Idle delay fade in lacks animation
This issue is basically a complement to #1744 (closed), except that this functionality was never implemented, AFAIK.
When you wiggle the mouse during the idle blackout, the screen snaps to full brightness immediately, with unpleasant blinding effect. A fade-out effect would make the experience more cohesive – and frankly nicer.
As mentioned in the linked issue, a simple reproduction is gsettings set org.gnome.desktop.session idle-delay 5
, a 5-second wait and a mouse wiggle.