How to give shadow to a custom painted circle in flutter

You can use a MaskFilter to create shadow effect. Just draw a circleB with slightly bigger radius using MaskFilter Paint before drawing your real circleA, you can get a circleA with shadow effect.

Check out this circle drew with below codes.

class Painter extends CustomPainter {

  @override
  void paint(Canvas canvas, Size size) {
    double radius = 100.0;
    canvas.translate(size.width/2, size.height/2); 
    Offset center = Offset(0.0, 0.0);
    // draw shadow first
    Path oval = Path()
        ..addOval(Rect.fromCircle(center: center, radius: radius+10));
    Paint shadowPaint = Paint() 
        ..color = Colors.black.withOpacity(0.3)
        ..maskFilter = MaskFilter.blur(BlurStyle.normal, 50);
    canvas.drawPath(oval, shadowPaint);
    // draw circle
    Paint thumbPaint = Paint()
        ..color = Colors.white
        ..style = PaintingStyle.fill;
    canvas.drawCircle(center, radius, thumbPaint);
  }

  @override
  bool shouldRepaint(Painter oldDelegate) {
    return false;
  }
}

You could also use the drawShadow method.

@override
void paint(Canvas canvas, Size size) {
  var path = Path();
  var myPaint = Paint();
  var center = Offset(size.width / 2, size.height / 2);

  myPaint.color = Color(0xff007AFF);

  path.addOval(Rect.fromCircle(center: center, radius: 50.0));

  canvas.drawShadow(path, Color(0xff000000), 3, true);
  canvas.drawPath(path, myPaint);
}

Result:

Wrap it in a Boxdecoration.It has BoxShadow property.

You can follow this link.

   new Container(
    decoration: new BoxDecoration(
      color: Colors.white,
      border: new Border.all(
          color: Colors.green,
          width: 5.0,
          style: BorderStyle.solid
      ),
      borderRadius: new BorderRadius.only(
        topLeft: new Radius.elliptical(40.0, 10.0),
        bottomLeft: new Radius.circular(20.0),
      ),
      boxShadow: [
        new BoxShadow(
          color: Colors.red,
          offset: new Offset(20.0, 10.0),
        )
      ],
      image: new DecorationImage(
          image: new AssetImage('assets/images/JL-Logo-150.png'),
      )