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

[Elvis Stansvik]

2018-02-09 16:58 GMT+01:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
> 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.

Things got in the way, but now there's a WIP MR from me:

    https://gitlab.kitware.com/vtk/vtk/merge_requests/3973

Marcus: I need your advice on
QVTKInteractorAdapter::SetDevicePixelRatio(...) (see question in the
MR).

Cheers,
Elvis

>
> 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.