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class BikeButton extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      height: 50.0,
      child: CustomPaint(
        painter: BikeButtonPainter(),
        child: Center(
          child: Text('Buy Tough Bike'.toUpperCase()),
        ),

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class BikeButtonPainter extends CustomPainter {
  final fillPaint = Paint()..color = Colors.grey;

  @override
  void paint(Canvas canvas, Size size) {
    // This [Rect] will fill the whole canvas we got
    var fillRect = Rect.fromPoints(Offset.zero, size.bottomRight(Offset.zero));

    canvas.drawRect(
      fillRect,

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/// In BikeList.build > Column.children
Container(
  decoration: BoxDecoration(
    boxShadow: const [
      BoxShadow(spreadRadius: 0.0, blurRadius: 20.0),
    ],
    color: Colors.grey.shade800,
  ),
  child: Row(
    children: <Widget>[

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// In BikeButtonPainter
// ...
static final rnd = Random();
static Offset randomOffset(Size size) {
  return Offset(
    rnd.nextDouble() * size.width,
    rnd.nextDouble() * size.height
  );
}
// ...

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// In BikeButtonPainter
// ...
final linePaint = Paint()..color = Colors.white24;
// ...

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@override
void paint(Canvas canvas, Size size) {
  // This [Rect] will fill the whole canvas we got
  var fillRect = Rect.fromPoints(Offset.zero, size.bottomRight(Offset.zero));
  var count = 100;
  
  // Background for our texture
  canvas.drawRect(fillRect, fillPaint);
  
  for (var i = 0; i < count; i++) {

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// in BikeButtonPainter.paint
// ...
var count = 1000;
// ...

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// in BikeButtonPainter.paint
// ...
var count = 10000;
// ...

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// in BikeButtonPainter
// ...

/// Defines how many lines per unit of area we want
final double density;

/// Expose to outside, allowing to override default value
BikeButtonPainter({
  this.density = .1,
});

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var start = Offset(1, 1);
var displacement = Offset(-2, -2);
var end = start + displacement;

print(end); // Offset(-1, -1);