/****************************************************************************
 * (Just a piece of) cel.sl
 *
 * from:
 *   _Advanced RenderMan: Creating CGI for Motion Picture_, 
 *   by Anthony A. Apodaca and Larry Gritz, Morgan Kaufmann, 1999.
 *
 ****************************************************************************/

#include "material.h"


color LocIllumCelDiffuse ( normal N; )
{
    color C = 0;
    extern point P;
    illuminance (P, N, PI/2) {
	/* Must declare because extern L & Cl because we're in a function */
	extern vector L;  extern color Cl; 
	float nondiff = 0;
	lightsource ("__nondiffuse", nondiff);
	if (nondiff < 1) {
	    C += Cl * ((1-nondiff) * smoothstep(0,0.1,N.normalize(L)));
	}
    }
    return C;
}

color MaterialCel (normal Nf;  color Cs;
                   float Ka, Kd, Ks, roughness, specsharpness;)
{
    extern vector I;
    vector IN = normalize(I), V = -IN;
    return   Cs * (Ka*ambient() + Kd*LocIllumCelDiffuse(Nf))
            + Ks * LocIllumGlossy (Nf, V, roughness/10, specsharpness);
}

surface
cel ( float Ka = 1, Kd = 1, Ks = .5, roughness = 0.25;)
{
    normal Nf = faceforward(normalize(N),I);

    Ci = MaterialCel (Nf, Cs, Ka, Kd, Ks, roughness, 0.25);
}