performance issue in drawing using flutter

Question

I'm using gestuereDetector to detect offset and CustomePaint to paint the offset in flutter. but after drawing the performance of drawing is becoming slow so please help me to solve this issue.

How can I make it more efficient. My code just follows the below

 Widget build(BuildContext context) {
    _currentPainter = new DrawPainting(_points);

    return new Container(
      child: new ConstrainedBox(
        constraints: const BoxConstraints.expand(),
        child: new GestureDetector(
          onPanUpdate: (DragUpdateDetails details) {
            setState(() {
              RenderBox referenceBox = context.findRenderObject();

              Offset localPosition =
              referenceBox.globalToLocal(details.globalPosition);
              _points = new List.from(_points)..add(localPosition);
            });
          },
          onPanEnd: (DragEndDetails details) =>_points.add(null),
          child: new CustomPaint(
            painter: _currentPainter,

          ),
        ),
      ),
    );
  }


class DrawPainting extends CustomPainter {
  List<Offset> points = [];
  Canvas _lastCanvas;
  Size _lastSize;
  DrawPainting(points){

    this.points = points;
  }

  void paint(Canvas canvas, Size size) {
    print({"the main paint is called .... ": {"size" : size}});
    _lastCanvas = canvas;
    _lastSize = size;
    Paint paint = new Paint()
      ..color = Colors.black
      ..strokeCap = StrokeCap.round
      ..strokeWidth = 8.0;


    for (int i = 0; i < points.length - 1; i++) {
      if (points[i] != null &&
          points[i + 1] != null &&
          (points[i].dx >= 0 &&
              points[i].dy >= 0 &&
              points[i].dx < size.width &&
              points[i].dy < size.height) &&
          (points[i + 1].dx >= 0 &&
              points[i + 1].dy >= 0 &&
              points[i + 1].dx < size.width &&
              points[i + 1].dy < size.height)){
        canvas.drawLine(points[i], points[i + 1], paint);
      }
    }
  }
  bool shouldRepaint(DrawPainting other) => other.points != points;
}

Answer 1

The performance issue in drawing app using flutter is resolved by using drawPath() and instead of using setState for each points to update use NotifyListener() to refresh than it will be more efficient than setState.