[Octave-bug-tracker] [bug #53807] KDE QDockWIdget titlebar mouse drag creates defective floated focus for Qt 5.3.2 -> 5.4.1

[Dan Sebald]

URL:
  <http://savannah.gnu.org/bugs/?53807>

                 Summary: KDE QDockWIdget titlebar mouse drag creates
defective floated focus for Qt 5.3.2 -> 5.4.1
                 Project: GNU Octave
            Submitted by: sebald
            Submitted on: Wed 02 May 2018 06:56:33 AM UTC
                Category: GUI
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Unexpected Error
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: Any

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Details:

I'm posting this bug report as a reference point to refer to in the C++ code. 
I will have the workaround as part of the code associated with Bug #53276. 
The code there is too fluid to be able to coordinate two separate changesets.

In debugging that Bug #53276 code on KDE, I ran into a puzzling issue in which
only if I dragged a panel (QDockWidget) from the QMainWindow to float it did
the focus behavior become corrupt.  Pressing on the title bar of the floated
window would show the variable name in highlighted text and background for a
fraction of a second and the focus would jump back to the main window.  Keep
pressing the title bar and it was only momentary focus.  In other words,
couldn't focus the floated window when floated by mouse drag.

With the QDockWidget in that state, I could click the tabs to make the
Variable Editor and its floated dock widget hide.  Showing again would then
have a correctly function focus behavior.  So, the fix appears to be
hiding-then-showing the QDockWidget in that situation.  I had to do the hide
and show as queued-connections in order to make the program flow go back to
the system inbetween the hide and show.

I searched a long time for this bug, but then when I took away the custom
title bar and used the default title bar, I knew straight away is was a Qt/KDE
bug.  Searching the Internet I found a Qt bug report that is extremely close
to what I described.  The Qt bug report is here:

https://bugreports.qt.io/browse/QTBUG-44813

That will at least give us another Qt bug in which we can use a version range
to isolate the added kludge.

Can close as fixed since there isn't anything to discuss or code to patch, but
I will post a code hunk to this report to illustrate the solution.




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