<languageVersion: 1.0;>
   
  kernel sharpen
  <   namespace : "com.rphelan";
      vendor : "Ryan Phelan";
      version : 1;
      description : "Applies a sharpen effect to an image."; >
  {
      parameter float amount
      <
          minValue:0.0;
          maxValue:20.0;
          defaultValue:1.0;
      >;
      
      parameter float radius
      <
          minValue:0.0;
          maxValue:1.0;
          defaultValue:0.1;
      >;
  
      input image4 src;
      output float4 dst;
      
      void
      evaluatePixel()
      {
          // Obtain the input pixel coordinate
          float2 coord = outCoord();
      
          // Obtain the input pixel color
          float4 inputColor = sampleLinear(src, coord);
  
          // Start with the original color
          dst.rgb = inputColor.rgb;
          
          // Offset the color by the surrounding pixels
          float2 hOffset = float2(radius, 0.0);
          float2 vOffset = float2(0.0, radius);
          float4 left = sampleLinear(src, coord - hOffset) * amount;
          float4 right = sampleLinear(src, coord + hOffset) * amount;
          float4 top = sampleLinear(src, coord - vOffset) * amount;
          float4 bottom = sampleLinear(src, coord + vOffset) * amount;
          
          dst.rgb += (top.rgb);
          dst.rgb -= (bottom.rgb);
          dst.rgb += left.rgb;
          dst.rgb -= right.rgb;
          
          // set the alpha value equal to the alpha of the input
          dst.a = inputColor.a;
      }
  }