Ubuntu Manpage: groff_font - GNU roff device and font description files

Name

       groff_font - GNU roff device and font description files

Description

The groff font and output device description formats are slight extensions of those used
by AT&T device-independent troff. In distinction to the AT&T implementation, groff lacks
a binary format; all files are text files. (Plan 9 troff has also abandoned the binary
format.) The device and font description files for a device name are stored in a devname
directory. The device description file is called DESC, and, for each font supported by
the device, a font description file is called f, where f is usually an abbreviation of a
font's name and/or style. For example, the ps (PostScript) device has groff font
description files for Times roman (TR) and Zapf Chancery Medium italic (ZCMI), among many
others, while the utf8 device (for terminal emulators) has only font descriptions for the
roman, italic, bold, and bold-italic styles (R, I, B, and BI, respectively).

Device and font description files are read by the formatter, troff, and by output drivers.
The programs typically delegate these files' processing to an internal library, libgroff,
ensuring their consistent interpretation.

DESC file format
The DESC file contains a series of directives; each begins a line. Their order is not
important, with two exceptions: (1) the res directive must precede any papersize
directive; and (2) the charset directive must come last (if at all). If a directive name
is repeated, later entries in the file override previous ones (except that the paper
dimensions are computed based on the res directive last seen when papersize is
encountered). Spaces and/or tabs separate words and are ignored at line boundaries.
Comments start with the “#” character and extend to the end of a line. Empty lines are
ignored.

family fam
The default font family is fam.

fonts n F1 ... Fn
Fonts F1, ..., Fn are mounted at font positions m+1, ..., m+n where m is the number
of styles (see below). This directive may extend over more than one line. A font
name of 0 causes no font to be mounted at the corresponding position.

hor n The horizontal motion quantum is n basic units. Horizontal quantities are rounded
to multiples of n.

image_generator program
Use program to generate PNG images from PostScript input. Under GNU/Linux, this is
usually gs(1), but under other systems (notably Cygwin) it might be set to another
name. The grohtml(1) driver uses this directive.

paperlength n
The vertical dimension of the output medium is n basic units (deprecated: use
papersize instead).

papersize format-or-dimension-pair-or-file-name ...
The dimensions of the output medium are as according to the argument, which is
either a standard paper format, a pair of dimensions, or the name of a plain text
file containing either of the foregoing. Recognized paper formats are the ISO and
DIN formats A0–A7, B0–B7, C0–C7, and D0–D7; the U.S. formats letter, legal,
tabloid, ledger, statement, and executive; and the envelope formats com10, monarch,
and DL. Matching is performed without regard for lettercase.

Alternatively, the argument can be a custom paper format length,width (with no
spaces before or after the comma). Both length and width must have a unit
appended; valid units are “i” for inches, “c” for centimeters, “p” for points, and
“P” for picas. Example: “12c,235p”. An argument that starts with a digit is
always treated as a custom paper format.

Finally, the argument can be a file name (e.g., /etc/papersize); if the file can be
opened, the first line is read and a match attempted against each other form. No
comment syntax is supported.

More than one argument can be specified; each is scanned in turn and the first
valid paper specification used.

paperwidth n
The horizontal dimension of the output medium is n basic units (deprecated: use
papersize instead).

pass_filenames
Direct troff to emit the name of the source file being processed. This is achieved
with the intermediate output command “x F”, which grohtml interprets.

postpro program
Use program as the postprocessor.

prepro program
Use program as a preprocessor. The html and xhtml output devices use this
directive.

print program
Use program as the print spooler. If omitted, groff's -l and -L options are
ignored.

res n The device resolution is n basic units per inch.

sizes s1 ... sn 0
The device has fonts at s1, ..., sn scaled points (see below). The list of sizes
must be terminated by a 0. Each si can also be a range of sizes m–n. The list can
extend over more than one line.

sizescale n
A typographical point is subdivided into n scaled points. The default is 1.

styles S1 ... Sm
The first m font mounting positions are associated with styles S1, ..., Sm.

tcommand
The postprocessor can handle the t and u intermediate output commands.

unicode
The output device supports the complete Unicode repertoire. This directive is
useful only for devices which produce character entities instead of glyphs.

If unicode is present, no charset section is required in the font description files
since the Unicode handling built into groff is used. However, if there are entries
in a font description file's charset section, they either override the default
mappings for those particular characters or add new mappings (normally for
composite characters).

The utf8, html, and xhtml output devices use this directive.

unitwidth n
Quantities in the font description files are in basic units for fonts whose type
size is n scaled points.

unscaled_charwidths
Make the font handling module always return unscaled glyph widths. The grohtml
driver uses this directive.

use_charnames_in_special
troff should encode named glyphs inside device control commands. The grohtml
driver uses this directive.

vert n The vertical motion quantum is n basic units. Vertical quantities are rounded to
multiples of n.

charset
This directive and the rest of the file are ignored. It is recognized for
compatibility with other troff implementations. In GNU troff, character set
repertoire is described on a per-font basis.

troff recognizes but ignores the directives spare1, spare2, and biggestfont.

The res, unitwidth, fonts, and sizes lines are mandatory. Directives not listed above are
ignored by troff but may be used by postprocessors to obtain further information about the
device.

Font description file format

On typesetting output devices, each font is typically available at multiple sizes. While
paper measurements in the device description file are in absolute units, measurements
applicable to fonts must be proportional to the type size. groff achieves this using the
precedent set by AT&T device-independent troff: one font size is chosen as a norm, and all
others are scaled linearly relative to that basis. The “unit width” is the number of
basic units per point when the font is rendered at this nominal size.

For instance, groff's lbp device uses a unitwidth of 800. Its Times roman font (“TR”) has
a spacewidth of 833; this is also the width of its comma, period, centered period, and
mathematical asterisk, while its “M” is 2,963 basic units. Thus, an “M” on the lbp device
is 2,963 basic units wide at a notional type size of 800 points. (800-point type is not
practical for most purposes, but using it enables the quantities in the font description
files to be expressed as integers.)

A font description file has two sections. The first is a sequence of directives, and is
parsed similarly to the DESC file described above. Except for the directive names that
begin the second section, their ordering is immaterial. Later directives of the same name
override earlier ones, spaces and tabs are handled in the same way, and the same comment
syntax is supported. Empty lines are ignored throughout.

name F The name of the font is F. “DESC” is an invalid font name. Simple integers are
valid, but their use is discouraged. (groff requests and escape sequences
interpret non-negative font names as mounting positions instead. Further, a font
named “0” cannot be automatically mounted by the fonts directive of a DESC file.)

spacewidth n
The width of an unadjusted inter-word space is n basic units.

The directives above must appear in the first section; those below are optional.

slant n
The font's glyphs have a slant of n degrees; a positive n slants in the direction
of text flow.

ligatures lig1 ... lign [0]
Glyphs lig1, ..., lign are ligatures; possible ligatures are ff, fi, fl, ffi, and
ffl. For compatibility with other troff implementations, the list of ligatures may
be terminated with a 0. The list of ligatures must not extend over more than one
line.

special
The font is special: when a glyph is requested that is not present in the current
font, it is sought in any mounted fonts that bear this property.

Other directives in this section are ignored by troff, but may be used by postprocessors
to obtain further information about the font.

The second section contains one or two subsections. These can appear in either order; the
first one encountered commences the second section. Each starts with a directive on a
line by itself. A charset subsection is mandatory unless the associated DESC file
contains the unicode directive. Another subsection, kernpairs, is optional.

The directive charset starts the character set subsection. (For typesetter devices, this
directive is misnamed since it starts a list of glyphs, not characters.) It precedes a
series of glyph descriptions, one per line. Each such glyph description comprises a set
of fields separated by spaces or tabs and organized as follows.

name metrics type code [entity-name] [-- comment]

name identifies the glyph: if name is a printable character c, it corresponds to the troff
ordinary character c. If name is a multi-character sequence not beginning with \, it
corresponds to the GNU troff special character escape sequence “\[name]”. A name
consisting of three minus signs, “---”, indicates that the glyph is unnamed: such glyphs
can be accessed only by the \N escape sequence in troff. A special character named “---”
can still be defined using .char and similar requests. The name “\-” defines the minus
sign glyph. Finally, name can be the horizontal motion escape sequences, \| and \^
(“thin” and “hair” spaces, respectively), in which case only the width metric described
below is applied; a font can thus customize the widths of these spaces.

The form of the metrics field is as follows (on one line; it may be broken here for
readability).

width[,[height[,[depth[,[italic-correction[,[left-italic-correction[,[
subscript-correction]]]]]]]]]]

There must not be any spaces, tabs, or newlines between these subfields, which are in
basic units expressed as decimal integers. Unspecified subfields default to 0. Since
there is no associated binary format, these values are not required to fit into the C
language data type char as they are in AT&T device-independent troff.

The width subfield gives the width of the glyph. The height subfield gives the height of
the glyph (upwards is positive); if a glyph does not extend above the baseline, it should
be given a zero height, rather than a negative height. The depth subfield gives the depth
of the glyph, that is, the distance below the baseline to which the glyph extends
(downwards is positive); if a glyph does not extend below the baseline, it should be given
a zero depth, rather than a negative depth. Italic corrections are relevant to glyphs in
italic or oblique styles. The italic-correction is the amount of space that should be
added after an oblique glyph to be followed immediately by an upright glyph. The left-
italic-correction is the amount of space that should be added before an oblique glyph to
be preceded immediately by an upright glyph. The subscript-correction is the amount of
space that should be added after an oblique glyph to be followed by a subscript; it should
be less than the italic correction.

For fonts used with typesetting devices, the type field gives a featural description of
the glyph: it is a bit mask recording whether the glyph is an ascender, descender, both,
or neither. When a \w escape sequence is interpolated, these values are bitwise or-ed
together for each glyph and stored in the ct register. In font descriptions for terminal
devices, all glyphs might have a type of zero, regardless of their appearance.

0 means the glyph lies entirely between the baseline and a horizontal line at the “x-
height” of the font, as with “a”, “c”, and “x”;

1 means the glyph descends below the baseline, like “p”;

2 means the glyph ascends above the font's x-height, like “A” or “b”); and

3 means the glyph is both an ascender and a descender—this is true of parentheses in
some fonts.

The code field gives a numeric identifier that the postprocessor uses to render the glyph.
The glyph can be specified to troff using this code by means of the \N escape sequence.
The code can be any integer (that is, any integer parsable by the C standard library's
strtol(3) function).

The entity-name field defines an identifier for the glyph that the postprocessor uses to
print the troff glyph name. This field is optional; it was introduced so that the grohtml
output driver could encode its character set. For example, the glyph \[Po] is represented
by “&pound;” in HTML 4.0. For efficiency, these data are now compiled directly into
grohtml. grops uses the field to build sub-encoding arrays for PostScript fonts
containing more than 256 glyphs. Anything on the line after the entity-name field or “--”
is ignored.

A line in the charset section can also have the form
name "
identifying name as another name for the glyph mentioned in the preceding line. Such
aliases can be chained.

The directive kernpairs starts a list of kerning adjustments to be made to adjacent glyph
pairs from this font. It contains a sequence of lines formatted as follows.
g1 g2 n
The foregoing means that when glyph g1 is typeset immediately before g2, the space between
them should be increased by n. Most kerning pairs should have a negative value for n.

Files

       /usr/share/groff/1.23.0/font/devname/DESC
              describes the output device name.

       /usr/share/groff/1.23.0/font/devname/F
              describes the font known as F on device name.

Name

Description

Font description file format

Files

See also