[vtkusers] Are there VTK events for actor's leaving and entering the viewport

[Weiguang Guan]

Hello,

In one of my visualization apps a sequence of English words flow in and 
out in an unpredictable manner. The application needs to respond to the 
appearing and disappearing of words accordingly. How to implement this 
function?

EnterEvent and LeaveEvent are caused by mouse cursor moving in/out, right?

Weiguang