mobile-app/lib/presentation/custom_widgets/widget_rounded_rect_indicator.dart

import 'package:flutter/material.dart';

class RoundedRectIndicator extends Decoration {
  final BoxPainter _painter;

  RoundedRectIndicator({
    @required Color color,
    @required double radius,
    double padding = 0.0,
    double weight = 3.0,
  }) : _painter = _RectPainter(color, radius, padding, weight);

  @override
  BoxPainter createBoxPainter([onChanged]) {
    return _painter;
  }
}

class _RectPainter extends BoxPainter {
  final Paint _paint;
  final double radius;
  final double padding;
  final double weight;
  final indicatorPaddingBottom = 4.0;

  _RectPainter(Color color, this.radius, this.padding, this.weight)
      : _paint = Paint()
          ..color = color
          ..isAntiAlias = true;

  @override
  void paint(Canvas canvas, Offset offset, ImageConfiguration cfg) {
    var width = cfg.size.width;
    var height = cfg.size.height;

    var left = 0.0;
    var top = height - indicatorPaddingBottom;
    var right = width;
    var bottom = height - weight - indicatorPaddingBottom;

    //calculate offset
    left = left + offset.dx + padding;
    right = right + offset.dx - padding;

    var rect = RRect.fromLTRBAndCorners(left, top, right, bottom,
        topLeft: Radius.circular(radius),
        bottomLeft: Radius.circular(radius),
        bottomRight: Radius.circular(radius),
        topRight: Radius.circular(radius));
    canvas.drawRRect(rect, _paint);
  }
}