This patch enhances the quality setting of the Glare node. Previously,
Medium and Low quality were implemented using a single tap interpolation
downsampling filter, which means small highlights that only span a small
number of pixels could be missed during downsampling, and that might
change across frames, causing flickering.
To fix this, we use a higher quality downsampling filter that averages
the entire 2x2 or 4x4 pixel blocks for the Medium and Low quality
settings respectively.
The upsampling pass also needs to be improved to avoid offsets, but this
will be implemented separately.
Pull Request: https://projects.blender.org/blender/blender/pulls/140237
0a4b92678c