Controlling the Display
***********************

Since 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.

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.

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.

C-l
     Clear screen and redisplay, scrolling the selected window to center point vertically within it (recenter).

C-v
     Scroll forward (a windowful or a specified number of lines) (scroll-up).

NEXT
     Likewise, scroll forward.

M-v
     Scroll backward (scroll-down).

PRIOR
     Likewise, scroll backward.

ARG C-l
     Scroll so point is on line ARG (recenter).

C-M-l
     Scroll heuristically to bring useful information onto the screen (reposition-window).

The most basic scrolling command is C-l (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.

The scrolling commands C-v and M-v let you move all the text in the window up or down a few lines.  C-v (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 C-l might.  C-v with a negative argument shows you more lines at the top of the window. M-v (scroll-down) is like C-v, but moves in the opposite direction.  The function keys NEXT and PRIOR are equivalent to C-v and M-v.

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 scroll-up because it moves the text upward on the screen.

To read the buffer a windowful at a time, use 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.  M-v with no argument moves backward with overlap similarly.  The number of lines of overlap across a C-v or M-v is controlled by the variable next-screen-context-lines; by default, it is 2.

Some users like the full-screen scroll commands to keep point at the same screen line.  To enable this behavior, set the variable scroll-preserve-screen-position to a non-nil value.  This mode is convenient for browsing through a file by scrolling by screenfuls; if you come back to the screen where you started, point goes back to the line where it started.  However, this mode is inconvenient when you move to the next screen in order to move point to the text there.

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.  Just C-u as argument, as in C-u C-l, scrolls point to the center of the selected window.

The C-M-l command (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.

Scrolling happens automatically if point has moved out of the visible portion of the text when it is time to display.  Normally, automatic scrolling centers point vertically within the window.  However, if you set scroll-conservatively to a small number N, then if you move point just a little off the screen---less than N lines---then Emacs scrolls the text just far enough to bring point back on screen. By default, scroll-conservatively is 0.

The variable scroll-margin restricts how close point can come to the top or bottom of a window.  Its value is a number of screen lines; if point comes within that many lines of the top or bottom of the window, Emacs recenters the window.  By default, scroll-margin is 0.

Horizontal Scrolling
====================

Horizontal 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.

C-x <
     Scroll text in current window to the left (scroll-left).

C-x >
     Scroll to the right (scroll-right).

When a window has been scrolled horizontally, text lines are truncated rather than continued (see 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.

The command C-x < (scroll-left) scrolls the selected window to the left by N columns with argument 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).

C-x > (scroll-right) scrolls similarly to the right.  The window cannot be scrolled any farther to the right once it is displayed 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 C-x >; any sufficiently large argument will restore the normal display.

You can request automatic horizontal scrolling by enabling Hscroll mode.  When this mode is enabled, Emacs scrolls a window horizontally whenever that is necessary to keep point visible and not too far from the left or right edge.  The command to enable or disable this mode is M-x hscroll-mode.

Follow Mode
===========

Follow 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.

To turn off Follow mode, type M-x follow-mode a second time.

Selective Display
=================

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 C-x $ (set-selective-display) with a numeric argument N.  Then lines with at least N columns of indentation disappear from the screen.  The only indication of their presence is that three dots (...) appear at the end of each visible line that is followed by one or more hidden ones.

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 selective-display-ellipses to nil, the three dots do not appear at the end of a line that precedes hidden lines.  Then there is no visible indication of the hidden lines.  This variable becomes local automatically when set.

Optional Mode Line Features
===========================

The 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 Minor Modes, for more information about minor modes and about how to use this command.

If the buffer is very large (larger than the value of 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.  If you have narrowed the buffer (see Narrowing), the displayed line number is relative to the accessible portion of the buffer.

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.  The information added to the mode line usually appears after the buffer name, before the mode names and their parentheses.  It looks like this:

     HH:MMpm L.LL

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 display-time-24hr-format to t.

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 display-time-use-mail-icon; this may save some space on the mode line.  You can customize display-time-mail-face to make the mail indicator prominent.

How Text Is Displayed
=====================

ASCII printing characters (octal codes 040 through 0176) in Emacs buffers are displayed with their graphics.  So 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 0377 are displayed with octal escape sequences; thus, character code 0243 (octal) is displayed as \243.  However, if you enable European display, most of these characters become non-ASCII printing characters, and are displayed using their graphics (assuming your terminal supports them). See Single-Byte Character Support.

Variables Controlling Display
=============================

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

The variable mode-line-inverse-video controls whether the mode line is displayed in inverse video (assuming the terminal supports it); nil means don't do so.  See Mode Line.  If you specify the foreground color for the modeline face, and mode-line-inverse-video is non-nil, then the default background color for that face is the usual foreground color. See Faces.

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

If the variable visible-bell is non-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.

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 no-redraw-on-reenter non-nil; this tells Emacs to assume, when resumed, that the screen page it is using still contains what Emacs last wrote there.

The variable 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.  See Echo Area.

If the variable ctl-arrow is nil, control characters in the buffer are displayed with octal escape sequences, except for newline and tab.  Altering the value of ctl-arrow makes it local to the current buffer; until that time, the default value is in effect.  The default is initially t.  See Display Tables (The Emacs Lisp Reference Manual).

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

If the variable truncate-lines is non-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 truncate-lines is nil, then long text lines display as more than one screen line, enough to show the whole text of the line. See Continuation Lines.  Altering the value of truncate-lines makes it local to the current buffer; until that time, the default value is in effect.  The default is initially nil.

If the variable truncate-partial-width-windows is non-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 truncate-lines.  For information about side-by-side windows, see Split Window.  See also Display (The Emacs Lisp Reference Manual).

The variable baud-rate holds 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.)

You can customize the way any particular character code is displayed by means of a display table.  See Display Tables (The Emacs Lisp Reference Manual).