This is a port of sculpt-dev's `SculptVertRef` refactor
(note that `SculptVertRef was renamed to PBVHVertRef`)
to master. `PBVHVertRef` is a structure that abstracts
the concept of a vertex in the sculpt code; it's simply
an `intptr_t` wrapped in a struct.
For `PBVH_FACES` and `PBVH_GRIDS` this struct stores a
vertex index, but for `BMesh` it stores a direct pointer
to a BMVert. The intptr_t is wrapped in a struct to prevent
the accidental usage of it as an index.
There are many reasons to do this:
* Right now `BMesh` verts are not logical sculpt verts;
to use the sculpt API they must first be converted to indices.
This requires a lot of indirect lookups into tables, leading to performance
loss. It has also led to greater code complexity and duplication.
* Having an abstract vertex type makes it feasible to have one unified
temporary attribute API for all three PBVH modes, which in turn
made it rather trivial to port sculpt brushes to DynTopo in
sculpt-dev (e.g. the layer brush, draw sharp, the smooth brushes,
the paint brushes, etc). This attribute API will be in a future patch.
* We need to do this anyway for the eventual move to C++.
Differential Revision: https://developer.blender.org/D14272
Reviewed By: Brecht Van Lommel
Ref D14272
d7cfb6ac71