Subfonts are the components of fonts that hold the character images.
A font comprises an array of subfonts; see cachechars(2). A new
Subfont is allocated and initialized with allocsubfont. See cachechars(2)
for the meaning of n, height, ascent, and info, and the arrangement
of characters in image i. The name is
used to identify the subfont in the subfont cache; see the descriptions
lookupsubfont and installsubfont (q.v.). The appropriate fields
of the returned Subfont structure are set to the passed arguments,
and the image is registered as a subfont with the graphics device
draw(3). Allocsubfont returns 0 on failure.
Freesubfont frees a subfont and all its associated structure including
the associated image. Since freesbufont calls free on f–>info, if
f–>info was not allocated by malloc(2) it should be zeroed before
A number of subfonts are kept in external files. The convention
for naming subfont files is:|
where size is approximately the height in pixels of the lower
case letters (without ascenders or descenders). If there is only
one version of the subfont, the .depth extension is elided. Class
describes the range of runes encoded in the subfont: ascii, latin1,
Subfonts are cached within the program, so a subfont shared between
fonts will be loaded only once. Installsubfont stores subfont
f under the given name, typically the file name from which it
was read. Uninstallsubfont removes the subfont from the cache.
Finally, lookupsubfont searches for a subfont with the given
name in the cache and returns it, or nil if no such subfont exists.
Subfontname is used to locate subfonts given their names within
the fonts. The default version constructs a name given the cfname,
its name within the font, fname, the name of the font, and the
maximum depth suitable for this subfont. This interface allows
a partially specified name within a font to be resolved at
run–time to the name of a file holding a suitable subfont. Although
it is principally a routine internal to the library, subfontname
may be substituted by the application to provide a less file–oriented
subfont naming scheme.
The format of a subfont file is described in font(6). Briefly,
it contains a image with all the characters in it, followed by
a subfont header, followed by character information. Readsubfont
reads a subfont from the file descriptor fd. The name is used
to identify the font in the cache. The dolock argument specifies
the routine should synchronize use of the Display with other processes;
for single–threaded applications it may always be zero. Readsubfonti
does the same for a subfont whose associated image is already
in memory; it is passed as the argument im. In other words, readsubfonti
reads only the header and character
information from the file descriptor.
Writesubfont writes on fd the part of a subfont file that comes
after the image. It should be preceded by a call to writeimage
Stringsubfont is analogous to string (see draw(2)) for subfonts.
Rather than use the underlying font caching primitives, it calls
draw for each character. It is intended for stand–alone environments
such as operating system kernels. Strsubfontwidth returns the
width of the string s in as it would appear if drawn with
stringsubfont in Subfont f.
Mkfont takes as argument a Subfont s and returns a pointer to
a Font that maps the character images in s into the Runes min