readcolmap.3 (1531B)
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)