public bool IsShadowed(Light l, Tuple p)
{
Tuple v = l.Position - p;
float distance = v.Magnitude();
Tuple direction = v.Normalize();
Ray r = new Ray(p, direction);
List <Intersection> intersections = Intersection(r);
RayTracer.Intersection h = RayTracer.Intersection.Hit(intersections);
return((h != null) && (h.T < distance));
}