109 lines
2.0 KiB
C
109 lines
2.0 KiB
C
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/*
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* This file is part of the UCB release of Plan 9. It is subject to the license
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* terms in the LICENSE file found in the top-level directory of this
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* distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No
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* part of the UCB release of Plan 9, including this file, may be copied,
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* modified, propagated, or distributed except according to the terms contained
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* in the LICENSE file.
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*/
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#include <u.h>
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#include <libc.h>
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#include <draw.h>
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/*
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* This original version, although fast and a true inverse of
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* cmap2rgb, in the sense that rgb2cmap(cmap2rgb(c))
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* returned the original color, does a terrible job for RGB
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* triples that do not appear in the color map, so it has been
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* replaced by the much slower version below, that loops
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* over the color map looking for the nearest point in RGB
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* space. There is no visual psychology reason for that
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* criterion, but it's easy to implement and the results are
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* far more pleasing.
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*
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int
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rgb2cmap(int cr, int cg, int cb)
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{
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int r, g, b, v, cv;
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if(cr < 0)
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cr = 0;
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else if(cr > 255)
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cr = 255;
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if(cg < 0)
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cg = 0;
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else if(cg > 255)
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cg = 255;
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if(cb < 0)
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cb = 0;
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else if(cb > 255)
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cb = 255;
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r = cr>>6;
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g = cg>>6;
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b = cb>>6;
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cv = cr;
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if(cg > cv)
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cv = cg;
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if(cb > cv)
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cv = cb;
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v = (cv>>4)&3;
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return ((((r<<2)+v)<<4)+(((g<<2)+b+v-r)&15));
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}
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*/
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int
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rgb2cmap(int cr, int cg, int cb)
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{
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int i, r, g, b, sq;
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uint32_t rgb;
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int best, bestsq;
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best = 0;
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bestsq = 0x7FFFFFFF;
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for(i=0; i<256; i++){
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rgb = cmap2rgb(i);
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r = (rgb>>16) & 0xFF;
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g = (rgb>>8) & 0xFF;
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b = (rgb>>0) & 0xFF;
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sq = (r-cr)*(r-cr)+(g-cg)*(g-cg)+(b-cb)*(b-cb);
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if(sq < bestsq){
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bestsq = sq;
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best = i;
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}
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}
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return best;
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}
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int
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cmap2rgb(int c)
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{
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int j, num, den, r, g, b, v, rgb;
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r = c>>6;
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v = (c>>4)&3;
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j = (c-v+r)&15;
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g = j>>2;
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b = j&3;
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den=r;
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if(g>den)
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den=g;
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if(b>den)
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den=b;
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if(den==0) {
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v *= 17;
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rgb = (v<<16)|(v<<8)|v;
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}
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else{
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num=17*(4*den+v);
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rgb = ((r*num/den)<<16)|((g*num/den)<<8)|(b*num/den);
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}
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return rgb;
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}
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int
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cmap2rgba(int c)
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{
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return (cmap2rgb(c)<<8)|0xFF;
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}
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