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     RGBPIX(2G)                                             RGBPIX(2G)

          RGB, rgbpix, rdcolmap, wrcolmap - handle color screens

          ulong rgbpix(Bitmap *b, RGB rgb)

          void  rdcolmap(Bitmap *b, RGB *map)

          void  wrcolmap(Bitmap *b, RGB *map)

          Colors are described by the red, green, and blue light
          intensities, in an RGB datum:

               struct RGB {
                     ulong red;
                     ulong green;
                     ulong blue;
               } RGB;

          Black is represented by zero in all three positions and
          white has the maximum unsigned long value in all three posi-

          Some of the graphics functions, such as point (see
          bitblt(2)), take a pixel value argument, which is a single
          unsigned long.  For a given bitmap, rgbpix returns the pixel
          value with a color closest to the color represented by the
          rgb argument.

          There is a colormap associated with each Bitmap.  A colormap
          is an array of RGBs, of length 2^(2^ldepth), giving the col-
          ors for pixels 0, 1, 2, etc.

          Rdcolmap reads the colormap for the given bitmap into the
          provided map, which must have enough space to hold it.
          Wrcolmap associates the given colormap with the given bit-
          map, if possible.  (The hardware might not allow this.)

          These functions work only for the screen bitmap.  This
          interface will have to be refined for screens with more than
          8 bits per pixel.