font, subfont - external format for fonts and subfonts
Fonts and subfonts are described in cachechars(2).
External fonts are described by a plain text file that can be read
using openfont. The format of the file is a header followed by any
number of subfont range specifications. The header contains two num‐
bers: the height and the ascent, both in pixels. The height is the
inter-line spacing and the ascent is the distance from the top of the
line to the baseline. These numbers are chosen to display consistently
all the subfonts of the font. A subfont range specification contains
two or three numbers and a file name. The numbers are the inclusive
range of characters covered by the subfont, with an optional starting
position within the subfont, and the file name names an external file
suitable for readsubfont (see graphics(2)). The minimum number of a
covered range is mapped to the specified starting position (default
zero) of the corresponding subfont. If the subfont file name does not
begin with a slash, it is taken relative to the directory containing
the font file. Each field must be followed by some white space. Each
numeric field may be C-format decimal, octal, or hexadecimal.
External subfonts are represented in a more rigid format that can be
read and written using readsubfont and writesubfont (see subfont(2)).
The format for subfont files is: an image containing character glyphs,
followed by a subfont header, followed by character information. The
image has the format for external image files described in image(6).
The subfont header has 3 decimal strings: n, height, and ascent. Each
number is right-justified and blank padded in 11 characters, followed
by a blank. The character info consists of n+1 6-byte entries, each
giving the Fontchar x (2 bytes, low order byte first), top, bottom,
left, and width. The x field of the last Fontchar is used to calculate
the image width of the previous character; the other fields in the last
Fontchar are irrelevant.
Note that the convention of using the character with value zero (NUL)
to represent characters of zero width (see draw(2)) means that fonts
should have, as their zeroth character, one with non-zero width.
SEE ALSOgraphics(2), draw(2), cachechars(2), subfont(2)FONT(6)