Thanks for your answer. I need to grab a secondary actor, let’s say a small sphere, but not a widget (a widget is not suitable for this case).
Apart from Unicam manipulator, there is no built-in way to disable the default behavior inside interactor.onLeftButtonPress/Release(), taking into account that my interactorStyle is roughly custom, i.e. it is not just vtkInteractorStyleTrackballCamera.newInstance(), which should give more possibilities?
What works now is using the left mouse button events and a keyboard key (like ALT), but it’s not that convenient…