Caustic Photon Map (caustics)

The global map has caustics in it, but they are usually very weak because only a few photons reach the surfaces that produce this effect, specially when they are small. It is necessary to construct an additional map only for caustics. We do this by:

• Launching the rays only over the objects that can generate caustics (reflective and refractive objects).
• We store the photons when they hit a diffuse surface (surface considered diffuse taking into account the russian roulette) only if previously it hit a reflective or refractive surface.
• Of course, if we use a caustic photon map, the photons that produce caustics (hit first a reflective/refractive surface, then diffuse) should be eliminated from the global caustic map, in order to accurately reproduce the scene.