@sinanmut When I create the 3D objects in the initializeGL function, it is fine paintGL function renders these objects. Later on when I want to add new objects to the scene I don't see these new ones being rendered by painGL function. Is there any flag that I have to add in paintGL fuinction or in initializeGL function?
Thanks,

vertexData() returns only the data in ram and not the real VBO which is stored in GPU-ram.
As soon as you mark it as dirty it gets completely copied into GPU.

Meanwhile I have implemented a direct opengl-way where I create the VBO myself.

Thanks anyway!
cu