GPU PRO 3

248 IV Shadows

Figure 2.4. Variable penumbra by applying contrast based on the distance from receiver

to caster.

2.5 Failure Case

The algorithm works best in large, relatively flat worlds. This is because the

technique relies on the premise that shadow-casters are usually disjoint (i.e., not

connected) when viewed in light space. There are cases where casters will overlap

in shadow-map space with a receiver in-between. In these cases, the receiving

surface will receive a blocky shadow from the caster that is overlapping with

a more distant caster in light space. Generally these cases are very rare and

hence these issues were ignored in games that shipp ...