circle-white-indicator.dart

class TabIndicatorPainter extends CustomPainter {
  Paint painter;
  double xPos, radiusOval;

  double radiusOvalOrigin = 20.0;

  TabIndicatorPainter(double xPos, double radiusOval) {
    painter = new Paint()
      ..color = Colors.white
      ..style = PaintingStyle.fill;
    this.xPos = xPos;
    this.radiusOval = radiusOval;
  }

  double processRadiusOval(double value) {
    if (value <= 30.0) {
      return value;
    } else if (value <= 40.0) {
      return value = radiusOvalOrigin + (40.0 - value);
    } else if (value <= 45) {
      return value = radiusOvalOrigin + (value - 40.0);
    } else {
      return value = radiusOvalOrigin + (50.0 - value);
    }
  }

  double processRadiusOval2(double value) {
    if (value <= 40.0) {
      return 0.0;
    } else if (value <= 45.0) {
      return value = value - 40.0;
    } else {
      return value = (50.0 - value);
    }
  }

  @override
  void paint(Canvas canvas, Size size) {
    canvas.drawOval(
        new Rect.fromLTRB(xPos - processRadiusOval2(radiusOval), 0.0, xPos + processRadiusOval(radiusOval), 20.0),
        painter);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    return true;
  }
}