Customizable refresh rate in Qt Quick

It would be useful in some cases to be able to set the refresh rate of specific parts of a Qt Quick UI, rather than repainting everything at 60 fps. For largely static parts of the UI for instance, it may add unnecessary resource consumption to forward-step the animations, update the graph and execute the draw calls every frame. Instead the contents can be stored in an off-screen buffer and be updated on a lower refresh rate, as it might be acceptable that some low priority animations are not running as smoothly as the high priority UIs.

With Layer.enabled, we already support delegating contents to an FBO, so a possibility would be to add an additional property to Layer, for instance Layer.refreshRate:

Item {
   Layer.enabled: true
   Layer.refreshRate: 1000.0 / 30.0 // Layer updates at 30 fps ( == 32 ms)
}

Note: On some hardware, drawing via an FBO may be inhibiting, but if we could later somehow enable delegating Layers to hardware layers through some hardware specific extension, then this solution would also work on the more restrictive GPUs.