`GLBatch::draw_indirect` has additional overhead compared to
`GLBatch::draw`, and can become a bottleneck in scenes that require
many draw calls (ie. with too many unique meshes).
The performance difference is almost exclusively caused by the
`GL_COMMAND_BARRIER_BIT` barrier that happens on every call.
This PR adds a `GPU_storagebuf_sync_as_indirect_buffer` function that
can be used to place the barrier only once after filling the indirect
buffer content.
This function is a no-op in Vulkan and Metal since they don't need the
barrier.
Pull Request: https://projects.blender.org/blender/blender/pulls/117561
5d132ac0c6