Flutter Squircle Shape

squircle.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';


class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Squircle',
      home: new Scaffold(
        appBar: new AppBar(title: new Text('Squircle')),
        body: new Center(
          child: new Container(
            width: 56.0,
            height: 56.0,
            child: new Material(
              color: Colors.blueGrey[400],
              shape: new SquircleBorder(
                side: BorderSide(color: Colors.blueGrey[800], width: 3.0),
              ),
              child: new Image.network('https://raw.githubusercontent.com/ScottS2017/local_package/master/lib/image/bipi/placeholder_icon.jpg'),
            ),
          ),
        ),
      )
    );
  }
}

class SquircleBorder extends ShapeBorder {
  final BorderSide side;
  final double superRadius;

  const SquircleBorder({
    this.side: BorderSide.none,
    this.superRadius: 5.0,
  })
    : assert(side != null),
      assert(superRadius != null);

  @override
  EdgeInsetsGeometry get dimensions => EdgeInsets.all(side.width);

  @override
  ShapeBorder scale(double t) {
    return new SquircleBorder(
      side: side.scale(t),
      superRadius: superRadius * t,
    );
  }

  @override
  Path getInnerPath(Rect rect, {TextDirection textDirection}) {
    return _squirclePath(rect.deflate(side.width), superRadius);
  }

  @override
  Path getOuterPath(Rect rect, {TextDirection textDirection}) {
    return _squirclePath(rect, superRadius);
  }

  static Path _squirclePath(Rect rect, double superRadius) {
    final c = rect.center;
    final dx = c.dx * (1.0 / superRadius);
    final dy = c.dy * (1.0 / superRadius);
    return new Path()
      ..moveTo(c.dx, 0.0)
      ..relativeCubicTo(c.dx - dx, 0.0, c.dx, dy, c.dx, c.dy)
      ..relativeCubicTo(0.0, c.dy - dy, -dx, c.dy, -c.dx, c.dy)
      ..relativeCubicTo(-(c.dx - dx), 0.0, -c.dx, -dy, -c.dx, -c.dy)
      ..relativeCubicTo(0.0, -(c.dy - dy), dx, -c.dy, c.dx, -c.dy)
      ..close();
  }

  @override
  void paint(Canvas canvas, Rect rect, {TextDirection textDirection}) {
    switch (side.style) {
      case BorderStyle.none:
        break;
      case BorderStyle.solid:
        var path = getOuterPath(rect.deflate(side.width / 2.0), textDirection: textDirection);
        canvas.drawPath(path, side.toPaint());
    }
  }
}