<languageVersion : 1.0;>
  
  kernel SteepParallaxMapping
  <   namespace : "com.derschmale";
      vendor : "";
      version : 1;
      description : "Steep Parallax Mapping is a bump mapping technique that can create parallax movement and self-occlusion. The normal map that has to be provided must contain height data in the alpha channel.";
  >
  {
      input image4 texture;
      input image4 heightMap;
      output pixel4 dst;
      
      parameter float3 eyePosition
          <   
              minValue : float3(-1000.0, -1000.0, -1000.0);
              maxValue : float3(1000.0, 1000.0, 1000.0);
              defaultValue : float3(0.0, 0.0, 1.0);
          >;
          
      parameter float bumpScale
          < 
              minValue : 0.0;
              maxValue : 1.0;
              defaultValue : 0.05;
          >;
      parameter int steps
          <
              minValue : 1;
              maxValue : 20;
              defaultValue : 10;
          >;
      
      
      void evaluatePixel()
      {
          float height = 1.0;
          float numSteps = float(steps);
          float step;
          float2 delta;
          float2 offsetCoord = outCoord();
          float3 eyeNorm = normalize(eyePosition);
          float sampleHeight = sampleNearest(heightMap, offsetCoord).r;
                  
          numSteps = mix(numSteps*2.0, numSteps, eyeNorm.z);
          
          step = 1.0/numSteps;
          delta = eyePosition.xy * bumpScale / (eyePosition.z * numSteps);
          
          /* can't loop, so hardcode the same piece over and over */
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          if (sampleHeight < height) {
              height -= step;
              offsetCoord += delta;
              sampleHeight = sampleNearest(heightMap, offsetCoord).r;
          }
          
          dst = sampleNearest(texture, offsetCoord);
          
          
      }
  }