Time in wayland presentation extension

Pekka Paalanen ppaalanen at gmail.com
Tue Dec 16 23:52:14 PST 2014

On Wed, 17 Dec 2014 08:14:23 +0100
Dan Oscarsson <Dan.Oscarsson at tieto.com> wrote:

> tis 2014-12-16 klockan 15:53 +0200 skrev Pekka Paalanen:
> > > The overlay based, which I expect is using hardware in its
> > > implementation, gives very good display of frames synchronised to vsync.
> > > It gives no flicker and is the one you want when you watch movies.
> > 
> > That still does not imply any hardware queue, does it?
> No, and I cannot find any web page or e-mail that says it definitely
> does use a hardware queue. Though it has all possibilities for it. With
> vdpau the video frames are inside the graphics card, so all needed
> information can be inside the graphics card and it can handle the flip
> to next video frame itself.

That's exactly what a Wayland compositor will be able to do with
Presentation queueing, if the kernel graphics drivers allow it. :-)

> > Btw. if you have a video player using overlay vdpau path, and you move
> > that window, does the overlay lag behind like in the old Xv times?
> I do not know as normally runs my player in full screen mode. Forgot to
> test that yesterday. vdpau will automatically switch to blit mode if
> overlay will not work (and later back when overlay is ok again), so a
> test may not guarantee that it is overlay mode I see.

That switching is exactly what a Wayland compositor is able to do
already (if the DRM KMS interfaces allowed it) for all apps that use
suitable buffers, not only VDPAU users. :-)

The difference with Wayland is that the compositor can synchronize
everything as needed. Whether you move or resize the video player
window, you will never see the "overlay lag" while still making optimal
use of all hardware overlays. That is serious goal for us.


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