Now that you have 8 intervals to your animation, and an AnimatedWidget to feed em to, the last step is just adding the PivotBar to your build method in _BarLoadingScreenState.

// in the [_PegProgressIndicatorState] class
  @override
  Widget build(BuildContext context) {
    return Center(
      child: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          PegAnimation(
            alignment: FractionalOffset.centerLeft,
            controller: _controller,
            animations: [
              stepOne,
              stepTwo,
            ],
            marginRight: 0.0,
            marginLeft: 0.0,
            isClockwise: true,
          ),
          PegAnimation(
            controller: _controller,
            animations: [
              stepThree,
              stepEight,
            ],
            marginRight: 0.0,
            marginLeft: 0.0,
            isClockwise: false,
          ),
          PegAnimation(
            controller: _controller,
            animations: [
              stepFour,
              stepSeven,
            ],
            marginRight: 0.0,
            marginLeft: 32.0,
            isClockwise: true,
          ),
          PegAnimation(
            controller: _controller,
            animations: [
              stepFive,
              stepSix,
            ],
            marginRight: 0.0,
            marginLeft: 32.0,
            isClockwise: false,
          ),
        ],
      ),
    );
  }

And that's it.