Synchronising flush with vsync

[kisvegabor]

@microwavesafe

I can see understand your reasoning about the tight integration. It does give maximum flexibility. It shouldn’t take too much effort to rewrite the HAL calls to register writes. I need to upgrade to V7 of the library first, but I will be able to take a look at it.

Great!

@microwavesafe

I was thinking a bit more on how this would work. If the GPU was performing a blend then we couldn’t allow the CPU to blend in the same area, as the result may depend on the result of the GPU. An out of sequence fill would also cause problems. So I think the logic would go something like this.

Maybe the logic can be simplified to check whether the GPU is busy before executing any CPU or GPU draws to be sure the GPU won’t overdraw the CPU rendered pixels.

I think we can check it in _lv_draw_blend_fill and _lv_draw_blend_map
becasue finally every drawing ends up here.