[krita] 3rdparty/ext_qt: Fix a "bended lines"+AMD+Qt5.6 bug

[Fazekas László]

> Just another thing, this annoys me in many (if not all) programs. If you
> are using a tablet's stylus, it disables the mouse completely. This is not
> a good thing. Sometimes the tip of the stylus is not accurate enough, so
> better to use the stylus in proximity and press the buttons on the mouse.
> I'm left handed, so I'm holding the stylus in my left hand and the mouse in
> my right hand. It's very effective. I can use the wheel on the mouse the
> same way. This is not a technical limitation, I already made programs with
> this feature (but not with Qt...).
>
>> I'm afraid this limitation is somewhat technical. The problem is that
>> tablet generates Mouse(!) events too. And in most of the cases these mouse
>> events do not correlate with what we get via native tablet events. It means
>> that if we will start processing mouse events while tablet is in proximity,
>> the lines will become dizzy, because of out-of-order events. What is more,
>> in most of the cases we cannot distinguish real mouse events and the
>> synthesized mouse events generated by the tablet. Right now people in Qt
>> are working on distinguishing them but I'm not sure when and if it is going
>> to work. There are too many variations where and how these synthesized
>> events are generated.
>>
>>
>>

I'm talking about the buttons and the wheel on the mouse. It's a design 
flaw that every systems are providing these as mouse properties and not 
keyboard buttons. There is no reason to disable any buttons while 
working with the tablet.

I think maybe it's possible to filter the mouse events only to get the 
state of the buttons when in tablet mode. However, it's perhaps not easy 
when the mouse and the tablet are sending different button states at the 
same time. But keeping the track with the ButtonPress and ButtonRelease 
events maybe still possible.

Fazek