OSL / Spiral

Hynotizing OSL...

This morning, with question on creating Spiral texture, I am doing OSL exercise by again looking at already existing code, this time from WebGL code:
http://stackoverflow.com/questions/4638317/how-to-implement-this-rotating-spiral-in-webgl

Thanks to the code example solution above, we get to see the result from few simple lines of code.

OSL Spiral

/*

float logspiral(float sita, float r, float phi, float n){
    sita += log(r) * phi;
    return fract(sita) * n);
}
*/

shader spiral(
    color ColorA = color(1,0,0),
    color ColorB = color(0,1,0),
    vector Vector = P,
    float Rotation = 0.0,
    float Thickness = 15.0,
    float ModAngle = 30.0,
    output color ColOut = color(0.2)

)

{
    color f;
    vector p = Vector;
    
    float angle = 0.0;
    float radius = length(p);
    if(p[0] != 0.0 && p[1] != 0.0){
        angle = degrees(atan2(p[0], p[1]));
    }
    float amod = mod(angle+30.0 * Rotation-120.0 * log(radius), ModAngle);
    if(amod<Thickness){
        f = color(0.0,0.0,0.0);
    } else {
        f = color(1.0,1.0,1.0);
    }


    //ColOut = f; // this maybe useful as mask
    
    ColOut = mix(ColorA, ColorB, f);

}

I think this is as simple as it gets to get a Spiral texture. But probably not the only way to get Spiral.

Texture Coordinate and Mapping

Still not sure if I am doing it correctly with the mapping, but this is my solution so far.

Further Milking of OSL Spiral

Almost always every basic function that creates a certain basic texture can be further tweaked and modified. Just by multiplying or adding values, it will adjust the look. This is the fun part.

/*

float logspiral(float sita, float r, float phi, float n){
    sita += log(r) * phi;
    return fract(sita) * n);
}
*/

shader spiral(
    color ColorA = color(1,0,0),
    color ColorB = color(0,1,0),
    int Freq = 2,
    vector Vector = P,
    float Rotation = 0.0,
    float Thickness = 15.0,
    float ModAngle = 30.0,
    output color ColOut = color(0.2)

)

{
    color f;
    vector p = Vector;
    
    float angle = 0.0;
    float radius = length(p);
    if(p[0] != 0.0 && p[1] != 0.0){
        angle = degrees(atan2(p[0], p[1]));
    }
    float amod = mod(angle * Freq * 0.25 + 10.0 * Rotation-120.0 * log(radius), ModAngle);
    if(amod<Thickness){
        f = color(0.0,0.0,0.0);
    } else {
        f = color(1.0,1.0,1.0);
    }


    //ColOut = f; // this maybe useful as mask
    
    ColOut = mix(ColorA, ColorB, f);

}

Other Related Links

http://stackoverflow.com/questions/7610631/glsl-mod-vs-hlsl-fmod