Julia fractal rendering with Adobe Pixel Bender

julia.pbk

<languageVersion : 1.0;>

#define PI              3.1415926535897932384626433832795

kernel JuliaViewer
<   namespace : "Newgrounds";
    vendor : "Newgrounds";
    version : 1;
    description : "Julia Set Fractal Viewer";
>
{
    parameter float2 viewPos<
        minValue: float2( -4.0, -4.0);
        maxValue: float2(4.0, 4.0);
        defaultValue: float2(0.0, 0.0); >;
    parameter float viewZoom<
        minValue: 0.5;
        maxValue: 200.0;
        defaultValue: 1.0; >;
    parameter float2 c<
        minValue: float2(-2.0, -2.0);
        maxValue: float2(2.0, 2.0);
        defaultValue: float2(0.0, 0.0); >;
        
    parameter float colorShift<
        minValue: -1.0;
        maxValue: 1.0;
        defaultValue: 0.0; >;
        
    const float     RENDER_HEIGHT       = 512.0;
    const float     RENDER_WIDTH        = 512.0;
    const int       MAX_ITERATIONS      = 256;
    const float     MAX_DIST            = 4.0;
    const pixel4    SET_COLOR           = pixel4(0, 0, 0, 1.0);
    
    output pixel4 dst;

    region needed(
        region output_region,
        imageRef input_image )
    {
        return nowhere();
    }
    
    region changed(
        region input_region,
        imageRef input_image )
    {
        return nowhere();
    }
    
    region generated()
    {
        return region(float4(0, 0, RENDER_WIDTH, RENDER_HEIGHT));
    }

    void
    evaluatePixel()
    {
        float2 z = float2( (outCoord().x*2.0/RENDER_WIDTH - 1.0 )/viewZoom + viewPos.x, (outCoord().y*2.0/RENDER_WIDTH - 1.0 )/viewZoom - viewPos.y );
        float dist;
        float colorVal;

        int count = 0;
        do
        {
            z = float2(z.x*z.x - z.y*z.y + c.x, 2.0*z.x*z.y + c.y);
            dist = z.x*z.x + z.y*z.y;
            count++;
        } while(dist < MAX_DIST && count < MAX_ITERATIONS);
                   
        if(count < MAX_ITERATIONS)
        {
            colorVal = float(count) + 1.0 - log2(log2(dist));
            colorVal /= 50.0;
            colorVal += colorShift;
            dst = pixel4( abs( mod(colorVal, 2.0) - 1.0), abs( mod(colorVal+.33, 2.0) - 1.0), abs( mod(colorVal+.66, 2.0) - 1.0), 1.0 );
        }
        else dst = SET_COLOR;

    }
}