code: package org.sunflow.core.shader;
  
  import org.sunflow.SunflowAPI;
  import org.sunflow.core.ParameterList;
  import org.sunflow.core.Ray;
  import org.sunflow.core.Shader;
  import org.sunflow.core.ShadingState;
  import org.sunflow.image.Color;
  import org.sunflow.math.OrthoNormalBasis;
  import org.sunflow.math.Vector3;
  
  public class ShinyDiffuseShader implements Shader {
      private Color diff;
      private float refl;
  
      public ShinyDiffuseShader() {
          diff = Color.GRAY;
          refl = 0.5f;
      }
  
      public boolean update(ParameterList pl, SunflowAPI api) {
          diff = pl.getColor("diffuse", diff);
          refl = pl.getFloat("shiny", refl);
          return true;
      }
  
      public Color getDiffuse(ShadingState state) {
          return diff;
      }
  
      public Color getRadiance(ShadingState state) {
          // make sure we are on the right side of the material
          state.faceforward();
          // direct lighting
          state.initLightSamples();
          state.initCausticSamples();
          Color d = getDiffuse(state);
          Color lr = state.diffuse(d);
          if (!state.includeSpecular())
              return lr;
          float cos = state.getCosND();
          float dn = 2 * cos;
          Vector3 refDir = new Vector3();
          refDir.x = (dn * state.getNormal().x) + state.getRay().getDirection().x;
          refDir.y = (dn * state.getNormal().y) + state.getRay().getDirection().y;
          refDir.z = (dn * state.getNormal().z) + state.getRay().getDirection().z;
          Ray refRay = new Ray(state.getPoint(), refDir);
          // compute Fresnel term
          cos = 1 - cos;
          float cos2 = cos * cos;
          float cos5 = cos2 * cos2 * cos;
  
          Color ret = Color.white();
          Color r = d.copy().mul(refl);
          ret.sub(r);
          ret.mul(cos5);
          ret.add(r);
          return lr.add(ret.mul(state.traceReflection(refRay, 0)));
      }
  
      public void scatterPhoton(ShadingState state, Color power) {
          Color diffuse;
          // make sure we are on the right side of the material
          state.faceforward();
          diffuse = getDiffuse(state);
          state.storePhoton(state.getRay().getDirection(), power, diffuse);
          float d = diffuse.getAverage();
          float r = d * refl;
          double rnd = state.getRandom(0, 0, 1);
          if (rnd < d) {
              // photon is scattered
              power.mul(diffuse).mul(1.0f / d);
              OrthoNormalBasis onb = state.getBasis();
              double u = 2 * Math.PI * rnd / d;
              double v = state.getRandom(0, 1, 1);
              float s = (float) Math.sqrt(v);
              float s1 = (float) Math.sqrt(1.0 - v);
              Vector3 w = new Vector3((float) Math.cos(u) * s, (float) Math.sin(u) * s, s1);
              w = onb.transform(w, new Vector3());
              state.traceDiffusePhoton(new Ray(state.getPoint(), w), power);
          } else if (rnd < d + r) {
              float cos = -Vector3.dot(state.getNormal(), state.getRay().getDirection());
              power.mul(diffuse).mul(1.0f / d);
              // photon is reflected
              float dn = 2 * cos;
              Vector3 dir = new Vector3();
              dir.x = (dn * state.getNormal().x) + state.getRay().getDirection().x;
              dir.y = (dn * state.getNormal().y) + state.getRay().getDirection().y;
              dir.z = (dn * state.getNormal().z) + state.getRay().getDirection().z;
              state.traceReflectionPhoton(new Ray(state.getPoint(), dir), power);
          }
      }
  }