<languageVersion : 1.0;>
  
  kernel NewFilter
  <   namespace : "Vortex";
      vendor : "Mr.doob";
      version : 1;
      description : "Vortex effect";
  >
  {
      input image4 src;
      output pixel4 dst;
      
      parameter float2 imgSize
      <
          defaultValue : float2(512.0, 512.0);
          minValue : float2(0.0,0.0);
          maxValue : float2(512.0,512.0);
      >;
      
      parameter float2 center
      <
          defaultValue : float2(256.0, 256.0);
          minValue : float2(0.0,0.0);
          maxValue : float2(512.0,512.0);        
      >;
      
      parameter float2 offset;
  
      void evaluatePixel()
      {        
          float2 pos = (outCoord() - center) / imgSize;
  
          float pi = 3.141592653589793;
          float a = atan(pos.y,pos.x);
          float r = sqrt(pow(pos.x,2.0)+pow(pos.y,2.0));
          
          float u = 0.0;
          float v = 0.0;
          float w = 0.0;
          
          u += offset.x;
          v += offset.y;
          
          // This is where the magic happens
          
          u += .5*a/pi + .1*r;
          v += pow(r,.1);
          w += 1.0;
  
          // End of the magic
  
          u *= imgSize.x;
          v *= imgSize.y;
          
          if (u < 0.0) u += imgSize.x * ceil(-u / imgSize.x);
          if (v < 0.0) v += imgSize.y * ceil(-v / imgSize.y);
          if (u > imgSize.x) u -= imgSize.x * floor(u / imgSize.x);
          if (v > imgSize.y) v -= imgSize.y * floor(v / imgSize.y);
          
          dst = sampleNearest(src,float2(u, v));
          dst.rgb *= w;
      }
  }