Public bug reported:
System: Ubuntu 22.04.1 LTS
Hardware: VmWare on i7 3770 configured with 4 CPUs, but wild users from field
reported same issue on different hardware.
Option 1: User logged in locally through Ubuntu on XOrg option in login screen.
Option 2: User logged in remotely via xrdp protocol that uses XOrg.
Problem manifested as sporadic missing repaints of application. Debugging shows
that missing repaints happen in case window title text changed just before
window image repainting.
Was able to create minimalistic X11 test application that on each keypress:
changes titlebar to random string and (immediately) paints some string inside.
From time to time titlebar changed but content inside is not painted, although
according to debug prints expose events arrived correctly all the time. However
if in such situation try to move window by grabbing its titlebar using mouse
(sometimes its enough just to move mouse over) - then content gets updated to
correct one and (according to debug printouts) this happens without getting
expose events by application.
Attached: source code of demo application and will try to attach also video
recording of demonstration.
Note that bug highly depends on timings (likely its a race condition somewhere
in XWayland or Window Manager and there is loop in code attenuated for highest
reproduction rate on my system. On other systems it may need adjustements.
** Affects: xwayland (Ubuntu)
Importance: Undecided
Status: New
** Attachment added: "Minimal reproduction application"
https://bugs.launchpad.net/bugs/2002456/+attachment/5640552/+files/x11app.tar.gz
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https://bugs.launchpad.net/bugs/2002456
Title:
Random window repaints missing if happen together with title change
Status in xwayland package in Ubuntu:
New
Bug description:
System: Ubuntu 22.04.1 LTS
Hardware: VmWare on i7 3770 configured with 4 CPUs, but wild users from field
reported same issue on different hardware.
Option 1: User logged in locally through Ubuntu on XOrg option in login
screen.
Option 2: User logged in remotely via xrdp protocol that uses XOrg.
Problem manifested as sporadic missing repaints of application. Debugging
shows that missing repaints happen in case window title text changed just
before window image repainting.
Was able to create minimalistic X11 test application that on each keypress:
changes titlebar to random string and (immediately) paints some string inside.
From time to time titlebar changed but content inside is not painted, although
according to debug prints expose events arrived correctly all the time. However
if in such situation try to move window by grabbing its titlebar using mouse
(sometimes its enough just to move mouse over) - then content gets updated to
correct one and (according to debug printouts) this happens without getting
expose events by application.
Attached: source code of demo application and will try to attach also video
recording of demonstration.
Note that bug highly depends on timings (likely its a race condition
somewhere in XWayland or Window Manager and there is loop in code attenuated
for highest reproduction rate on my system. On other systems it may need
adjustements.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/xwayland/+bug/2002456/+subscriptions
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