Slideshow keeps GPU active while display is off

With the slideshow screensaver enabled, GPU power repeatedly spikes to 50–106 W after DPMS switches the display off. The spikes stop immediately when the display is woken.

Versions: xfce4-screensaver 4.20.2 xfce4-power-manager 4.20.1 Xorg, NVIDIA RTX 3090, driver 610.57.04

Expected: pause the slideshow while all displays are off, then resume it when a display is active again.

The crossfade implementation is extremely inefficient even when display is on. It works, but for a 4k monitor, it is too much power usage. crossfade with 1 opacity value on a gpu requires very little power, but here there's no gpu shaders and the power consumption is massive for 40fps.