Cycles automatic denoiser picker assumed that OIDN could not be
run on the GPU while the CPU was the render device. So if the user was
using their CPU for rendering, the automatic denoiser picker would
"fallback" to a different denoiser (OptiX or CPU OIDN). This was true
in Blender 4.1, but changed in 4.2. The UI assumed that OIDN could run
on the GPU if there was a compatible OIDN GPU device.
This lead to a issue on systems using the CPU for rendering
while having a NVIDIA GPU installed in the system. The
UI suggested that OIDN would be used, and would switch between
CPU and GPU depending on user preferences. But the automatic
denoiser picker in Cycle's backend said OIDN could not run on
the GPU in this situation and would always "fallback" to the
OptiX denoiser running on the NVIDIA GPU.
This created a mismatch between the UI and what Cycles was
acutally doing. This issue did not effect other GPU vendors because
their "fallback" was the OIDN denoiser.
This commit fixes this issue by aligning the Cycles automatic
denoiser picker in the backend with the UI. Using OIDN if a GPU
is supported, falling back to OptiX if it's not supported,
falling back to OIDN CPU if OptiX isn't supported,
then falling back to no denoiser if that's not supported.
Pull Request: https://projects.blender.org/blender/blender/pulls/123530
47158e1606