Access to framebuffer Cocos2d/3d

I am trying to combine the String Augmented Reality Framework with cocos as the 3d renderer. In the setu开发者_运维知识库p I need to provide String with the OpenGL context and the framebuffer.

 stringOGL = [[StringOGL alloc] initWithDelegate: self context: myEAGLContext frameBuffer: myFrameBuffer leftHanded: NO]; 

I get the context like this:

 [[[CCDirector sharedDirector] openGLView] context] 

But how to get the frameBuffer?