The mesh triangulation data is stored in CPU memory with the same format
as the triangles GPU index buffer. Because of that we can skip creating a
temporary copied owned by the GPU API. One way to do that is to just
upload the data directly and avoid keeping a reference to it. However, we
can only upload GPU data from the main thread with OpenGL, so instead
reference the data and keep track of whether to free it.
When drawing a mesh with a single material and 1.8 million faces, this
change gives a 12-15% improvement in framerate, from about 32 to 37 FPS.
Part of #116901.
Pull Request: https://projects.blender.org/blender/blender/pulls/122175
108ab1df2d