DFJoyStick是完全用Flutter实现的Widget，默认是8方向的，可以设置背景图片和一些基本样式。

/// 摇杆
Positioned(
    bottom: MediaQuery.of(context).padding.bottom + 30,
    left: 30,
    child: DFJoyStick(
       //backgroundImage: "assets/images/ui/joystick.png",
       //handleImage: "assets/images/ui/joystick_btn.png",
       onChange: (double radians, String direction) {
           _playerSprite?.play(action: DFAnimation.RUN, direction: direction, radians: radians);
       },
       onCancel: (direction) {
           _playerSprite?.play(action: DFAnimation.IDLE, direction: direction);
       },
    ),
),