This patch adds two new inputs to the Glare node, Highlights Smoothness
and Max Highlights. Smoothness allows the user to control how smooth the
highlights are after thresholding and Max allows the user to suppress
very high brightness pixels.
Those are essentially similar to the Knee and Clamp options in old EEVEE
bloom, though they work differently.
The issue with the Knee parameter in old EEVEE bloom, aside from being
named after a body part, is that it actually isn't smooth or continuous
around zero if the threshold is sufficiently close to zero relative to
the Knee parameter. That's because zero lies in the smoothing kernel
region in those cases, and since zero pixels becoming highlights is very
bad, EEVEE just returned zero as a special case for zero brightness, but
values like 0.0001 will be full blown highlights.
The new nicely named Smoothness input uses adaptive smoothing such that
the smoothing kernel size will be reduced as the threshold nears zero,
such that smoothed highlights will be continuous and smooth around zero.
The Max Highlights input is similar to clamped, it it suppresses very
bright highlights such that their brightness doesn't exceed the
specified max.
This is a partial implementation of #124176 to address #131325.
Pull Request: https://projects.blender.org/blender/blender/pulls/132864
3b28cf276e