mouse.signal_axis_motion.connect(sigc::bind_return(sigc::mem_fun(this, &Viewer::axis_motion), false));
light.set_position(GL::Vector4(0, 0, 1, 0));
mouse.signal_axis_motion.connect(sigc::bind_return(sigc::mem_fun(this, &Viewer::axis_motion), false));
light.set_position(GL::Vector4(0, 0, 1, 0));