[vtkusers] Stereo using SetViewShear()?

[Shang Mu]

I'm new to vtk and get confused with the vtkCamera::SetViewShear().

Why do you use "shear" to create a stereo scene instead of just set the 
correct frustum/camera pair from the beginning?

I studied the source code and found that vtkCamera::SetViewShear() / 
vtkPerspectiveTransform::Shear() does the same thing as 
vtkCamera::SetWindowCenter() / vtkPerspectiveTransform::Frustum() can do. 
IMO, the frustum way is much more intuitive. The "Shear()" way needs me to 
put the camera away from the eye position, which is against our normal way 
of thinking. And I do not think anyone can begin using "Shear()" without 
reading the source code or the long comment before the function defination. 
Is there any advantage to use shearing rather than set the frustum directly? 
Am I missing something?

Thanks for any clarification!

Shang