surface glass(float eta=1.5;
		float	Ka = 1;
		float	Kd = 1;
		float	Ks = 1;
		float	roughness = 0.5;) {
	vector	R,T;
	vector  	In;
	float		Kr,Kt;	

	// Normalize some vectors
	N	=	normalize(N);
	In	=	normalize(I);

	// Compute the reflection and refraction
	fresnel(In,N,(I.N < 0 ? 1/eta : eta),Kr,Kt,R,T);

	// Add the direct illumination if applicable
	if ((In.N) < 0) {
	}

	// Trace the reflection / refraction
	if (Kr > 0.01)	Ci	+=	Kr*trace(P,R);
	if (Kt > 0.01)	Ci	+=	Kt*trace(P,T);

	Ci	*=	Os;
	Oi	=	Os;
}

