/* Copyrighted Pixar 1989 */
/* From the RenderMan Companion p.352 */
/* Listing 16.16  Displacement shader to dent a surface */

surface
bulb(
    float Ks = 1.0,
	  Ka = 0.1,
	  Kd = 0.3,
	  Ksilh = 0.05,
	  roughness = 0.1,
	  silhrough = 0.55;
    color specularcolor = 1)

{
     point Nf = faceforward(normalize(N), I);
     point V = -normalize(I);

     Oi = Os;
     Ci = Oi*Cs*(Ka*ambient() + Kd*diffuse(Nf)) +
	  specularcolor*Ks*specular(Nf, V, roughness)
	  + specularcolor*Ksilh*(pow(1.0 - (V.Nf),1/silhrough));
}