Comment 27 for bug 765813

ickle said a while ago 'Prepared flip multiple times' error might just be a misunderstanding of the hardware.
It indeed does not seem to have any ill effect so maybe the debug message could be removed or put at a higher debug level (ratelimit would be good to have if it's not removed).

Today I finally found the real culprit : sync to vblank.
With vblank_mode=0, I don't see any flickering, either in fullscreen or window.

But by default (vblank on), I get flickering in both window and fullscreen mode.

Looking at the framerate in several games, it seems quite clear that the flickering happens when constant 60 fps (refresh rate) cannot be maintained.
So when the scene is too complex for the gpu, it seems to flicker at every frame associated with fps jumps.
When the scene is very simple, I see a constant 60fps and not any flickering.
And all the granularity between these two extremes.