trackoffical_app/lib/view/ingame/layer/layer_trace.dart

import 'layer_controller.dart';



class LayerTrace extends GetView<LayerController>  {
  const LayerTrace({
    super.key,
    required this.onMapTrace,
    required this.color,
  });
  final List<Offset> onMapTrace;
  final Color color;


  @override
  Widget build(BuildContext context) {
    return SizedBox(
      width: context.width,
      height: context.height,
      child: Obx((){
        final matrix = controller.mapTransformMatrix.value;
        if(matrix.isZero()){
          return const SizedBox();
        }

        final onScreenTrace = onMapTrace.reversed.map((e) =>
            controller.mapOffsetToScreen(e)).toList();

        return CustomPaint(painter: _LayerTracePainter(onScreenTrace, color));
      }),
    );
  }
}

class _LayerTracePainter extends CustomPainter {

  final List<Offset> _points;
  final painter = Paint()
    ..strokeWidth = 3
    ..style = PaintingStyle.stroke
    ..isAntiAlias = true;
  final Color color;

  _LayerTracePainter(this._points, this.color);

  @override
  void paint(Canvas canvas, Size size) {
    if (_points.length > 1 ) {
      var alpha = 255;
      final lineCount = _points.length - 1;
      final alphaStep = (alpha / lineCount).round();

      for (var i = 1; i < _points.length; i++) {
        final p2 = _points[i];
        final p1 = _points[i - 1];

        painter.color = color.withAlpha(alpha);
        canvas.drawLine(p1, p2, painter);
        alpha -= alphaStep;
        if (alpha < 0) {
          alpha = 0;
        }
      }
    }
  }

  @override
  bool shouldRepaint(_LayerTracePainter oldDelegate) => false;
}