MultiplayerAPIExtension in Godot – Complete Guide

Welcome to our tutorial on extending the capabilities of multiplayer programming in Godot 4 using the MultiplayerAPIExtension class. Multiplayer games continue to captivate players around the world, offering dynamic interactions and collaborative or competitive gameplay experiences that single-player games cannot match. Learning how to augment the multiplayer functionality within Godot can add an incredible layer of depth and personalization to your game projects. Whether you aim to log activity, customize network behavior, or simply understand the internal workings of multiplayer systems, extending the default MultiplayerAPI can be a rewarding venture for any developer.

What Is MultiplayerAPIExtension?

In Godot 4, the MultiplayerAPIExtension class offers a way for developers to enhance or even replace the engine’s default multiplayer functionality. This extendable API gives you the power to customize networking behavior, such as how remote procedure calls (RPCs) are handled, object replication configuration, and the management of multiplayer peers.

What Is It Used For?

Developers turn to MultiplayerAPIExtension to create a tightly controlled multiplayer experience. By modifying the default behavior, you can implement specific requirements for your game such as advanced logging, custom replication strategies, or other unique multiplayer features. Extending the MultiplayerAPI can become an essential part of developing a robust multiplayer game in Godot.

Why Should I Learn It?

Understanding and learning how to implement MultiplayerAPIExtension can set your game apart and offer a level of customization that could not be achieved by using the default MultiplayerAPI alone. It’s a skill that allows for sophisticated game mechanics and can lead to a better multiplayer experience for players. Furthermore, having control over multiplayer aspects of your game enables better debugging, optimization, and more reliable gameplay, which are critical in retaining an active player base in today’s competitive market.

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Creating a Custom MultiplayerAPI Extension

To start extending the MultiplayerAPI in Godot 4, we need to create a new class that inherits from `MultiplayerAPIExtension`. First, let’s set up a simple extension that prints a message every time a remote procedure call (RPC) is made:

class MyMultiplayerAPIExtension extends MultiplayerAPIExtension:
    func _rpc(sender_id, target_id, rpc_name, rpc_mode, args):
        print("RPC called: %s by peer %d" % [rpc_name, sender_id])
        .rpc(sender_id, target_id, rpc_name, rpc_mode, args)  # Call the original function

In this example, we’re overriding the `_rpc` method which Godot calls internally whenever an RPC is executed. Note how we also call the base method with `.rpc(…)` to ensure the original functionality isn’t lost.

Customizing RPC Handling

The above example is a simple one. Now let’s extend it to do something more useful. We can customize the behavior based on the name of the RPC to add specific conditions before proceeding:

func _rpc(sender_id, target_id, rpc_name, rpc_mode, args):
    if rpc_name == "important_function":
        if is_peer_allowed(sender_id):
            .rpc(sender_id, target_id, rpc_name, rpc_mode, args)
            print("Peer %d is not allowed to call %s" % [sender_id, rpc_name])
        .rpc(sender_id, target_id, rpc_name, rpc_mode, args)

func is_peer_allowed(peer_id):
    # Check if the peer is authorized (for example, making sure they're not muted)
    return true  # or false based on your conditions

Here, we have a check in place to determine if a peer is authorized to call the `important_function`. We’re using a hypothetical `is_peer_allowed` function to do the check.

Intercepting and Modifying RPC Arguments

What if we want to modify the arguments passed to an RPC before they’re processed? That’s also possible. Let’s assume we have a method `modify_args` which returns modified arguments. We can then use those arguments in the RPC call:

func _rpc(sender_id, target_id, rpc_name, rpc_mode, args):
    var modified_args = modify_args(rpc_name, args)
    .rpc(sender_id, target_id, rpc_name, rpc_mode, modified_args)

func modify_args(rpc_name, args):
    # Modify arguments based on RPC name or any logic
    if rpc_name == "update_position":
        args[0] += 10  # Just an example of modifying the first argument
    return args

In this snippet, we’re intercepting the `update_position` RPC and modifying its first argument, for instance, changing a position vector or score value before it’s processed by the server or client.

Handling Synchronization of Networked Objects

For networked objects, it’s crucial to handle their synchronization efficiently. Let’s assume we want to manage how and when these objects are updated across the network. Below is an example where we override the `_notify_sync_object` method:

func _notify_sync_object(object_id, obj, sync_flags):
    if obj.has_method("custom_sync"):
        .notify_sync_object(object_id, obj, sync_flags)

class MyNetworkedObject extends Node:
    func custom_sync(sync_flags):
        # Do custom state synchronization

In this case, `_notify_sync_object` is used to notify about synchronization needs of a networked object. We’re checking if the object has a method called `custom_sync`. If it does, we’re calling that instead of the default behavior, allowing us a lot of flexibility to define precisely how our objects communicate their state.

Using these foundational code snippets, you can begin to see how it’s possible to gain fine-grained control over multiplayer interactions in your game. These are just the basics, and we’ll build on these concepts in the next part of our tutorial. Stay tuned as we venture deeper into the world of customized multiplayer with Godot 4.Continuing from our previous examples, let’s delve into enhancing the MultiplayerAPI further by implementing additional custom behaviors and handling different multiplayer scenarios.

Conditionally Sending RPC Calls

Sometimes, we may wish to send an RPC only if certain conditions are met, say, a player has reached a particular state or score. We can do this by overriding the `_rpc` function and inserting our condition checks before the call is processed:

func _rpc(sender_id, target_id, rpc_name, rpc_mode, args):
    if rpc_name == "send_highscore" and args[0] > 1000:
        .rpc(sender_id, target_id, rpc_name, rpc_mode, args)
        print("Highscore RPC not called, score too low.")

This snippet checks if the score (assumed to be the first argument of the RPC ‘send_highscore’) is greater than 1000 before the RPC is sent.

Overriding Connection Initialization

When a new player connects to your game, you might want to perform additional setup steps. By overriding the `_connection_init` method, we can include custom logic at the connection initialization phase:

func _connection_init(peer_id):
    print("Initializing connection for peer: %d" % peer_id)

func setup_player(peer_id):
    # Perform any player setup here such as assigning teams, initializing stats, etc.

In the code above, we intercept the initial connection of a peer and call our `setup_player` function before continuing with the normal connection initialization process.

Modifying RPC Mode at Runtime

At times, you might need to adjust the RPC mode in response to game events. You can override `_rpc_configure` method for such scenarios. This function allows you to change the RPC mode before the call:

func _rpc_configure(target_id, rpc_name, rpc_mode):
    rpc_mode = determine_rpc_mode(rpc_name, rpc_mode)
    .rpc_configure(target_id, rpc_name, rpc_mode)

func determine_rpc_mode(rpc_name, current_mode):
    # Logic to determine and return a new rpc_mode based on your game's logic
    if rpc_name == "update_score":
        return MultiplayerAPI.RPC_MODE_REMOTESYNC
    return current_mode

Here, `determine_rpc_mode` decides whether to change the RPC mode for the given RPC name, which in this case changes `update_score` to be synchronized across all clients using `RPC_MODE_REMOTESYNC`.

Handling Disconnections

Handling peer disconnections gracefully is vital for a smooth multiplayer experience. Overriding `_peer_disconnected` allows you to take custom actions when a player leaves:

func _peer_disconnected(peer_id):
    print("Peer %d has disconnected." % peer_id)

func handle_disconnection(peer_id):
    # Any custom cleanup here, like removing the player's character, releasing resources, etc.

In the snippet above, custom disconnection handling is performed before calling the base method to allow Godot to process the disconnection normally.

With these extensions and customizations to the MultiplayerAPIExtension class, your Godot multiplayer games can gain a much higher level of control and sophistication. Efficient and well-thought-out multiplayer systems are instrumental in the success of multiplayer games, and with Godot 4, the tools are in your hands to create an engaging and robust multiplayer experience.

Keep experimenting with these methods to find what best suits the needs of your game. As always, ensure you test your extended API thoroughly to ensure your multiplayer behavior is reliable, secure, and fun for your players. Happy coding!Continuing our exploration of custom multiplayer behaviors in Godot 4, let’s look at additional examples that can enhance your game’s network functionality.

Managing Reliable and Unreliable RPCs

In networking, some messages are critical and must be received, known as reliable communications. Others can be lost without much impact, known as unreliable. Here’s how you might ensure only certain RPCs are sent reliably:

func _rpc(sender_id, target_id, rpc_name, rpc_mode, args):
    if rpc_name in ["request_game_state", "send_important_data"]:
        rpc_mode = MultiplayerAPI.RPC_MODE_RELIABLE    # Send these RPCs reliably
        rpc_mode = MultiplayerAPI.RPC_MODE_UNRELIABLE  # Everything else can be sent unreliably
    .rpc(sender_id, target_id, rpc_name, rpc_mode, args)

In this example, we are adjusting the `rpc_mode` based on the critical nature of the RPC being called.

Syncing Objects Across Peers

Synchronizing objects’ state across peers is a common task in multiplayer games. Let’s say we want to manually handle the positioning of a character to mitigate issues like latency or cheating. We could do something like:

func _notify_sync_object(object_id, obj, sync_flags):
    if obj is PlayerCharacter:
        .notify_sync_object(object_id, obj, sync_flags)

class PlayerCharacter extends KinematicBody:
    func sync_position():
        # Logic for syncing this character's position with other peers

In this custom sync, we have identified player character objects and called a `sync_position` method that we’ve defined for their special treatment.

Enhancing Peer Connection Verification

Validating new connections can be pivotal in a secure multiplayer game. We can override the `_peer_connected` callback to check if the peer meets certain criteria before allowing a full connection:

func _peer_connected(peer_id):
    if is_peer_valid(peer_id):
        print("Connection from peer %d rejected." % peer_id)
        # Potentially kick the peer if they don't meet the criteria

func is_peer_valid(peer_id):
    # Validation logic such as checking a whitelist, checking version compatibility, etc.
    return true  # Assume peer is valid

func welcome_peer(peer_id):
    # Send a welcome message or set up necessary game state for this peer

Such checks help ensure only authorized or compatible clients join the game session.

Overriding Bandwidth Limits

Suppose you want to control the bandwidth used for RPC calls. This might be essential in scenarios where you want to limit the data usage for players on mobile networks or when the game is running on servers with bandwidth caps.

func _rpc(sender_id, target_id, rpc_name, rpc_mode, args):
    if should_limit_bandwidth():
    .rpc(sender_id, target_id, rpc_name, rpc_mode, args)

func should_limit_bandwidth():
    # Logic to check if bandwidth should be limited
    return true

func reduce_rpc_size(args):
    # Trim or compress the data to be sent

In this code, we include logic to potentially reduce the size of each RPC call when bandwidth limitations need to be enforced.

Custom Notification of RPC Success or Failure

Not all RPCs are guaranteed to succeed, and sometimes you’d like to know when they fail or confirm their success. Below is an illustration of how you might handle RPC confirmation:

func _rpc(sender_id, target_id, rpc_name, rpc_mode, args):
    var success = try_rpc(sender_id, target_id, rpc_name, rpc_mode, args)
    if success:
        print("RPC %s succeeded." % rpc_name)
        print("RPC %s failed." % rpc_name)

func try_rpc(sender_id, target_id, rpc_name, rpc_mode, args):
    # Attempt the RPC and return true on success, false on failure

The `try_rpc` function would contain the logic for attempting the RPC and handling exceptions or failure states.

By integrating such custom code snippets, your game’s multiplayer functionality becomes more robust and tailored to specific gameplay needs. Remember that the beauty of extending the MultiplayerAPI is in the flexibility it affords you as a developer. You have the power to tweak, optimize, and enforce the ways in which your game handles network communications, making for a tailored and streamlined experience for your players. Keep testing and iterating on your multiplayer logic to achieve the best balance between performance, security, and user enjoyment. Happy developing!

Continue Your Godot Development Journey

Having explored the fascinating world of custom multiplayer in Godot 4, you might be wondering about the next steps to take on your path to becoming a proficient game developer. At Zenva, we offer a wide range of resources to further your learning and help you build a robust portfolio of games. Our Godot Game Development Mini-Degree is an excellent starting point to delve deeper into Godot 4, covering a broad spectrum of topics that range from mastering GDScript to creating intricate 2D and 3D games.

This comprehensive program is designed to be accessible for beginners while also supplying content for those who have grasped the basics. As you progress through the courses, you’ll gain practical experience and develop in-demand skills suitable for the current game development industry. Upon completion, you’ll not only have a wealth of knowledge but also a portfolio of projects to showcase your newfound abilities.

For those interested in a broader selection of topics within Godot, be sure to explore our full suite of Godot courses. These courses at Zenva are tailored to provide you with high-quality, flexible learning experiences that can adapt to any schedule and are available on any device. Whether you’re just starting or looking to specialize in a particular area of game development, we’re here to support your learning journey.

Take the next step in mastering Godot and game development – join us at Zenva, and let’s create amazing gaming experiences together.


As you journey through the realms of game development, mastering the art of multiplayer in Godot 4 with classes like MultiplayerAPIExtension unlocks a universe of possibilities. It’s not just about making games; it’s about crafting experiences that bring people together, challenge them, and provide endless entertainment through shared digital worlds. Whether you dream of creating the next indie hit or contributing to a blockbuster title, the skills honed here are the keys to that reality.

At Zenva, we’re excited to support you at every step of your game development journey. Don’t let the adventure stop here; continue to build, learn, and grow with us by diving into our Godot Game Development Mini-Degree. The path to becoming a game development champion is one click away—embrace the knowledge, unleash your creativity, and let’s transform the gaming landscape together.

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