Masking/Transition

transitionmasking.dart

  @override
  void initState() {
    super.initState();

    _controller = AnimationController(
        duration: const Duration(seconds: 2), vsync: this)
      ..addStatusListener((status) {
        if (status == AnimationStatus.completed) {
          Navigator.pop(context);
        }
      });

    transitionTween = Tween<double>(
      begin: 50.0,
      end: 200.0,
    ).animate(
      CurvedAnimation(
        parent: _controller,
        curve: Curves.ease,
      ),
    );
    borderRadius = BorderRadiusTween(
      begin: BorderRadius.circular(75.0),
      end: BorderRadius.circular(0.0),
    ).animate(
      CurvedAnimation(
        parent: _controller,
        curve: Curves.ease,
      ),
    );
    _controller.forward();
  }