code: public void setDiffuseIntensity(float r, float g, float b, float a) {
         setVec4("diffuse_intensity", r, g, b, a);
     }
docs: Set the diffuse light intensity.
  
  This designates the color of the diffuse reflection.
  It is multiplied by the material diffuse color to derive
  the hue of the diffuse reflection for that material.
  The built-in phong shader {@link GVRPhongShader} uses a {@code vec4} uniform named
  {@code diffuse_intensity} to control the intensity of diffuse light reflected.
  
  @param r red component (0 to 1)
  @param g green component (0 to 1)
  @param b blue component (0 to 1)
  @param a alpha component (0 to 1)