[RFC xserver 3/3] Xwayland: use _XWAYLAND_ALLOW_COMMITS property

[Olivier Fourdan]

Hi Pekka,

> [...]
> Patches 1 and 2 OTOH would be ready for merging on my behalf.

Yes, I think the two first patches are fine.
 
> Olivier asked about _NET_WM_SYNC_REQUEST - do you want me to fully
> implement the basic sync protocol too before accepting this series?

I was hoping/wondering if using _XWAYLAND_ALLOW_COMMITS could help the X11 window manager/X11 compositor to better sync the updates from the client with the refresh of the server side decorations (which includes drop shadows) to reduce the artefacts with server side decorations and drop shadows when resizing apps implementing the _NET_WM_SYNC_REQUEST protocol under Xwayland

But if anything, imho, it's up to the X11 window manager/X11 compositor to use both mechanism when dealing with Xwayland, since the window manager/X11 compositor "knows" about both properties and when it's best to paint.

So FWIW, I don't think it's necessary to add _NET_WM_SYNC_REQUEST to Xwayland, when using _XWAYLAND_ALLOW_COMMITS. I'll play with mutter and _XWAYLAND_ALLOW_COMMITS to see how that goes :)
 
> [...]
> I expect the property to be written only from the XWM. Should I verify
> that somehow? Can I even identify the XWM here?

I guess any client (or even user playing with xprop [1]) could add/change the property to any toplevel X11 window and Xwayland would stop committing the surfaces, but what would be the point of doing that?

Cheers,
Olivier

[1] "xprop -id ... -format _XWAYLAND_ALLOW_COMMITS 32c -set  _XWAYLAND_ALLOW_COMMITS 0" brings the update to a halt :)