Real-Time Multiplayer with Supabase Realtime and Flutter

Introduction

Real-time multiplayer games create engaging experiences by updating game state across devices instantly. Supabase Realtime provides a WebSocket layer on top of Postgres, making it easy to push database changes to clients. Combined with Flutter’s reactive UI and strong community packages, you can build multiplayer mobile games with minimal boilerplate. This tutorial covers project setup, data modeling, state synchronization, real-time event handling, and performance tweaks to get your turn-based or action game online quickly.

Setting Up Supabase

First, sign up at supabase.io and create a new project. Under the Database → Tables editor, define tables for players, rooms, and game_state. Enable Realtime for each table by toggling “Realtime” on the SQL editor or via the dashboard UI. Set up Row Level Security (RLS) policies so authenticated users can only access allowed rows. Install the Supabase Flutter SDK with:

// pubspec.yaml
dependencies:
  supabase_flutter: ^1.0.0

Initialize Supabase in your main.dart before runApp:

await Supabase.initialize(
  url: 'https://xyz.supabase.co',
  anonKey: 'your-anon-key',
);

This establishes the WebSocket connection for realtime updates.

Designing Game State and Models

In your Flutter project, mirror your SQL schema with Dart classes. For example, a GameState model holds room ID, player positions, and turn data:

class GameState {
  final String roomId;
  final Map<String, dynamic> positions;
  final String currentPlayer;
  GameState({required this.roomId, required this.positions, required this.currentPlayer});
  factory GameState.fromJson(Map<String, dynamic> json) => GameState(
    roomId: json['room_id'],
    positions: Map<String, dynamic>.from(json['positions']),
    currentPlayer: json['current_player'],
  );
}

Use a repository pattern to encapsulate Supabase queries: fetching initial state, inserting new moves, and listening to streams. This separation keeps UI code clean.

Synchronizing State in Real Time

Leverage Supabase Realtime subscriptions to stream changes. Use the from(table).stream() API to subscribe and decode rows into your models:

final stream = Supabase.instance.client
  .from('game_state:room_id=eq.$roomId')
  .stream(primaryKey: ['id'])
  .map((maps) => maps.map((m) => GameState.fromJson(m)).toList());
stream.listen((states) {
  final latest = states.last;
  gameStateController.add(latest);
});

Bind this stream to a StreamBuilder in your widget tree. Whenever a new row is inserted or updated, Supabase pushes the change immediately, and Flutter rebuilds the UI with the latest GameState.

Handling Multiplayer Logic in Flutter

Implement join/create room flows with simple Supabase CRUD calls. When a player makes a move, call update on the game_state table:

await Supabase.instance.client
  .from('game_state')
  .update({ 'positions': newPositions, 'current_player': nextPlayer })
  .eq('room_id', roomId);

Use a state management solution (Provider, Riverpod, or Bloc) to distribute GameState updates. When the stream emits a new event, dispatch it to the UI and game logic. React to opponent moves by comparing currentPlayer and trigger animations or turn timers accordingly. Ensure each player’s UI subscribes only to their room’s channel to minimize noise.

Optimizing Performance and Scalability

For fast-paced games, batch rapid updates or debounce events to reduce network chatter. Use Supabase’s presence feature to track connected users and display online status. Implement optimistic UI updates by applying moves locally before confirmation, rolling back on errors. Limit the size of payloads by storing only deltas (changes) instead of full state if bandwidth is a concern. Finally, scale your Supabase instance vertically or shard tables across schemas for large player counts.

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Conclusion

By combining Supabase Realtime’s WebSocket streams with Flutter’s reactive architecture, you can deliver smooth, low-latency multiplayer experiences. This approach requires minimal backend code: define tables, configure RLS policies, and handle CRUD operations. On the client side, map your data models, subscribe to real-time channels, and update the UI via state management. With these building blocks and performance optimizations in place, you’re ready to launch your real-time Flutter game.