Why is the circle divided into 4 pieces?

Development
1

원이아닌원

vtkNew<vtkRenderWindowInteractor> Interactor; 
m_pvtkImageViewer->SetupInteractor(Interactor);

vtkNew<vtkRegularPolygonSource> polygonSource;
polygonSource->SetNumberOfSides(360);
polygonSource->SetRadius(20);
polygonSource->SetNormal(0.0, 0.0, 1.0);
polygonSource->SetCenter(20, 20, 1);
polygonSource->SetGeneratePolygon(FALSE);
polygonSource->SetGeneratePolyline(TRUE);
polygonSource->Update(); 

vtkNew<vtkPolyDataMapper> mapper;
mapper->SetInputConnection(polygonSource->GetOutputPort());

vtkNew<vtkNamedColors> colors;
vtkNew<vtkActor> actor;
actor->SetMapper(mapper);

actor->GetProperty()->SetLineWidth(10.0);

actor->GetProperty()->ShadingOn();
actor->GetProperty()->SetPointSize(1);

actor->GetProperty()->SetColor(1.0, 0.2, 0.6);
actor->GetProperty()->SetOpacity(0.7); 

m_pvtkImageViewer->GetRenderer()->SetUseFXAA(TRUE);
m_pvtkImageViewer->GetRenderWindow()->SetMultiSamples(0); 

m_pvtkImageViewer->GetRenderer()->AddActor(actor); 

m_pvtkImageViewer->GetImageActor()->InterpolateOff();
m_pvtkImageViewer->GetRenderer()->ResetCamera();
m_pvtkImageViewer->GetRenderer()->SetBackground(40.0 / 255.0, 60.0 / 255.0, 90.0 / 255.0);
m_pvtkImageViewer->Render();

I wanted to draw a circle, but when I set the thickness, 4 pieces came out.
Help me…