A change merged into quattro plays a new background's intro clip, then hands the shell the new background once the clip ends. If the intro is refused, the ordinary transition runs. Nothing plays when intros or animations are off, or when the background does not change.

That first change cut straight to the clip and left the desktop black until the first frame. A follow-up merged into quattro fades the intro in the way a theme switch does, and puts the new background in place before the clip plays so the old background does not flash at the end.

Those steps had been sequenced from a script that polled for each one. Pull request 16884, also merged into quattro, moves the sequence into the shell, where each step waits on the event that allows it.