groff: Manipulating Spacing
5.9 Manipulating Spacing
========================
-- Request: .sp [distance]
Space downwards DISTANCE. With no argument it advances 1 line. A
negative argument causes 'gtroff' to move up the page the specified
distance. If the argument is preceded by a '|' then 'gtroff' moves
that distance from the top of the page. This request causes a line
break, and that adds the current line spacing to the space you have
just specified. The default scaling indicator is 'v'.
For convenience you may wish to use the following macros to set the
height of the next line at a given distance from the top or the
bottom of the page:
.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 bottom of the next
line will be at 10 cm from the paper edge at the bottom.
If a vertical trap is sprung during execution of 'sp', the amount
of vertical space after the trap is discarded. For example, this
.de xxx
..
.
.wh 0 xxx
.
.pl 5v
foo
.sp 2
bar
.sp 50
baz
results in
foo
bar
baz
The amount of discarded space is available in the number register
'.trunc'.
To protect 'sp' against vertical traps, use the 'vpt' request:
.vpt 0
.sp -3
.vpt 1
-- Request: .ls [nnn]
-- Register: \n[.L]
Output NNN-1 blank lines after each line of text. With no
argument, 'gtroff' uses the previous value before the last 'ls'
call.
.ls 2 \" This causes double-spaced output
.ls 3 \" This causes triple-spaced output
.ls \" Again double-spaced
The line spacing is associated with the current environment (⇒
Environments).
The read-only number register '.L' contains the current line
spacing setting.
⇒Changing Type Sizes, for the requests 'vs' and 'pvs' as
alternatives to 'ls'.
-- Escape: \x'spacing'
-- Register: \n[.a]
Sometimes, extra vertical spacing is only needed occasionally, e.g.
to allow space for a tall construct (like an equation). The '\x'
escape does this. The escape is given a numerical argument,
usually enclosed in quotes (like '\x'3p''); the default scaling
indicator is 'v'. If this number is positive extra vertical space
is inserted below the current line. A negative number adds space
above. If this escape is used multiple times on the same line, the
maximum of the values is used.
⇒Escapes, for details on parameter delimiting characters.
The '.a' read-only number register contains the most recent
(non-negative) extra vertical line space.
Using '\x' can be necessary in combination with the '\b' escape, as
the following example shows.
This is a test with the \[rs]b escape.
.br
This is a test with the \[rs]b escape.
.br
This is a test with \b'xyz'\x'-1m'\x'1m'.
.br
This is a test with the \[rs]b escape.
.br
This is a test with the \[rs]b escape.
produces
This is a test with the \b escape.
This is a test with the \b escape.
x
This is a test with y.
z
This is a test with the \b escape.
This is a test with the \b escape.
-- Request: .ns
-- Request: .rs
-- Register: \n[.ns]
Enable "no-space mode". In this mode, spacing (either via 'sp' or
via blank lines) is disabled. The 'bp' request to advance to the
next page is also disabled, except if it is accompanied by a page
number (see ⇒Page Control, for more information). This mode
ends when actual text is output or the 'rs' request is encountered,
which ends no-space mode. The read-only number register '.ns' is
set to 1 as long as no-space mode is active.
This request is useful for macros that conditionally insert
vertical space before the text starts (for example, a paragraph
macro could insert some space except when it is the first paragraph
after a section header).