Drawing performance issue in flutter

[Manusb]

Hi all,

here is the code the problem is after drawing continuously the drawing speed become very slow compare to previous.

Thanks for any help.

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;

}

[Eric Seidel]

From a quick glance at the code it makes sense that drawing speed would slow down over time since every intput event adds more points to draw.  You might want to pursue a strategy of rasterizing some of your earlier inputs into a bitmap instead of just always adding to an ever-growing list of points. :)

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