Light to close poly


When you use the zfail approch to render shadow volums and your light source get to close the poly, then the capped volume will collaps. How can I avoid that…???

I have read in nvidia docs that you are supposed to clip the volume some how, but I don’t understand how? If somene could give me a hint I would apprichiate that


You don’t need to clip if you use the “infinite shadow volumes” approach ( Cass & Kilgard ). Since you said “z-fail” and not “Carmack’s Reverse”, I guess you already know of this method.

If you’re not sure what to do to clip the shadows ( a special CSG operation between “infinite” shadow volumes and another object like an axis aligned box ), then I wouldn’t recommend it. There are quite a few potential problems that are hard to solve.

If you really want to try it, here are a few tips,

(1) Don’t clip shadow volume front faces.
(2) Projected back faces should be carved from the box.
(3) The silhouette quads are “infinite” until you clip them ( use rays, not line segments ).