CIImage Color Wheel.jstalk

var filter = [COSQuickCIFilter quickFilterWithKernel:"""
bool isOdd(int v) {
    float dividend = float(v) / 2.0;
    return dividend != floor(dividend);
}

vec4 hsvToRgb(vec4 hsv) {
    float h = hsv.r;
    float s = hsv.g;
    float v = hsv.b;
    int i = int(floor(h));
    float f = isOdd(i) ? h - float(i) : 1.0 - (h - float(i));
    float m = v * (1.0 - s);
    float n = v * (1.0 - s * f);
    vec4 result = (i == 0) ? vec4(v, n, m, hsv.a) : ((i == 1) ?
        vec4(n, v, m, hsv.a) : ((i == 2) ? vec4(m, v, n, hsv.a) : ((i == 3) ?
        vec4(m, n, v, hsv.a) : ((i == 4) ? vec4(n, m, v, hsv.a) : ((i == 5) ?
        vec4(v, m, n, hsv.a) : vec4(v, n, m, hsv.a))))));
    
    return (h == -1.0) ? vec4(v, v, v, hsv.a) : result;
}

kernel vec4 colorWheel(float radius) {
    
    vec2 center = vec2(radius, radius);
    vec2 v0 = destCoord();
    vec2 v1 = vec2(v0.x, radius);
    float a = distance(v0, v1);
    float b = distance(v1, center);
    
    float angle = atan(a,b);
    
    float pi = 3.14159265;
    angle = (v0.x>radius)?((v0.y>radius)?
        (atan(b,a)+pi/2.0):atan(a,b)+pi):
        (v0.y<radius)?(atan(b,a)+(pi*1.5)):atan(a,b);
    
    vec4 theColor = vec4(1.0);
    
    theColor.r = (angle * 3.0) / pi;
    
    // make it a cirlce
    float dist = length(destCoord() - center);
    theColor.a = clamp(radius - dist, 0.0, 1.0);
    
    return premultiply(hsvToRgb(theColor));
}"""];

[filter addKernelArgument:[NSNumber numberWithInt:100]];

[COSImageTools viewCIImage:[filter outputImage] inWindowNamed:"Color Wheel" extent:CGRectMake(0, 0, 200, 200)];