开发环境：

1. Windows 11 家庭中文版
2. Microsoft Visual Studio Community 2019
3. VTK-9.3.0.rc0
4. vtk-example
5. 参考代码
6. 目的：学习与总结

demo解决问题：renderWindow中创建一个夹角测量控件，通过三个点确定一个夹角

1. 典型的控件类继承关系：vtkObject > vtkInteractorObsever > vtkAbstractWidget > vtkAngleWidget
2. 交互对象设置：angleWidget->SetInteractor(renderWindowInteractor);
3. 控件使能：renderWindowInteractor->Start();之前angleWidget->On();
4. vtkRenderWindow 与vtkRenderWindowInteractor详解

prj name: AngleWidget

#include <vtkAngleWidget.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>

int main(int, char*[])
{
  vtkNew<vtkNamedColors> colors;

  // A renderer and render window
  vtkNew<vtkRenderer> renderer;
  vtkNew<vtkRenderWindow> renderWindow;
  renderWindow->AddRenderer(renderer);
  renderWindow->SetWindowName("AngleWidget");

  // An interactor
  vtkNew<vtkRenderWindowInteractor> renderWindowInteractor;
  renderWindowInteractor->SetRenderWindow(renderWindow);

  vtkNew<vtkAngleWidget> angleWidget;
  angleWidget->SetInteractor(renderWindowInteractor);
  angleWidget->CreateDefaultRepresentation();

  // Render
  renderer->SetBackground(colors->GetColor3d("MidnightBlue").GetData());
  renderWindow->Render();
  renderWindowInteractor->Initialize();
  renderWindow->Render();
  angleWidget->On();
  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}