[Bug 28771] Vsync always on

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Mon Jul 19 10:29:31 PDT 2010


https://bugs.freedesktop.org/show_bug.cgi?id=28771

--- Comment #17 from Alex Deucher <agd5f at yahoo.com> 2010-07-19 10:29:31 PDT ---
(In reply to comment #13)
> Can GL have a switch like XV has - or should games in theory be able to turn
> off, but are prevented by a bug?

I'm not sure how you'd expose it.  You could make it a driver option, but then
you'd have to restart X to change it.  There's no GLX extension to cover
tearing as far as I know.

> 
> Digression - I notice that XV with vsync on can't live with frame rate =
> refresh rate, which I sometimes use for "proper" deinterlaced TV. GL vsync is
> fine and GL wait vline is much better that XV. Is this a driver issue or is it
> just that mplayers gl driver makes mplayer behave differently to it's xv
> driver?

Xv in general does not provide any mechanism for application synchronization. 
I.e., here's no vblank events provided by Xv for app synchronization.  That's
what the GLX vsync extensions do.

The driver uses the vline wait for avoid tearing for both Xv and GL buffer
swaps, they have nothing to do with the GLX vsync extensions.  Those extensions
only provide events that the application can use for synchronization.  If you
remove the vline wait code, you can still synchronize your application to the
refresh rate, but you might still get tearing depending when the GL buffer swap
happens.

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