[Octave-bug-tracker] [bug #51442] graphics_toolkit qt does not work with Qt 5 in Xwayland and Intel mesa driver

[John W. Eaton]

Follow-up Comment #16, bug #51442 (project octave):

I also see the problem with qt5 and can confirm that resizing the window makes
the plot appear.

If I run Octave, attach gdb to the octave-gui process, set a breakpoint in the
QtHandles::Container::resizeEvent function and then execute "sombrero" at the
octave prompt, execution stops in the resizeEvent function and the figure is
properly displayed when I continue execution.  If I delete the breakpoint or
type "continue" for gdb prior to executing "sombrero", then the plot doesn't
appear properly.

To me, this suggests some kind of timing or threading issue.  And if I make
the attached change (inserting a delay in the
QtHandles::Container::resizeEvent function), it seems the plot will appear
correctly given a sufficient delay.  On my system, a delay of 0.2 seconds
appears to be sufficient to make the plot always appear correctly.  With a
smaller delay the plot is sometimes correct and sometimes not.  Oddly, it
seems to fail more often if the cursor is in the plot window when it is
drawn.

I'm not saying that a delay is the right fix, only that this behavior points
to some kind of timing issue.  If so, then maybe there is something we can do
to avoid the problem?


(file #41192)
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