Example showcasing how to use the ContactCallback

.gitignore

@@ -10,6 +10,8 @@ pubspec.lock
 doc/api/
 .flutter-plugins
 .vscode/
+**/.flutter-plugins
+**/.flutter-plugins-dependencies
 
 android/
 ios/

doc/examples/box2d/contact_callbacks/.gitignore

@@ -0,0 +1,70 @@
+# Miscellaneous
+*.class
+*.log
+*.pyc
+*.swp
+.DS_Store
+.atom/
+.buildlog/
+.history
+.svn/
+
+# IntelliJ related
+*.iml
+*.ipr
+*.iws
+.idea/
+
+# Visual Studio Code related
+.vscode/
+
+# Flutter/Dart/Pub related
+**/doc/api/
+.dart_tool/
+.flutter-plugins
+.packages
+.pub-cache/
+.pub/
+/build/
+
+# Android related
+**/android/**/gradle-wrapper.jar
+**/android/.gradle
+**/android/captures/
+**/android/gradlew
+**/android/gradlew.bat
+**/android/local.properties
+**/android/**/GeneratedPluginRegistrant.java
+
+# iOS/XCode related
+**/ios/**/*.mode1v3
+**/ios/**/*.mode2v3
+**/ios/**/*.moved-aside
+**/ios/**/*.pbxuser
+**/ios/**/*.perspectivev3
+**/ios/**/*sync/
+**/ios/**/.sconsign.dblite
+**/ios/**/.tags*
+**/ios/**/.vagrant/
+**/ios/**/DerivedData/
+**/ios/**/Icon?
+**/ios/**/Pods/
+**/ios/**/.symlinks/
+**/ios/**/profile
+**/ios/**/xcuserdata
+**/ios/.generated/
+**/ios/Flutter/App.framework
+**/ios/Flutter/Flutter.framework
+**/ios/Flutter/Generated.xcconfig
+**/ios/Flutter/app.flx
+**/ios/Flutter/app.zip
+**/ios/Flutter/flutter_assets/
+**/ios/ServiceDefinitions.json
+**/ios/Runner/GeneratedPluginRegistrant.*
+
+# Exceptions to above rules.
+!**/ios/**/default.mode1v3
+!**/ios/**/default.mode2v3
+!**/ios/**/default.pbxuser
+!**/ios/**/default.perspectivev3
+!/packages/flutter_tools/test/data/dart_dependencies_test/**/.packages

doc/examples/box2d/contact_callbacks/.metadata

@@ -0,0 +1,10 @@
+# This file tracks properties of this Flutter project.
+# Used by Flutter tool to assess capabilities and perform upgrades etc.
+#
+# This file should be version controlled and should not be manually edited.
+
+version:
+  revision: 7fc14a55af64462763d28abfb4e610086c6e0f39
+  channel: dev
+
+project_type: app

doc/examples/box2d/contact_callbacks/README.md

@@ -0,0 +1,4 @@
+# box2d contact callbacks
+
+A Flame game showcasing how to use box2d_game's contact callbacks.
+Balls will bounce around and change colour when they come in contact.

doc/examples/box2d/contact_callbacks/lib/boundaries.dart

@@ -0,0 +1,57 @@
+import 'dart:ui';
+
+import 'package:box2d_flame/box2d.dart';
+import 'package:flame/box2d/box2d_component.dart';
+import 'package:flame/box2d/viewport.dart';
+import 'package:flame/palette.dart';
+
+List<Wall> createBoundaries(Box2DComponent box) {
+  final Viewport viewport = box.viewport;
+  final Vector2 screenSize = Vector2(viewport.width, viewport.height)
+      *viewport.scale;
+  final Vector2 topLeft = viewport.getScreenToWorld(Vector2.zero());
+  final Vector2 bottomRight = viewport.getScreenToWorld(screenSize);
+  final Vector2 topRight = Vector2(bottomRight.x, topLeft.y);
+  final Vector2 bottomLeft = Vector2(topLeft.x, bottomRight.y);
+
+  return [
+    Wall(topLeft, topRight, box),
+    Wall(topRight, bottomRight, box),
+    Wall(bottomRight, bottomLeft, box),
+    Wall(bottomLeft, topLeft, box),
+  ];
+}
+
+class Wall extends BodyComponent {
+  Paint paint = BasicPalette.white.paint;
+  final Vector2 start;
+  final Vector2 end;
+
+  Wall(this.start, this.end, Box2DComponent box) : super(box) {
+    _createBody(start, end);
+  }
+
+  @override
+  void renderPolygon(Canvas canvas, List<Offset> coordinates) {
+    Offset start = coordinates[0];
+    Offset end = coordinates[1];
+    canvas.drawLine(start, end, paint);
+  }
+
+  void _createBody(Vector2 start, Vector2 end) {
+    final PolygonShape shape = PolygonShape();
+    shape.setAsEdge(start, end);
+
+    final fixtureDef = FixtureDef();
+    fixtureDef.setUserData(this); // To be able to determine object in collision
+    fixtureDef.shape = shape;
+    fixtureDef.restitution = 0.0;
+    fixtureDef.friction = 0.1;
+
+    final bodyDef = BodyDef();
+    bodyDef.position = Vector2.zero();
+    bodyDef.type = BodyType.STATIC;
+
+    body = world.createBody(bodyDef)..createFixtureFromFixtureDef(fixtureDef);
+  }
+}

doc/examples/box2d/contact_callbacks/lib/main.dart

@@ -0,0 +1,122 @@
+import 'dart:math' as math;
+import 'package:box2d_contact_callbacks/boundaries.dart';
+import 'package:flame/box2d/box2d_component.dart';
+import 'package:flame/box2d/box2d_game.dart';
+import 'package:flame/box2d/contact_listeners.dart';
+import 'package:flame/flame.dart';
+import 'package:flame/palette.dart';
+import 'package:flutter/material.dart';
+import 'package:box2d_flame/box2d.dart';
+
+void main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+  await Flame.util.fullScreen();
+  runApp(GameController().widget);
+}
+
+class Ball extends BodyComponent {
+  Paint originalPaint, currentPaint;
+
+  Ball(Vector2 position, Box2DComponent box) : super(box) {
+    originalPaint = _randomPaint();
+    currentPaint = originalPaint;
+    Vector2 worldPosition = viewport.getScreenToWorld(position);
+    _createBody(5.0, worldPosition);
+  }
+
+  Paint _randomPaint() {
+    math.Random rng = math.Random();
+    return PaletteEntry(Color.fromARGB(rng.nextInt(255), rng.nextInt(255),
+        rng.nextInt(255), rng.nextInt(255))).paint;
+  }
+
+  void _createBody(double radius, Vector2 position) {
+    final CircleShape shape = CircleShape();
+    shape.radius = radius;
+
+    final fixtureDef = FixtureDef();
+    // To be able to determine object in collision
+    fixtureDef.setUserData(this);
+    fixtureDef.shape = shape;
+    fixtureDef.restitution = 1.0;
+    fixtureDef.density = 1.0;
+    fixtureDef.friction = 0.1;
+
+    final bodyDef = BodyDef();
+    bodyDef.position = position;
+    bodyDef.type = BodyType.DYNAMIC;
+
+    body = world.createBody(bodyDef)..createFixtureFromFixtureDef(fixtureDef);
+  }
+
+  @override
+  bool destroy() {
+    // Implement your logic for when the component should be removed
+    return false;
+  }
+
+  @override
+  void renderCircle(Canvas c, Offset p, double radius) {
+    Paint blue = PaletteEntry(Colors.blue).paint;
+    c.drawCircle(p, radius, currentPaint);
+    double angle = body.getAngle();
+    Offset lineRotation =
+        Offset(math.sin(angle) * radius, math.cos(angle) * radius);
+    c.drawLine(p, p + lineRotation, blue);
+  }
+}
+
+class BallContactCallback implements ContactCallback {
+  @override
+  List<Type> objects = [Ball, Ball];
+
+  BallContactCallback();
+
+  @override
+  void begin(Object contact1, Object contact2) {
+    Ball ball1 = contact1 as Ball;
+    Ball ball2 = contact2 as Ball;
+    if (ball1.currentPaint != ball1.originalPaint) {
+      ball1.currentPaint = ball2.currentPaint;
+    } else {
+      ball2.currentPaint = ball1.currentPaint;
+    }
+  }
+
+  @override
+  void end(Object ship, Object material) {}
+}
+
+class MyGame extends Box2DGame {
+  MyGame(Box2DComponent box) : super(box) {
+    final List<BodyComponent> boundaries = createBoundaries(box);
+    boundaries.forEach(add);
+    addContactCallback(BallContactCallback());
+  }
+
+  @override
+  void onTapDown(TapDownDetails details) {
+    super.onTapDown(details);
+    final Vector2 position =
+        Vector2(details.globalPosition.dx, details.globalPosition.dy);
+    add(Ball(position, box));
+  }
+}
+
+class MyBox2D extends Box2DComponent {
+  MyBox2D() : super(scale: 4.0, gravity: -10.0);
+
+  @override
+  void initializeWorld() {}
+}
+
+class GameController {
+  MyGame _game;
+
+  GameController() {
+    final MyBox2D box = MyBox2D();
+    _game = MyGame(box);
+  }
+
+  Widget get widget => _game.widget;
+}

doc/examples/box2d/contact_callbacks/pubspec.yaml

@@ -0,0 +1,17 @@
+name: box2d_contact_callbacks
+description: Flame sample game showcasing the structure for box2d games
+
+version: 1.0.0+1
+
+environment:
+  sdk: ">=2.1.0 <3.0.0"
+
+dependencies:
+  flutter:
+    sdk: flutter
+  flame:
+    path: ../../../../
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter