In a test scene with mixed rough and non-rough materials, this saves
upwards of 0.15 ms of GPU time with very little visual artifacting
(GTX 1080, 2560×1440).
- Fade reflection towards inner margin and clip it at screen edges
instead of external margin.
- Round edges of the fade margin if both are being cut off to prevent
sharp corners.
Co-authored-by: puchik <puchik@users.noreply.github.com>
