Enhancements for Render composite request

[Barry Scott]

Soeren Sandmann wrote:
>
> The first requires time-stamped fence events, and if a compositing
> manager is present, a protocol to allow it to relay those events back
> to the application. The application can then
>
>         Ask for fence event
>         Render things offscreen
>         Inform the compositing manager that it should update and 
>            send a fence event when it has submitted its rendering
>         Wait for fence event to come back
We do it like this:

Composite manager waits for VBLANK (to avoid tearing)
Composite manager updates screen
Composite manager sends "draw now" to all the window owners
Windows owners draw to off screen windows and wait for next "draw now" 
event.

Barry