[vtk-developers] vtkImagePlaneWidget windowlevel events

[dean.inglis at camris.ca]

I figured out the problem and the solution is
to have shift+r or control+r be the trigger
for resetwindowlevel since the interactor style
is typically interactorstyletrackballcamera and
not interactorstyleimage, wherein shift+'r'
or control+'r' trigger reset camera.  So,
unless there are any objections,
vtkImagePlaneWidget will now invoke the following
additional events specific to window-levelling:
StartWindowLevelEvent
WindowLevelEvent
EndWindowLevelEvent
ResetWindowLevelEvent

When invoked, the current window-level values
are passed as calldata :
double wl[2] = { this->CurrentWindow, this->CurrentLevel };
this->InvokeEvent(vtkCommand::ResetWindowLevelEvent, wl);

AFAIK, the only backward compatibility issues
will be use scenarios wherein a user added a 
callback to listen for start/end/interactionevents
to monitor window-level.  Those callbacks should
then be changed accordingly.

Dean