Currently there are two vertex buffers that contain mesh normals. First, the
normals are extracted and stored interleaved with positions. Then there is
a second vertex buffer for just normals. Interleaving them makes some
sense, since they change together, but it fights with the contiguous storage
benefits of `Mesh` and generally makes code more difficult to optimize.
This PR removes the normals interleaved with the positions and changes
the code for extracting positions and normals from meshes to be simpler
and faster, mainly by not using the "extract iterators" as described by the
#116901 design task. That moves most of the branching outside of hot
loops, so we don't do the same work for every mesh element. This also
gives us the option of not calculating or extracting normals in more
situations like wireframe display in the future.
This is only a small part of the work for #116901, so the state of the code
after this PR will have more design inconsistencies. I'll keep working to
resolve those in the future.
In general I observed at least a 5-40% improvement in FPS in playback
of files with large meshes.
Pull Request: https://projects.blender.org/blender/blender/pulls/116902
bace4c9a29