Well, screen space ambient occlusion is an approximation of global illumination, usually casts rays in a half-sphere, and IIRC Ubisoft already temporally re-used samples for that back in AC:Unity.I'm asking myself if CBR can't also be used for speeding up some global
illumination? For, let's say we cover the sphere (over which we will
integrate) with a set of well chosen points (not random) and compute the
illumination over half of these points (in a checkerboard fashion) while
backward integrating the other half from a previous frame, like in classic
CBR, yet all done on the sphere, then we would only need half the rays saving
about half the computation. Anyone?
Of course, that was in screen space, but I think the basic idea is quite similar to what you are proposing.