/**
* Trace the shadow ray, attenuating the sample's color by the opacity of
* intersected objects.
*
* @param state shading state representing the point to be shaded
*/
public void traceShadow(ShadingState state)
{
Color opacity = state.traceShadow(shadowRay);
Color.blend(ldiff, Color.BLACK, opacity, ldiff);
Color.blend(lspec, Color.BLACK, opacity, lspec);
}