Better light mapping for spotlight light entities

[no-lex]

Currently, spotlight entities use a planar map to store lighting information, with the map being oriented normal to the spotlight direction. This works fairly well for narrow beam spotlights, but for wide angle spotlights located near walls, the "shadow acne" is readily apparent.

Ways to solve this unsightly phenomenon would primarily focus on changing the projection from monoplanar to some other method. Possible solutions are:

• single paraboloid mapping
• standard cube mapping (or, five face open-top cube mapping)
• tetrahedral mapping (or, open faced tetrahedral mapping)
• conic mapping

These would have less distortion on the corners, and so would have less apparent visual artifacts.