This patch implements the Classic Kuwahara node for the Realtime Compositor.
A naive O(radius^2) implementation is used for radii up to 5 pixels, and a
constant O(1) implementation based on summed area tables is used for higher
radii at the cost of building and storing the tables.
This is different from the CPU implementation in that it computes the variance
as the average of the variance of each of the individual channels. This is done
to avoid computing yet another SAT table for luminance. The CPU implementation
will be adapted to match this in a future commit.
The SAT implementation is based on the algorithm described in:
Nehab, Diego, et al. "GPU-efficient recursive filtering and summed-area tables."
Additionally, the Result class now allows full precision texture allocation, which
was necessary for storing the SAT tables.
Pull Request: https://projects.blender.org/blender/blender/pulls/109292
940558f9ac