Subversion Repositories planix.SVN

#include <u.h>
#include <libc.h>
#include <draw.h>

/*
 * This original version, although fast and a true inverse of
 * cmap2rgb, in the sense that rgb2cmap(cmap2rgb(c))
 * returned the original color, does a terrible job for RGB
 * triples that do not appear in the color map, so it has been
 * replaced by the much slower version below, that loops
 * over the color map looking for the nearest point in RGB
 * space.  There is no visual psychology reason for that
 * criterion, but it's easy to implement and the results are
 * far more pleasing. 
 *
int
rgb2cmap(int cr, int cg, int cb)
{
        int r, g, b, v, cv;

        if(cr < 0)
                cr = 0;
        else if(cr > 255)
                cr = 255;
        if(cg < 0)
                cg = 0;
        else if(cg > 255)
                cg = 255;
        if(cb < 0)
                cb = 0;
        else if(cb > 255)
                cb = 255;
        r = cr>>6;
        g = cg>>6;
        b = cb>>6;
        cv = cr;
        if(cg > cv)
                cv = cg;
        if(cb > cv)
                cv = cb;
        v = (cv>>4)&3;
        return ((((r<<2)+v)<<4)+(((g<<2)+b+v-r)&15));
}
*/

int
rgb2cmap(int cr, int cg, int cb)
{
        int i, r, g, b, sq;
        ulong rgb;
        int best, bestsq;

        best = 0;
        bestsq = 0x7FFFFFFF;
        for(i=0; i<256; i++){
                rgb = cmap2rgb(i);
                r = (rgb>>16) & 0xFF;
                g = (rgb>>8) & 0xFF;
                b = (rgb>>0) & 0xFF;
                sq = (r-cr)*(r-cr)+(g-cg)*(g-cg)+(b-cb)*(b-cb);
                if(sq < bestsq){
                        bestsq = sq;
                        best = i;
                }
        }
        return best;
}

int
cmap2rgb(int c)
{
        int j, num, den, r, g, b, v, rgb;

        r = c>>6;
        v = (c>>4)&3;
        j = (c-v+r)&15;
        g = j>>2;
        b = j&3;
        den=r;
        if(g>den)
                den=g;
        if(b>den)
                den=b;
        if(den==0) {
                v *= 17;
                rgb = (v<<16)|(v<<8)|v;
        }
        else{
                num=17*(4*den+v);
                rgb = ((r*num/den)<<16)|((g*num/den)<<8)|(b*num/den);
        }
        return rgb;
}

int
cmap2rgba(int c)
{
        return (cmap2rgb(c)<<8)|0xFF;
}