[darkpore]

Would GeometryInstances go directly into an acceleration structure? Surely objects which point to the geometryinstance and each have a worldspace transform are what go in the scene level acceleration structure...

Generally it's advisable to templatize acceleration structures so they can natively cope with triangles, objects and possibly other primitives (spheres and curves) separately.

[Twinklebear]

Right, the instances go into a scene level acceleration structure and for each triangle mesh we build an object level acceleration structure on the triangles. I was planning to do something like a BVH<T: Geometry> so then I don't need a separate BVH type for instances and triangles, since Instance implements the Geometry trait. I'm not sure if there's a better alternative that would help get around the DifferentialGeometry issue since in this case the instance members of geometry types (Spheres, Triangles) and Instances must have the same signature.