Current implementation uses a CPU roundtrip to transfer render result
to the Xr Swapchain. This PR adds support for sharing the render result
on Linux systems by using file descriptors.
To extend this solution to win32 or dx handles can be done by extending
the data transfer modes, register the correct extensions. When not
using the same GPU between Blender and OpenXR the CPU roundtrip
will still be used.
Solution has been validated with monado simulator and seems to be as
fast as OpenGL.
Performance can be improved by using GPU based synchronization.
Current API is limited as we cannot chain the different renders and
swapchains.
Pull Request: https://projects.blender.org/blender/blender/pulls/136933
Now that all relevant code is C++, the indirection from the C struct
`GPUVertBuf` to the C++ `blender::gpu::VertBuf` class just adds
complexity and necessitates a wrapper API, making more cleanups like
use of RAII or other C++ types more difficult.
This commit replaces the C wrapper structs with direct use of the
vertex and index buffer base classes. In C++ we can choose which parts
of a class are private, so we don't risk exposing too many
implementation details here.
Pull Request: https://projects.blender.org/blender/blender/pulls/119825
