groff: Font File Format
8.2.2 Font File Format
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A "font file", also (and probably better) called a "font description
file", has two sections. The first section is a sequence of lines each
containing a sequence of blank delimited words; the first word in the
line is a key, and subsequent words give a value for that key.
'name F'
The name of the font is F.
'spacewidth N'
The normal width of a space is N.
'slant N'
The glyphs of the font have a slant of N degrees. (Positive means
forward.)
'ligatures LIG1 LIG2 ... LIGN [0]'
Glyphs LIG1, LIG2, ..., LIGN are ligatures; possible ligatures are
'ff', 'fi', 'fl', 'ffi' and 'ffl'. For backwards compatibility,
the list of ligatures may be terminated with a 0. The list of
ligatures may not extend over more than one line.
'special'
The font is "special"; this means that when a glyph is requested
that is not present in the current font, it is searched for in any
special fonts that are mounted.
Other commands are ignored by 'gtroff' but may be used by
postprocessors to store arbitrary information about the font in the font
file.
The first section can contain comments, which start with the '#'
character and extend to the end of a line.
The second section contains one or two subsections. It must contain
a 'charset' subsection and it may also contain a 'kernpairs' subsection.
These subsections can appear in any order. Each subsection starts with
a word on a line by itself.
Font File Format-Footnote-1::) The 'charset' line is followed by a
sequence of lines. Each line gives information for one glyph. A line
comprises a number of fields separated by blanks or tabs. The format is
NAME METRICS TYPE CODE [ENTITY-NAME] ['--' COMMENT]
NAME identifies the glyph name(2) (⇒Font File Format-Footnote-2):
If NAME is a single character C then it corresponds to the 'gtroff'
input character C; if it is of the form '\C' where C is a single
character, then it corresponds to the special character '\[C]';
otherwise it corresponds to the special character '\[NAME]'. If it is
exactly two characters XX it can be entered as '\(XX'. Note that
single-letter special characters can't be accessed as '\C'; the only
exception is '\-', which is identical to '\[-]'.
'gtroff' supports 8-bit input characters; however some utilities have
difficulties with eight-bit characters. For this reason, there is a
convention that the entity name 'charN' is equivalent to the single
input character whose code is N. For example, 'char163' would be
equivalent to the character with code 163, which is the pounds sterling
sign in the ISO Latin-1 character set. You shouldn't use 'charN'
entities in font description files since they are related to input, not
output. Otherwise, you get hard-coded connections between input and
output encoding, which prevents use of different (input) character sets.
The name '---' is special and indicates that the glyph is unnamed;
such glyphs can only be used by means of the '\N' escape sequence in
'gtroff'.
The TYPE field gives the glyph type:
'1'
the glyph has a descender, for example, 'p';
'2'
the glyph has an ascender, for example, 'b';
'3'
the glyph has both an ascender and a descender, for example, '('.
The CODE field gives the code that the postprocessor uses to print
the glyph. The glyph can also be input to 'gtroff' using this code by
means of the '\N' escape sequence. CODE can be any integer. If it
starts with '0' it is interpreted as octal; if it starts with '0x' or
'0X' it is interpreted as hexadecimal. Note, however, that the '\N'
escape sequence only accepts a decimal integer.
The ENTITY-NAME field gives an ASCII string identifying the glyph
that the postprocessor uses to print the 'gtroff' glyph NAME. This
field is optional and has been introduced so that the 'grohtml' device
driver can encode its character set. For example, the glyph '\[Po]' is
represented as '£' in HTML 4.0.
Anything on the line after the ENTITY-NAME field resp. after '--' is
ignored.
The METRICS field has the form:
WIDTH[','HEIGHT[','DEPTH[','ITALIC-CORRECTION
[','LEFT-ITALIC-CORRECTION[','SUBSCRIPT-CORRECTION]]]]]
There must not be any spaces between these subfields (it has been split
here into two lines for better legibility only). Missing subfields are
assumed to be 0. The subfields are all decimal integers. Since there
is no associated binary format, these values are not required to fit
into a variable of type 'char' as they are in 'ditroff'. 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 from the baseline to the lowest point 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. The ITALIC-CORRECTION subfield gives the
amount of space that should be added after the glyph when it is
immediately to be followed by a glyph from a roman font. The
LEFT-ITALIC-CORRECTION subfield gives the amount of space that should be
added before the glyph when it is immediately to be preceded by a glyph
from a roman font. The SUBSCRIPT-CORRECTION gives the amount of space
that should be added after a glyph before adding a subscript. This
should be less than the italic correction.
A line in the 'charset' section can also have the format
NAME "
This indicates that NAME is just another name for the glyph mentioned in
the preceding line.
The word 'kernpairs' starts the kernpairs section. This contains a
sequence of lines of the form:
C1 C2 N
This means that when glyph C1 appears next to glyph C2 the space between
them should be increased by N. Most entries in the kernpairs section
have a negative value for N.
Info Catalog
groff: DESC File Format
groff: Font Files