ABSTRACT
The solution came in the form of a reversed argument: if we cannot globally model the way the light influences the objects, why not locally model the way the objects influence the light? Given that in a diffusely lit environment, shadows and reflections have limited spatial influence, some sort of halo around the model could function as a light subtraction volume (see Figures 16.3 and 16.4). In order to model directional lighting, the shadow volume could be expanded in the direction away from the light source and contracted to zero in the opposite direction. The colorbleeding volume could be expanded toward the light in the same manner. We call these volumes shadow proxies,1 because they serve as a stand-in for the actual geometry. The volume of a proxy covers the maximum spatial extent of the shadow and color bleeding of the geometry that the proxy represents. The technique is therefore limited to finite shadow volumes and is most useful for diffusely lit environments. This is similar to the Ambient Occlusion Fields technique by [Kontkanen and Laine 05], although with ShadowProxies, modeling and modulating the shadow volumes is done on the fly rather than precalculating the light accessibility of the geometry into a cubemap.
