[vtkusers] draw a region of interest using the mouse

[LI XIN]

Hello vtkusers,

I  have a question about doing ROI using MFC and VTK. I have displayed the image by assigning a vtkRenderWindow to a pre-existing window in my MFC MDI app. Then I would like to use MFC's LineTo function to draw on the image with mouse. But I found that it didn't work. It seemed that I could not draw on a vtkRenderWindow. 

What should I do?

Thanks!

Xin