Right, makeTextureBuffer() doesn’t need this parameter, because it’s implicit in this case (it takes it from the object you have called it on). So if you’re only using makeTextureBuffer() to create your offscreen buffer, you should be already good.
Hmm, unless you are calling makeTextureBuffer() before the first frame has rendered and the window is initially open, in which case it won’t have a GSG yet. Is that the case? Try calling base.graphicsEngine.openWindows() before you call makeTextureBuffer().
David