Sculpt Brush Refactor #118145
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Background
Currently there are several design issues with sculpt code that make feature development and performance improvements too hard. Much of the code is written in a way that makes applying proven "modern" optimization concepts like data-oriented design too complicated or difficult.
On top of that, sculpt code often works, while things like semantic consistency and larger architectural challenges are still big issues.
The largest difficulty comes from the method of sharing code between sculpting implementations for the three different supported data structures: Mesh, BMesh, and multires grids. The current approach is to pass everything through the same code path using a large macro. At runtime, per vertex, the code switches based on the active data structure. Besides the obvious downsides of those constant checks embedded in hot loops, it poses a larger challenge by forcing code to be written for a single element (vertex) at a time. One of the simplest ways to improve performance is to process many elements together.
Design Changes
Here are the high level design goals of the brush refactor.
PBVH, so it is only used as an acceleration structure for raycasting that splits up geometry into multiple pieces.SculptSession. Instead access data as necessary during modal operations, and avoid redundant references in long term structs.PBVHNode, separate node storage per PBVH type. Reduce per-node overhead to a minumum.Specific To Do
An incomplete list of to do items. Should be extended as necessary.
SculptBrushTestFnto works on arraysIndexMaskto address PBVH nodes by indexdeform_imats. Invert on demand insteadBKE_pbvh_vertex_iter_beginPBVHVertRefSculptSession, store in temporary context-like struct built on each callPBVHorig_vbis and potentially do something with itSculptFakeNeighbors) API with code specific to the pose brushThis redesign will bring a huge performance improvement by taking a more cache friendly data oriented design
"Use separate implementations of each brush per PBVH type. Code reuse should instead come from the use of common utilties, rather than systems that force different data through the same code path."
There's no need to make individual brush implementations per PBVH type. The vast majority of brushes should use the common utilities you mentioned. The draw brush is the easiest case, but you should be able to build a few utilities for clay brushes (which are all based on projecting vertices to a plane).