[vtkusers] Locking camera rotation along camera axis

[John Drescher]

> I am using a vtkRenderWindowInteractor with interactor style
> vtkInteractorStyleTrackballCamera. I need to restrict camera rotation so
> that the camera can't be rotated around the view axis. In other words, the
> camera's x axis shall always be in the world's xy plane.
>
> How can I achieve this?
>

Create your own interactor style class inheriting from
vtkInteractorStyleTrackballCamera and inside that disable the rotation
or any other features you do not want.

John