height_picker.dart

class _HeightPickerState extends State<HeightPicker> {
  double get _pixelsPerUnit {
    return _drawingHeight / widget.totalUnits;
  }

  double get _sliderPosition {
    double halfOfBottomLabel = labelsFontSize / 2;
    int unitsFromBottom = widget.height - widget.minHeight;
    return halfOfBottomLabel + unitsFromBottom * _pixelsPerUnit;
  }

  ///returns actual height of slider to be able to slide
  double get _drawingHeight {
    double totalHeight = widget.widgetHeight;
    double marginBottom = marginBottomAdapted(context);
    double marginTop = marginTopAdapted(context);
    return totalHeight - (marginBottom + marginTop + labelsFontSize);
  }

  @override
  Widget build(BuildContext context) {
    return Stack(
      children: <Widget>[
        _drawSlider(),
        _drawLabels(),
      ],
    );
  }

  Widget _drawSlider() {
    return Positioned(
      child: HeightSlider(height: widget.height),
      left: 0.0,
      right: 0.0,
      bottom: _sliderPosition,
    );
  }
  ...
}