/* 04.03.1991 */
surface	ACShader (
			float Ka = 1.0;
			float Kd = 0.1;
			float Ks = 1.0;
			float Kt = 0.0;
			float transpAtt = 0;
			float shine = 20;
			color specularRGB = color(0.8, 0.8, 0.8);
			color emissionRGB = color(0, 0, 0);
			float emissionAtt = 0;
			)

{	color	Cspec;
	point	Nf, V;
	float	dist;
	
	Nf = faceforward(normalize(N), I);
	V = normalize(-I);
	
	Os = 1 - Kt   /* *pow(abs(V.Nf), transpAtt)  */;
	Ci = Os * Cs * (Ka * ambient() + Kd * diffuse(Nf));

	dist = depth(P);
	Ci += Os * emissionRGB / (1.0 + dist * emissionAtt);

	Cspec = (shine > 0.5) ? specularRGB * Ks * specular(Nf, V, 1.0/shine) : 0;
	Ci += Cspec;
	Oi = Os;
}