man bitmap () - external format for bitmaps


bitmap - external format for bitmaps


#include <libc.h> #include <libg.h>


Bitmaps are described in graphics(3g). Fonts and bitmaps are stored in external files in machine-independent formats.

Bitmap files are read and written using rdbitmapfile and wrbitmapfile (see balloc(3g)). 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 containing pixel r.max.x1. A pixel with x-coordinate = x in a bitmap with ldepth = l will appear as contiguous bits in a byte, with the pixel's high order bit starting at the byte's bit number 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(3g) also deal with rows in this format, stored in user memory.

Some small images, in particular 4848 face files and 1616 cursors, are 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.) 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.