hmm, the ping-pong idea sounds nice at first, until it stops a few
interations ahead like this:
round 0: RSOCP (10 secs render)
round 1: 100 RSOCP + radiosity (2 min render)
round 2: 100 RSOCP with fresnel and IOR + some hundred boxes around to
provide some interesting reflections + radiosity (12 hours render)
....
you get the point...
