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Soft shadows
Tuesday, July 13, 2004 | Permalink

Source code
SoftShadows.zip (1.6 MB)

The fastest way to compute is to precompute. Which is also one of the main reasons why lightmaps are still hanging around. Lightmaps have a number of great advantages. They are very cheap, and you can get soft shadows for free. The disadvantage though is that it's static. You can't move the light and you the geometry must be static. This demo however shows a way to get a bit of dynamic lighting into lightmaps. By storing a bunch of lightmaps for a range of different light positions, and interpolating between the closest lightmaps, you can animate the light and get soft dynamic shadows very cheaply. The idea could also be used for dynamic geometry with a static light in a similiar way. This demo doesn't implement that though.
It won't work for arbitrary light positions, but most lights in real world applications don't move around arbitrarily. If they are dynamic they are often swinging in a cable, or otherwise limited in their movement to a simple animation. In these cases, this technique can be used for rendering soft shadows extremely cheap.

This demo should work on Radeon 9500 and up and GF 5200 and up.