19.6 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>

<PAGEDOWN>

Likewise, scroll forward.

M-v

Scroll backward (scroll-down).

<PRIOR>

<PAGEUP>

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 scrolls the selected window so that point is halfway down from the top of the window. On a text terminal, it also clears the screen and redisplays all windows. That is useful in case the screen is garbled (see Screen Garbled).

To read the buffer a windowful at a time, use C-v (scroll-up) with no argument. This scrolls forward by nearly the whole window height. The effect is to take the two lines at the bottom of the window and put them at the top, followed by nearly a whole windowful of lines that were not previously visible. If point was in the text that scrolled off the top, it ends up at the new top of the window.

M-v (scroll-down) with no argument scrolls backward in a similar way, also with overlap. 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. The function keys <NEXT> and <PRIOR>, or <PAGEDOWN> and <PAGEUP>, are equivalent to C-v and 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 scroll-up because it moves the text upward on the screen. The keys <PAGEDOWN> and <PAGEUP> derive their names and customary meanings from a different convention that developed elsewhere; hence the strange result that <PAGEDOWN> runs scroll-up.

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. In this mode, when scrolling shifts point off the screen, or into the scrolling margins, Emacs moves point to keep the same vertical position within the window. 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. C-u C-l scrolls to put point at the center (vertically) 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 when point moves out of the visible portion of the text. 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.

When the window does scroll by a longer distance, you can control how aggressively it scrolls, by setting the variables scroll-up-aggressively and scroll-down-aggressively. The value of scroll-up-aggressively should be either nil, or a fraction f between 0 and 1. A fraction specifies where on the screen to put point when scrolling upward. More precisely, when a window scrolls up because point is above the window start, the new start position is chosen to put point f part of the window height from the top. The larger f, the more aggressive the scrolling.

nil, which is the default, scrolls to put point at the center. So it is equivalent to .5.

Likewise, scroll-down-aggressively is used for scrolling down. The value, f, specifies how far point should be placed from the bottom of the window; thus, as with scroll-up-aggressively, a larger value is more aggressive.

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.