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