How to synchronize Play Services Real Time Multiplayer

Introduction

Play Services Real Time Multiplayer allows you to create engaging multiplayer experiences for your Android games. This article will guide you through the process of synchronizing game state across all connected players.

Prerequisites

Before diving into the synchronization process, make sure you have the following:

• A Google Play Games Services account
• An Android Studio project with Play Services Real Time Multiplayer integrated
• Basic understanding of network programming concepts

Synchronization Strategies

1. State Synchronization

In state synchronization, you replicate the complete game state to all players. This ensures everyone is on the same page, but it can be resource-intensive for large games.

Steps:

• Define a Game State: Create a data structure (e.g., a class or dictionary) that encapsulates all the critical information of your game, such as player positions, scores, and objects.
• Serialize the State: Use a serialization method like JSON or Protocol Buffers to convert the game state into a format that can be transmitted over the network.
• Broadcast Updates: Regularly send the serialized state to all connected players using the Real Time Messaging API.
• Deserialize and Apply: On the receiving end, deserialize the state and update the local game representation accordingly.

2. Event-Based Synchronization

Event-based synchronization focuses on sending specific events that modify the game state, rather than the entire state itself. This approach is more efficient for smaller changes.

Steps:

• Define Events: Identify significant events that affect the game state (e.g., player movement, object creation, attacks). Design event structures to represent these events.
• Send Events: When an event occurs, send it to all connected players using the Real Time Messaging API.
• Process Events: On the receiving end, process each event and update the local game state accordingly.

Choosing the Right Strategy

The best synchronization strategy depends on the specifics of your game:

Code Example: Event-Based Synchronization

This example demonstrates sending a “player movement” event using Play Services Real Time Messaging:

// Send a movement event to all connected players
public void sendPlayerMovement(float x, float y) {
  // Create a new movement event
  MovementEvent event = new MovementEvent(x, y);

  // Serialize the event to a byte array
  byte[] serializedEvent = event.serialize();

  // Send the event to all connected players
  for (Player player : mRoom.getPlayers()) {
    mRoom.sendReliableMessage(player, serializedEvent, MessageConstants.EVENT_MOVEMENT);
  }
}

// Define a class to represent a movement event
public class MovementEvent {
  public float x;
  public float y;

  public MovementEvent(float x, float y) {
    this.x = x;
    this.y = y;
  }

  // Method to serialize the event
  public byte[] serialize() {
    // Implement serialization logic
    // ...
    return serializedBytes;
  }
}

// On the receiving end, process the movement event
@Override
public void onRealTimeMessageReceived(Room room, Player player, byte[] data,
  int messageId) {
  if (messageId == MessageConstants.EVENT_MOVEMENT) {
    // Deserialize the event
    MovementEvent event = MovementEvent.deserialize(data);

    // Update the local player position
    player.setPosition(event.x, event.y);
  }
}

Conclusion

By understanding and applying these synchronization strategies, you can create seamless real-time multiplayer experiences for your Android games. Choose the appropriate approach based on your game’s complexity and network constraints. Remember to consider factors like latency, bandwidth, and event frequency to achieve optimal gameplay.