Opengl multipass render
-
Assuming you are using Qt5.0, you could use:
http://qt-project.org/doc/qt-5.0/qtgui/openglwindow.html
http://qt-project.org/doc/qt-5.0/qtgui/qopenglshaderprogram.html
http://qt-project.org/doc/qt-5.0/qtgui/qopenglframebufferobject.html