term% ls -F
term% cat index.txt
READCOLMAP(2)                 System Calls Manual                READCOLMAP(2)

       RGB, readcolmap, writecolmap - access display color map

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

       int  readcolmap(Display *d, RGB *map)

       int  writecolmap(Display *d, RGB *map)

       Colors  are  described by their 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 positions.

       A  color  map is an array of RGBs, of length 2^depth, giving the colors
       for pixels 0, 1, 2, etc.  On displays with color mapped  pixels  (typi‐
       cally  8-bit displays), one retrieves RGB color information by treating
       the pixel data as an offset into the color map.

       Readcolmap reads the color map for the given display into the  provided
       map,  which  must have enough space to hold it.  Writecolmap associates
       the given color map with the given display, if possible.  (The hardware
       might  not allow this.)  Both return 0 on success, or -1 on error, set‐
       ting errstr.

       Changing the hardware color map does not change the color map  used  by
       the  draw(2)  operator  to  convert  between  mapped  and true color or
       greyscale images, which is described in color(6).


       graphics(2), draw(3), color(6)