Why does Java (XWayland / Weston) resize a Window to 1x1 pixel when HDMI is unplugged (and does not resize back when HDMI is plugged)

[Pekka Paalanen]

On Thu, 8 Jun 2023 19:13:39 +0200
Martin Petzold <martin.petzold at tavla.de> wrote:

> Am 08.06.23 um 14:45 schrieb Martin Petzold:
> > Hi Pekka,
> >
> > Am 08.06.23 um 14:37 schrieb Pekka Paalanen:  
> >> On Thu, 8 Jun 2023 14:21:31 +0200
> >> Martin Petzold <martin.petzold at tavla.de> wrote:
> >>  
> >>> I am fixed to this Kernel, will be hard to get Weston 12 running.  
> >> Hi,
> >>
> >> why would you say that? Did you try? Or do you mean that building
> >> Weston and a few dependencies (not kernel, not Mesa) from source is too
> >> much?  
> >
> > We are compiling our own kernel version for embedded i.MX8. Also the 
> > Debian is our custom build and we are able to adjust to other packages 
> > or compile parts. We know how to do that. However, we are fixed to 
> > 5.10.52 for several reasons. And I need to cross-compile Weston then, 
> > which is maybe challenging?
> >
> > I can try to compile on device and test. But which dependencies also 
> > need to be compiled then? XWayland? Wayland? Libraries?
> >  
> >>
> >> FWIW, when you unplug the last display, leaving none, then there is no
> >> display area. Weston does not pretend a fake display, there just is
> >> none. I don't know how Xwayland reacts to that, and how that Java suite
> >> reacts to what Xwayland does. Those would be something to look into, if
> >> Weston upgrade does not help.  
> > Yes, it must be XWayland. Maybe there is any configuration to fix it?  
> >>
> >> Xwayland might have a fake something when all real displays are gone,
> >> and maybe nothing then re-associates your app window from the fake
> >> monitor to a real monitor once a real monitor appears again? No idea.
> >>
> >> Maybe check what xrandr says while you have no displays connected? That
> >> might give a clue, assuming the Java stack listens to RandR.
> >>  
> >  
> Interesting: It changes from XWAYLAND0 to XWAYLAND1 to XWAYLAND2 and 
> also if I have it UNPLUGGED the screen is there.
> 
> HDMI PLUGGED (on boot)
> 
> xrandr --current
> Screen 0: minimum 16 x 16, current 1920 x 1080, maximum 32767 x 32767
> XWAYLAND0 connected 1920x1080+0+0 (normal left inverted right x axis y 
> axis) 1110mm x 620mm
>     1920x1080     59.96*+
> 
> HDMI UNPLUGGED
> 
> xrandr --current
> Screen 0: minimum 16 x 16, current 1920 x 1080, maximum 32767 x 32767
> XWAYLAND1 connected 1920x1080+0+0 (normal left inverted right x axis y 
> axis) 1150mm x 650mm
>     1920x1080     59.96*+
> 
> HDMI RE-PLUGGED
> 
> xrandr --current
> Screen 0: minimum 16 x 16, current 1920 x 1080, maximum 32767 x 32767
> XWAYLAND2 connected 1920x1080+0+0 (normal left inverted right x axis y 
> axis) 1110mm x 620mm
>     1920x1080     59.96*+

This is interesting, but does not look like a problem in itself: the
desktop size remains reasonable at all times, even when nothing is
connected.

If upgrading to more recent upstream versions does not help, then there
are two possibilities:
- Java stack reacts strangely to the above
- Weston's XWM resizes the window strangely

We could at least confirm the Weston behaviour then.


Thanks,
pq
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