BVH · bounding volume hierarchy
A tree of boxes for ray tracing.
Clark proposed wrapping every object in a bounding box, then organising those boxes in a tree. Rays test the root box; if hit, recurse to children; if not, prune. The whole structure is rebuilt or refit per frame in dynamic scenes. Without BVHs, modern ray tracing would not exist.
Each leaf wraps an object; each internal node's box bounds its children's boxes. Ray traversal: front-to-back recursive descent, pruning subtrees whose box the ray misses. Quality of the tree matters enormously — SAH (Surface Area Heuristic) is the standard build metric.
Every modern ray tracer. NVIDIA RTX hardware. Embree. PBRT. Unreal's Lumen. Unity's ray-traced ambient occlusion.
A BVH built poorly can be 10× slower than one built well. SAH-built BVHs are why hardware-accelerated ray tracing on a 1080p frame is possible in real time.