class SpriteWidget extends StatefulWidget {
  final Image image;
  final Size spriteSize;

  final Duration duration;

  SpriteWidget({
    Key key,
    @required this.image,
    @required this.spriteSize,
    @required this.duration,
  }) : super(key: key);

  @override
  _SpriteWidgetState createState() => _SpriteWidgetState();
}

class _SpriteWidgetState extends State<SpriteWidget> {
  Image get image => widget.image;

  Size get spriteSize => widget.spriteSize;

  Duration get duration => widget.duration;
  // 當(dāng)前顯示的圖片位置
  int currentIndex = 0;
  int currentTimes = 0;
  
  int startIndex = 0;

  int endIndex = 1;
  int playTimes = 0;

  // 定時(shí)器用來(lái)更新精靈圖加載
  Timer timer;

  @override
  void initState() {
    currentIndex = startIndex;
    timer = Timer.periodic(duration, (timer) {
      if (currentTimes <= playTimes) {
        setState(() {
          if (currentIndex >= endIndex) {
            if (playTimes != 0) currentTimes++;
            if (currentTimes < playTimes || playTimes == 0)
              currentIndex = startIndex;
            else
              currentIndex = endIndex;
          } else
            currentIndex++;
        });
      }
    });
    super.initState();
  }

  @override
  void dispose() {
    super.dispose();
    timer?.cancel();
  }

  @override
  Widget build(BuildContext context) {
    // 使用container+Positioned來(lái)限制圖片顯示區(qū)域
    return Container(
      width: spriteSize.width,
      height: spriteSize.height,
      child: Stack(
        children: [
          Positioned(
              left: -spriteSize.width * currentIndex,
              top: -spriteSize.height * currentIndex,
              child: image)
        ],
      ),
    );
  }
}

  bonfire: ^2.0.0
  flame: ^1.0.0

abstract class BaseRole {
  // 速度
  double velocity;
  late Sprite sprite;

  BaseRole({
    this.velocity = 10,
  });

  dynamic load();

  void run();
}
class UserRole extends BaseRole {
  Vector2 offset = Vector2(0.0, 0.0);
  Vector2 size = Vector2(48.0, 48.0);

  @override
  void run() {
    double x = (48 + offset.x) % 192;
    double y = 0;
    offset = Vector2(x, y);
    sprite.srcPosition = offset;
    sprite.srcSize = size;
  }

  @override
  Future load() async {
    sprite = await Sprite.load(
      'user_role.png',
      srcPosition: offset,
      srcSize: size,
    );
    return sprite;
  }
}

class UserRoleComponent extends SpriteComponent {
  late UserRole userRole;

  UserRoleComponent()
      : super(
          size: Vector2.all(100),
        );

  double minDt = 1 / 8; // 30 fps
  double dtOverflow = 0;

  @override
  Future<void>? onLoad() async {
    userRole = UserRole();
    sprite = await userRole.load();
    super.onLoad();
  }

  @override
  void update(double dt) {
    dtOverflow += dt;
    if (dtOverflow < minDt) {
      return;
    }
    userRole.run();
    dtOverflow = 0;
  }
}