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How to build a real-time multiplayer game with Flutter Flame

2023-02-14

37 minute read

Flutter is a UI library to build apps that run on any platform, but it can also build interactive games thanks to an open-source game engine built on top of Flutter called Flame. Flame takes care of things like collision detection or loading image sprites to bring game development to all the Flutter devs. We can take it a step further to introduce real-time communication features so that players can play against each other in real-time.

In this article, we will use Flutter, Flame, and Supabase's real-time features to build a real-time multiplayer shooting game. You can find the complete code of this tutorial here.

Overview of the final game

The game is a simple shooting game. Each player has a UFO, and you can move it by dragging your finger across the screen. The UFO will emit bullets automatically in three directions, and the objective of the game is to hit the opponents with bullets before your UFO gets destroyed by the opponent’s bullets. The position and the health points are synced using a low-latency web socket connection provided by Supabase.

Before entering the main game, there is a lobby where you can wait for other players to show up. Once another player shows up, you can hit start, which will kick off the game on both ends.

We will first build the Flutter widgets used to build the basic UI, then build the Flame game and finally handle the network connection to share the data between connected clients.

Build the App

Step 1. Create the Flutter App

We will start out by creating the Flutter app. Open your terminal and create a new app named with the following command.


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flutter create flame_realtime_shooting

Open the created app with your favorite IDE and let’s get started with coding!

Step 2. Building the Flutter widgets

We will have a simple directory structure to build this app. Since we only have a few widgets, we will just add them inside main.dart file.


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├── lib/
_10
| ├── game/
_10
│ │ ├── game.dart
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│ │ ├── player.dart
_10
│ │ └── bullet.dart
_10
│ └── main.dart

Create the Main Game Page

We will create minimal Flutter widgets for this app as most of the game logic will be handled in the Flame Game classes later. Our game will have a single page with two dialogs before the game starts and after the game ends. The page will simply contain the GameWidget while displaying a nice background image. We will make it a StatefulWidget, because we will add methods to handle sending and receiving real-time data later on. Add the following to main.dart file.


_81
import 'package:flame/game.dart';
_81
import 'package:flame_realtime_shooting/game/game.dart';
_81
import 'package:flutter/material.dart';
_81
_81
void main() {
_81
runApp(const MyApp());
_81
}
_81
_81
class MyApp extends StatelessWidget {
_81
const MyApp({super.key});
_81
_81
@override
_81
Widget build(BuildContext context) {
_81
return const MaterialApp(
_81
title: 'UFO Shooting Game',
_81
debugShowCheckedModeBanner: false,
_81
home: GamePage(),
_81
);
_81
}
_81
}
_81
_81
class GamePage extends StatefulWidget {
_81
const GamePage({Key? key}) : super(key: key);
_81
_81
@override
_81
State<GamePage> createState() => _GamePageState();
_81
}
_81
_81
class _GamePageState extends State<GamePage> {
_81
late final MyGame _game;
_81
_81
@override
_81
Widget build(BuildContext context) {
_81
return Scaffold(
_81
body: Stack(
_81
fit: StackFit.expand,
_81
children: [
_81
Image.asset('assets/images/background.jpg', fit: BoxFit.cover),
_81
GameWidget(game: _game),
_81
],
_81
),
_81
);
_81
}
_81
_81
@override
_81
void initState() {
_81
super.initState();
_81
_initialize();
_81
}
_81
_81
Future<void> _initialize() async {
_81
_game = MyGame(
_81
onGameStateUpdate: (position, health) async {
_81
// TODO: handle gmae state update here
_81
},
_81
onGameOver: (playerWon) async {
_81
// TODO: handle when the game is over here
_81
},
_81
);
_81
_81
// await for a frame so that the widget mounts
_81
await Future.delayed(Duration.zero);
_81
_81
if (mounted) {
_81
_openLobbyDialog();
_81
}
_81
}
_81
_81
void _openLobbyDialog() {
_81
showDialog(
_81
context: context,
_81
barrierDismissible: false,
_81
builder: (context) {
_81
return _LobbyDialog(
_81
onGameStarted: (gameId) async {
_81
// handle game start here
_81
},
_81
);
_81
});
_81
}
_81
}

You will see some errors, because we are importing some files that we haven’t created yet, but don’t worry, because we will get to it soon.

Create the Lobby Dialog

Flutter Flame shooting game lobby dialog

Lobby dialog class on the surface is a simple Alert dialog, but will hold its own states like the list of players that are waiting at the lobby. We will also add some classes to handle the presence data on the lobby later on, but for now we will just have a simple AlertDialog. Add the following code at the end of main.dart file.


_45
class _LobbyDialog extends StatefulWidget {
_45
const _LobbyDialog({
_45
required this.onGameStarted,
_45
});
_45
_45
final void Function(String gameId) onGameStarted;
_45
_45
@override
_45
State<_LobbyDialog> createState() => _LobbyDialogState();
_45
}
_45
_45
class _LobbyDialogState extends State<_LobbyDialog> {
_45
final List<String> _userids = [];
_45
bool _loading = false;
_45
_45
/// TODO: assign unique identifier for the user
_45
final myUserId = '';
_45
_45
@override
_45
Widget build(BuildContext context) {
_45
return AlertDialog(
_45
title: const Text('Lobby'),
_45
content: _loading
_45
? const SizedBox(
_45
height: 100,
_45
child: Center(child: CircularProgressIndicator()),
_45
)
_45
: Text('${_userids.length} users waiting'),
_45
actions: [
_45
TextButton(
_45
onPressed: _userids.length < 2
_45
? null
_45
: () async {
_45
setState(() {
_45
_loading = true;
_45
});
_45
_45
// TODO: notify the other player the start of the game
_45
},
_45
child: const Text('start'),
_45
),
_45
],
_45
);
_45
}
_45
}

Step 3. Building the Flame components

Creating the FlameGame

Now the fun part starts! We will start out by creating our game class. We create a MyGame class that extends the FlameGame class. FlameGame takes care of collision detection and pan-detection, and it will also be the parent of all the components that we will add to the game. The game contains 2 components, Player and Bullet. MyGame is a class that wraps around all components of the game and can control the child components.

Structure of the shooting game

Let's add flame to our app. Run the following command:


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flutter pub add flame

We can then create MyGame class. Add the following code in lib/game.dart file.


_160
import 'dart:async';
_160
_160
import 'package:flame/game.dart';
_160
import 'package:flame/components.dart';
_160
import 'package:flame/events.dart';
_160
import 'package:flame/image_composition.dart' as flame_image;
_160
import 'package:flame_realtime_shooting/game/bullet.dart';
_160
import 'package:flame_realtime_shooting/game/player.dart';
_160
import 'package:flutter/material.dart';
_160
_160
class MyGame extends FlameGame with PanDetector, HasCollisionDetection {
_160
MyGame({
_160
required this.onGameOver,
_160
required this.onGameStateUpdate,
_160
});
_160
_160
static const _initialHealthPoints = 100;
_160
_160
/// Callback to notify the parent when the game ends.
_160
final void Function(bool didWin) onGameOver;
_160
_160
/// Callback for when the game state updates.
_160
final void Function(
_160
Vector2 position,
_160
int health,
_160
) onGameStateUpdate;
_160
_160
/// `Player` instance of the player
_160
late Player _player;
_160
_160
/// `Player` instance of the opponent
_160
late Player _opponent;
_160
_160
bool isGameOver = true;
_160
_160
int _playerHealthPoint = _initialHealthPoints;
_160
_160
late final flame_image.Image _playerBulletImage;
_160
late final flame_image.Image _opponentBulletImage;
_160
_160
@override
_160
Color backgroundColor() {
_160
return Colors.transparent;
_160
}
_160
_160
@override
_160
Future<void>? onLoad() async {
_160
final playerImage = await images.load('player.png');
_160
_player = Player(isMe: true);
_160
final spriteSize = Vector2.all(Player.radius * 2);
_160
_player.add(SpriteComponent(sprite: Sprite(playerImage), size: spriteSize));
_160
add(_player);
_160
_160
final opponentImage = await images.load('opponent.png');
_160
_opponent = Player(isMe: false);
_160
_opponent.add(SpriteComponent.fromImage(opponentImage, size: spriteSize));
_160
add(_opponent);
_160
_160
_playerBulletImage = await images.load('player-bullet.png');
_160
_opponentBulletImage = await images.load('opponent-bullet.png');
_160
_160
await super.onLoad();
_160
}
_160
_160
@override
_160
void onPanUpdate(DragUpdateInfo info) {
_160
_player.move(info.delta.global);
_160
final mirroredPosition = _player.getMirroredPercentPosition();
_160
onGameStateUpdate(mirroredPosition, _playerHealthPoint);
_160
super.onPanUpdate(info);
_160
}
_160
_160
@override
_160
void update(double dt) {
_160
super.update(dt);
_160
if (isGameOver) {
_160
return;
_160
}
_160
for (final child in children) {
_160
if (child is Bullet && child.hasBeenHit && !child.isMine) {
_160
_playerHealthPoint = _playerHealthPoint - child.damage;
_160
final mirroredPosition = _player.getMirroredPercentPosition();
_160
onGameStateUpdate(mirroredPosition, _playerHealthPoint);
_160
_player.updateHealth(_playerHealthPoint / _initialHealthPoints);
_160
}
_160
}
_160
if (_playerHealthPoint <= 0) {
_160
endGame(false);
_160
}
_160
}
_160
_160
void startNewGame() {
_160
isGameOver = false;
_160
_playerHealthPoint = _initialHealthPoints;
_160
_160
for (final child in children) {
_160
if (child is Player) {
_160
child.position = child.initialPosition;
_160
} else if (child is Bullet) {
_160
child.removeFromParent();
_160
}
_160
}
_160
_160
_shootBullets();
_160
}
_160
_160
/// shoots out bullets form both the player and the opponent.
_160
///
_160
/// Calls itself every 500 milliseconds
_160
Future<void> _shootBullets() async {
_160
await Future.delayed(const Duration(milliseconds: 500));
_160
_160
/// Player's bullet
_160
final playerBulletInitialPosition = Vector2.copy(_player.position)
_160
..y -= Player.radius;
_160
final playerBulletVelocities = [
_160
Vector2(0, -100),
_160
Vector2(60, -80),
_160
Vector2(-60, -80),
_160
];
_160
for (final bulletVelocity in playerBulletVelocities) {
_160
add((Bullet(
_160
isMine: true,
_160
velocity: bulletVelocity,
_160
image: _playerBulletImage,
_160
initialPosition: playerBulletInitialPosition,
_160
)));
_160
}
_160
_160
/// Opponent's bullet
_160
final opponentBulletInitialPosition = Vector2.copy(_opponent.position)
_160
..y += Player.radius;
_160
final opponentBulletVelocities = [
_160
Vector2(0, 100),
_160
Vector2(60, 80),
_160
Vector2(-60, 80),
_160
];
_160
for (final bulletVelocity in opponentBulletVelocities) {
_160
add((Bullet(
_160
isMine: false,
_160
velocity: bulletVelocity,
_160
image: _opponentBulletImage,
_160
initialPosition: opponentBulletInitialPosition,
_160
)));
_160
}
_160
_160
_shootBullets();
_160
}
_160
_160
void updateOpponent({required Vector2 position, required int health}) {
_160
_opponent.position = Vector2(size.x * position.x, size.y * position.y);
_160
_opponent.updateHealth(health / _initialHealthPoints);
_160
}
_160
_160
/// Called when either the player or the opponent has run out of health points
_160
void endGame(bool playerWon) {
_160
isGameOver = true;
_160
onGameOver(playerWon);
_160
}
_160
}

There is a lot going here, so let’s break it down. Within the onLoad method, we are loading all of the sprites used throughout the game. Then we are adding the player and opponent component.

Within onPanUpdate, we handle the user dragging on the screen. Note that we are calling the onGameStateUpdate callback to pass the player’s position so that we can share it to the opponent’s client later when we handle network connections. On the other hand, we have the updateOpponent method, which is used to update the opponent’s state with the information coming in from the network. We will also add logic to call it from the Flutter widgets later.

Upon starting the game, _shootBullets() is called, which shoots out bullets both from the player and the opponent. _shootBullets() is a recursive function that calls itself every 500 milliseconds. If the bullet hits the player, it is caught inside the udpate() method, which is called on every frame. There we calculate the new player’s health points.

Creating the Player Component

Player component has the UFO sprite and represents the player and the opponent. It extends the PositionComponent from Flame. Add the following in lib/player.dart


_103
import 'dart:async';
_103
_103
import 'package:flame/collisions.dart';
_103
import 'package:flame/components.dart';
_103
import 'package:flame_realtime_shooting/game/bullet.dart';
_103
import 'package:flutter/material.dart';
_103
_103
class Player extends PositionComponent with HasGameRef, CollisionCallbacks {
_103
Vector2 velocity = Vector2.zero();
_103
_103
late final Vector2 initialPosition;
_103
_103
Player({required bool isMe}) : _isMyPlayer = isMe;
_103
_103
/// Whether it's me or the opponent
_103
final bool _isMyPlayer;
_103
_103
static const radius = 30.0;
_103
_103
@override
_103
Future<void>? onLoad() async {
_103
anchor = Anchor.center;
_103
width = radius * 2;
_103
height = radius * 2;
_103
_103
final initialX = gameRef.size.x / 2;
_103
initialPosition = _isMyPlayer
_103
? Vector2(initialX, gameRef.size.y * 0.8)
_103
: Vector2(initialX, gameRef.size.y * 0.2);
_103
position = initialPosition;
_103
_103
add(CircleHitbox());
_103
add(_Gauge());
_103
await super.onLoad();
_103
}
_103
_103
void move(Vector2 delta) {
_103
position += delta;
_103
}
_103
_103
void updateHealth(double healthLeft) {
_103
for (final child in children) {
_103
if (child is _Gauge) {
_103
child._healthLeft = healthLeft;
_103
}
_103
}
_103
}
_103
_103
@override
_103
void onCollision(Set<Vector2> intersectionPoints, PositionComponent other) {
_103
super.onCollision(intersectionPoints, other);
_103
if (other is Bullet && _isMyPlayer != other.isMine) {
_103
other.hasBeenHit = true;
_103
other.removeFromParent();
_103
}
_103
}
_103
_103
/// returns the mirrored percent position of the player
_103
/// to be broadcasted to other clients
_103
Vector2 getMirroredPercentPosition() {
_103
final mirroredPosition = gameRef.size - position;
_103
return Vector2(mirroredPosition.x / gameRef.size.x,
_103
mirroredPosition.y / gameRef.size.y);
_103
}
_103
}
_103
_103
class _Gauge extends PositionComponent {
_103
double _healthLeft = 1.0;
_103
_103
@override
_103
FutureOr<void> onLoad() {
_103
final playerParent = parent;
_103
if (playerParent is Player) {
_103
width = playerParent.width;
_103
height = 10;
_103
anchor = Anchor.centerLeft;
_103
position = Vector2(0, 0);
_103
}
_103
return super.onLoad();
_103
}
_103
_103
@override
_103
void render(Canvas canvas) {
_103
super.render(canvas);
_103
canvas.drawRect(
_103
Rect.fromPoints(
_103
const Offset(0, 0),
_103
Offset(width, height),
_103
),
_103
Paint()..color = Colors.white);
_103
canvas.drawRect(
_103
Rect.fromPoints(
_103
const Offset(0, 0),
_103
Offset(width * _healthLeft, height),
_103
),
_103
Paint()
_103
..color = _healthLeft > 0.5
_103
? Colors.green
_103
: _healthLeft > 0.25
_103
? Colors.orange
_103
: Colors.red);
_103
}
_103
}

You can see that it has a _isMyPlayer property, which is true for the player and false for the opponent. If we take a look at the onLoad method, we can use this to position it either at the top if it’s the opponent, or at the bottom if it’s the player. We can also see that we are adding a CircleHitbox, because we need to detect collisions between it and the bullets. Lastly, we are adding _Gauge as its child, which is the health point gauge you see on top of each players. Within onCollision callback, we are checking if the collided object is the opponent’s bullet, and if it is, we flag the bullet as hasBeenHit and remove it from the game.

getMirroredPercentPosition method is used when sharing the position with the opponent’s client. It calculates the mirrored position of the player. updateHealth is called when the health changes and updates the bar length of the _Gauge class.

Adding bullets

Lastly we will add the Bullet class. It represents a single bullet coming out from the player and the opponent. Within onLoad it adds the sprite to apply the nice image and CircleHitbox so that it can collide with other objects. You can also see that it receives a velocity in the constructor, the position is updated using the velocity and the elapsed time within the update method. This is how you can have it move in a single direction at a constant speed.


_55
import 'dart:async';
_55
_55
import 'package:flame/collisions.dart';
_55
import 'package:flame/components.dart';
_55
import 'package:flame/image_composition.dart' as flame_image;
_55
_55
class Bullet extends PositionComponent with CollisionCallbacks, HasGameRef {
_55
final Vector2 velocity;
_55
_55
final flame_image.Image image;
_55
_55
static const radius = 5.0;
_55
_55
bool hasBeenHit = false;
_55
_55
final bool isMine;
_55
_55
/// Damage that it deals when it hits the player
_55
final int damage = 5;
_55
_55
Bullet({
_55
required this.isMine,
_55
required this.velocity,
_55
required this.image,
_55
required Vector2 initialPosition,
_55
}) : super(position: initialPosition);
_55
_55
@override
_55
Future<void>? onLoad() async {
_55
anchor = Anchor.center;
_55
_55
width = radius * 2;
_55
height = radius * 2;
_55
_55
add(CircleHitbox()
_55
..collisionType = CollisionType.passive
_55
..anchor = Anchor.center);
_55
_55
final sprite =
_55
SpriteComponent.fromImage(image, size: Vector2.all(radius * 2));
_55
_55
add(sprite);
_55
await super.onLoad();
_55
}
_55
_55
@override
_55
void update(double dt) {
_55
super.update(dt);
_55
position += velocity * dt;
_55
_55
if (position.y < 0 || position.y > gameRef.size.y) {
_55
removeFromParent();
_55
}
_55
}
_55
}

Step 4. Add real-time communications between players

At this point, we have a working shooting game except the opponent does not move, because we have not added any ways to communicate between clients. We will use Supabase’s realtime features for this, because it gives us an out of the box solution to handle low-latency real-time communication between players. If you do not have a Supabase project created yet, head over to database.new to create one.

Before we get into any coding, let’s install the Supabase SDK into our app. We will also use the uuid package to generate random unique ids for the users. Run the following command:


_10
flutter pub add supabase_flutter uuid

Once pub get is complete, let’s initialize Supabase. We will override the main function to initialize Supabase. You can get your Supabase URL and Anon Key at Project Setting > API. Copy and paste them into the Supabase.initialize call.


_11
void main() async {
_11
await Supabase.initialize(
_11
url: 'YOUR_SUPABASE_URL',
_11
anonKey: 'YOUR_ANON_KEY',
_11
realtimeClientOptions: const RealtimeClientOptions(eventsPerSecond: 40),
_11
);
_11
runApp(const MyApp());
_11
}
_11
_11
// Extract Supabase client for easy access to Supabase
_11
final supabase = Supabase.instance.client;

RealtimeClientOptions here is a parameter to override how many events per second each client will send to Supabase. The default is 10, but we want to override to 40 to provide a more in-synced experience.

With this, we are ready to get into adding the real-time features now.

Handle the Lobby to wait for Other Players to show up

We will start by rewriting the _Lobby class the first thing we have to do in the lobby is to wait and detect other online users also at the lobby. We can implement this using the presence feature in Supabase.

Add initState and inside it initialize a RealtimeChannel instance. We can call it _lobbyChannel. If we take a look at the subscribe() method, we can see that upon successful subscription to the lobby channel, we are tracking our the unique user ID that we create uplon initialization. We are listening to the sync event to get notified whenever anyone is “present”. Within the callback, we are extracting the userIds of all the users in the lobby and set it as the state.A game starts when someone taps on the Start button. If we take a look at the onPressed callback, we see that we are sending a broadcast event to the lobby channel with two participant ids and a randomly generated game ID. Broadcast is a feature of Supabase to send and receive lightweight low-latency data between clients, and when the two participants, one of them being the person tapping on the start button, is received on both ends, a game starts. We can observe within initState inside the callback for game_start event that upon receiving a broadcast event, it checks if the player is one of the participants, and if it is, it will call the onGameStarted call back and pop the navigator removing the dialog. The game has begun!


_94
class _LobbyDialogState extends State<_LobbyDialog> {
_94
List<String> _userids = [];
_94
bool _loading = false;
_94
_94
/// Unique identifier for each players to identify eachother in lobby
_94
final myUserId = const Uuid().v4();
_94
_94
late final RealtimeChannel _lobbyChannel;
_94
_94
@override
_94
void initState() {
_94
super.initState();
_94
_94
_lobbyChannel = supabase.channel(
_94
'lobby',
_94
opts: const RealtimeChannelConfig(self: true),
_94
);
_94
_lobbyChannel
_94
.onPresenceSync((payload, [ref]) {
_94
// Update the lobby count
_94
final presenceStates = _lobbyChannel.presenceState();
_94
_94
setState(() {
_94
_userids = presenceStates
_94
.map((presenceState) => (presenceState.presences.first)
_94
.payload['user_id'] as String)
_94
.toList();
_94
});
_94
})
_94
.onBroadcast(
_94
event: 'game_start',
_94
callback: (payload, [_]) {
_94
// Start the game if someone has started a game with you
_94
final participantIds = List<String>.from(payload['participants']);
_94
if (participantIds.contains(myUserId)) {
_94
final gameId = payload['game_id'] as String;
_94
widget.onGameStarted(gameId);
_94
Navigator.of(context).pop();
_94
}
_94
})
_94
.subscribe(
_94
(status, _) async {
_94
if (status == RealtimeSubscribeStatus.subscribed) {
_94
await _lobbyChannel.track({'user_id': myUserId});
_94
}
_94
},
_94
);
_94
}
_94
_94
@override
_94
void dispose() {
_94
supabase.removeChannel(_lobbyChannel);
_94
super.dispose();
_94
}
_94
_94
@override
_94
Widget build(BuildContext context) {
_94
return AlertDialog(
_94
title: const Text('Lobby'),
_94
content: _loading
_94
? const SizedBox(
_94
height: 100,
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child: Center(child: CircularProgressIndicator()),
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)
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: Text('${_userids.length} users waiting'),
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actions: [
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TextButton(
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onPressed: _userids.length < 2
_94
? null
_94
: () async {
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setState(() {
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_loading = true;
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});
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_94
final opponentId =
_94
_userids.firstWhere((userId) => userId != myUserId);
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final gameId = const Uuid().v4();
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await _lobbyChannel.sendBroadcastMessage(
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event: 'game_start',
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payload: {
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'participants': [
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opponentId,
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myUserId,
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],
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'game_id': gameId,
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},
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);
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},
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child: const Text('start'),
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),
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],
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);
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}
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}

Sharing Game States with the Opposing Player

Once a game begins, we need to synchronize the game states between the two clients. In our case, we will sync only the player’s position and health points. Whenever a player moves, or the player’s health points change, the onGameStateUpdate callback on our MyGame instance that will fire notifying the update along with its position and health point. We will broadcast those information to the opponent’s client via Supabase broadcast feature.

Fill in the _initialize method like the following to initialize the game.


_121
class GamePage extends StatefulWidget {
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const GamePage({Key? key}) : super(key: key);
_121
_121
@override
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State<GamePage> createState() => _GamePageState();
_121
}
_121
_121
class _GamePageState extends State<GamePage> {
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late final MyGame _game;
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_121
/// Holds the RealtimeChannel to sync game states
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RealtimeChannel? _gameChannel;
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_121
@override
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Widget build(BuildContext context) {
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return Scaffold(
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body: Stack(
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fit: StackFit.expand,
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children: [
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Image.asset('assets/images/background.jpg', fit: BoxFit.cover),
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GameWidget(game: _game),
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],
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),
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);
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}
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@override
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void initState() {
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super.initState();
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_initialize();
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}
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Future<void> _initialize() async {
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_game = MyGame(
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onGameStateUpdate: (position, health) async {
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ChannelResponse response;
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do {
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response = await _gameChannel!.sendBroadcastMessage(
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event: 'game_state',
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payload: {'x': position.x, 'y': position.y, 'health': health},
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);
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// wait for a frame to avoid infinite rate limiting loops
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await Future.delayed(Duration.zero);
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setState(() {});
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} while (response == ChannelResponse.rateLimited && health <= 0);
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},
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onGameOver: (playerWon) async {
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await showDialog(
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barrierDismissible: false,
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context: context,
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builder: ((context) {
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return AlertDialog(
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title: Text(playerWon ? 'You Won!' : 'You lost...'),
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actions: [
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TextButton(
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onPressed: () async {
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Navigator.of(context).pop();
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await supabase.removeChannel(_gameChannel!);
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_openLobbyDialog();
_121
},
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child: const Text('Back to Lobby'),
_121
),
_121
],
_121
);
_121
}),
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);
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},
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);
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_121
// await for a frame so that the widget mounts
_121
await Future.delayed(Duration.zero);
_121
_121
if (mounted) {
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_openLobbyDialog();
_121
}
_121
}
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_121
void _openLobbyDialog() {
_121
showDialog(
_121
context: context,
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barrierDismissible: false,
_121
builder: (context) {
_121
return _LobbyDialog(
_121
onGameStarted: (gameId) async {
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// await a frame to allow subscribing to a new channel in a realtime callback
_121
await Future.delayed(Duration.zero);
_121
_121
setState(() {});
_121
_121
_game.startNewGame();
_121
_121
_gameChannel = supabase.channel(gameId,
_121
opts: const RealtimeChannelConfig(ack: true));
_121
_121
_gameChannel!
_121
.onBroadcast(
_121
event: 'game_state',
_121
callback: (payload, [_]) {
_121
final position = Vector2(
_121
payload['x'] as double, payload['y'] as double);
_121
final opponentHealth = payload['health'] as int;
_121
_game.updateOpponent(
_121
position: position,
_121
health: opponentHealth,
_121
);
_121
_121
if (opponentHealth <= 0) {
_121
if (!_game.isGameOver) {
_121
_game.isGameOver = true;
_121
_game.onGameOver(true);
_121
}
_121
}
_121
},
_121
)
_121
.subscribe();
_121
},
_121
);
_121
});
_121
}
_121
}

You can see that within _openLobbyDialog, there is an onGameStarted callback for when the game has started. Once a game has been started, it creates a new channel using the game ID as the channel name and starts listening to game state updates from the opponent.You can see that within the onGameOver callback, we are showing a simple dialog. Upon tapping Back to Lobby, the user will be taken back to the lobby dialog, where they can start another game if they want to.

Post game dialog

With all of that put together, we have a functioning real-time multiplayer shooting game. Grab a friend, run the app with flutter run, and have fun with it!

Conclusions

We learned how to create an interactive shooting game. We took advantage of Flutter’s dialogs to create a quick and easy lobby and post-game UI. Then we created the game using Flame. We learned how to detect and handle collisions and experienced how easy creating a sophisticated game was using Flame. Finally, we added capabilities to share game states with other clients to complete a real-time multiplayer experience without managing our own infrastructure using Supabase.

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