[Interest] High-dpi fixing for Qt 5.5

[Elvis Stansvik]

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
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