how to add multiple sliders on one slider? #Flutter

Using Stack with three sliders did not work because it was being overlapped.

I have made this Slider3X of being curious. There are few things need to fix here, start and end points missing some fractional position.

Code on Gist, dart pad

class Slider3x extends StatefulWidget {
  const Slider3x({
    Key? key,
    required this.onSliderUpdate,
    this.size = const Size(5, 10),
    this.min = 0,
    this.max = 1.0,
    this.colorX = Colors.green,
    this.colorY = Colors.blue,
    this.colorZ = Colors.redAccent,
  }) : super(key: key);

  final Function(double? x, double? y, double? z) onSliderUpdate;

  ///size of moveable 3x point , forgot the name maybe thumbs
  final Size size;
  final double? min;
  final double? max;

  final Color colorX;
  final Color colorY;
  final Color colorZ;

  @override
  State<Slider3x> createState() => _Slider3xState();
}

class _Slider3xState extends State<Slider3x> {
  /// three slider position
  double? x;
  double? y;
  double? z;

  final double tapSpacesArea = .05;

  // currect active slider , help to prevent overlLAp while sliding
  int activeSliderNumber = 0;

  //* Update sldier
  void _updateSlider(double dx, double maxWidth) {
    final tapPosition = dx;

    //* update logic
    if (tapPosition <= 0 || tapPosition >= maxWidth) {
      return;
    }

    //* update on UI based on slider number
    if (activeSliderNumber == 0) {
      setState(() {
        x = tapPosition;
      });
    } else if (activeSliderNumber == 1) {
      setState(() {
        y = tapPosition;
      });
    } else if (activeSliderNumber == 2) {
      setState(() {
        z = tapPosition;
      });
    }

    //pass value on main widget
    widget.onSliderUpdate(
      dp(_generateSliderValue(maxWidth: maxWidth, x: x!)),
      dp(_generateSliderValue(maxWidth: maxWidth, x: y!)),
      dp(_generateSliderValue(maxWidth: maxWidth, x: z!)),
    );
  }

  //round number
  double dp(double val, {int places = 2}) {
    num mod = pow(10.0, places);
    return ((val * mod).round().toDouble() / mod);
  }

  //* calculate slider value
  double _generateSliderValue({
    required double maxWidth,
    required double x,
  }) {
    // x is slider original position on width:maxWidth

    return (widget.max! - widget.min!) * (x / maxWidth) + widget.min!;
  }

  //* select ActiveSlider, fixed overLap issue
  //* slider Selector logic
  void _selectSlider({
    required double maxWidth,
    required double tapPosition,
  }) {
    final maxArea = maxWidth * tapSpacesArea;

    if ((tapPosition - x!).abs() < maxArea) {
      setState(() {
        activeSliderNumber = 0;
      });
    } else if ((tapPosition - y!).abs() < maxArea) {
      setState(() {
        activeSliderNumber = 1;
      });
    } else if ((tapPosition - z!).abs() < maxArea) {
      setState(() {
        activeSliderNumber = 2;
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(8.0),
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: [
          SizedBox(
            height: 50,
            child: LayoutBuilder(builder: (context, constraints) {
              final maxWidth = constraints.maxWidth - 10;
              x = x ?? 0;
              y = y ?? constraints.maxWidth / 2;
              z = z ?? maxWidth;
              return Stack(
                alignment: Alignment.center,
                children: [
                  Positioned(
                    left: x,
                    child: Container(
                      height: activeSliderNumber == 0
                          ? widget.size.height * 1.5
                          : widget.size.height,
                      width: widget.size.width,
                      color: widget.colorX,
                    ),
                  ),
                  //* paint Y
                  Positioned(
                    left: y,
                    child: Container(
                      height: activeSliderNumber == 1
                          ? widget.size.height * 1.5
                          : widget.size.height,
                      width: widget.size.width,
                      color: widget.colorY,
                    ),
                  ),
                  //* paint z
                  Positioned(
                    left: z,
                    child: Container(
                      height: activeSliderNumber == 2
                          ? widget.size.height * 1.5
                          : widget.size.height,
                      width: widget.size.width,
                      color: widget.colorZ,
                    ),
                  ),

                  const Divider(
                    endIndent: 10,
                  ),

                  GestureDetector(
                    onTapDown: (details) => _selectSlider(
                        maxWidth: maxWidth,
                        tapPosition: details.localPosition.dx),
                    onPanUpdate: (details) =>
                        _updateSlider(details.localPosition.dx, maxWidth),
                  ),
                ],
              );
            }),
          ),
          Row(
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: [
              Text(
                widget.min.toString(),
              ),
              Text(
                widget.max.toString(),
              ),
            ],
          )
        ],
      ),
    );
  }
}