CSU540 Computer Graphics - Fall 2005 - Futrelle - Final Semester Programming Assignment #3 (SP3)

Shadows -- Professor Futrelle

DUE 11:59 PM, WEDNESDAY, DECEMBER 7th, 2005

Version of 7 December 2005

See note at end about a simple two-triangle shadow test. 12/7/05.

You can use your SP2 model

The assignment, SP3:

• The goal is to produce shadows in your scene.


• For each ray, if you get a hit on any triangles, use the closest triangle hit point, the visible triangle for that ray, as a new eyepoint, e' and form a new ray of the form e' + tL, where L is in the direction of the light source.


• If your new ray hits any triangle at all, then the point e' can't "see" the light source and is therefore in a shadow.


• Every point in a shadow should be illuminated only with ambient light. If not in a shadow, with the light source plus ambient.


• One slight cautionary note: Because of round-off, your new ray may appear to hit the surface that you hit with your initial ray. You can guard against this by setting e' = e' + epsilon x n, for some small epsilon that separates e' by at least a few pixels from the surface - with n being the normal to the triangle. After this adjustment it is still legitimate for the new ray to hit the triangle it's starting from. A surface can shadow itself. This self shadowing is also signaled by the negative n•L inner product.


• Make sketches of different possibilities to assure yourself that you understand what's going on.

That's all there is to it. Do the above, and shadows will appear.

Below is a figure that illustrates the simplest possible shadowing situation - one triangle shading one other triangle. This might help you to get your code designed and working properly.

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