The GPU module has 2 different styles when reading back data from
GPU buffers. The SSBOs used a memcpy to copy the data to a
pre-allocated buffer. IndexBuf/VertBuf gave back a driver/platform
controlled pointer to the memory.
Readback is done for test cases returning mapped pointers is not safe.
For this reason we settled on using the same approach as the SSBO.
Copy the data to a caller pre-allocated buffer.
Reason why this API is currently changed is that the Vulkan API is more
strict on mapping/unmapping buffers that can lead to potential issues
down the road.
Pull Request #104571
This patch adds a placeholder for the vulkan backend.
When activated (`WITH_VULKAN_BACKEND=On` and `--gpu-backend vulkan`)
it might open a blender screen, but nothing should be visible as
none of the functions are implemented or otherwise crash on a nullptr.
This is expected as this is just a placeholder. The goal is to add shader compilation
+validation to this backend as one of the next steps so we can validate
changes to existing shaders on OpenGL, Metal and Vulkan at the same time.
Reviewed By: fclem
Differential Revision: https://developer.blender.org/D16338
