FONT(7)                Miscellaneous Information Manual                FONT(7)

       font, subfont - external format for fonts and subfonts

       #include <draw.h>

       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 specifications.  The header contains two
       numbers: 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(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 subfont 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 character, one with non-zero width.

   Font Names
       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:


       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 International 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 references working, paths
       beginning with /lib/font/bit are interpreted 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

       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


       really means


       and similarly


       really means


       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:


              font directories

       graphics(3), draw(3), cachechars(3), subfont(3)