Currently QWidgetBackingStore::UpdateLater behavior is implemented posting an UpdateRequest event to the event loop, which is then serviced during the next round of event processing. See QWidgetBackingStore::sendUpdateRequest() and QEvent::UpdateRequest handling in qwidget.cpp

It is desirable to let the platform plugin drive such updates instead. This would for example allow driving animations with CVDisplayLinks on OS X.

We have an API for this already: QWindow::requestUpdate(), where the default behavior uses the event loop like Widgets does today. Remaining task is to switch Widgets over to using that.