Next: Character Classes, Previous: Font Positions, Up: Using Fonts [Contents][Index]
A glyph is a graphical representation of a character. While a character is an abstraction of semantic information, a glyph is something that can be seen on screen or paper. A character has many possible representation forms (for example, the character ‘A’ can be written in an upright or slanted typeface, producing distinct glyphs). Sometimes, a sequence of characters map to a single glyph: this is a ligature—the most common is ‘fi’.
Space characters never become glyphs in GNU troff. If not
discarded (as when trailing on text lines), they are represented by
horizontal motions in the output.
A symbol is simply a named glyph. Within gtroff, all
glyph names of a particular font are defined in its font file. If the
user requests a glyph not available in this font, gtroff looks
up an ordered list of special fonts. By default, the PostScript
output device supports the two special fonts ‘SS’ (slanted symbols)
and ‘S’ (symbols) (the former is looked up before the latter).
Other output devices use different names for special fonts. Fonts
mounted with the fonts keyword in the DESC file are
globally available. To install additional special fonts locally (i.e.,
for a particular font), use the fspecial request.
GNU troff searches for a symbol as follows.
char request, use it.
This hides a symbol with the same name in the current font.
fchar request, use it.
fspecial call if appropriate.
fschar request for the
current font, use it.
special
call.
schar request, use it.
fonts line in
the DESC file often contains empty positions, which are filled
later on. For example, consider the following:
fonts 3 0 0 FOO
This mounts font foo at font position 3. We assume that
FOO is a special font, containing glyph foo, and that no
font has been loaded yet. The line
.fspecial BAR BAZ
makes font BAZ special only if font BAR is active. We
further assume that BAZ is really a special font, i.e., the font
description file contains the special keyword, and that it also
contains glyph foo with a special shape fitting to font
BAR. After executing fspecial, font BAR is loaded
at font position 1, and BAZ at position 2.
We now switch to a new font XXX, trying to access glyph
foo that is assumed to be missing. There are neither
font-specific special fonts for XXX nor any other fonts made
special with the special request, so gtroff starts the
search for special fonts in the list of already mounted fonts, with
increasing font positions. Consequently, it finds BAZ before
FOO even for XXX, which is not the intended behaviour.
See Device and Font Description Files, and Special Fonts, for more details.
The groff_char(7) man page houses a complete list of predefined special character names, but the availability of any as a glyph is device- and font-dependent. For example, say
man -T dvi groff_char > groff_char.dvi
to obtain those available with the DVI device and default font
configuration.116 If you want to use an additional macro package to change
the fonts used, groff (or gtroff) must be run directly.
groff -T dvi -m ec -m an groff_char.7 > groff_char.dvi
Special character names not listed in groff_char(7) are
derived algorithmically, using a simplified version of the Adobe Glyph
List (AGL) algorithm, which is described in
https://github.com/adobe-type-tools/agl-aglfn. The (frozen)
set of names that can’t be derived algorithmically is called the
groff glyph list (GGL).
uXXXX[X[X]]. X must be an
uppercase hexadecimal digit. Examples: u1234, u008E,
u12DB8. The largest Unicode value is 0x10FFFF. There must be at
least four X digits; if necessary, add leading zeroes (after the
‘u’). No zero padding is allowed for character codes greater than
0xFFFF. Surrogates (i.e., Unicode values greater than 0xFFFF
represented with character codes from the surrogate area U+D800-U+DFFF)
are not allowed either.
‘u’ component1 ‘_’ component2 ‘_’ component3 …
Example: u0045_0302_0301.
For simplicity, all Unicode characters that are composites must be
maximally decomposed to NFD;117 for example,
u00CA_0301 is not a valid glyph name since U+00CA (LATIN
CAPITAL LETTER E WITH CIRCUMFLEX) can be further decomposed into U+0045
(LATIN CAPITAL LETTER E) and U+0302 (COMBINING CIRCUMFLEX
ACCENT). u0045_0302_0301 is thus the glyph name for U+1EBE,
LATIN CAPITAL LETTER E WITH CIRCUMFLEX AND ACUTE.
u0100 (LATIN
LETTER A WITH MACRON) is automatically decomposed into
u0041_0304. Additionally, a glyph name of the GGL is preferred
to an algorithmically derived glyph name; groff also
automatically does the mapping. Example: The glyph u0045_0302 is
mapped to ^E.
^E_u0301 is invalid.
Typeset a special character name (two-character name nm) or a composite glyph consisting of base-glyph overlaid with one or more combining-components. For example, ‘\[A ho]’ is a capital letter “A” with a “hook accent” (ogonek).
There is no special syntax for one-character names—the analogous form
‘\n’ would collide with other escape sequences. However, the
four escape sequences \', \-, \_, and \`,
are translated on input to the special character escape sequences
\[aa], \[-], \[ul], and \[ga], respectively.
A special character name of length one is not the same thing as an
ordinary character: that is, the character a is not the same as
\[a].
If name is undefined, a warning in category ‘char’ is produced and the escape is ignored. See Warnings, for information about the enablement and suppression of warnings.
GNU troff resolves \[…] with more than a single
component as follows:
uXXXX form.
uXXXX that is found in the list of
decomposable glyphs is decomposed.
No check for the existence of any component (similar to tr
request) is done.
Examples:
\[A ho]‘A’ maps to u0041, ‘ho’ maps to u02DB, thus the
final glyph name would be u0041_02DB. This is not the expected
result: the ogonek glyph ‘ho’ is a spacing ogonek, but for a
proper composite a non-spacing ogonek (U+0328) is necessary. Looking
into the file composite.tmac, one can find ‘.composite ho u0328’, which changes the mapping of ‘ho’ while a composite glyph
name is constructed, causing the final glyph name to be
u0041_0328.
\[^E u0301]\[^E aa]\[E a^ aa]\[E ^ ']‘^E’ maps to u0045_0302, thus the final glyph name is
u0045_0302_0301 in all forms (assuming proper calls of the
composite request).
It is not possible to define glyphs with names like ‘A ho’
within a groff font file. This is not really a limitation;
instead, you have to define u0041_0328.
'xxx'Typeset the special character
xxx.
Normally,
it is more convenient to use
‘\[xxx]’,
but
\C
has some advantages:
it is compatible with AT&T device-independent
troff
(and therefore available in compatibility
mode118)
and can interpolate special characters with
‘]’
in their names.
The delimiter need not be a neutral apostrophe;
recall Delimiters.
Map ordinary or special character name c1 to c2 when
c1 is a combining component in a composite character. See above
for examples. This is a strict rewriting of the special character name;
no check is performed for the existence of a glyph for either.
Typically, composite is used to map a spacing character to a
combining one. A set of default mappings for many accents can be found
in the file composite.tmac, loaded by the default troffrc
at startup.
You can obtain a report of mappings defined by composite on the
standard error stream with the pcomposite request.
See Debugging.
'n'Format indexed character numbered
n
in the current font
(n is
not
the input character code).
n can
be any non-negative decimal integer.
Most devices number glyphs with codes between 0 and 255 only;
the
utf8
output device uses codes in the range 0–65535.
If the current font does not contain a glyph with that code,
special fonts are
not
searched.
The
\N
escape sequence can be conveniently used in conjunction with the
char
request.
.char \[phone] \f[ZD]\N'37'
The code of each glyph is given in the fourth column in the font
description file after the charset command. It is possible to
include unnamed glyphs in the font description file by using a name of
‘---’; the \N escape sequence is the only way to use these.
No kerning is applied to glyphs accessed with \N. The delimiter
need not be a neutral apostrophe; see Delimiters.
A few escape sequences are also special characters.
'An escaped neutral apostrophe is a synonym for \[aa] (acute
accent).
`An escaped grave accent is a synonym for \[ga] (grave accent).
An escaped hyphen-minus is a synonym for \[-] (minus sign).
An escaped underscore (“low line”) is a synonym for \[ul]
(underrule). On typesetting devices, the underrule is font-invariant
and drawn lower than the underscore ‘_’.
Assign properties encoded by non-negative integer n to each character or class119. c. Spaces need not separate c arguments.
Characters, whether ordinary, special, or indexed, have certain associated properties. The first argument is the sum of the desired flags and the remaining arguments are the characters to be assigned those properties. arguments.
The non-negative integer n is the sum of any of the following. Some combinations are nonsensical, such as ‘33’ (1 + 32).
1Recognize the character as ending a sentence if followed by a newline or two spaces. Initially, characters ‘.?!’ have this property.
2Enable breaks before the character. A line is not broken at a character with this property unless the characters on each side both have non-zero hyphenation codes. This exception can be overridden by adding 64. Initially, no characters have this property.
4Enable breaks after the character. A line is not broken at a character with this property unless the characters on each side both have non-zero hyphenation codes. This exception can be overridden by adding 64. Initially, characters ‘\-\[hy]\[em]’ have this property.
8Mark the glyph associated with this character as overlapping other instances of itself horizontally. Initially, characters ‘\[ul]\[rn]\[ru]\[radicalex]\[sqrtex]’ have this property.
16Mark the glyph associated with this character as overlapping other instances of itself vertically. Initially, the character ‘\[br]’ has this property.
32Mark the character as transparent for the purpose of end-of-sentence recognition. In other words, an end-of-sentence character followed by any number of characters with this property is treated as the end of a sentence if followed by a newline or two spaces. This is the same as having a zero space factor in TeX. Initially, characters ‘"')]*\[dg]\[dd]\[rq]\[cq]’ have this property.
64Ignore hyphenation codes of the surrounding characters. Use this in combination with values 2 and 4 (initially, no characters have this property).
For example, if you need an automatic break point after the en-dash in numeric ranges like “3000–5000”, insert
.cflags 68 \[en]
into your document. However, this practice can lead to bad layout if
done thoughtlessly; in most situations, a better solution instead of
changing the cflags value is to insert \: right after the
hyphen at the places that really need a break point.
The remaining values were implemented for East Asian language support; those who use alphabetic scripts exclusively can disregard them.
128Prohibit a line break before the character, but allow a line break after the character. This works only in combination with flags 256 and 512 and has no effect otherwise. Initially, no characters have this property.
256Prohibit a line break after the character, but allow a line break before the character. This works only in combination with flags 128 and 512 and has no effect otherwise. Initially, no characters have this property.
512Allow line break before or after the character. This works only in combination with flags 128 and 256 and has no effect otherwise. Initially, no characters have this property.
In contrast to values 2 and 4, the values 128, 256, and 512 work pairwise. If, for example, the left character has value 512, and the right character 128, no break will be automatically inserted between them. If we use value 6 instead for the left character, a break after the character can’t be suppressed since the neighboring character on the right doesn’t get examined.
"][contents]"][contents]"][contents]"][contents]Define an ordinary, special, or indexed character c as contents.
Omitting contents gives c an empty definition.
GNU
troff removes a leading neutral double quote
‘"’
from
contents,
permitting initial embedded spaces in it,
and reads it to the end of the input line in copy mode.
See Copy Mode.
Defining
(or redefining)
a
character c
creates a formatter object
that
GNU
troff recognizes like any other ordinary,
special,
or indexed character on input,
and produces
contents
on output.
When
formatting
c,
GNU
troff processes
contents
in a temporary environment and enscapsulates the result
in a node;120
disabling compatibility mode
and setting the escape character
to \
while interpreting
contents.
Any emboldening,
constant spacing,
or track kerning applies to this object
rather than to individual glyphs resulting from the formatting of
contents.
A character defined by these requests
can be used just like a glyph provided by the output device.
In particular,
other characters can be translated to it with the
tr
and
trin requests;
it can be made the tab or leader fill character with the
tc
and
lc
requests,
respectively;
sequences of it can be drawn with the
\l
and
\L
escape sequences;
and,
if the
hcode
request is used on
c,
it is subject to automatic hyphenation.
However, a user-defined character c does not participate at its boundaries in kerning adjustments or italic corrections.
The formatter prevents infinite recursion
by treating an occurrence
of a character in its own definition
as if it were undefined;
when interpolating such a character,
GNU
troff emits a warning in category ‘char’.121
The tr and trin requests take precedence if char
accesses the same symbol.
.tr XY
X
⇒ Y
.char X Z
X
⇒ Y
.tr XX
X
⇒ Z
The fchar request defines a fallback glyph: gtroff only
checks for glyphs defined with fchar if it cannot find the glyph
in the current font. gtroff carries out this test before
checking special fonts.
fschar defines a fallback glyph for font f:
gtroff checks for glyphs defined with fschar after the
list of fonts declared as font-specific special fonts with the
fspecial request, but before the list of fonts declared as global
special fonts with the special request.
Finally, the schar request defines a global fallback glyph:
gtroff checks for glyphs defined with schar after the
list of fonts declared as global special fonts with the special
request, but before the already mounted special fonts.
See Character Classes.
Caution:
These requests remove a leading neutral double quote
‘"’
and treat the remainder of the input line
as their second argument,
including any spaces,
up to a newline or comment escape sequence.
See the discussion of the
ds
request in Strings.
Remove definition of each
ordinary,
special,
or
indexed
character
c,
undoing the effect of a
char,
fchar,
or
schar
request.
Spaces need not separate
c
arguments.
The character definition removed
(if any)
is the first encountered in the resolution process documented above.
Glyphs,
which are defined by font description files,
cannot be removed.
rfschar
removes character definitions created by
fschar
for
font f.
Next: Character Classes, Previous: Font Positions, Up: Using Fonts [Contents][Index]