The groff font format is roughly a superset of the ditroff font format. Unlike the ditroff font format, there is no associated binary format. The font files for device name are stored in a directory devname. There are two types of file: a device description file called DESC and for each font F a font file called F. These are text files; there is no associated binary format.
DESC file format
The DESC file can contain the following types of line:
There are n machine units per inch.
The horizontal resolution is n machine units.
The vertical resolution is n machine units.
The scale factor for pointsizes. By default this has a value of 1. One scaled point is equal to one point/n. The arguments to the unitwidth and sizes commands are given in scaled points.
Quantities in the font files are given in machine units for fonts whose point size is n scaled points.
Call program as a preprocessor.
Use program as the postprocessor.
This means that the postprocessor can handle the t and u output commands.
sizes s1 s2...sn 0
This means that the device has fonts at s1, s2,...sn scaled points. 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.
styles S1 S2...Sm
The first m font positions will be associated with styles S1...Sm.
fonts n F1 F2 F3...Fn
Fonts F1...Fn will be mounted in the font positions m+1,...,m+n where m is the number of styles. This command may extend over more than one line. A font name of 0 will cause no font to be mounted on the corresponding font position.
The default font family is fam.
This command indicates that troff should encode named characters inside special commands.
requests that troff tells the driver the source file name being processed. This is achieved by another tcommand: F filename.
This line and everything following in the file are ignored. It is allowed for the sake of backwards compatibility.
Use program as the spooler program for printing. If omitted, the -l and -L options of groff are ignored.
The res, unitwidth, fonts and sizes lines are compulsory. Other commands are ignored by troff but may be used by postprocessors to store arbitrary information about the device in the DESC file.
Here a list of obsolete keywords which are recognized by groff but completely ignored: spare1, spare2, biggestfont.
Font file format
A font 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.
The name of the font is F.
The normal width of a space is n.
The characters of the font have a slant of n degrees. (Positive means forward.)
ligatures lig1 lig2...lign [__0__?
Characters 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.
The font is special; this means that when a character is requested that is not present in the current font, it will be searched for in any special fonts that are mounted.
Other commands are ignored by troff 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.
The word charset starts the charset subsection. The charset line is followed by a sequence of lines. Each line gives information for one character. A line comprises a number of fields separated by blanks or tabs. The format is
name identifies the character: if name is a single character c then it corresponds to the groff input character c; if it is of the form \c where c is a single character, then it corresponds to the groff input character \c; otherwise it corresponds to the groff input character [__''name''__? (if it is exactly two characters xx it can be entered as xx). Groff supports eight bit characters; however some utilities has difficulties with eight bit characters. For this reason, there is a convention that the name charn is equivalent to the single character whose code is n . For example, char163 would be equivalent to the character with code 163 which is the pounds sterling sign in ISO Latin-1. The name --- is special and indicates that the character is unnamed; such characters can only be used by means of the N escape sequence in troff.
The type field gives the character type:
means the character has an descender, for example, p;
means the character has an ascender, for example, b;
means the character has both an ascender and a descender, for example, (.
The code field gives the code which the postprocessor uses to print the character. The character can also be input to groff using this code by means of the N escape sequence. The code can be any integer. If it starts with a 0 it will be interpreted as octal; if it starts with 0x or 0X it will be intepreted as hexadecimal.
The entity_name field gives an ascii string identifying the glyph which the postprocessor uses to print the character. This field is optional and has been introduced so that the html device driver can encode its character set. For example, the character `[Po?' is represented as `''
Anything on the line after the encoding field resp. after `--' will be ignored.
The metrics field has the form:
There must not be any spaces between these subfields. 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 subfields gives the width of the character. The height subfield gives the height of the character (upwards is positive); if a character 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 character, that is, the distance below the lowest point below the baseline to which the character extends (downwards is positive); if a character does not extend below above 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 character when it is immediately to be followed by a character from a roman font. The left_italic_correction subfield gives the amount of space that should be added before the character when it is immediately to be preceded by a character from a roman font. The subscript_correction gives the amount of space that should be added after a character before adding a subscript. This should be less than the italic correction.
A line in the charset section can also have the format
This indicates that name is just another name for the character mentioned in the preceding line.
The word kernpairs starts the kernpairs section. This contains a sequence of lines of the form:
c1 c2 n
Device description file for device name.
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