How to use original OpenGL in VTK program?

I am new to vtk, can you tell me how to use vtk and opengl in the one window (such as QVTKOpenGLWindow)?
For examle, there is a cube painted by vtk, how to add a triangle by opengl in same window?
Thanks.

Some things have been rendered in the QOpenGLWindow through opengl, how to add more through vtk to render, vtkExternalOpenGLRenderWindow?

Hello, friend,

Please, take a look at this: https://vtk.org/Wiki/VTK/Examples/Cxx/Visualization/RenderPassExistingContext But its approach is the opposite: you create a standalone OpenGL window and then pass its OpenGL context to VTK to use for rendering.

regards,

Paulo