Fltk And OpenSG

HI…

I am trying to use Fltk with OpenSG.
OpenSG manual says that it provides PassiveWindow class to integrate with any GUI system.
I am trying to do that, but not getting success.
My window renders only Black.

Do anybody have any example to show, how to use Fltk with OpenSG.
It would really help me getting forward with OpenSG.

------Jaideep