Complex Illumination Paths

Figure 4: Overview (left) and solution (middle) for the secondary test case. A simple modification creates a scene with a reflected caustic (right).

This scene checks complex illumination paths. It consists of a ground plane with a light underneath. The light shines on a diffuse surface to the side of the ground plane. All illumination on the visible objects is from this secondary luminaire (Figure 4). The secondary luminaire and the block on the ground plane create a very definite shadow and the light reflected off the block creates a visible indirect effect. Light can arrive in the umbra of this shadow only after 3 or more other interactions with diffuse surfaces.

A simple change to this scene can create a good test of the correct handling of specular objects. Replacing the diffuse cube with a mirrored cube creates a scene with a reflection of a caustic caused by a secondary source. It also eliminates the possibility of light reaching the umbra.