Shadow map problem

look at trapezoidal shadow mapping. It distorts the shadow map so that the area closest to the camera has a higher resolution. I think this is what quite a lot of people do for outdoor scenes.

http://hungryspoon.com/PX_web/paper/shadow%20mapping/

Thanks, I'll read up on that :).

Any comments/suggestions on distance for shadowing are welcome too.

The basic method of doing large-scale outdoor shadows is a orthogonally projected shadow map. The shadow map stretched over a very large area then, resulting in a very low shadow resolution. Building on that there are several methods to improve shadow map resolution close to the viewer. Light Space Perspective Shadow Mapping and the Trapezoidal Shadow Mapping mentioned before work by applying a pespective transform on the shadow map projection. Cascaded Shadow Mapping or Parallel Split Shadow Mapping work by using multiple shadow maps for different distances. There are more techniques, but I don't recall their names.

Personally I use a technique presented in a thread here at Gamedev.net: http://www.gamedev.net/community/forums/topic.asp?topic_id=405955&whichpage=1 . It works by appying a circular distortion to the shadow map much like a fish eye lense that makes objects close to the viewer larger on the shadow map, thus improving the shadow resolution.

Advantages: single pass, single shadow map. Does not depend on the view angle, does have a performance hit close to zero.

Disadvantages: nonlinear distortion, resolution improvement is limited by distortion artifacts.

Bye, Thomas