This patch adds an alternative path for devices/OSs
which do not support native texture atomics in Metal.
Support is encapsulated within the backend, ensuring
any allocated texture with the USAGE_ATOMIC flag is
allocated with a backing buffer, upon which atomic
operations happen.
The shader generation is also changed for the atomic
case, which instructs the backend to insert additional
buffer bind-points for the buffer resource. As Metal
also only supports buffer-backed textures for
textureBuffers or 2D textures, TextureArrays and
3D textures are emulated within a 2D texture, with
sample locations being indirected.
All usage of atomic textures MUST now utilise the
correct atomic texture types in the high level shader
and GPUShaderCreateInfo declarations.
Authored by Apple: Michael Parkin-White
Pull Request: https://projects.blender.org/blender/blender/pulls/115956
9313750f0a