Re: [Dri-devel] Bad tearing with quake2 and LIBGL_SYNC_REFRESH

[Brian P. <br...@tu...>]

Felix K=FChling wrote:
> Hi,
>=20
> even with LIBGL_SYNC_REFRESH I get bad tearing with quake2. I looked
> into the source a bit and now I'm scratching my head about this
> question: Does waiting for a vblank do anything useful if you havn't
> flushed the 3D hardware graphics pipeline before? I believe the driver
> should call something equivalent to glFinish before driWaitForVBlank if
> LIBGL_SYNC_REFRESH is set.
>=20
> Further in case of a non-zero swap interval you will throttle the frame
> rate but there is no guarantee that the swap will occur during a retrac=
e
> if the application or the driver havn't called glFinish. I guess
> applications explicitly using swap intervals are aware of that. But
> LIBGL_SYNC_REFRESH is supposed to work for applications that don't even
> know they are waiting for a vblank. So the driver should call glFinish
> for them.
>=20
> I hope I'm not completely off with my theories ;-)

When glXSwapBuffers is called, the rendering context currently bound=20
to the window (if any) is flushed (ala glFinish) automatically.  Then,=20
glXSwapBuffers should wait for the end of the screen refresh before=20
swapping.

That said, I don't know why you're seeing tearing.

-Brian