Custom Shape in Flutter with Custom Painter

import 'dart:ui' as ui show lerpDouble;

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

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Card(
              shape: RoundedCustomRectangleBorder(
                  borderRadius: BorderRadius.circular(10),
                  side: const BorderSide(color: Colors.red)),
              child: const SizedBox(
                width: 100,
                height: 100,
              ),
            )
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class RoundedCustomRectangleBorder extends OutlinedBorder {
  /// Creates a rounded rectangle border.
  ///
  /// The arguments must not be null.
  const RoundedCustomRectangleBorder({
    BorderSide side = BorderSide.none,
    this.borderRadius = BorderRadius.zero,
  }) : super(side: side);

  /// The radii for each corner.
  final BorderRadiusGeometry borderRadius;

  @override
  EdgeInsetsGeometry get dimensions {
    return EdgeInsets.all(side.width);
  }

  @override
  ShapeBorder scale(double t) {
    return RoundedRectangleBorder(
      side: side.scale(t),
      borderRadius: borderRadius * t,
    );
  }

  @override
  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
    if (a is RoundedRectangleBorder) {
      return RoundedRectangleBorder(
        side: BorderSide.lerp(a.side, side, t),
        borderRadius:
            BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t)!,
      );
    }
    if (a is CircleBorder) {
      return _RoundedRectangleCustomToCircleBorder(
        side: BorderSide.lerp(a.side, side, t),
        borderRadius: borderRadius,
        circleness: 1.0 - t,
      );
    }
    return super.lerpFrom(a, t);
  }

  @override
  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
    if (b is RoundedRectangleBorder) {
      return RoundedRectangleBorder(
        side: BorderSide.lerp(side, b.side, t),
        borderRadius:
            BorderRadiusGeometry.lerp(borderRadius, b.borderRadius, t)!,
      );
    }
    if (b is CircleBorder) {
      return _RoundedRectangleCustomToCircleBorder(
        side: BorderSide.lerp(side, b.side, t),
        borderRadius: borderRadius,
        circleness: t,
      );
    }
    return super.lerpTo(b, t);
  }

  /// Returns a copy of this RoundedRectangleBorder with the given fields
  /// replaced with the new values.
  @override
  RoundedRectangleBorder copyWith(
      {BorderSide? side, BorderRadiusGeometry? borderRadius}) {
    return RoundedRectangleBorder(
      side: side ?? this.side,
      borderRadius: borderRadius ?? this.borderRadius,
    );
  }

  @override
  Path getInnerPath(Rect rect, {TextDirection? textDirection}) {
    return Path()
      ..addRRect(borderRadius
          .resolve(textDirection)
          .toRRect(rect)
          .deflate(side.width));
  }

  @override
  Path getOuterPath(Rect rect, {TextDirection? textDirection}) {
    return Path()..addRRect(borderRadius.resolve(textDirection).toRRect(rect));
  }

  @override
  void paint(Canvas canvas, Rect rect, {TextDirection? textDirection}) {
    switch (side.style) {
      case BorderStyle.none:
        break;
      case BorderStyle.solid:
        final double width = side.width;
        if (width == 0.0) {
          canvas.drawRRect(borderRadius.resolve(textDirection).toRRect(rect),
              side.toPaint());
        } else {
          final RRect outer = borderRadius.resolve(textDirection).toRRect(rect);
          final RRect inner = outer.deflate(width);
          final Paint paint = Paint()..color = side.color;
          final Paint paint2 = Paint()..color = Colors.white;

          canvas.drawDRRect(outer, inner, paint);
          canvas.drawPath(
              Path()..addPath(getTrianglePath(40, 40), const Offset(-30, -19)),
              paint);
          canvas.drawPath(
              Path()
                ..addPath(gettickpath(const Size(35, 35)), const Offset(79, 0)),
              paint2);
        }
    }
  }

  Path getTrianglePath(double x, double y) {
    return Path()
      ..moveTo(x * 2.240499, y * 0.4641165)
      ..lineTo(x * 3.039413, y * 0.4641165)
      ..arcToPoint(Offset(x * 3.240499, y * 0.6652069),
          radius: Radius.elliptical(x * 0.2010859, y * 0.2010904),
          rotation: 0,
          largeArc: false,
          clockwise: true)
      ..lineTo(x * 3.240499, y * 1.464117)
      ..close();
  }

  Path gettickpath(Size size) {
    Path path_0 = Path();
    path_0.moveTo(size.width * 0.1513658, size.height * 0.5394244);
    path_0.lineTo(size.width * 0.006621293, size.height * 0.3682648);
    path_0.arcToPoint(Offset(size.width * 0.006621293, size.height * 0.3311515),
        radius: Radius.elliptical(
            size.width * 0.02537649, size.height * 0.02780121),
        rotation: 0,
        largeArc: false,
        clockwise: true);
    path_0.lineTo(size.width * 0.03812633, size.height * 0.2940383);
    path_0.arcToPoint(Offset(size.width * 0.06963136, size.height * 0.2940383),
        radius: Radius.elliptical(
            size.width * 0.02115734, size.height * 0.02317892),
        rotation: 0,
        largeArc: false,
        clockwise: true);
    path_0.lineTo(size.width * 0.1671953, size.height * 0.4093256);
    path_0.lineTo(size.width * 0.3761818, size.height * 0.1623874);
    path_0.arcToPoint(Offset(size.width * 0.4076869, size.height * 0.1623874),
        radius: Radius.elliptical(
            size.width * 0.02115734, size.height * 0.02317892),
        rotation: 0,
        largeArc: false,
        clockwise: true);
    path_0.lineTo(size.width * 0.4391919, size.height * 0.1995007);
    path_0.arcToPoint(Offset(size.width * 0.4391919, size.height * 0.2366139),
        radius: Radius.elliptical(
            size.width * 0.02537649, size.height * 0.02780121),
        rotation: 0,
        largeArc: false,
        clockwise: true);
    path_0.lineTo(size.width * 0.1828709, size.height * 0.5394244);
    path_0.arcToPoint(Offset(size.width * 0.1513658, size.height * 0.5394244),
        radius: Radius.elliptical(
            size.width * 0.02115734, size.height * 0.02317892),
        rotation: 0,
        largeArc: false,
        clockwise: true);
    path_0.close();
    return path_0;
  }

  @override
  bool operator ==(Object other) {
    if (other.runtimeType != runtimeType) {
      return false;
    }
    return other is RoundedRectangleBorder &&
        other.side == side &&
        other.borderRadius == borderRadius;
  }

  @override
  int get hashCode => Object.hash(side, borderRadius);

  @override
  String toString() {
    return '${objectRuntimeType(this, 'RoundedRectangleBorder')}($side, $borderRadius)';
  }
}

class _RoundedRectangleCustomToCircleBorder extends OutlinedBorder {
  const _RoundedRectangleCustomToCircleBorder({
    BorderSide side = BorderSide.none,
    this.borderRadius = BorderRadius.zero,
    required this.circleness,
  }) : super(side: side);

  final BorderRadiusGeometry borderRadius;

  final double circleness;

  @override
  EdgeInsetsGeometry get dimensions {
    return EdgeInsets.all(side.width);
  }

  @override
  ShapeBorder scale(double t) {
    return _RoundedRectangleCustomToCircleBorder(
      side: side.scale(t),
      borderRadius: borderRadius * t,
      circleness: t,
    );
  }

  @override
  ShapeBorder? lerpFrom(ShapeBorder? a, double t) {
    if (a is RoundedRectangleBorder) {
      return _RoundedRectangleCustomToCircleBorder(
        side: BorderSide.lerp(a.side, side, t),
        borderRadius:
            BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t)!,
        circleness: circleness * t,
      );
    }
    if (a is CircleBorder) {
      return _RoundedRectangleCustomToCircleBorder(
        side: BorderSide.lerp(a.side, side, t),
        borderRadius: borderRadius,
        circleness: circleness + (1.0 - circleness) * (1.0 - t),
      );
    }
    if (a is _RoundedRectangleCustomToCircleBorder) {
      return _RoundedRectangleCustomToCircleBorder(
        side: BorderSide.lerp(a.side, side, t),
        borderRadius:
            BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t)!,
        circleness: ui.lerpDouble(a.circleness, circleness, t)!,
      );
    }
    return super.lerpFrom(a, t);
  }

  @override
  ShapeBorder? lerpTo(ShapeBorder? b, double t) {
    if (b is RoundedRectangleBorder) {
      return _RoundedRectangleCustomToCircleBorder(
        side: BorderSide.lerp(side, b.side, t),
        borderRadius:
            BorderRadiusGeometry.lerp(borderRadius, b.borderRadius, t)!,
        circleness: circleness * (1.0 - t),
      );
    }
    if (b is CircleBorder) {
      return _RoundedRectangleCustomToCircleBorder(
        side: BorderSide.lerp(side, b.side, t),
        borderRadius: borderRadius,
        circleness: circleness + (1.0 - circleness) * t,
      );
    }
    if (b is _RoundedRectangleCustomToCircleBorder) {
      return _RoundedRectangleCustomToCircleBorder(
        side: BorderSide.lerp(side, b.side, t),
        borderRadius:
            BorderRadiusGeometry.lerp(borderRadius, b.borderRadius, t)!,
        circleness: ui.lerpDouble(circleness, b.circleness, t)!,
      );
    }
    return super.lerpTo(b, t);
  }

  Rect _adjustRect(Rect rect) {
    if (circleness == 0.0 || rect.width == rect.height) {
      return rect;
    }
    if (rect.width < rect.height) {
      final double delta = circleness * (rect.height - rect.width) / 2.0;
      return Rect.fromLTRB(
        rect.left,
        rect.top + delta,
        rect.right,
        rect.bottom - delta,
      );
    } else {
      final double delta = circleness * (rect.width - rect.height) / 2.0;
      return Rect.fromLTRB(
        rect.left + delta,
        rect.top,
        rect.right - delta,
        rect.bottom,
      );
    }
  }

  BorderRadius? _adjustBorderRadius(Rect rect, TextDirection? textDirection) {
    final BorderRadius resolvedRadius = borderRadius.resolve(textDirection);
    if (circleness == 0.0) {
      return resolvedRadius;
    }
    return BorderRadius.lerp(resolvedRadius,
        BorderRadius.circular(rect.shortestSide / 2.0), circleness);
  }

  @override
  Path getInnerPath(Rect rect, {TextDirection? textDirection}) {
    return Path()
      ..addRRect(_adjustBorderRadius(rect, textDirection)!
          .toRRect(_adjustRect(rect))
          .deflate(side.width));
  }

  @override
  Path getOuterPath(Rect rect, {TextDirection? textDirection}) {
    return Path()
      ..addRRect(
          _adjustBorderRadius(rect, textDirection)!.toRRect(_adjustRect(rect)));
  }

  @override
  _RoundedRectangleCustomToCircleBorder copyWith(
      {BorderSide? side,
      BorderRadiusGeometry? borderRadius,
      double? circleness}) {
    return _RoundedRectangleCustomToCircleBorder(
      side: side ?? this.side,
      borderRadius: borderRadius ?? this.borderRadius,
      circleness: circleness ?? this.circleness,
    );
  }

  @override
  void paint(Canvas canvas, Rect rect, {TextDirection? textDirection}) {
    switch (side.style) {
      case BorderStyle.none:
        break;
      case BorderStyle.solid:
        final double width = side.width;
        if (width == 0.0) {
          canvas.drawRRect(
              _adjustBorderRadius(rect, textDirection)!
                  .toRRect(_adjustRect(rect)),
              side.toPaint());
        } else {
          final RRect outer = _adjustBorderRadius(rect, textDirection)!
              .toRRect(_adjustRect(rect));
          final RRect inner = outer.deflate(width);
          final Paint paint = Paint()..color = side.color;
          canvas.drawDRRect(outer, inner, paint);
        }
    }
  }

  @override
  bool operator ==(Object other) {
    if (other.runtimeType != runtimeType) {
      return false;
    }
    return other is _RoundedRectangleCustomToCircleBorder &&
        other.side == side &&
        other.borderRadius == borderRadius &&
        other.circleness == circleness;
  }

  @override
  int get hashCode => Object.hash(side, borderRadius, circleness);

  @override
  String toString() {
    return 'RoundedRectangleBorder($side, $borderRadius, ${(circleness * 100).toStringAsFixed(1)}% of the way to being a CircleBorder)';
  }
}

Result