1 #include <u.h>
2 #include <libc.h>
3 #include <draw.h>
4
5 /*
6 * This original version, although fast and a true inverse of
7 * cmap2rgb, in the sense that rgb2cmap(cmap2rgb(c))
8 * returned the original color, does a terrible job for RGB
9 * triples that do not appear in the color map, so it has been
10 * replaced by the much slower version below, that loops
11 * over the color map looking for the nearest point in RGB
12 * space. There is no visual psychology reason for that
13 * criterion, but it's easy to implement and the results are
14 * far more pleasing.
15 *
16 int
17 rgb2cmap(int cr, int cg, int cb)
18 {
19 int r, g, b, v, cv;
20
21 if(cr < 0)
22 cr = 0;
23 else if(cr > 255)
24 cr = 255;
25 if(cg < 0)
26 cg = 0;
27 else if(cg > 255)
28 cg = 255;
29 if(cb < 0)
30 cb = 0;
31 else if(cb > 255)
32 cb = 255;
33 r = cr>>6;
34 g = cg>>6;
35 b = cb>>6;
36 cv = cr;
37 if(cg > cv)
38 cv = cg;
39 if(cb > cv)
40 cv = cb;
41 v = (cv>>4)&3;
42 return ((((r<<2)+v)<<4)+(((g<<2)+b+v-r)&15));
43 }
44 */
45
46 int
rgb2cmap(int cr,int cg,int cb)47 rgb2cmap(int cr, int cg, int cb)
48 {
49 int i, r, g, b, sq;
50 ulong rgb;
51 int best, bestsq;
52
53 best = 0;
54 bestsq = 0x7FFFFFFF;
55 for(i=0; i<256; i++){
56 rgb = cmap2rgb(i);
57 r = (rgb>>16) & 0xFF;
58 g = (rgb>>8) & 0xFF;
59 b = (rgb>>0) & 0xFF;
60 sq = (r-cr)*(r-cr)+(g-cg)*(g-cg)+(b-cb)*(b-cb);
61 if(sq < bestsq){
62 bestsq = sq;
63 best = i;
64 }
65 }
66 return best;
67 }
68
69 int
cmap2rgb(int c)70 cmap2rgb(int c)
71 {
72 int j, num, den, r, g, b, v, rgb;
73
74 r = c>>6;
75 v = (c>>4)&3;
76 j = (c-v+r)&15;
77 g = j>>2;
78 b = j&3;
79 den=r;
80 if(g>den)
81 den=g;
82 if(b>den)
83 den=b;
84 if(den==0) {
85 v *= 17;
86 rgb = (v<<16)|(v<<8)|v;
87 }
88 else{
89 num=17*(4*den+v);
90 rgb = ((r*num/den)<<16)|((g*num/den)<<8)|(b*num/den);
91 }
92 return rgb;
93 }
94
95 int
cmap2rgba(int c)96 cmap2rgba(int c)
97 {
98 return (cmap2rgb(c)<<8)|0xFF;
99 }
100