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(elisp)Textual Scrolling
Textual Scrolling ================= "Textual scrolling" means moving the text up or down though a window. It works by changing the value of the window's display-start location. It may also change the value of `window-point' to keep point on the screen. Textual scrolling was formerly called "vertical scrolling," but we changed its name to distinguish it from the new vertical fractional scrolling feature (Note: Vertical Scrolling). In the commands `scroll-up' and `scroll-down', the directions "up" and "down" refer to the motion of the text in the buffer at which you are looking through the window. Imagine that the text is written on a long roll of paper and that the scrolling commands move the paper up and down. Thus, if you are looking at text in the middle of a buffer and repeatedly call `scroll-down', you will eventually see the beginning of the buffer. Some people have urged that the opposite convention be used: they imagine that the window moves over text that remains in place. Then "down" commands would take you to the end of the buffer. This view is more consistent with the actual relationship between windows and the text in the buffer, but it is less like what the user sees. The position of a window on the terminal does not move, and short scrolling commands clearly move the text up or down on the screen. We have chosen names that fit the user's point of view. The textual scrolling functions (aside from `scroll-other-window') have unpredictable results if the current buffer is different from the buffer that is displayed in the selected window. Note: Current Buffer. - Command: scroll-up &optional count This function scrolls the text in the selected window upward COUNT lines. If COUNT is negative, scrolling is actually downward. If COUNT is `nil' (or omitted), then the length of scroll is `next-screen-context-lines' lines less than the usable height of the window (not counting its mode line). `scroll-up' returns `nil'. - Command: scroll-down &optional count This function scrolls the text in the selected window downward COUNT lines. If COUNT is negative, scrolling is actually upward. If COUNT is omitted or `nil', then the length of the scroll is `next-screen-context-lines' lines less than the usable height of the window (not counting its mode line). `scroll-down' returns `nil'. - Command: scroll-other-window &optional count This function scrolls the text in another window upward COUNT lines. Negative values of COUNT, or `nil', are handled as in `scroll-up'. You can specify which buffer to scroll by setting the variable `other-window-scroll-buffer' to a buffer. If that buffer isn't already displayed, `scroll-other-window' displays it in some window. When the selected window is the minibuffer, the next window is normally the one at the top left corner. You can specify a different window to scroll, when the minibuffer is selected, by setting the variable `minibuffer-scroll-window'. This variable has no effect when any other window is selected. Note: Minibuffer Misc. When the minibuffer is active, it is the next window if the selected window is the one at the bottom right corner. In this case, `scroll-other-window' attempts to scroll the minibuffer. If the minibuffer contains just one line, it has nowhere to scroll to, so the line reappears after the echo area momentarily displays the message "Beginning of buffer". - Variable: other-window-scroll-buffer If this variable is non-`nil', it tells `scroll-other-window' which buffer to scroll. - User Option: scroll-margin This option specifies the size of the scroll margin--a minimum number of lines between point and the top or bottom of a window. Whenever point gets within this many lines of the top or bottom of the window, the window scrolls automatically (if possible) to move point out of the margin, closer to the center of the window. - User Option: scroll-conservatively This variable controls how scrolling is done automatically when point moves off the screen (or into the scroll margin). If the value is zero, then redisplay scrolls the text to center point vertically in the window. If the value is a positive integer N, then redisplay scrolls the window up to N lines in either direction, if that will bring point back into view. Otherwise, it centers point. The default value is zero. A value of `nil' is equivalent to .5, since it centers point. This variable automatically becomes buffer-local when set in any fashion. - User Option: scroll-up-aggressively The value of this variable should be either `nil' or a fraction F between 0 and 1. If it is a fraction, that 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. A value of `nil' is equivalent to .5, since its effect is to center point. This variable automatically becomes buffer-local when set in any fashion. - User Option: scroll-down-aggressively Likewise, 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 scrolls more aggressively. - User Option: scroll-step This variable is an older variant of `scroll-conservatively'. The difference is that it if its value is N, that permits scrolling only by precisely N lines, not a smaller number. This feature does not work with `scroll-margin'. The default value is zero. - User Option: scroll-preserve-screen-position If this option is non-`nil', the scroll functions move point so that the vertical position of the cursor is unchanged, when that is possible. - User Option: next-screen-context-lines The value of this variable is the number of lines of continuity to retain when scrolling by full screens. For example, `scroll-up' with an argument of `nil' scrolls so that this many lines at the bottom of the window appear instead at the top. The default value is `2'. - Command: recenter &optional count This function scrolls the selected window to put the text where point is located at a specified vertical position within the window. If COUNT is a nonnegative number, it puts the line containing point COUNT lines down from the top of the window. If COUNT is a negative number, then it counts upward from the bottom of the window, so that -1 stands for the last usable line in the window. If COUNT is a non-`nil' list, then it stands for the line in the middle of the window. If COUNT is `nil', `recenter' puts the line containing point in the middle of the window, then clears and redisplays the entire selected frame. When `recenter' is called interactively, COUNT is the raw prefix argument. Thus, typing `C-u' as the prefix sets the COUNT to a non-`nil' list, while typing `C-u 4' sets COUNT to 4, which positions the current line four lines from the top. With an argument of zero, `recenter' positions the current line at the top of the window. This action is so handy that some people make a separate key binding to do this. For example, (defun line-to-top-of-window () "Scroll current line to top of window. Replaces three keystroke sequence C-u 0 C-l." (interactive) (recenter 0)) (global-set-key [kp-multiply] 'line-to-top-of-window)
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