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WebSVN – planix.SVN – Blame – /os/branches/planix-v0/sys/src/libdraw/rgb.c – Rev 2

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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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	ulong 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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}