code: public void setAmbientIntensity(float r, float g, float b, float a) {
         setVec4("ambient_intensity", r, g, b, a);
     }
docs: Set the ambient light intensity.
  
  This designates the color of the ambient reflection.
  It is multiplied by the material ambient color to derive
  the hue of the ambient reflection for that material.
  The built-in phong shader {@link GVRPhongShader} uses a {@code vec4} uniform named
  {@code ambient_intensity} to control the intensity of ambient 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)