[PATCH xserver] present: fix msc offset calculation in window mode

[Roman Gilg]

On Fri, Apr 20, 2018 at 6:23 PM, Olivier Fourdan <fourdan at gmail.com> wrote:
> Unfortunately, contrary to my initial tests, the black window still occurs
> randomly even with that patch applied.
That's unfortunate. How severe is it? Is it just for a short period or
longer? I believe you said on IRC that it once stayed black and never
resumed but you weren't sure if just the client froze.

One idea I have regarding the issue is, that I believe on Unrealize
the remaining queued events are not sent back to Present, but simply
discarded on xwl_present_cleanup. I think these events should still be
delivered to Present instead.

But maybe the best way forward instead would be to do what Michel
proposed: add a persistent private struct to Xwayland and not reuse
the xwl_window one, which gets destroyed on every Unrealize. This way
the window's Xwayland Present msc counter could keep running while the
window is unrealized and we could more reliable process events still
waiting for their target msc.

The problem is that I'm on a Plasma dev sprint by today till next
weekend and won't be able to work on the issue in this time. After
that I would try to setup my build enviornment for the Xserver again
and find a solution to the problem. If this is not possible in regards
to the planned Xserver release, we need to find another solution.