[vtk-developers] Fractional DPI scaling not supported by QVTKOpenGLWidget?

[Elvis Stansvik]

2018-02-09 15:24 GMT+01:00 Cory Quammen <cory.quammen at kitware.com>:
> Elvis,
>
> I don't believe there is a reason we can't use the qreal version of
> devicePixelRatioF(). I think the F may have gotten dropped in a series of
> commits to improve DPI support.
>
> A patch would be welcome.

Great, I'll take a stab at it.

Elvis

>
> Thanks,
> Cory
>
> On Fri, Feb 9, 2018 at 4:51 AM, Elvis Stansvik
> <elvis.stansvik at orexplore.com> wrote:
>>
>> 2018-02-09 10:31 GMT+01:00 Karsten Tausche
>> <karsten.tausche at student.hpi.uni-potsdam.de>:
>> > Hi Elvis,
>> >
>> > I have a workaround for this in my own code: Basically I have a subclass
>> > of
>> > QVTKOpenGLWidget, which disables the base class DPI support and passes
>> > Qt's
>> > DPI value manually to the internal vtkRenderWindow. See
>> >
>> > https://github.com/kateyy/geohazardvis/blob/master/gui/data_view/t_QVTKWidget.cpp
>> > especially lines 288 and 306.
>> >
>> > (In the code, don't get confused about the name of the class, it
>> > provides
>> > some support to inherit from QVTKWidget2, but you can assume
>> > OPTION_USE_QVTKOPENGLWIDGET to be enabled.)
>>
>> Aha, thanks a lot Karsten. I'll see if I can do something similar in
>> our own QVTKOpenGLWidget subclass.
>>
>> (Still of course interested in if any of the VTK devs have looked into
>> supporting this out of the box.)
>>
>> Elvis
>>
>> >
>> > Cheers,
>> > Karsten
>> >
>> >
>> > On 09-02-18 08:43, Elvis Stansvik wrote:
>> >
>> > Den 5 feb. 2018 3:20 em skrev "Elvis Stansvik"
>> > <elvis.stansvik at orexplore.com>:
>> >
>> > Hi all,
>> >
>> > My pointy-haired boss got a new laptop with a high-DPI monitor, and
>> > started using a fractional DPI scaling factor (under KDE screen
>> > settings). He's now reporting that our Qt/VTK app has problems with
>> > this. The VTK windows are not correctly sized.
>> >
>> > I've also gotten the same report from a Windows 10 user that had this
>> > problem.
>> >
>> > I had a look at the VTK code that sizes the render window [1]:
>> >
>> >   const int devicePixelRatio_ = this->devicePixelRatio();
>> >   const QSize widgetSize = this->size();
>> >   const QSize deviceSize = widgetSize * devicePixelRatio_;
>> >
>> > and then
>> >
>> >   this->RenderWindow->SetSize(deviceSize.width(), deviceSize.height());
>> >
>> > Note the use of the int devicePixelRatio() API, not qreal
>> > devicePixelRatioF() (available from Qt 5.6).
>> >
>> > Does this mean there's no way to get correctly sized VTK windows when
>> > using a fractional DPI scaling factor? If so, has anyone looked into
>> > supporting this? Would it be a lot of work?
>> >
>> >
>> > Noone knows? :)
>> >
>> > If it's (like I suspect) currently not supported, I'd be willing to try
>> > to
>> > fix it myself. But it would be good to know whether there are dragons
>> > here
>> > (maybe that's why it's not supported yet) or if someone else is already
>> > working on it.
>> >
>> > Elvis
>> >
>> >
>> > Best regards,
>> > Elvis
>> >
>> > [1]
>> >
>> > https://gitlab.kitware.com/vtk/vtk/blob/master/GUISupport/Qt/QVTKOpenGLWidget.cxx#L340-351
>> >
>> >
>> >
>> >
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>
>
> --
> Cory Quammen
> Staff R&D Engineer
> Kitware, Inc.