Within a given bottom-level acceleration structure there can be anynumber: (1) triangle meshes, or (2) procedural primitives initiallydescribed only by an axis aligned bounding box (AABB). A bottom-levelacceleration structure can only contain a single geometry type. Thesegeometry types are described more later. Given a definition of a set ofthese geometries (via array of D3D12_RAYTRACING_GEOMETRY_DESC), theapplication calls BuildRaytracingAccelerationStructure()on a CommandList to ask the system to build an opaque accelerationstructure representing it into GPU memory owned by the application. Thisacceleration structure is what the system will use to intersect rayswith the geometry.