[Interest] High-dpi fixing for Qt 5.5

[John Weeks]

Do it in the showEvent()?

> On Mar 2, 2018, at 8:16 AM, Elvis Stansvik <elvstone at gmail.com> wrote:
> 
> 2018-03-02 16:26 GMT+01:00 Martins, Sérgio <sergio.martins at kdab.com>:
>> On 2018-03-02 15:21, Elvis Stansvik wrote:
>>> 
>>> 2018-03-02 16:18 GMT+01:00 Elvis Stansvik <elvstone at gmail.com>:
>>>> 
>>>> 2018-03-02 15:54 GMT+01:00 Nikos Chantziaras <realnc at gmail.com>:
>>>>> 
>>>>> On 02/03/18 16:37, Elvis Stansvik wrote:
>>>>>> 
>>>>>> 
>>>>>> [...]
>>>>>> How can I (as application developer) get notified of screen changes of
>>>>>> non-QWindow-backed widgets?
>>>>> 
>>>>> 
>>>>> 
>>>>> There seems to be two ways to do this. One is using one of the QScreen
>>>>> signals:
>>>>> 
>>>>>  http://doc.qt.io/qt-5/qscreen.html
>>>> 
>>>> 
>>>> Hm, I should have made my question more clear.
>>>> 
>>>> The typical way I've seen is to connect to the screenChanged signal of
>>>> the closest ancestral QWindow (window()->windowHandle()).
>>>> 
>>>> But, I've found that it's not reliable for certain widgets/certain
>>>> platforms to do e.g:
>>>> 
>>>>    QTimer::singleShot(0, [this]() {
>>>>        connect(window()->windowHandle(), &QWindow::screenChanged,
>>>>                this, &MyWidget::handleScreenChanged);
>>>>    });
>>>> 
>>>> in my constructor, because depending on how the widget is constructed,
>>>> the parentage up to a top-level window may not have been established
>>>> yet, even if I do it in a single-shot timer like this.
>>> 
>>> 
>>> I should clarify this: What I mean is that I've seen situations when
>>> window()->windowHandle() is 0 here, even if the widget is constructed
>>> with a full parentage up to a top-level widget.
>> 
>> 
>> Hi,
>> 
>> Call QWidget::create() on your top-level constructor, and it will ensure it
>> it has a QWindow
> 
> Thanks, that's one way of doing it, but reading further, it seems
> QWidget delays doing this for a reason. E.g. see the docs for
> Qt::AA_ImmediateWidgetCreation, which I could also use to tell Qt to
> call create(..) immediately during construction. That attribute is due
> to be removed in Qt 6 though.
> 
> I don't think I like the idea of jumping the gun on QWidget here and
> calling create(..) myself.
> 
> Surely there must be some way to reliably know when a widget is moved
> to another screen (or anoter top-level window), short of hooking up to
> internal events?
> 
> Elvis
> 
>> 
>> 
>> Regards,
>> --
>> Sérgio Martins | sergio.martins at kdab.com | Senior Software Engineer
>> Klarälvdalens Datakonsult AB, a KDAB Group company
>> Tel: Sweden (HQ) +46-563-540090, USA +1-866-777-KDAB(5322)
>> KDAB - The Qt, C++ and OpenGL Experts
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-Johnm Weeks