[vtkusers] Black renderwindow with vtkGPUVolumeRayCastMapper/MaximumIntensityProjection

[Sophonet]

Hi Sankhesh,

thanks for pushing me towards the next step of testing. Indeed, the VTK 
test which I have mentioned below works. After having spent some time on 
trying to localize the problem, it seems that this is related to the 
fact that my application is using Qt (5.10 - with desktop OpenGL 
backend, which works for all my other VTK-based visualizations).

I have followed all the suggestions for setting up a QVTKOpenGLWidget, 
but using the same code as in the test, the four viewers remain empty 
(which is what I am observing in my application as well). Code snippets 
are below...

Any hints on how to use vtkGPUVolumeRayCastMapper in a Qt 5 application 
with the OpenGL2 backend?

Thanks,

      Sophonet

---
void TestGPURayCastBlendModes(vtkRenderWindow *renwin)
{
   // The code from the corresponding function in
   // 
https://github.com/Kitware/VTK/blob/master/Rendering/Volume/Testing/Cxx/TestGPURayCastFourComponentsMIP.cxx
   // with minor modifications to use the given renderwindow, and after 
removing
   // the few testing-statements
}

int main(int argc, char *argv[])
{
	QSurfaceFormat::setDefaultFormat(QVTKOpenGLWidget::defaultFormat());
	QApplication app(argc, argv);

	QMainWindow *mainWindow = new QMainWindow();

	QVTKOpenGLWidget *widget = new QVTKOpenGLWidget(mainWindow);

	auto *renwin = vtkGenericOpenGLRenderWindow::New();
	widget->SetRenderWindow(renwin);
	mainWindow->setCentralWidget(widget);

	mainWindow->show();
	TestGPURayCastBlendModes(renwin);
         return app.exec();
}



On 2018-02-19 13:38, Sankhesh Jhaveri wrote:
> Hi,
> 
> Well the difference between in my suggestion was that the minimum
> scalar value was also getting an opacity weighing ensuring that you
> should at least see a white cube if the volume has all the same
> values. However, it that also doesn't show you anything, perhaps
> there's something else going on.
> 
> Could you try running the VTK tests to see if the volume rendering
> ones run and pass?
> 
> Thanks,
> Sankhesh
> 
> On Mon, Feb 19, 2018, 4:05 AM Sophonet <vtk12af6bc42 at kant.sophonet.de>
> wrote:
> 
>> Hi Sankhesh,
>> 
>> thanks for your message - just tried your suggestion, which is
>> basically
>> what I have already tried in the commented part of the code below.
>> As
>> expected, it did not change the result, my renderwindow is still
>> black.
>> 
>> Any other hint?
>> 
>> Best regards,
>> 
>> Sophonet
>> 
>> On 2018-02-09 17:57, Sankhesh Jhaveri wrote:
>>> Hi Sophonet,
>>> 
>>> Try setting the scalar opacity function over the whole range of
>> scalar
>>> values.
>>> 
>>> Something like:
>>> 
>>> double * range = data->GetScalarRange();
>>> vtkNew<vtkPiecewiseFunction> f;
>>> f->AddPoint(range[0], 0.1);
>>> f->AddPoint(range[1], 1.0);
>>> property->SetScalarOpacity(f);
>>> 
>>> Hope that helps,
>>> Sankhesh
>>> 
>>> ​
>>> 
>>> On Sat, Feb 3, 2018 at 5:37 AM Sophonet
>>> <vtk12af6bc42 at kant.sophonet.de> wrote:
>>> 
>>>> Hi list,
>>>> 
>>>> in an earlier version of my software using VTK7.x and the OpenGL
>>>> backend, MIP rendering was working using
>> vtkGPUVolumeRayCastMapper
>>>> and
>>>> MaximumIntensityProjection.
>>>> 
>>>> However, in VTK 8.x (e.g. VTK 8.1.0), using the OpenGL2 backend,
>> the
>>>> renderwindow stays black/empty - VTK does not show an error
>> message,
>>>> and
>>>> the IsRenderSupported (see below) does not seem to fail.
>>>> 
>>>> Any hints what is wrong with the code below? By the way: I have
>>>> added
>>>> the volumeProperty (and the piecewise function) after following a
>>>> current VTK test program
>>>> 
>>> 
>> 
> (https://github.com/Kitware/VTK/blob/master/Rendering/Volume/Testing/Cxx/TestGPURayCastFourComponentsMIP.cxx).
>>>> 
>>>> vtkimagedata is a scalar medical image (unsigned short), so
>> nothing
>>>> special.
>>>> 
>>>> Thanks,
>>>> 
>>>> Sophonet
>>>> 
>>>> vtkNew<vtkGPUVolumeRayCastMapper> mapper;
>>>> mapper->SetInputData(vtkimagedata);
>>>> mapper->SetBlendModeToMaximumIntensity();
>>>> 
>>>> vtkNew<vtkVolume> volume;
>>>> volume->SetMapper(mapper);
>>>> // ... connect to renderer etc.
>>>> 
>>>> //NOTE: The following lines from VTK's
>>>> TestGPURayCastFourComponentsMIP.cxx did not solve the problem
>>>> //vtkNew<vtkVolumeProperty> volumeProperty;
>>>> //volumeProperty->IndependentComponentsOn();
>>>> 
>>>> //volumeProperty->SetInterpolationType(VTK_LINEAR_INTERPOLATION);
>>>> //volumeProperty->SetShade(1);
>>>> 
>>>> //vtkNew<vtkPiecewiseFunction> f;
>>>> //f->AddPoint(0, 0.0);
>>>> //f->AddPoint(255, 1.0);
>>>> //volumeProperty->SetScalarOpacity(f);
>>>> 
>>>> //int valid =
>>>> mapper->IsRenderSupported(vtkrenderer_->GetRenderWindow(),
>>>> volumeProperty);
>>>> 
>>>> // NOTE: No exception was thrown on my system
>>>> //if (valid == 0)
>>>> //  throw std::runtime_error("MIP rendering is not supported");
>>>> //volume->SetProperty(volumeProperty);
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>>> --
>>> 
>>> SANKHESH JHAVERI
>>> 
>>> _SR. RESEARCH & DEVELOPMENT ENGINEER_ | KITWARE [2] | (518)
>> 881-4417
>>> 
>>> ​
>>> 
>>> Links:
>>> ------
>>> [1] http://www.kitware.com
>>> [2] http://www.kitware.com/
>  --
> 
> SANKHESH JHAVERI
> 
> _SR. RESEARCH & DEVELOPMENT ENGINEER_ | KITWARE [2] | (518) 881-4417
> 
> ​
> 
> Links:
> ------
> [1] http://www.kitware.com
> [2] http://www.kitware.com/