This commit rewrites the PBVH drawing using many of the principles from the
ongoing sculpt refactor. First of all, per BVH node overhead is minimized.
Previously the main entry point to the drawing API was per node, so there
was significant overhead fetching global data and maintaining caches on
a per-node basis. Now all of that "global" work happens for the entire
geometry.
We also now avoid creating wireframe index buffers and batches unless
the viewport actually requests wireframe data. This was theoretically
possible before, but the whole logic flow was so convoluted that the
optimization was too difficult. Similarly, multithreading is used more
consistently now. Because of OpenGL, flushing vertex/index buffers to
the GPU has to happen on the main thread, but everything else can be
multithreaded. With outer loops processing all relevant PBVH nodes,
it's now trivial to apply multithreading wherever possible.
Testing performance, overall this commit results in a 10% improvement in
the time between opening a file with a large mesh sculpt and the first
possible interaction. Specifically I measured a change from 8.4 to 7.6
seconds on a completely visible 16 million vertex mesh with a Ryzen 7950x.
I also measured a decrease in memory usage from 4.79 to 4.31 GB.
For multires I observed a similar improvement in memory usage,
though less of a performance improvement.
There are still significant opportunities for future improvement. #122775
would be particularly helpful. #99983 would be helpful too, though more
complicated, and #97665 describes the problems a bit more generally.
Part of #118145.
Pull Request: https://projects.blender.org/blender/blender/pulls/127002
d601bf7e3d