bvh_internal

The last step of a bounding volume hierarchy build: each internal node's bounds, the fold of the leaves its run of sorted places covers, read from the pyramid bvh_pyramid wrote. It reads codes and order (to find each node's run), pyr and the leaves of nodes, over the params np and pyr_size, and writes the bounds words of nodes 0 .. np - 2 of nodes in place, after which the ray kernel can traverse it. The geometry.bvh node runs it last. Dispatch over np - 1, one invocation per internal node. Exact.