how to use the 3d and mpr widget? 

dear sir，

the read me doc shows a very excellent 3d viewer，but I  failed to make it by change 2d widget to 3d widget. there is not a 3D image shown.  i don't know how to make it work correctly. would you please give some instructions here?  I am a very beginner of vtk programming.  thank you very much. 