This code was strongly inspired by work from Konstantin Podsvirov

References :
- https://wiki.qt.io/OsgQtQuick-Demo
- https://github.com/podsvirov
- https://github.com/podsvirov/osgqtquick

known issues:
- http://forum.osgearth.org/VERTEX-glCompileShader-quot-oe-mp-vertModel-quot-FAILED-tt7588106.html#none
