When using a small brush size, if enough latency is encountered,
sculpting can become unresponsive. See #131334 for more in-depth
information on this issue.
In general, this is most apparent to users with the Smooth brush and
any brushes with auto-smoothing enabled. Much of the work for this
brush action is in retrieving and averaging the neighboring vertex
positions. This is wasted work for vertices outside of the brush radius,
as ultimately they will have no displacement applied to them.
To help mitigate this performance regression, this PR adds a variant
of functions that calculate neighboring vertices that takes in the
precalculated `factor` to skip further processing. Additionally, some
methods are restructured to take advantage of this.
This change represents a speedup of 4x, from `0.40ms` without this
patch to `0.10ms` with it on a cube with 400k vertices and a brush
radius of 10px. For most brush size to BVH Node / Mesh ratios, we see
improvements, as we can avoid processing most nodes that a brush only
affects a small number of vertices of. For cases where the entire mesh
is affected by a brush, this patch does introduce a small but
measurable slowdown of 0.31ms to 0.33ms.
Ref: #136006
Pull Request: https://projects.blender.org/blender/blender/pulls/136274
d3d776fd3c