#iChannel0 "file://./Textures/colorful.jpg"
#iChannel0::WrapMode "Mirror"

float pow2(float x) {
    return x*x;
}

/* euclidian */
float colDist(vec3 col1, vec3 col2) {
    return distance(col1, col2);
}

/* optimized L*a*b*-like */
float colDist2(vec3 col1, vec3 col2) {
    float r_mean = (col1.r + col2.r) * 256./2.0;

    float r = (col1.r - col2.r) * 256.;
    float g = (col1.g - col2.g) * 256.;
    float b = (col1.b - col2.b) * 256.;

    //float dc = sqrt((2.0+r_mean/256.) * pow2(r) 
    //    + 4.0*pow2(g) 
    //    + (2.0 + (255.-r_mean)/256.) * pow2(b) );
    float dc = sqrt( (512.+r_mean)*r*r/256.
        + 4.*g*g + 
        (767.-r_mean)*b*b/256.);

    return dc;
}

vec3 bestColor(vec3 col, vec3 pal[22]) {
    //col = pow(col, vec3(1./2.2));
    //col.r = pow(col.r,1./1.7);
    //col.g = pow(col.g,1./1.7);
    //col.b = pow(col.b,1./2.2);
    float mdist = colDist2(col, pal[0]);
    vec3 bcolor = pal[0];
    
    for(int i=0;i<22;i++) {
        float d = colDist2(col, pal[i]);
        if (d < mdist ) {
            mdist = d;
            bcolor = pal[i];
        }
    }  
    return bcolor;
}


void mainImage ( out vec4 fragColor, in vec2 fragCoord) {

    vec3 pal[22];

    pal[0]=vec3(0.953125,0.953125,0.953125);
    pal[1] = vec3(0.578125,0.6875,0.7578125);
    pal[2] = vec3(0.3359375,0.421875,0.5234375);
    pal[3] = vec3(0.19921875,0.234375,0.33984375);
    pal[4] = vec3(0.1015625,0.109375,0.171875);
    pal[5] = vec3(0.99609375,0.80078125,0.45703125);
    pal[6] = vec3(0.93359375,0.48828125,0.33984375);
    pal[7] = vec3(0.55859375,0.3359375,0.23046875);
    pal[8] = vec3(0.3984375,0.22265625,0.19140625);
    pal[9] = vec3(0.65234375,0.9375,0.4375);
    pal[10] = vec3(0.21875,0.71484375,0.390625);
    pal[11] = vec3(0.14453125,0.44140625,0.47265625);
    pal[12] = vec3(0.84765625,0.33984375,0.38671875);
    pal[13] = vec3(0.921875,0.19921875,0.296875);
    pal[14] = vec3(0.69140625,0.2421875,0.32421875);
    pal[15] = vec3(0.4609375,0.2578125,0.5390625);
    pal[16] = vec3(0.36328125,0.15234375,0.36328125);
    pal[17] = vec3(0.26953125,0.15625,0.234375);
    pal[18] = vec3(0.5859375,0.78125,0.93359375);
    pal[19] = vec3(0.25390625,0.6484375,0.9609375);
    pal[20] = vec3(0.23046875,0.36328125,0.78515625);
    pal[21] = vec3(0.24609375,0.24609375,0.453125);


    vec2 uv = (fragCoord/iResolution.y);
    
    vec4 col = vec4(0,0,0,1.0);

    vec3 texCol = texture(iChannel0, uv).rgb;
    vec3 tmp = bestColor( texCol, pal);

    col.rgb = tmp;
    fragColor = col;
}