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

[Olivier Fourdan]

Hi,


On 20 April 2018 at 18:11, Michel Dänzer <michel at daenzer.net> wrote:

> On 2018-04-20 05:10 PM, Roman Gilg wrote:
> > Instead of getting the current msc value from the window, which might be
> > different to old one directly take the last saved msc value saved in
> > the window_priv struct.
> >
> > Signed-off-by: Roman Gilg <subdiff at gmail.com>
> > ---
> [...[
> This is working around an issue in xwl_present_get_ust_msc (it doesn't
> return consistent MSC values for a window which has been unmapped and
> mapped again). This change might do the wrong thing with another backend
> which has real CRTCs and returns consistent MSC values for them.
>
> That said, maybe this is the best that can be done to address the
> immediate issue, but it might be good to at least add a comment saying
> this is a kludge which should be revisited after 1.20.


Unfortunately, contrary to my initial tests, the black window still occurs
randomly even with that patch applied.

I won't be available to investigate that next week, so for anyone willing
to reproduce:

1. Install skypeforlinux
2. run skypeforlinux, open the menu, etc.
3. close the window (the client actually keeps running in the background)
4. reopen the window by running “skypeforlinux” again from the command line

→ The window shows up as a black frame for a random amount of seconds,
before the content becomes visible.

Cheers,
Olivier
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