code: package org.sunflow.core.shader;
  
  import org.sunflow.SunflowAPI;
  import org.sunflow.core.LightSample;
  import org.sunflow.core.ParameterList;
  import org.sunflow.core.Shader;
  import org.sunflow.core.ShadingState;
  import org.sunflow.image.Color;
  
  public class ViewCausticsShader implements Shader {
      public boolean update(ParameterList pl, SunflowAPI api) {
          return true;
      }
  
      public Color getRadiance(ShadingState state) {
          state.faceforward();
          state.initCausticSamples();
          // integrate a diffuse function
          Color lr = Color.black();
          for (LightSample sample : state)
              lr.madd(sample.dot(state.getNormal()), sample.getDiffuseRadiance());
          return lr.mul(1.0f / (float) Math.PI);
  
      }
  
      public void scatterPhoton(ShadingState state, Color power) {
      }
  }