Comment # 12 on bug 91656 from Marek Olšák

(In reply to Daniel Scharrer from comment #11)
> There is also a glClear though. Currently the texture read ends up with the
> data before the clear (uninitialized for the first frame, unitialized
> content with the fog of war blended on top n times for subsequent frames).
> Are you saying the texture reads should get the color from the clear without
> any synchronization?

No, glClear+glDraw indeed requires a barrier in between.