[PATCH xserver v2 5/5] xwayland: use _XWAYLAND_ALLOW_COMMITS property

[Pekka Paalanen]

On Wed, 18 Jan 2017 10:42:22 -0500 (EST)
Olivier Fourdan <ofourdan at redhat.com> wrote:

> Hi Pekka,
> 
> ----- Original Message -----
> > here is an update on the Weston side:
> > https://lists.freedesktop.org/archives/wayland-devel/2017-January/032712.html
> > 
> > The related Weston patches series has shrunk from 24 to 3 patches as
> > lots of them have been merged. The stuff about _XWAYLAND_ALLOW_COMMITS
> > is still pending.
> > 
> > Given the development on Weston side, would you demand implementing
> > NET_WM_SYNC_REQUEST support in Weston before deciding whether to merge
> > _XWAYLAND_ALLOW_COMMITS support in Xwayland, or is the rationale in the
> > remaining Weston patches enough to justify it already?  
> 
> I meant to reply your previous email but didn't quite finish it,
> sorry...
> 
> What I meant to say there is NET_WM_SYNC and _XWAYLAND_ALLOW_COMMITS
> are two different things and I don't think you can reach the same
> goals using NET_WM_SYNC_REQUEST.
> 
> The goal of NET_WM_SYNC is to make sure the window manager is not
> flooding the client with configure requests while the user resizes
> the window. Without NET_WM_SYNC, you can easily see the client
> window/repaint lagging behind when resizing even with an X11
> compositor - That's quite different from what _XWAYLAND_ALLOW_COMMITS
> is meant for.
> 
> Not all apps use NET_WM_SYNC, actually few do (mostly gtk and qt
> based apps) when considering the large number of X11 apps available,
> so you cannot rely on NET_WM_SYNC being available, whereas having
> _XWAYLAND_ALLOW_COMMITS in Xwayland make it available for all X11
> clients running on Wayland with a compositor taking advantage of it.
> 
> So, *IMHO* _XWAYLAND_ALLOW_COMMITS should not depend on weston
> implementing NET_WM_SYNC_REQUEST. Sorry if I caused some confusion. 

Hi Olivier,

I'm glad we agree. :-)

In my current Weston implementation, ALLOW_COMMITS is only used for the
initial map. I suppose it could also be used to guarantee flicker-free
decorations: just before sending Configure disable commits, and
enable commits after the decorations have been "drawn" in the new size.
Do you think that might be a good idea to implement in the future?

Then there is the question of whether NET_WM_SYNC should automatically
disable/enable commits in Xwayland or do we just implement that in XWM
via _XWAYLAND_ALLOW_COMMITS, but that's completely orthogonal.


Thanks,
pq
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