fbo.bind();
        setUpViewport(FBO_WIDTH, FBO_HEIGHT);
        // draw stuff
        fbo.unbind();
        setUpViewport(FBO_WIDTH, FBO_HEIGHT);

    public void setUpViewport(int width, int height) {
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        gluPerspective(50f, ((float)width) / ((float)height), 0.1f, 64f);
        glViewport(0, 0, width, height);
        glMatrixMode(GL_MODELVIEW);
    }