As anyone who ever wrote a raytracer would know (or find out soon): Primary rays cache. Secondary rays trash! Brazil guys wrote a decent raytracer (entirely ba

As anyone who ever wrote a raytracer would know (or find out soon): Primary rays cache. Secondary rays trash! Brazil guys wrote a decent raytracer (entirely based on Glassner's book) and are really competent devs in general (both of them). Current state of the art, performance oriented, offline renderer is Arnold by SolidAngle, with more smart guys behind it. I think we will see convergence of offline and online RT soon enough. There are already steps being made in that direction, in offline world, towards RT previews.