I'm opening this MR as an RFC. It's an initial attempt to support OpenGL persistent memory mapping in the new wow64. The implementation is not complete yet (details below), but it's intentionally kept as simple as possible for a proof of concept.
Since we can't control where OpenGL maps memory, the idea is to use the available Vulkan extension with enough glue between them. Because of how GL–VK interop works, this requires creating a memory object on the Vulkan side and importing it into OpenGL. Once that's done, all operations on such buffers are performed through GL, except for mapping, which is handled by Vulkan. This is achieved by hooking `gl*BufferStorage` and reimplementing it on top of `glImportMemoryFdEXT` for mappable buffers. Recently introduced buffer wrappers make further tracking of these buffers straightforward.
If we move forward with this, the feature will need to be enabled based on available driver capabilities (for now, it's force-enabled). Some parts might also be worth moving into win32u.
This alone seems enough to claim persistent memory support and thus expose OpenGL 4.6 on the new wow64. Performance looks good in my limited testing, although that hasn't been a focus yet. Possible improvements include: - Currently only GL buffers created with `gl*BufferStorage` are affected. Other cases still fall back to the slow memcpy path. - The draft just picks the first host-visible coherent memory type exposed by Vulkan. We could try harder to pick an optimal type taking into account GL flags. - The draft allocates a new Vulkan memory and fd for each mapped buffer. This is inefficient for small buffers, for which a suballocator could help. - The draft always picks the first GPU reported by Vulkan. We may need to ensure that the selected device matches the one OpenGL actually uses.
An alternative would be a new OpenGL extension. A driver-level solution could be more efficient, and it would certainly be nice to have. However, since such an extension doesn't exist yet, and even if we have it soon, I think it's still valuable to have a fallback solution that works with existing drivers.
-- v2: opengl32: Support wow64 buffer storage and persistent memory mapping using Vulkan. opengl32: Wrap buffer storage functions. opengl32: Use stored extensions in filter_extensions. opengl32: Use stored extension list in is_extension_supported. opengl32: Compute supported extensions in make_context_current. opengl32: Split extensions by null bytes in the registry.