/*
surface shader:
	oilstain

creator:
	Nick Meshes, DePaul University

description:
	based on metallic
	should produce brighter greener colors

parameters:
	none
*/

#define GREEN color (0,0,0.5)
#define BLUE0 color (0,0.1,0.4)
#define BLUE1 color (0,0.2,0.3)
#define BLUE2 color (0,0.25,0.25)
#define BLUE3 color (0,0.3,0.2)
#define BLUE4 color (0,0.35,0.15)
#define BLUE5 color (0,0.4,0.1)
#define BLUE6 color (0,0.5,0)

surface oilstain(){
	point Nf = normalize(faceforward(N,I));
	point nI = normalize(-I);
	point R;
	point Rworld;
	color Ct = color (1,1,1);
	float whichone;
	
	R = 2 * Nf * (Nf . nI) - nI;
	Rworld = normalize(ntransform("world", R));
	whichone = 0.5 * zcomp(Rworld) + 0.5;
	Ct = spline(whichone, BLUE6, BLUE6, BLUE6, BLUE6, BLUE6, BLUE6, 
				BLUE5, BLUE4, BLUE3, BLUE2, BLUE1, BLUE0, GREEN );
	Oi = Os;
	Ci = Os * Cs * Ct;
}