Drawing synchronised with display refresh

There is currently no way for a display backend to cause redrawing activity to be synchronised with the natural update rate of a display without requiring updates to be blocking in some cases.

Blocking update calls cause the rendering thread to become unresponsive, and on some platforms this can cause the application to be unable to process critical events such as key presses.

Non blocking updates cannot synchronise with the display update, resulting in ugly "tearing" as well as potentially wasting CPU in rendering frames that will never be fully visible on screen.

The animation framework and declarative framework should not render a rate other then the display refresh rate, and should be synchronised with it.

A solution to this is needed, and needs to be integrated at least with VG, GL, Symbian DSA, and X (if possible) backends.