ExternalVTKWidget volume rendering high CPU usage

Support
1

Hello,

I am using my custom rendering engine and I would like to use vtk to render volume data on it. Also, I am using ExternalVTKWidget to use vtk with the engine’s opengl context. I Followed the examples of ExternalVTKWidget , and it works with meshes and isosurfaces. At the moment of load volume data, the frame rate is low. The Visual Studio profiler reports a high use of the CPU when it reaches the function:

int vtkOpenGLRenderer::UpdateGeometry(vtkFrameBufferObjectBase* fbo)

I’m not sure if something is wrong at the moment of loading the data. Maybe using the wrong readers or mappers.

I wonder if someone has ever had this problem.

The following is the code I use to load volume data:

vtkSmartPointer<vtkFixedPointVolumeRayCastMapper> volumeMapper =
    vtkSmartPointer<vtkFixedPointVolumeRayCastMapper>::New();

  std::string filePath = std::string("FullHead.mhd");
  vtkSmartPointer<vtkMetaImageReader> metaReader =
    vtkSmartPointer<vtkMetaImageReader>::New();
  metaReader->SetFileName(filePath.c_str());
  metaReader->Update();


  vtkSmartPointer<vtkAlgorithm> reader =
    vtkSmartPointer<vtkAlgorithm>::New();
  vtkSmartPointer<vtkImageData> input =
    vtkSmartPointer<vtkImageData>::New();

  input = metaReader->GetOutput();
  reader = metaReader;
  volumeMapper->SetInputConnection(reader->GetOutputPort());

  vtkSmartPointer<vtkVolumeProperty> volumeProperty =
    vtkSmartPointer<vtkVolumeProperty>::New();
  volumeProperty->SetInterpolationTypeToLinear();
  volumeProperty->SetIndependentComponents(true);

  vtkSmartPointer<vtkPiecewiseFunction> opacityFun =
    vtkSmartPointer<vtkPiecewiseFunction>::New();
  volumeProperty->SetScalarOpacity(opacityFun);

  vtkSmartPointer<vtkColorTransferFunction> colorFun =
    vtkSmartPointer<vtkColorTransferFunction>::New();
  volumeProperty->SetColor(colorFun);

  vtkSmartPointer<vtkVolume> volume =
    vtkSmartPointer<vtkVolume>::New();
  volume->SetMapper(volumeMapper);
  volume->SetProperty(volumeProperty);
  volume->SetUserTransform(transform);

  colorFun->AddRGBSegment(0.0, 1.0, 1.0, 1.0, 255.0, 1.0, 1.0, 1.0);
  opacityFun->AddSegment(opacityLevel - 0.5 * opacityWindow, 0.0,
    opacityLevel + 0.5 * opacityWindow, 1.0);
  volumeMapper->SetBlendModeToMaximumIntensity();

  _vtkRenderer->AddVolume(volume);
  _vtkRenderer->ResetCamera();

I appreciate the help in advance.

2

Use vtkGPUVolumeRayCastMapper instead of the legacy CPU mapper for faster rendering. You can get several magnitudes faster volume rendering if you have a discrete GPU and 2-4x faster if you just have integrated graphics.

3

replacing vtkFixedPointVolumeRayCastMapper by vtkGPUVolumeRayCastMapper did the trick.

Thank you @lassoan

1 Like