Code review comment for lp:~alan-griffiths/mir/fix-1535894-alt

> 1. Needs info: I thought the goal here was to skip rendering on idle displays.
> That code doesn't seem to be present yet, so maybe it comes later? It would
> be: composite() returns "I had nothing new to render" so then post() never
> gets called. You either need to composite and post, or do neither. But never
> composite without post (wasted of GPU), and never post without composite
> (uninitialized pixels appear on screen).

Nope.

The point of *this* MP is that the DisplayBufferCompositor knows which surfaces it has rendered and interrogates them to see if they have further buffers pending.

With the logic in scene we were counting buffers belonging to surfaces that had not contributed to rendering. (And would not be consumed by the consequent render pass.)

In the scenario from the linked bug the nested server would repeatedly schedule a recomposite of whichever display on which nothing had been posted.

> 2. Needs fixing: Please add the FIXME comment back in. It's an important one
> we shouldn't forget.

OK