1 .TH READCOLMAP 3
2 .SH NAME
3 RGB, readcolmap, writecolmap \- access display color map
4 .SH SYNOPSIS
5 .B #include <u.h>
6 .br
7 .B #include <libc.h>
8 .br
9 .B #include <draw.h>
10 .PP
11 .PP
12 .ta \w'\fLvoid 'u
13 .PP
14 .B
15 int	readcolmap(Display *d, RGB *map)
16 .PP
17 .B
18 int	writecolmap(Display *d, RGB *map)
19 .fi
20 .SH DESCRIPTION
21 Colors are described by their red, green, and blue
22 light intensities, in an
23 .B RGB
24 datum:
25 .IP
26 .EX
27 .ta 6n
28 typedef
29 struct RGB {
30 	ulong red;
31 	ulong green;
32 	ulong blue;
33 } RGB;
34 .EE
35 .PP
36 Black is represented by zero in all three positions and
37 white has the maximum
38 .B unsigned
39 .B long
40 value in all three positions.
41 .PP
42 A color map is an array of
43 .BR RGB s,
44 of length
45 .if t \x'-.8n'2\u\s-1\fIdepth\fP\s+1\d,
46 .if n 2^\fIdepth\fP,
47 giving the colors for pixels 0, 1, 2, etc.
48 On displays with color mapped pixels
49 (typically 8-bit displays),
50 one retrieves RGB color information
51 by treating the pixel data as an offset
52 into the color map.
53 .PP
54 .I Readcolmap
55 reads the color map for the given display into the provided
56 .IR map ,
57 which must have enough space to hold it.
58 .I Writecolmap
59 associates the given color map with the given display, if possible.
60 (The hardware might not allow this.)
61 Both return 0 on success, or \-1 on error, setting
62 .IR errstr .
63 .PP
64 Changing the hardware color map does not change
65 the color map used by the
66 .MR draw (3)
67 operator to convert between
68 mapped and true color or greyscale images,
69 which is described in 
70 .MR color (7) .
71 .SH SOURCE
72 .B \*9/src/libdraw
73 .SH "SEE ALSO"
74 .MR graphics (3) ,
75 .MR draw (3) ,
76 .MR color (7)