flame/packages/flame_forge2d/example/lib/main.dart

import 'package:flame/camera.dart' as camera;
import 'package:flame/components.dart';
import 'package:flame/events.dart';
import 'package:flame/game.dart';
import 'package:flame_forge2d/flame_forge2d.dart';
import 'package:flutter/widgets.dart';

void main() {
  runApp(GameWidget(game: Forge2DExample()));
}

class Forge2DExample extends Forge2DGame {
  final cameraWorld = camera.World();
  late final CameraComponent cameraComponent;

  @override
  Future<void> onLoad() async {
    cameraComponent = CameraComponent(world: cameraWorld);
    cameraComponent.viewfinder.anchor = Anchor.topLeft;
    addAll([cameraComponent, cameraWorld]);

    cameraWorld.add(Ball(size / 2));
    cameraWorld.addAll(createBoundaries());
  }

  List<Component> createBoundaries() {
    final topLeft = Vector2.zero();
    final bottomRight = screenToWorld(cameraComponent.viewport.size);
    final topRight = Vector2(bottomRight.x, topLeft.y);
    final bottomLeft = Vector2(topLeft.x, bottomRight.y);

    return [
      Wall(topLeft, topRight),
      Wall(topRight, bottomRight),
      Wall(bottomLeft, bottomRight),
      Wall(topLeft, bottomLeft),
    ];
  }
}

class Ball extends BodyComponent with TapCallbacks {
  final Vector2 _position;

  Ball(this._position);

  @override
  Body createBody() {
    final shape = CircleShape();
    shape.radius = 5;

    final fixtureDef = FixtureDef(
      shape,
      restitution: 0.8,
      density: 1.0,
      friction: 0.4,
    );

    final bodyDef = BodyDef(
      userData: this,
      angularDamping: 0.8,
      position: _position,
      type: BodyType.dynamic,
    );

    return world.createBody(bodyDef)..createFixture(fixtureDef);
  }

  @override
  void onTapDown(_) {
    body.applyLinearImpulse(Vector2.random() * 5000);
  }
}

class Wall extends BodyComponent {
  final Vector2 _start;
  final Vector2 _end;

  Wall(this._start, this._end);

  @override
  Body createBody() {
    final shape = EdgeShape()..set(_start, _end);
    final fixtureDef = FixtureDef(shape, friction: 0.3);
    final bodyDef = BodyDef(
      userData: this,
      position: Vector2.zero(),
    );

    return world.createBody(bodyDef)..createFixture(fixtureDef);
  }
}