1 character set
@findex standard-display-european
@cindex @code{iso-syntax} library
  Emacs can display accented characters, assuming the font in use
supports them.  The @kbd{M-x standard-display-european} command toggles
European character display.  When enabled, Emacs displays characters
according to the ISO 8859 Latin-1 encoding for European languages; when
disabled, Emacs uses octal notation for all characters not specified by
the ordinary ASCII standard.  Load the library @code{iso-syntax} to specify
the correct syntactic properties for the character codes 128 and above.

  With a prefix argument, @kbd{M-x standard-display-european} enables
European character display if and only if the argument is positive.

  If your terminal can send character codes 128 and up to represent
ISO Latin-1 characters, execute the following expression to
enable Emacs to understand them:

@example
(set-input-mode (car (current-input-mode))
                (nth 1 (current-input-mode))
                0)
@end example

@noindent
@kindex C-x 8
@cindex @code{iso-insert} library
Otherwise, you can load the library @code{iso-insert} to turn the
key @kbd{C-x 8} into a ``compose character'' prefix for insertion
of the extra ISO Latin-1 printing characters.

@node Optional Display
@section Optional Display Features

@cindex Line Number mode
@cindex mode, Line Number
@findex line-number-mode
  To add the current line number of point to the mode line, enable Line
Number mode with the command @kbd{M-x line-number-mode}.  The line
number appears before @var{pos}, with the letter @samp{L} to indicate
what it is.  @xref{Minor Modes}, for more information about minor modes
and about how to use this command.

@vindex line-number-display-limit
  If the buffer is very large (larger than the value of
@code{line-number-display-limit}), then the line number doesn't appear.
Emacs doesn't compute the line number when the buffer is large, because
that would be too slow.

@findex display-time
@cindex time (on mode line)
  Emacs can optionally display the time and system load in all mode
lines.  To enable this feature, type @kbd{M-x display-time}.  The
information added to the mode line usually appears after the buffer
name, before the mode names and their parentheses.  It looks like this:

@example
@var{hh}:@var{mm}pm @var{l.ll} [@var{d}]
@end example

@noindent
Here @var{hh} and @var{mm} are the hour and minute, followed always by
@samp{am} or @samp{pm}.  @var{l.ll} is the average number of running
processes in the whole system recently.  @var{d} is an approximate index
of the ratio of disk activity to cpu activity for all users.  (Some
fields may be missing if your operating system cannot support them.)

@cindex mail (on mode line)
  The word @samp{Mail} appears after the load level if there is mail
for you that you have not read yet.

  Customization note: the variable @code{mode-line-inverse-video} controls
whether the mode line is displayed in inverse video (assuming the terminal
supports it); @code{nil} means no inverse video.  The default is @code{t}.
@xref{Display Vars}.

@node Display Vars
@section Variables Controlling Display

  This section contains information for customization only.  Beginning
users should skip it.

@vindex mode-line-inverse-video
  The variable @code{mode-line-inverse-video} controls whether the mode
line is displayed in inverse video (assuming the terminal supports it);
@code{nil} means don't do so.  @xref{Mode Line}.

@vindex inverse-video
  If the variable @code{inverse-video} is non-@code{nil}, Emacs attempts
to invert all the lines of the display from what they normally are.

@vindex visible-bell
  If the variable @code{visible-bell} is non-@code{nil}, Emacs attempts
to make the whole screen blink when it would normally make an audible bell
sound.  This variable has no effect if your terminal does not have a way
to make the screen blink.@refill

@vindex no-redraw-on-reenter
  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 @samp{ti} and @samp{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 @code{no-redraw-on-reenter}
non-@code{nil}; this tells Emacs to assume, when resumed, that the
screen page it is using still contains what Emacs last wrote there.

@vindex echo-keystrokes
  The variable @code{echo-keystrokes} controls the echoing of multi-character
keys; its value is the number of seconds of pause required to cause echoing
to start, or zero meaning don't echo at all.  @xref{Echo Area}.

@vindex ctl-arrow
  If the variable @code{ctl-arrow} is @code{nil}, control characters in
the buffer are displayed with octal escape sequences, all except newline
and tab.  Altering the value of @code{ctl-arrow} makes it local to the
current buffer; until that time, the default value is in effect.  The
default is initially @code{t}.  @xref{Display Tables,, Display Tables,
elisp, The Emacs Lisp Reference Manual}.

@vindex tab-width
  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 @code{tab-width}, which is made local by
changing it, just like @code{ctl-arrow}.  Note that how the tab character
in the buffer is displayed has nothing to do with the definition of
@key{TAB} as a command.  The variable @code{tab-width} must have an
integer value between 1 and 1000, inclusive.

@vindex selective-display-ellipses
  If you set the variable @code{selective-display-ellipses} to @code{nil},
the three dots do not appear at the end of a line that precedes invisible
lines.  Then there is no visible indication of the invisible lines.
This variable too becomes local automatically when set.

@c @vindex truncate-lines  @c No index entry here, because we have one
@c in the continuation section.
  If the variable @code{truncate-lines} is non-@code{nil}, then each
line of text gets just one screen line for display; if the text line is
too long, display shows only the part that fits.  If
@code{truncate-lines} is @code{nil}, then long text lines display as
more than one screen line, enough to show the whole text of the line.
@xref{Continuation Lines}.  Altering the value of @code{truncate-lines}
makes it local to the current buffer; until that time, the default value
is in effect.  The default is initially @code{nil}.

@c @vindex truncate-partial-width-windows  @c Idx entry is in Split Windows.
  If the variable @code{truncate-partial-width-windows} is
non-@code{nil}, it forces truncation rather than continuation in any
window less than the full width of the screen or frame, regardless of
the value of @code{truncate-lines}.  For information about side-by-side
windows, see @ref{Split Window}.  See also @ref{Display,, Display,
elisp, The Emacs Lisp Reference Manual}.

@vindex baud-rate
  The variable @code{baud-rate} holds the the output speed of the
terminal, as far as Emacs knows.  Setting this variable does not change
the speed of actual data transmission, but the value is used for
calculations such as padding.  It also affects decisions about whether
to scroll part of the screen or redraw it instead---even when using a
window system, (We designed it this way, despite the fact that a window
system has no true ``output speed'', to give you a way to tune these
decisions.)
