FONT(7) FONT(7)
NAME
font, subfont - external format for fonts and subfonts
SYNOPSIS
#include <draw.h>
DESCRIPTION
Fonts and subfonts are described in cachechars(3).
External bitmap 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 specifica-
tions. The header contains two numbers: the height and the
ascent, both in pixels. The height is the inter-line spac-
ing and the ascent is the distance from the top of the line
to the baseline. These numbers are chosen to display con-
sistently 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(3)). 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(3)). The format for subfont files
is: an image containing character glyphs, followed by a sub-
font header, followed by character information. The image
has the format for external image files described in
image(7). 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(3)) means that fonts should have, as their zeroth char-
acter, one with non-zero width.
Font Names
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FONT(7) FONT(7)
Font names in Plan 9 from User Space are a small language
describing a font. The most basic form is the name of an
existing bitmap font file, following the convention:
/lib/font/bit/name/range.size.font
where size is approximately the height in pixels of the
lower case letters (without ascenders or descenders). Range
gives some indication of which characters will be available:
for example ascii, latin1, euro, or unicode. Euro includes
most European languages, punctuation marks, the Interna-
tional Phonetic Alphabet, etc., but no Oriental languages.
Unicode includes every character for which appropriate-sized
images exist on the system.
In Plan 9 from User Space, the font files are rooted in
$PLAN9/font instead of /lib/font/bit, but to keep old refer-
ences working, paths beginning with /lib/font/bit are inter-
preted as references to the actual font directory.
Fonts need not be stored on disk in the Plan 9 format. If
the font name has the form /mnt/font/name/size/font, fontsrv
is invoked to synthesize a bitmap font from the operating
system's installed vector fonts. The command fontsrv -p .
lists the available fonts. See fontsrv(4) for more.
If the font name has the form scale*fontname, where scale is
a small decimal integer, the fontname is loaded and then
scaled by pixel repetition.
The Plan 9 bitmap fonts were designed for screens with pixel
density around 100 DPI. When used on screens with pixel
density above 200 DPI, the bitmap fonts are automatically
pixel doubled. Similarly, fonts loaded from fontsrv(4) are
automatically doubled in size by varying the effective size
path element. In both cases, the effect is that a single
font name can be used on both low- and high-density displays
(or even in a window moved between differing displays) while
keeping roughly the same effective size.
For more control over the fonts used on low- and high-
density displays, if the font name has the form
lowfont,highfont, lowfont is used on low-density displays
and highfont on high-density displays. In effect, the
behavior described above is that the font name
/lib/font/bit/lucsans/euro.8.font
really means
/lib/font/bit/lucsans/euro.8.font,2*/lib/font/bit/lucsans/euro.8.font
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FONT(7) FONT(7)
and similarly
/mnt/font/LucidaGrande/15a/font
really means
/mnt/font/LucidaGrande/15a/font,/mnt/font/LucidaGrande/30a/font
Using an explicit comma-separated font pair allows finer
control, such as using a Plan 9 bitmap font on low-density
displays but switching to a system-installed vector font on
high-density displays:
/lib/font/bit/lucsans/euro.8.font,/mnt/font/LucidaGrande/30a/font
FILES
/usr/local/plan9/font/* font directories
SEE ALSO
graphics(3), draw(3), cachechars(3), subfont(3)
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