The initial goal of this PR is to avoid creating vertex and index
buffers as part of the "request" phase of the drawing loop. Conflating
requesting and creating index buffers might not sound so bad, but it
ends up significantly complicating the whole process. It is also
incompatible with a future buffer cache that would allow avoiding
re-uploading mesh buffers.
Specifically, this means removing the use of `DRW_vbo_request` and
`DRW_ibo_request` from the mesh batch extraction process. Instead, a
list of buffer types is gathered based on the requested batches. Then
that list is filtered to find the batches that haven't been requested
yet. Overall I find the new process much easier to understand.
A few examples of simplifications this allows are avoiding allocating
`MeshRenderData` on the heap, and the removal of its `use_final_mesh`
member. That's just replaced by passing the necessary information
through the call stack.
Another notable difference is that for meshes, EEVEE's velocity module
now requests a batch that contains the buffer rather than just requesting
the buffer itself. This is just simpler to get working since it doesn't require
a separate code path.
The task graph argument for extraction is unused after this change. It wasn't
used effectively anyway; a simpler method of multithreading extractions is
used in this PR. I didn't remove it completely because it will probably be
repurposed in the next step of this project.
The next step in this project is to replace `MeshBufferList` with a
global cache that's keyed based on the mesh data that compromises each
batch, when possible (i.e. for non edit-mode meshes). This changes above
should be applied to other object types too.
Pull Request: https://projects.blender.org/blender/blender/pulls/135699
9b70851d91