[elihu]

An interesting caveat is that ray tracing has a high up-front cost, but rendering time is less sensitive to scene complexity than traditional polygon rasterization. Beyond a certain level of scene complexity, ray tracing can be faster, it's just that games are generally limited by what can fit in memory of a modern graphics card.

Regarding Pixar, they actually avoided ray tracing until they decided they really did need accurate reflections for the movie Cars. The reason is that traditional rendering is memory parallel: you can render a scene that won't fit in memory on a single computer by spreading the scene across a cluster. With ray tracing, the memory access patterns aren't predictable, so you have to have the whole scene fit in memory on every compute node. This doesn't matter for games because games don't divide the graphics computation across multiple machines.