Paper: Real-time Soft Shadows from Area Lights

One of the reasons this paper was so appealing is that it was by a Swedish grad student from outside the "usual suspects" of the SIGGRAPH community. It was simply an outstanding idea, clearly implemented.

Basically, the paper extends the idea of shadow volumes in a way that, in combination with programmable pixel shaders, allows area light sources to accurately cast true soft shadows into the scene. As with shadow volumes, the shadows can fall on all objects in the scene, including the shadow-casting objects, and are true soft shadows in the sense that they are sharper close to the shadow-casting object and fuzzier farther away.

While this implementation is not yet something we'd grab and put in our game, it's clearly feasible in the next-generation console timeframe (well, assuming Sony sees the light on programmable pixel shaders). They demoed moderate-complexity characters (mostly the nVidia alien) casting soft shadows at a few frames per second onto scenes during their talk. And, this was done with more complexity than we would actually use in a game (in particular, it's not clear we'd cast shadows with the same geometry we use for the rendered character).

The specifics of the visibility calculation are involved, so I'll leave that to those who wish to read the paper (Andrew, Dave Benson, and I all have copies of the proceedings). However, it's exciting to watch this coming up as a possibility in the future!

The full title of this paper was "A Geometry-based Soft Shadow Volume Algorithm using Graphics Hardware" by Ulf Assarsson and Tomas Akenine-Moller from Chalmers Institute of Technology.