vtkSelectVisiblePoints filter output has 0 points

Question

I’m trying to obtain a polyData with only the visible part of a 3D model. To that extent, I’m passing the original data through a vtkSelectVisiblePoints filter.

I’m using a mock renderer, mapper and actor because I want to post-process the visible points before displaying them.

However, the output of the vtkSelectVisiblePoints filter contains “0” points for some reason…

Using the following example: http://www.vtk.org/Wiki/VTK/Examples/Cxx/PolyData/SelectVisiblePoints

I came up with the following piece of code:

  // Render window and interactor
  vtkSmartPointer<vtkRenderWindow> renderWindow =
    vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->SetSize(800, 800);

  vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
    vtkSmartPointer<vtkRenderWindowInteractor>::New();

  renderWindowInteractor->SetRenderWindow(renderWindow);


  // Mock renderer, mapper and actor
  vtkSmartPointer<vtkRenderer> mockRenderer =
    vtkSmartPointer<vtkRenderer>::New();

  renderWindow->AddRenderer(mockRenderer);

  vtkSmartPointer<vtkPolyDataMapper> mockMapper =
    vtkSmartPointer<vtkPolyDataMapper>::New();
  mockMapper->SetInput(reader->GetOutput());

  vtkSmartPointer<vtkActor> mockActor = vtkSmartPointer<vtkActor>::New();
  mockActor->SetMapper(mockMapper);
  mockRenderer->AddActor(mockActor);

  // Set camera to the correct position
  mockRenderer->GetActiveCamera()->SetPosition(0, -1, 0);
  mockRenderer->GetActiveCamera()->SetFocalPoint(0, 0, 0);
  mockRenderer->GetActiveCamera()->SetViewUp(0, 1, 0);
  mockRenderer->ResetCamera();

  vtkSmartPointer<vtkSelectVisiblePoints> selectVisiblePoints =
    vtkSmartPointer<vtkSelectVisiblePoints>::New();
  selectVisiblePoints->SetInput(reader->GetOutput());
  selectVisiblePoints->SetRenderer(mockRenderer);
  selectVisiblePoints->Update();

  std::cout << "Visible nr of points = " << selectVisiblePoints->GetOutput()->GetNumberOfPoints() << std::endl;

  renderWindow->RemoveRenderer(mockRenderer);

… prints 0.

However, if I call renderWindow->Render(), the visible part of the model is correctly displayed...

Am I missing anything...?

The problem is that in order to make points visible you need to render them first. — Arnas Ivanavičius
Indeed, after adding renderWindow->Render(); and then selectVisiblePoints->Update(); , the number of points is correctly displayed. Please post your comment as a reply so that I can accept it. — Ioanna

Ioanna Ioanna · Accepted Answer · 2016-09-02T15:19:16

The answer was right there, in the documentation of the filter:

Warning You must carefully synchronize the execution of this filter. The filter refers to a renderer, which is modified every time a render occurs. Therefore, the filter is always out of date, and always executes. You may have to perform two rendering passes

It worked as expected if I added the //new lines, like Arnas also suggested in his comment:

  vtkSmartPointer<vtkSelectVisiblePoints> selectVisiblePoints = 
    vtkSmartPointer<vtkSelectVisiblePoints>::New();
  selectVisiblePoints->SetInput(originalData);
  selectVisiblePoints->SetRenderer(renderer);
  selectVisiblePoints->Update();

  renderWindow->Render(); // new
  selectVisiblePoints->Update(); // new

  std::cout << "Visible nr of points = " << selectVisiblePoints->GetOutput()->GetNumberOfPoints() << std::endl;

vtkSelectVisiblePoints filter output has 0 points

1 Answers