Allow for bodyDef and fixtureDefs to be prepared earlier

doc/bridge_packages/flame_forge2d/forge2d.md

@@ -51,8 +51,13 @@ A simple `Forge2DGame` implementation example can be seen in the
 ## BodyComponent
 
 The `BodyComponent` is a wrapper for the `Forge2D` body, which is the body that the physics engine
-is interacting with. To create a `BodyComponent` you need to override `createBody()` and create and
-return your created body.
+is interacting with. To create a `BodyComponent` you can either:
+
+- override `createBody()` and create and return your created body;
+- use the default `createBody()` implementation: pass a `BodyDef` instance (and optionally a list
+of `FixtureDef` instances) to BodyComponent' constructor' `bodyDef` (and `fixtureDefs`) arguments;
+- use the default `createBody()` implementation: assign a `BodyDef` instance to `this.bodyDef`, and
+optionally a list of `FixtureDef` instances to `this.fixtureDefs`.
 
 The `BodyComponent` is by default having `renderBody = true`, since otherwise, it wouldn't show
 anything after you have created a `Body` and added the `BodyComponent` to the game. If you want to
@@ -61,7 +66,7 @@ turn it off you can just set (or override) `renderBody` to false.
 Just like any other Flame component you can add children to the `BodyComponent`, which can be very
 useful if you want to add for example animations or other components on top of your body.
 
-The body that you create in `createBody` should be defined according to Flame's coordinate system,
+The body that you create should be defined according to Flame's coordinate system,
 not according to the coordinate system of Forge2D (where the Y-axis is flipped).
 
 :exclamation: In Forge2D you shouldn't add any bodies as children to other components,

packages/flame_forge2d/example/lib/main.dart

@@ -36,32 +36,22 @@ class Forge2DExample extends Forge2DGame {
 }
 
 class Ball extends BodyComponent with TapCallbacks {
- final Vector2 initialPosition;
-
  Ball({Vector2? initialPosition})
- : initialPosition = initialPosition ?? Vector2.zero();
-
- @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: initialPosition,
- type: BodyType.dynamic,
- );
-
- return world.createBody(bodyDef)..createFixture(fixtureDef);
- }
+ : super(
+ fixtureDefs: [
+ FixtureDef(
+ CircleShape()..radius = 5,
+ restitution: 0.8,
+ density: 1.0,
+ friction: 0.4,
+ ),
+ ],
+ bodyDef: BodyDef(
+ angularDamping: 0.8,
+ position: initialPosition ?? Vector2.zero(),
+ type: BodyType.dynamic,
+ ),
+ );
 
  @override
  void onTapDown(_) {
@@ -80,7 +70,6 @@ class Wall extends BodyComponent {
  final shape = EdgeShape()..set(_start, _end);
  final fixtureDef = FixtureDef(shape, friction: 0.3);
  final bodyDef = BodyDef(
- userData: this,
  position: Vector2.zero(),
  );
 

packages/flame_forge2d/lib/body_component.dart

@@ -10,7 +10,11 @@ import 'package:flutter/foundation.dart';
 /// Since a pure BodyComponent doesn't have anything drawn on top of it,
 /// it is a good idea to turn on [debugMode] for it so that the bodies can be
 /// seen
-abstract class BodyComponent<T extends Forge2DGame> extends Component
+///
+/// You can use the optional [bodyDef] and [fixtureDefs] arguments to create
+/// the [BodyComponent]' body without having to create the definitions within
+/// the component.
+class BodyComponent<T extends Forge2DGame> extends Component
  with HasGameReference<T>, HasPaint
  implements
  CoordinateTransform,
@@ -21,6 +25,8 @@ abstract class BodyComponent<T extends Forge2DGame> extends Component
  super.children,
  super.priority,
  this.renderBody = true,
+ this.bodyDef,
+ this.fixtureDefs,
  super.key,
  }) {
  this.paint = paint ?? (Paint()..color = defaultColor);
@@ -29,6 +35,15 @@ abstract class BodyComponent<T extends Forge2DGame> extends Component
  static const defaultColor = Color.fromARGB(255, 255, 255, 255);
  late Body body;
 
+ /// Default implementation of [createBody] will use this value, if provided.
+ ///
+ /// If you do not provide a BodyDef here, you must override [createBody].
+ BodyDef? bodyDef;
+
+ /// Default implementation of [createBody] adds these fixtures to the body
+ /// that it creates from [bodyDef].
+ List<FixtureDef>? fixtureDefs;
+
  @override
  Vector2 get position => body.position;
 
@@ -43,7 +58,15 @@ abstract class BodyComponent<T extends Forge2DGame> extends Component
 
  /// You should create the Forge2D [Body] in this method when you extend
  /// the BodyComponent.
- Body createBody();
+ Body createBody() {
+ assert(
+ bodyDef != null,
+ 'Ensure this.bodyDef is not null or override createBody',
+ );
+ final body = world.createBody(bodyDef!);
+ fixtureDefs?.forEach(body.createFixture);
+ return body;
+ }
 
  @mustCallSuper
  @override

packages/flame_forge2d/test/body_component_test.dart

@@ -1,4 +1,4 @@
-import 'package:flame/components.dart' show PositionComponent;
+import 'package:flame/components.dart' show ComponentKey, PositionComponent;
 import 'package:flame/extensions.dart';
 import 'package:flame_forge2d/flame_forge2d.dart';
 import 'package:flame_test/flame_test.dart';
@@ -350,5 +350,54 @@ void main() {
  },
  );
  });
+ group('createBody', () {
+ test('should throw an error if bodyDef is null', () {
+ final bodyComponent = BodyComponent();
+ expect(bodyComponent.createBody, throwsAssertionError);
+ });
+
+ group('should create body', () {
+ final flameTester = FlameTester(Forge2DGame.new);
+
+ flameTester.testGameWidget(
+ 'with no fixtures',
+ setUp: (game, tester) async {
+ final bodyComponent = BodyComponent(
+ bodyDef: BodyDef(position: Vector2(33, 44)),
+ key: ComponentKey.named('tested'),
+ );
+ game.world.add(bodyComponent);
+ },
+ verify: (game, tester) async {
+ expect(
+ game.findByKeyName<BodyComponent>('tested')!.body.position,
+ Vector2(33, 44),
+ );
+ },
+ );
+
+ flameTester.testGameWidget(
+ 'with a set of fixtures',
+ setUp: (game, tester) async {
+ final bodyComponent = BodyComponent(
+ bodyDef: BodyDef(),
+ fixtureDefs: [
+ FixtureDef(CircleShape()..radius = 10),
+ FixtureDef(CircleShape()..radius = 20),
+ FixtureDef(CircleShape()..radius = 30),
+ ],
+ key: ComponentKey.named('tested'),
+ );
+ game.world.add(bodyComponent);
+ },
+ verify: (game, tester) async {
+ final bodyComponent = game.findByKeyName<BodyComponent>('tested')!;
+ expect(bodyComponent.body.fixtures[0].shape.radius, 10);
+ expect(bodyComponent.body.fixtures[1].shape.radius, 20);
+ expect(bodyComponent.body.fixtures[2].shape.radius, 30);
+ },
+ );
+ });
+ });
  });
 }