c++ - vtkSelectVisiblePoints 过滤器输出有 0 个点

Question

我正在尝试获取仅包含 3D 模型可见部分的 polyData。就此而言，我通过 vtkSelectVisiblePoints 过滤器传递原始数据。

我正在使用模拟渲染器、映射器和 Actor ，因为我想在显示可见点之前对其进行后处理。

但是，由于某种原因，vtkSelectVisiblePoints 过滤器的输出包含“0”点……

使用以下示例: http://www.vtk.org/Wiki/VTK/Examples/Cxx/PolyData/SelectVisiblePoints

我想到了以下代码:

  // 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);

... 打印 0。

但是，如果我调用 renderWindow->Render()，模型的可见部分会正确显示...

我是否遗漏了什么...？

Answer 1

答案就在那里，在 documentation of the filter 中:

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 Therefore, the filter is always out of date, and always executes.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

如果我添加 //new 行，它会按预期工作，就像 Arnas 在他的评论中建议的那样:

  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;