This patches optimizes the Fog Glow Glare node to be about 25x faster
for 4K images. This is mainly achieved by utilizing the FFTW library and
multi-threading support code. Further improvements are still possible by
caching kernels, but the CPU compositor does not support caching yet.
The old Hartley transform was removed, so the node no longer works when
FFTW is disabled as a build time option, much like the OIDN node. A new
BLI library was introduced for FFTW, it includes some helper routines
relevant for FFTW as well as an initialization routine that sets up
multithreading using TBB as well as thread safety.
Build system support for threaded FFTW was also added, which defines the
relevant variables to detect threading support as well as add the
relevant libraries.
We do not currently have the threaded FFTW libs in our precompiled libs,
so the threading code is disabled until the libs lands in the coming
weeks. So currently, the code is only about 9x faster.
The only functional change is that the kernel is now odd sized, which
should produce more accurate results, but the final result is almost
identical and mostly undetectable.
The plan is to port this to the GPU as well similar to how we implement
OIDN until we have a GPU FFT implementation. GPU compositor can also do
caching, so it should be faster, being able to compute a 4K image in
under half a second.
Pull Request: https://projects.blender.org/blender/blender/pulls/121653
d4bf23771d