How to add a neon glow effect to an widget border / shadow?

Question

Is there any way to create effects like these using flutter (a CustomPaint with a special shadder or something like this)?

For example. I have this container and I drew some lines on it using a CustomPainter. Could I draw these lines using a neon effect just like the pictures? The Paint class has a shader property that I thought I could set up to achieve this goal, but I don't realize how.

Container(
          color: Colors.white,
          width: 300,
          height: 300,
          child: CustomPaint(
            painter: NeonPainter(),

          ),


        ),



class NeonPainter extends CustomPainter {
  Paint neonPaint = Paint();


  NeonPainter() {
    neonPaint.color = const Color(0xFF3F5BFA);
    neonPaint.strokeWidth = 2.5;
    neonPaint.shader = /// how to create a shader or something for that?
    neonPaint.someOtherProperty///

  }

  @override
  void paint(Canvas canvas, Size size) {
    drawLine(canvas, size.width / 2 - 50, size.height / 2, size.width / 2 + 50,
        size.height / 2);
    drawLine(canvas, size.width / 2 + 50, size.height / 2, size.width / 2 + 100,
        size.height / 2 + 50);
    drawLine(canvas, size.width / 2 + 100, size.height / 2 + 50,
        size.width / 2 - 100, size.height / 2 + 50);
    drawLine(
        canvas, size.width / 2 - 100, size.height / 2 + 50, size.width / 2 - 50,
        size.height / 2);
  }

  void drawLine(canvas, double x1, double y1, double x2, double y2) {
    canvas.drawLine(Offset(x1, y1), Offset(x2, y2), neonPaint);
  }

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

Answer 1

use boxShadow property twice inside Container widget decoration. for outer glow use spreadRadius positive value and for inner glow use negetive value. sample code is given below..

Container(
    decoration: BoxDecoration(
        borderRadius: BorderRadius.all(
          Radius.circular(18.0),
        ),
        color: Colors.white,
        boxShadow: [
          BoxShadow(
            color: Colors.pink,
            spreadRadius: 4,
            blurRadius: 10,
          ),
           BoxShadow(
            color: Colors.pink,
            spreadRadius: -4,
            blurRadius: 5,
          )
        ]),
    child: FlatButton(
      onPressed:(){},
      child: Text("submit"),
      
      shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(18.0),
      ),
    ),
  ),

Answer 2

You can use BoxShadow widget.. You can set color, blurRadius, SpreadRadius and offset to achieve what you want..

Note in example I have used it to get a drop shadow.. But you can get a glow if you set the properties correctly..

 Container(
            decoration: BoxDecoration(
                borderRadius: BorderRadius.circular(50),
                boxShadow: [
                  BoxShadow(
                    color: Color(0xFF000000).withAlpha(60),
                    blurRadius: 6.0,
                    spreadRadius: 0.0,
                    offset: Offset(
                      0.0,
                      3.0,
                    ),
                  ),
                ]),