term% cat index.txt READCOLMAP(2) System Calls Manual READCOLMAP(2)
NAME
RGB, readcolmap, writecolmap - access display color map
SYNOPSIS
#include <u.h>
#include <libc.h>
#include <draw.h>
void readcolmap(Display *d, RGB *map)
void writecolmap(Display *d, RGB *map)
DESCRIPTION
Colors are described by their red, green, and blue light intensities,
in an RGB datum:
typedef
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).
SOURCE
/sys/src/libdraw
SEE ALSO
graphics(2), draw(3), color(6)
READCOLMAP(2)