[vtkusers] New functionality: Observing events from class member functions

[Jim Peterson]

David Doria wrote:
> Thanks to the hard work of Utkarsh and David Gobbi, we can now observe
> VTK events from class member functions!
>
> The idea is:
>
> class MyClass
> {
>   public:
>     void KeypressCallbackFunction(vtkObject* caller,
>                     long unsigned int eventId,
>                     void* callData )
>     {
>       std::cout << "Caught event in MyClass" << std::endl;
>     }
>
> };
>
> ... else where ...
>
> MyClass myClass;
> renderWindowInteractor->AddObserver(vtkCommand::KeyPressEvent,
> &myClass, &MyClass::KeypressCallbackFunction);
>
> (This in in contrast to the old method of creating a
> vtkCallbackCommand object and passing it a static class function,
> yuck!)
>
> A full demonstration can be found here:
> http://www.vtk.org/Wiki/VTK/Examples/Cxx/Interaction/ObserverMemberFunction
>
> Hopefully this new addition will improve the organization of everyones
> code. It certainly has with mine!
>   
This is excellent news, The callback structure is one of the reasons I 
gravitated to the Java interface in the first place. The Java callbacks 
do not have an equivalent of the void* data parameter, but since the 
callback in an instance object, My feeling is this parameter is rendered 
relatively unecessary.

Great work to all involved.

Jim