Manipulating Spacing (The GNU Troff Manual)

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5.11 Manipulating Spacing

+ + + +

A break causes the formatter to update the vertical drawing position at +which the new text baseline is aligned. You can alter this location. +

Request: .sp [distance] ¶

Break and move the next text baseline down by distance, or until +springing a page location trap.⁶² +If invoked with the no-break control character, sp moves the +pending output line’s text baseline by distance. A negative +distance will not reduce the position of the text baseline below +zero. Inside a diversion, any distance argument is ignored. The +default scaling unit is ‘v’. If distance is not specified, +‘1v’ is assumed. +

.pl 5v \" Set page length to 5 vees.
+.de xx
+\-\-\-
+.  br
+..
+.wh 0 xx \" Set a trap at the top of the page.
+foo on page \n%
+.sp 2v
+bar on page \n%
+.sp 50v \" This will cause a page break.
+baz on page \n%
+.pl \n(nlu \" Truncate page to current position.
+    ⇒ ---
+    ⇒ foo on page 1
+    ⇒
+    ⇒
+    ⇒ bar on page 1
+    ⇒ ---
+    ⇒ baz on page 2
+

+ +

You might use the following macros to set the baseline of the next +output text at a given distance from the top or the bottom of the page. +We subtract one line height (\n[.v]) because the | +operator moves to one vee below the page top (recall Numeric Expressions). +

.de y-from-top-down
+.  sp |\\$1-\\n[.v]u
+..
+.
+.de y-from-bot-up
+.  sp |\\n[.p]u-\\$1-\\n[.v]u
+..
+

+ +

A call to ‘.y-from-bot-up 10c’ means that the next text baseline +will be 10 cm from the bottom edge of the paper. +

+ +

Request: .ls [count] ¶

+ +

Set the line spacing; add count−1 blank lines after each +line of text. With no argument, GNU troff uses the previous +value before the last ls call. The default is 1. +

+ + +

The read-only register .L contains the current line spacing; it +is associated with the environment (see Environments). +

+ +

The ls request is a coarse mechanism. See Changing the Type Size, for the requests vs and pvs as alternatives to +ls. +

Escape sequence: \x'spacing' ¶

Sometimes, an output line requires additional vertical spacing, for +instance to allow room for a tall construct like an inline equation with +exponents or subscripts (particularly if they are iterated). The +\x escape sequence takes a delimited measurement (like +‘\x'3p'’) to increase the vertical spacing of the pending output +line. The default scaling unit is ‘v’. If the measurement is +positive, extra vertical space is inserted below the current line; a +negative measurement adds space above. If \x is applied to the +pending output line multiple times, the maxima of the positive and +negative adjustments are separately applied. The delimiter need not be +a neutral apostrophe; see Delimiters. +

+ +

The .a read-only register contains the extra vertical spacing +after the text baseline of the most recently emitted output line. +(In other words, it is the largest positive argument to \x +encountered on that line.) This quantity is exposed via a register +because if an output line requires this “extra post-vertical line +spacing”, and the subsequent output line requires “extra pre-vertical +line spacing” (a negative argument to \x), then applying both +can lead to excessive spacing between the output lines. Text that is +piling high on line n might not require (as much) extra +pre-vertical line spacing if line n−1 carries extra +post-vertical line spacing. +

Use of \x can be necessary in combination with the +bracket-building escape sequence \b,⁶³ as the following example shows. +

.nf
+This is a test of \[rs]b (1).
+This is a test of \[rs]b (2).
+This is a test of \b'xyz'\x'-1m'\x'1m' (3).
+This is a test of \[rs]b (4).
+This is a test of \[rs]b (5).
+    ⇒ This is a test of \b (1).
+    ⇒ This is a test of \b (2).
+    ⇒                   x
+    ⇒ This is a test of y (3).
+    ⇒                   z
+    ⇒ This is a test of \b (4).
+    ⇒ This is a test of \b (5).
+

+ +

Without \x, the backslashes on the lines marked ‘(2)’ and +‘(4)’ would be overprinted. +

Request: .ns ¶

Request: .rs ¶

+ + + + + +

Enable no-space mode. Vertical spacing, whether by sp +requests or blank input lines, is disabled. The bp request to +advance to the next page is also disabled, unless it is accompanied by a +page number (see Page Control). No-space mode ends automatically +when text⁶⁴ is formatted for output ⁶⁵ or the rs request is invoked, which ends +no-space mode. The read-only register .ns interpolates a Boolean +value indicating the enablement of no-space mode. +

A paragraphing macro might ordinarily insert vertical space to separate +paragraphs. A section heading macro could invoke ns to suppress +this spacing for the first paragraph in a section. +

+ + + +