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Plan 9 - man page for bitmap (plan9 section 6)

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BITMAP(6)										BITMAP(6)

       bitmap - external format for bitmaps

       #include <libg.h>

       Bitmaps	are  described in graphics(2).	Fonts and bitmaps are stored in external files in
       machine-independent formats.

       Bitmap files are read and written using rdbitmapfile and wrbitmapfile (see balloc(2)).	A
       bitmap file starts with 5 decimal strings: ldepth, r.min.x, r.min.y, r.max.x, and r.max.y.
       Each number is right-justified and blank padded in 11 characters,  followed  by	a  blank.
       The  rest of the file contains the r.max.y-r.min.y rows of bitmap data.	A row consists of
       the byte containing pixel r.min.x and all the bytes up to and including the byte  contain-
       ing  pixel  r.max.x-1.	A  pixel  with x-coordinate = x in a bitmap with ldepth = ld will
       appear as w = 2^ld contiguous bits in a byte, with the pixel's high order bit starting  at
       the  byte's  bit number w*(x mod (8/w)), where bits within a byte are numbered 0 to 7 from
       the high order to the low order bit.  If w is greater than 8, it is a multiple  of  8,  so
       pixel  values take up an integral number of bytes.  Rows contain integral number of bytes,
       so there may be some unused pixels at either end of a row.

       The rdbitmap and wrbitmap functions described in balloc(2) also deal  with  rows  in  this
       format, stored in user memory.

       Some  small  images,  in  particular 48x48 face files as used by seemail (see mail(1)) and
       16x16 cursors, can be stored textually, suitable for inclusion in C source.  Each line  of
       text  represents one scan line as a comma-separated sequence of hexadecimal bytes, shorts,
       or words in C format.  For cursors, each line defines a pair  of  bytes.   (It  takes  two
       images to define a cursor; each must be stored separately to be processed by programs such
       as tweak(1).)  Face files of one bit per pixel are stored as a sequence of  shorts,  those
       of larger pixel sizes as a sequence of longs.  Software that reads these files must deduce
       the image size from the input; there is no header.  These formats reflect  history  rather
       than design.

       tweak(1), graphics(2), bitblt(2), balloc(2), face(6), font(6)

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