Photon Mapping: What is it?
Okay, really quick, photon mapping is where we cast photons from the light out into the scene we are drawing and store their interactions with the geometry in a photon map. Then we to a raytrace on the scene, but when we do our lighting calculations we use the information in the photon map as well as direct illumination. This gives us indirect illumination, and with the addition of a second photon map we can do good, cheap caustics. For more info check wikipedia. This is an extension of my previous project which is a ray tracer, you can read about it on its blog.