groff: Page Motions
5.22 Page Motions
=================
Manipulating Spacing, for a discussion of the main request for
vertical motion, 'sp'.
-- Request: .mk [reg]
-- Request: .rt [dist]
The request 'mk' can be used to mark a location on a page, for
movement to later. This request takes a register name as an
argument in which to store the current page location. With no
argument it stores the location in an internal register. The
results of this can be used later by the 'rt' or the 'sp' request
(or the '\v' escape).
The 'rt' request returns _upwards_ to the location marked with the
last 'mk' request. If used with an argument, return to a position
which distance from the top of the page is DIST (no previous call
to 'mk' is necessary in this case). Default scaling indicator is
'v'.
Here a primitive solution for a two-column macro.
.nr column-length 1.5i
.nr column-gap 4m
.nr bottom-margin 1m
.
.de 2c
. br
. mk
. ll \\n[column-length]u
. wh -\\n[bottom-margin]u 2c-trap
. nr right-side 0
..
.
.de 2c-trap
. ie \\n[right-side] \{\
. nr right-side 0
. po -(\\n[column-length]u + \\n[column-gap]u)
. \" remove trap
. wh -\\n[bottom-margin]u
. \}
. el \{\
. \" switch to right side
. nr right-side 1
. po +(\\n[column-length]u + \\n[column-gap]u)
. rt
. \}
..
.
.pl 1.5i
.ll 4i
This is a small test that shows how the
rt request works in combination with mk.
.2c
Starting here, text is typeset in two columns.
Note that this implementation isn't robust
and thus not suited for a real two-column
macro.
Result:
This is a small test that shows how the
rt request works in combination with mk.
Starting here, isn't robust
text is typeset and thus not
in two columns. suited for a
Note that this real two-column
implementation macro.
The following escapes give fine control of movements about the page.
-- Escape: \v'e'
Move vertically, usually from the current location on the page (if
no absolute position operator '|' is used). The argument E
specifies the distance to move; positive is downwards and negative
upwards. The default scaling indicator for this escape is 'v'.
Beware, however, that 'gtroff' continues text processing at the
point where the motion ends, so you should always balance motions
to avoid interference with text processing.
'\v' doesn't trigger a trap. This can be quite useful; for
example, consider a page bottom trap macro that prints a marker in
the margin to indicate continuation of a footnote or something
similar.
There are some special-case escapes for vertical motion.
-- Escape: \r
Move upwards 1v.
-- Escape: \u
Move upwards .5v.
-- Escape: \d
Move down .5v.
-- Escape: \h'e'
Move horizontally, usually from the current location (if no
absolute position operator '|' is used). The expression E
indicates how far to move: positive is rightwards and negative
leftwards. The default scaling indicator for this escape is 'm'.
This horizontal space is not discarded at the end of a line. To
insert discardable space of a certain length use the 'ss' request.
There are a number of special-case escapes for horizontal motion.
-- Escape: \<SP>
An unbreakable and unpaddable (i.e. not expanded during filling)
space. (Note: This is a backslash followed by a space.)
-- Escape: \~
An unbreakable space that stretches like a normal inter-word space
when a line is adjusted.
-- Escape: \|
A 1/6th em space. Ignored for TTY output devices (rounded to
zero).
However, if there is a glyph defined in the current font file with
name '\|' (note the leading backslash), the width of this glyph is
used instead (even for TTYs).
-- Escape: \^
A 1/12th em space. Ignored for TTY output devices (rounded to
zero).
However, if there is a glyph defined in the current font file with
name '\^' (note the leading backslash), the width of this glyph is
used instead (even for TTYs).
-- Escape: \0
A space the size of a digit.
The following string sets the TeX logo:
.ds TeX T\h'-.1667m'\v'.224m'E\v'-.224m'\h'-.125m'X
-- Escape: \w'text'
-- Register: \n[st]
-- Register: \n[sb]
-- Register: \n[rst]
-- Register: \n[rsb]
-- Register: \n[ct]
-- Register: \n[ssc]
-- Register: \n[skw]
Return the width of the specified TEXT in basic units. This allows
horizontal movement based on the width of some arbitrary text (e.g.
given as an argument to a macro).
The length of the string `abc' is \w'abc'u.
=> The length of the string `abc' is 72u.
Font changes may occur in TEXT, which don't affect current
settings.
After use, '\w' sets several registers:
'st'
'sb'
The highest and lowest point of the baseline, respectively, in
TEXT.
'rst'
'rsb'
Like the 'st' and 'sb' registers, but takes account of the
heights and depths of glyphs. In other words, this gives the
highest and lowest point of TEXT. Values below the baseline
are negative.
'ct'
Defines the kinds of glyphs occurring in TEXT:
0
only short glyphs, no descenders or tall glyphs.
1
at least one descender.
2
at least one tall glyph.
3
at least one each of a descender and a tall glyph.
'ssc'
The amount of horizontal space (possibly negative) that should
be added to the last glyph before a subscript.
'skw'
How far to right of the center of the last glyph in the '\w'
argument, the center of an accent from a roman font should be
placed over that glyph.
-- Escape: \kp
-- Escape: \k(ps
-- Escape: \k[position]
Store the current horizontal position in the _input_ line in number
register with name POSITION (one-character name P, two-character
name PS). Use this, for example, to return to the beginning of a
string for highlighting or other decoration.
-- Register: \n[hp]
The current horizontal position at the input line.
-- Register: \n[.k]
A read-only number register containing the current horizontal
output position (relative to the current indentation).
-- Escape: \o'abc'
Overstrike glyphs A, B, C, ...; the glyphs are centered, and the
resulting spacing is the largest width of the affected glyphs.
-- Escape: \zg
Print glyph G with zero width, i.e., without spacing. Use this to
overstrike glyphs left-aligned.
-- Escape: \Z'anything'
Print ANYTHING, then restore the horizontal and vertical position.
The argument may not contain tabs or leaders.
The following is an example of a strike-through macro:
.de ST
.nr ww \w'\\$1'
\Z@\v'-.25m'\l'\\n[ww]u'@\\$1
..
.
This is
.ST "a test"
an actual emergency!
Info Catalog
groff: Writing Macros
groff: gtroff Reference
groff: Drawing Requests