BALLOC(2)                                               BALLOC(2)

          balloc, bfree, rdbitmap, wrbitmap, rdbitmapfile,
          wrbitmapfile - allocating, freeing, reading, writing bitmaps

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

          Bitmap *balloc(Rectangle r, int ldepth)

          void   bfree(Bitmap *b)

          void   rdbitmap(Bitmap *b, int ymin, int ymax, uchar *data)

          void   wrbitmap(Bitmap *b, int ymin, int ymax, uchar *data)

          Bitmap *rdbitmapfile(int fd)

          void   wrbitmapfile(int fd, Bitmap *b)

          A new bitmap is allocated with balloc; it will have the
          extent and ldepth (log base 2 of the number of bits per
          pixel) given by its arguments, and will be filled with
          zeros. The id field will have been set to the identifying
          number used by /dev/bitblt (see bit(3)), and the cache field
          will be zero.  Balloc returns 0 if the server has run out of
          bitmap resources.  Bfree frees the resources used by its
          argument bitmap.

          The remaining functions deal with moving groups of pixel
          values between bitmaps and user space or external files.
          There is a fixed format for the exchange and storage of bit-
          map data (see bitmap(6)).

          Rdbitmap reads rows of pixels from bitmap b into data. The
          rows read have y=ymin,ymin+1, ... ymax-1. Those rows must be
          within the range allowed by b.r.

          Wrbitmap replaces the specified rows of pixels in bitmap b
          with data.

          Rdbitmapfile creates a bitmap from data contained an exter-
          nal file (see bitmap(6) for the file format); fd is a file
          descriptor obtained by opening such a file for reading.  The
          returned bitmap is allocated using balloc.

          Wrbitmapfile writes bitmap b onto file descriptor fd, which
          should be open for writing.  The format is as described for

     BALLOC(2)                                               BALLOC(2)


          Rdbitmapfile and wrbitmapfile do not close fd.


          graphics(2), bitblt(2), bit(3), bitmap(6)

          These functions return 0 on failure, usually due to insuffi-
          cient memory.

          May set errstr.

          Ldepth must be 0, 1, 2, or 3.