I currently have implemented shadow volumes in a 3d GL engine I'm writing. The shadow volumes use the standard approach, using the stencil buffer, but things are pretty damn slow.
I'm only drawing about 50 - 100 polygons into the buffer, and the problem actually doesn't seem to be polygon related but fill-rate related because reducing the polygons doesn't have an enormous effect but reducing their size does.
I'm currently running my demo on an Athlon 800 with a GeForce2 so one would expect that things would be snappy, but I have the feeling that using the stencil buffer is simply a slow ordeal. I'm not positive that the buffer operations run in hardware, but if they aren't I don't know what to do about it anyway.
Anyone else have any experience with real-time shadow volume drawing/stenciling and how fast/slow it is? Any suggestions?