Success!  I've removed the paintComponent method from the JPanel I extended, and passed it the canvas object instead of the framebuffer. Thanks to the example I also found the right way to get it to draw: use fb.updateGLOnly() and then canvas.repaint(). Everything else regarding key and mouse events on the JPanel works as before (once I changed the listeners to work on the canvas rather than the JPanel itself). Thanks for your help!!!

But er... one last thing  You wouldn't happen to know how to get the Graphics drawing functions to work on top of the canvas? See, I get the Graphics object from the canvas during the render method, and when I try to run drawString at any point, I cannot see the text. I suppose this has to do with the fb.updateGLOnly() bit.

I suppose I am using LWJGL since I am using the openGL renderer? Hm.

Anyway, here is the code for my render function:

fb.clear();

        world.renderScene(fb);
        world.draw(fb);
        fb.update();

        fb.addPostProcessor( new IPostProcessor() {

            private boolean initialised = false;

            public boolean isInitialized()
            {
                return initialised;
            }

            public void dispose()
            {

            }

            public void process()
            {

            }

            public void init( FrameBuffer buffer )
            {
                boolean FBOEnabled = GLContext.getCapabilities().GL_EXT_framebuffer_object;
                System.out.println( FBOEnabled );
            }
        });

        fb.runPostProcessors();
The error comes in the first line of public void init: null pointer error.