//A directioanl Light source (diffuse)
class DLight extends Light{
    private Point3D l;   //light direction
    
    public DLight(float R, float G, float B, float dx, float dy, float dz) {
	super(R,G,B);
	l = new Point3D(dx,dy,dz);
	l.normalize();
    }
    public void Illuminate(Vertex3D V, Point3D eye, Surface S) {
	int f = PctInt.from_float(-(l.dot(V.normal)));
	if (f < 0) 
	    return; //no light.
	f = PctInt.mult(f,S.kd);
	Ivertex(f,S,V);
    }
}