[Development] QWidget mouse events - different order

[Rick Stockton]

On 12/18/2013 01:10 PM, Andreas Aardal Hanssen wrote:
> On 18 Dec 2013, at 22:07, Rayner Pupo Gómez <rpgomez at uci.cu> wrote:
Inner-most quote is from Martin Koller.

>>> I've discovered that with Qt5 I get a different order of mouse events on
>>> a QWidget than with Qt4 (openSuse 13.1 Linux, X11):
>>> double clicking a widget results in Qt4 in:
>>> mousePressEvent 
>>> mouseReleaseEvent 
>>> mouseDoubleClickEvent 
>>> mousePressEvent 
>>> mouseReleaseEvent
>>> but in Qt5 in:
>>> mousePressEvent 
>>> mouseReleaseEvent 
>>> mousePressEvent 
>>> mouseDoubleClickEvent 
>>> mouseReleaseEvent 
>>> I tested with Qt4.8.5 and Qt5.2.
>>> Is this behavioral change intended, undefined, a bug ?
>>> (it results in my app not behaving as before ...)
>>> -- 
>> I think it's a mistake to rely on the order of this kind of events, there are 
>> fired asynchronously, your logic cant depend on this
> Wrong! The order is very essential and can and must be relied on.
> The behaviour in Qt 5 is questionable. I believe the double-click must come first to be able to distinguish from two presses.
>
> I also wonder if it's accurate / true that Qt 4 sends the second press after the double-click. AFAIR:
>
> Press
> Release
> DoubleClick
> Release
>
> Is the right events for double-clicking.
>
> Andreas
Andreas, I'm confirming the QT5 behavior, to be as Martin describe. BUT,
the Qt4 behavior seems to be as YOU recall - no ButtonPress" at all for
the fast-enough second click which invoked a "DoubleClick event.
I used "qtbase/examples/widgets/widgets/mousebuttons" program (the
executable is named "buttontester"). Running inside Qt Creator, with
5.2, output from double-clicking of "LeftButton" is:

   Starting
/opt/Qt5.2.0/5.2.0/Src/qtbase/examples/widgets/widgets/build-mousebuttons-Desktop_Qt_5_2_0_GCC_64bit-Debug/buttontester...

  "Mouse Press: raw button=1 Qt=LeftButton
  heldbuttons LeftButton "
  "Mouse Release: raw button=1 Qt=LeftButton
  heldbuttons NoButton"
  "Mouse Press: raw button=1 Qt=LeftButton
   heldbuttons LeftButton "
  "Mouse DoubleClick: raw button=1 Qt=LeftButton
   heldbuttonsLeftButton "
  "Mouse Release: raw button=1 Qt=LeftButton
   heldbuttons NoButton"

  
/opt/Qt5.2.0/5.2.0/Src/qtbase/examples/widgets/widgets/build-mousebuttons-Desktop_Qt_5_2_0_GCC_64bit-Debug/buttontester
exited with code 0


But, Migrating the program back to 4.8.5 (just remove the include of
Qtwidgets, and all the lines which test for buttons > Qt::MiddleButton)
I confirm YOUR "AFAIR" behavior, and not the behavior in Martin's message:


  "Mouse Press: raw button=1  Qt=LeftButton
  heldbuttons LeftButton "
  "Mouse Release: raw button=1  Qt=LeftButton
   heldbuttons NoButton"
  "Mouse DoubleClick: raw button=1  Qt=LeftButton
   heldbuttonsLeftButton "
  "Mouse Release: raw button=1  Qt=LeftButton
   heldbuttons NoButton"


Given the fact that many "single-click" programs involve rapid clicking,
(they ignore the DoubleClick completely, and execute per the second
MousePress) - IMO, we should provide both events, and write a doco
change instead of revising the code to match Qt4 behavior.


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