How do spherical bounding boxes equal free skinning?
In my case, using a hierarchy of surfels, each surfel also has a bounding sphere. So for characters i only need to ensure the bounds are large enough to bound children under any animation. (Ensuring large enough is a matter of precalculation.)
Animation is then just transforming the surfels, which i need to do anyways, so the BVH update is free for me. There is no extra complexity like mid levels or taking character bones into account.
The same would work for triangles. You would only need to transform the BVH using the same skinning system as for the mesh itself, but no bottom up dependencies.
It would also work for bounding boxes, in case you do not need to guarantee the parent box bounds child boxes, and the guarantee to bound only the triangles would suffice (which is the case for RT).
I think this will become the norm. Tracing speed suffers, but FF HW will compensate and dynamic geometry has no more extra cost.
So no refitting, just transform the bottom AS and rebuild the top levels as usual.
It might be worth to shrink the bounds so they bound triangles exactly to prevent the hit on tracing speed for the lowest levels of the tree.
