https://bugs.kde.org/show_bug.cgi?id=514812

            Bug ID: 514812
           Summary: Resizing KDiff3 on Wayland causes panels to turn black
                    and entire UI to be disabled
    Classification: Applications
           Product: kdiff3
      Version First 1.12.3
       Reported In:
          Platform: Fedora RPMs
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: application
          Assignee: [email protected]
          Reporter: [email protected]
  Target Milestone: ---

Created attachment 188666
  --> https://bugs.kde.org/attachment.cgi?id=188666&action=edit
Screenshot of KDiff3 with disabled UI and black editor panels

SUMMARY
When I resize a window in KDiff3, the text views turn black, the entire UI is
disabled, and there is a grayed-out progress bar and Cancel button in the
status bar.

STEPS TO REPRODUCE
1. Open KDiff3 in a Plasma Wayland session.
2. Load or paste one or more files.
3. Resize the window quickly.

Maximizing or unmaximizing the app once at a time, or resizing the window by
exactly one pixel at a time, is safe. Any resize operation disables the UI,
turns the text views white, and adds a progress bar and grayed-out Cancel
button to the status bar, until the repainting finishes. If you send a second
resize event before the window finishes repainting, the text views turn black
and the UI never gets reenabled.

I think this is an issue where under Wayland, the app receives events and
triggers repaints while the previous resize operation is still in progress, and
this reentrant repaint sends the app into a broken state unable to finish
redrawing.

This issue does not happen in `QT_QPA_PLATFORM=xcb kdiff3`, which runs under
XWayland.

OBSERVED RESULT
The app hangs in an unusable state.

EXPECTED RESULT
The app does not hang.

SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 43
KDE Plasma Version: 6.5.5
KDE Frameworks Version: 6.22.0
Qt Version: 6.10.1
Kernel Version: 6.18.5-200.fc43.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i7-8559U CPU @ 2.70GHz
Memory: 16 GiB of RAM (15.5 GiB usable)
Graphics Processor: Intel® Iris® Plus Graphics 655
Manufacturer: Intel(R) Client Systems
Product Name: NUC8i7BEH
System Version: J72992-303

ADDITIONAL INFORMATION
This seems related to Bug 486401, because both are about how Wayland events are
delivered or processed differently than X11. However this bug applies to
resizing rather than scrolling, and makes the app unusable rather than just
slow.

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