I am trying to implement some Bounding Volume Hierarchy(BVH) in parallel using Job System for my own intersection/raycasting system, and searching ways to do that, I found Unity already has it in the Physics package! so I thought why not learn from it. But the problem is I don’t know what kind of BVH is actually used.
I tried to understand how it is built by reading codes in BoundingVolumeHierarchy.cs & BoundingVolumeHierarchyBuilder.cs but I couldn’t get it. There are only a few comments and there is no explanation about BVH in the documents, so it is pretty difficult to understand how BVH is built. (Also, since it is a preview package, I can’t run it line by line with debugging. It is hard to even find where a function is used from the function in Visual Studio because “Find All References” doesn’t work.)
Can anyone help me learn about Unity’s BVH structure a bit?
Hi torano, it’s an AABB tree. Each node has an AABB that contains all of that node’s descendants. Leaf nodes’ AABBs contain the things stored in the tree, for example rigid bodies in the broadphase or triangles in a mesh. Nodes have four children each. There are multiple ways to build the tree, one popular method is the surface area heuristic.
To MaxAbernethy, AABB tree is just like BVH, and there are a lot of ways to build if I am not mistaken, right? How it is built actually in the physics package?
I learned a little bit of BVH already reading PBRT book(only BVH part), so I know how to build a basic BVH like building BVH recursively with SAH, building LBVH/HLBVH with morton codes. But Unity seems to use another way from the code I guess.