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Sculpt mode uses a coarse BVH tree, PBVH. The leaves are fairly large compared to most BVHs; this is because the leaves are used to split the GPU mesh.

Data modes

PBVH has three different modes, each of which has a different data backing:

  • PBVH_FACES: Mesh data.
  • PBVH_BMESH: Dynamic topology, uses BMesh.
  • PBVH_GRIDS: Multiresolution data.

You get can the mode with BKE_pbvh_type.

Vertex/Face references

The PBVH API stores vertex references in a special structure, PBVHVertRef. It contains a single intptr_t value, the meaning of which varies by PBVH data mode. PBVH_BMESH stores pointers in the value, while the other two store indices. The null reference is PBVH_REF_NONE.

Vertex Iteration

You can iterate over the vertices in a PBVHNode. There are two modes for this, PBVH_ITER_UNIQUE and PBVH_ITER_ALL. PBVH_ITER_UNIQUE iterates over the vertices uniquely assigned to this node, while PBVH_ITER_ALL iterates over the vertices that belong to this node's faces.

PBVHVertIter vd;
BKE_pbvh_vertex_iter_begin(pbvh, node, vd, PBVH_ITER_UNIQUE) {
  //PBVHVertIter has various bits of data:
  //    - position
  //    - normal
  //vd.mask  - pointer to mask
  //vd.color - active color attribute data, if it exists