Callback function to handle incoming MIDI messages.

def _message_callback(self, msg):
        """Callback function to handle incoming MIDI messages."""
        if msg.type == 'polytouch':
            button = button_from_press(msg.note)
            if button:
                self.on_button(button, msg.value != 0)
            elif msg.note == 127:
                self.on_fader_touch(msg.value != 0)
        elif msg.type == 'control_change' and msg.control == 0:
            self._msb = msg.value
        elif msg.type == 'control_change' and msg.control == 32:
            self._fader = (self._msb << 7 | msg.value) >> 4
            self.on_fader(self._fader)
        elif msg.type == 'pitchwheel':
            self.on_rotary(1 if msg.pitch < 0 else -1)
        else:
            print('Unhandled:', msg)