surface ptc_occlusion string ptc_file default ptc float bias 01 maxdis

surface ptc_occlusion(
	string ptc_file = "default.ptc"; 
	float bias = 0.01, maxdist = 10; )
{
	normal Nf = faceforward( normalize(N), I );

	Ci = 1 - occlusion( P, Nf, 
		"filename", ptc_file, "pointbased", 1,
		"bias", 0.1, "clamp", 0, "hitsides", "front" );
}