I think they do both simultaneously, it's just that the cursor sprite/plane is overlaid during scan out and the software cursor is rendered in the next frame to

I think they do both simultaneously, it's just that the cursor sprite/plane is overlaid during scan out and the software cursor is rendered in the next frame to be rendered by the compositor. The cursor sprite/plane can turn on or off pretty much mid-frame, whereas the frame that's about to be rendered could be two frames away from the one that's about to be scanned out. What you actually need to do is track when the first frame with the software cursor is about to be presented, then turn off the cursor sprite/plane. I think technically speaking all of the information needed to implement this is present somewhere, but I'm sure it's quite complicated to actually implement, possibly made worse by interface layering issues :)