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11. Controlling the Display

Since only part of a large buffer fits in the window, XEmacs 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.

C-l
Clear frame and redisplay, scrolling the selected window to center point vertically within it (recenter).
C-v
pgdn
next
Scroll forward (a windowful or a specified number of lines) (scroll-up). On most X keyboards, you can get this functionality using the key labelled `Page Down', which generates either next or pgdn.
M-v
pgup
prior
Scroll backward (scroll-down). On most X keyboards, you can get this functionality using the key labelled `Page Up', which generates either prior or pgup.
arg C-l
Scroll so point is on line arg (recenter).
C-x <
C-pgdn
C-next
Scroll text in current window to the left (scroll-left).
C-x >
C-pgup
C-prior
Scroll to the right (scroll-right).
C-x $
Make deeply indented lines invisible (set-selective-display).

11.1 Scrolling  Moving text up and down in a window.
11.2 Horizontal Scrolling  Moving text left and right in a window.
11.3 Selective Display  Hiding lines with lots of indentation.
11.4 Variables Controlling Display  Information on variables for customizing display.


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11.1 Scrolling

If a buffer contains text that is too large to fit entirely within the window that is displaying the buffer, XEmacs shows a contiguous section of the text. The section 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 frame and redisplay, scrolling the selected window to center point vertically within it (recenter).
C-v
pgdn
next
Scroll forward (a windowful or a specified number of lines) (scroll-up).
M-v
pgup
prior
Scroll backward (scroll-down).
arg C-l
Scroll so point is on line arg (recenter).

The most basic scrolling command is C-l (recenter) with no argument. It clears the entire frame 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. Meta-v (scroll-down) is like C-v, but moves in the opposite direction.

To read the buffer a windowful at a time, use C-v with no argument. C-v 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. Point moves to the new top of the window if it was in the text scrolled off the top. M-v with no argument moves backward with similar 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 two.

Another way to scroll is using C-l with a numeric argument. C-l does not clear the frame when given an argument; it only scrolls the selected window. With a positive argument n, C-l 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 frame. 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 frame.

Scrolling happens automatically if point has moved out of the visible portion of the text when it is time to display. Usually scrolling is done to put point vertically centered within the window. However, if the variable scroll-step has a non-zero 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 happens.

Scrolling happens automatically if point has moved out of the visible portion of the text when it is time to display. Usually scrolling is done to put point vertically centered within the window. However, if the variable scroll-step has a non-zero 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 happens.

If you set scroll-step to a small value because you want to use arrow keys to scroll the screen without recentering, the redisplay preemption will likely make XEmacs keep recentering the screen when scrolling fast, regardless of scroll-step. To prevent this, set scroll-conservatively to a small value, which will have the result of overriding the redisplay preemption.


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11.2 Horizontal Scrolling

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

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 (see section 4.7 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. 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 displaying normally (with each line starting at the window's left margin); attempting to do so has no effect.


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11.3 Selective Display

XEmacs can hide lines indented more than a certain number of columns (you specify how many columns). This allows you to get an overview of a part of a program.

To hide lines, type C-x $ (set-selective-display) with a numeric argument n. (See section 4.9 Numeric Arguments, for information on giving the argument.) Lines with at least n columns of indentation disappear from the screen. The only indication of their presence are three dots (`...'), which appear at the end of each visible line that is followed by one or more invisible ones.

The invisible lines are still present in the buffer, and most editing commands see them as usual, so it is very easy to put 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.

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

To make everything visible again, type C-x $ with no argument.


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11.4 Variables Controlling Display

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

When you reenter XEmacs after suspending, XEmacs 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 XEmacs is entered and exited, respectively) switch between pages of memory so as to use one page for XEmacs and another page for other output. In that case, you might want to set the variable no-redraw-on-reenter to non-nil so that XEmacs will assume, when resumed, that the screen page it is using still contains what XEmacs 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 section 1.2 The Echo Area.

If the variable ctl-arrow is nil, control characters in the buffer are displayed with octal escape sequences, all except newline and tab. If its value is t, then control characters will be printed with an up-arrow, for example ^A.

If its value is not t and not nil, then characters whose code is greater than 160 (that is, the space character (32) with its high bit set) will be assumed to be printable, and will be displayed without alteration. This is the default when running under X Windows, since XEmacs assumes an ISO/8859-1 character set (also known as "Latin1"). The ctl-arrow variable may also be set to an integer, in which case all characters whose codes are greater than or equal to that value will be assumed to be printable.

Altering the value of ctl-arrow makes it local to the current buffer; until that time, the default value is in effect. See section 27.3.4 Local Variables.

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.

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


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