[vtk-developers] Strange renderering with mixed polydata/volume with QVTKOpenGLWidget

[Elvis Stansvik]

2017-05-22 13:39 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
> 2017-05-18 16:14 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>> 2017-05-18 15:59 GMT+02:00 Utkarsh Ayachit <utkarsh.ayachit at kitware.com>:
>>> For now, try doing this:
>>>   auto surfaceFormat = QVTKOpenGLWidget::defaultFormat()
>>>   surfaceFormat.setSamples(0);
>>>   surfaceFormat.setAlphaBufferSIze(0);
>>>   QSurfaceFormat::setDefaultFormat(surfaceFormat);
>>
>> Thanks for the suggestion. I tried it out on the Mac, but it looks
>> like it made no difference :/
>
> I'm really sorry, this must have been a PEBKAC from me, because now
> that I tried it again, it actually does solve the problem (!). I must
> have made some mistake first time I tried it.
>
> Rendering on the Mac is now correct. I will have to wait until I get
> access to the Windows/nVidia machine again to confirm that it solves
> it there too, but I'm hopeful that it does.
>
> (Note: I sent off a couple of e-mails earlier today with some
> screenshots from the Mac, that ended up in the moderation queue due to
> the screenshots being > 1000 KB).
>
> Many thanks for this tip Utkarsh.

As a side note: I found this in the source code for ITK-SNAP [1]:

// Starting with Qt 5.6, the OpenGL implementation uses OpenGL 2.0
// In this version of OpenGL, transparency is handled differently and
// looks wrong.
QSurfaceFormat gl_fmt;
gl_fmt.setMajorVersion(argdata.opengl_major);
gl_fmt.setMinorVersion(argdata.opengl_minor);
/*
gl_fmt.setSwapBehavior(QSurfaceFormat::DoubleBuffer);
gl_fmt.setRedBufferSize(1);
gl_fmt.setGreenBufferSize(1);
gl_fmt.setBlueBufferSize(1);
gl_fmt.setDepthBufferSize(1);
gl_fmt.setStencilBufferSize(0);
gl_fmt.setAlphaBufferSize(0);
*/

I'm guessing the comment is referring to the same issue I saw. Note
the commented setAlphaBufferSize(0). So is setting the GL version
explicitly like this the proper workaround?

Elvis

[1] https://github.com/pyushkevich/itksnap/blob/master/GUI/Qt/main.cxx#L572-L574

>
> Elvis
>
>>
>> Elvis
>>
>>>
>>>
>>> Utkarsh
>>>
>>> On Thu, May 18, 2017 at 8:57 AM, Elvis Stansvik
>>> <elvis.stansvik at orexplore.com> wrote:
>>>>
>>>> I'm porting our program to the new QVTKOpenGLWidget.
>>>>
>>>> In one place, we're using a semi-transparent polygonal cube to show
>>>> the selection of an area. We're doing volume rendering using
>>>> vtkGPUVolumeRayCastMapper in the same renderer, and the polygonal
>>>> selection marker is enclosing the volume in the X/Y dimensions.
>>>>
>>>> See the attached linux_selection_correct.png for how this is supposed
>>>> to look, and you'll understand what I mean. The light blue area is the
>>>> selection marker.
>>>>
>>>> This has always worked fine, but after porting from QVTKWidget to
>>>> QVTKOpenGLWidget, the rendering looks strange on Windows (nvidia) and
>>>> macOS (2013 MBP, intel iris). See the attached
>>>> windows_nvidia_selection.png and macos_selection.png.
>>>>
>>>> The selection is visualized using
>>>>
>>>>   vtkCubeSource -> vtkPolyDataMapper
>>>>
>>>> and a vtkActor configured like this:
>>>>
>>>>     auto selectionColor = palette().color(QPalette::Highlight);
>>>>
>>>>     m_selectionMarkerActor->SetMapper(selectionMarkerMapper);
>>>>     m_selectionMarkerActor->GetProperty()->SetColor(selectionColor.redF(),
>>>>
>>>> selectionColor.greenF(),
>>>>
>>>> selectionColor.blueF());
>>>>     m_selectionMarkerActor->GetProperty()->SetOpacity(0.1);
>>>>     m_selectionMarkerActor->GetProperty()->SetAmbient(1.0);
>>>>     m_selectionMarkerActor->GetProperty()->SetDiffuse(0.0);
>>>>     m_selectionMarkerActor->GetProperty()->SetSpecular(0.0);
>>>>
>>>> Any idea why the rendering looks so strange on Windows/nvidia and
>>>> macOS/iris, respectively, when using the new widget class?
>>>>
>>>> We're using a recent VTK from Git master.
>>>>
>>>> We're doing the recommended
>>>>
>>>>     QSurfaceFormat::setDefaultFormat(QVTKOpenGLWidget::defaultFormat());
>>>>
>>>> to set the default surface format before QApplication construction.
>>>>
>>>> In the particular QVTKOpenGLWidget used here, we modify the format with
>>>>
>>>>     auto surfaceFormat = format();
>>>>     surfaceFormat.setSamples(0);
>>>>     setFormat(surfaceFormat);
>>>>
>>>> to disable multisampling.
>>>>
>>>> Very grateful for any advise on how to solve this.
>>>>
>>>> Cheers,
>>>> Elvis
>>>>
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>>>