I was experimenting with creating shadows from not fully formed whirlpools, such as this one:
The direction of the light was essentially from bottom to top in this image. I think I understand most of what is happening here after I drew this diagram. The red arrows are of course light rays, the black lines are various normals, and the blue figure represents the flat water surface and that convex part that is beginning to form the whirlpool.:
The halo is formed from converging rays. Also, the halo at the top is brighter than the bottom because the the rays on the flat surface and the convex surface bend toward each other at the top, while at the bottom they bend in the same direction. So the rays converge faster at the top and as a result you get more light.
But I am confused by how uniform the shadow appears to be. I would have thought there would have been one area that would have been darkest (where most of the light is scattered from - this would depend, I think, on the angle between the source and the water surface) and then gradually get less dark as you moved away from that point?
Maybe this is true but my eye is not sensitive enough, or the water is not deep enough, to see this?
