[harywilke]

REYES (Render Everything You've Ever Seen) has been the basis of PRMan since the start. Recently PRMan has shifted away from this approach and towards more ray tracing. see the following for descriptions of REYES: http://renderman.pixar.com/view/reyes-renderman-under-the-ho... or the 1987 paper by Cook, Carpenter and Catmul http://graphics.pixar.com/library/Reyes/paper.pdf

[Keyframe]

Indeed, and it's now one of several rendering methods in PRMan - newer one is RIS: http://renderman.pixar.com/resources/current/RenderMan/risOv...

Sidenote, you could have always done raytracing in PRMan, even with REYES. You just bring your own trace(). BMRT was often used as a trace() engine, until they came up with Entropy and Pixar sued them out of existence (NVidia bought them).