/*	
	Example shader for point-based occlusion.
	Raytracing is not required.
	Refer to the Pixar document, pointbased.html
	The source code for these shaders was taken
	from Pixar's AppNotes. Malcolm Kesson 15 Oct 08
*/
surface
wgsBakePTC(string bakename = "";
{
normal Nn = normalize(N);
float a = area(P, "dicing"); // micropolygon area
color areaval;

// average opacity
float opacity = 0.333333 * (Os[0] + Os[1] + Os[2]); 
a *= opacity; // reduce area if non-opaque  

if(a > 0)
	bake3d(bakename, "_area", P, Nn,
					 "interpolate", 1, "_area", a);
		//we can add more data to bake if we want, like N
			//	bake3d(bakename, "_area,N", P, Nn,
			//	"interpolate", 1, "_area", a, "N", Nn);
Ci = Cs * Os;
Oi = Os;
}