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High-level multiplayer

High-level vs low-level API

以下では、Godotの高レベルネットワークと低レベルネットワークの違いといくつかの基本事項について説明します。基本をとばして最初のノードにネットワークを追加する場合は、以下の Initializing the network までスキップしてください。ただし、後で残りも読んでください!

Godot always supported standard low-level networking via UDP, TCP and some higher-level protocols such as HTTP and SSL. These protocols are flexible and can be used for almost anything. However, using them to synchronize game state manually can be a large amount of work. Sometimes that work can't be avoided or is worth it, for example when working with a custom server implementation on the backend. But in most cases, it's worthwhile to consider Godot's high-level networking API, which sacrifices some of the fine-grained control of low-level networking for greater ease of use.

これは、低レベルプロトコルの固有の制限によるものです:

  • TCPは、パケットが常に確実に順序どおりに到着することを保証しますが、一般に、エラー修正のために待ち時間が長くなります。また、手順に「接続(connection)」を必要とし、マルチプレイヤーゲームのようなアプリケーションには向かない目的に合わせて最適化されているので、非常に複雑なプロトコルでもあります。パケットはより大きなバッチで送信されるようにバッファリングされ、パケットごとのオーバーヘッドが少なくなり、待ち時間が長くなります。これはHTTPのようなものには便利ですが、一般的にはゲームには役立ちません。この一部は、(例えば、TCP接続の「Nagleのアルゴリズム」を無効にすることによって)設定および無効にすることができます。

  • UDPはより単純なプロトコルであり、パケットのみを送信します(「接続」の概念はありません)。エラー修正を行わないので処理がかなり速くなりますが(低遅延)、パケットは途中で失われたり、間違った順序で受信されたりする可能性があります。それに加えて、UDPのMTU(最大パケットサイズ)は一般的に小さい(数百バイトのみ)ため、大きなパケットを送信することは、パケットを分割し、再編成し、一部が失敗した場合に再試行することを意味します。

一般に、TCPは信頼性が高く、順序があり、低速であると考えることができます。それに対し、UDPは信頼性がなく、順序がなく、高速であるといえます。パフォーマンスが大きく異なるため、多くの場合、ゲームに必要なTCPの部分(オプションの信頼性とパケット順序)を再構築し、不要な部分(輻輳/トラフィック制御機能、Nagleのアルゴリズムなど)を回避することは理にかなっています。このため、ほとんどのゲームエンジンにはこのような実装が付属しており、Godotも例外ではありません。

要約すると、低レベルのネットワークAPIを使用して最大限の制御を行い、すべてを素のネットワークプロトコルの上に実装するか、または `SceneTree <class_SceneTree>`に基づいた高レベルAPIを使用するかです。これは、一般的に最適化された方法で、シーンの後ろで重い処理を引き受けます。

注釈

Most of Godot's supported platforms offer all or most of the mentioned high- and low-level networking features. As networking is always largely hardware and operating system dependent, however, some features may change or not be available on some target platforms. Most notably, the HTML5 platform currently offers WebSockets and WebRTC support but lacks some of the higher-level features, as well as raw access to low-level protocols like TCP and UDP.

注釈

More about TCP/IP, UDP, and networking: https://gafferongames.com/post/udp_vs_tcp/

Gaffer On Games has a lot of useful articles about networking in Games (here), including the comprehensive introduction to networking models in games.

Godotの組み込みネットワークではなく、選択した低レベルネットワークライブラリを使用する場合は、次の例を参照してください: https://github.com/PerduGames/gdnet3

警告

Adding networking to your game comes with some responsibility. It can make your application vulnerable if done wrong and may lead to cheats or exploits. It may even allow an attacker to compromise the machines your application runs on and use your servers to send spam, attack others or steal your users' data if they play your game.

これは、ネットワーキングが関係する場合に常に当てはまり、Godotとは関係ありません。もちろん実験はできますが、ネットワークアプリケーションをリリースするときは、考えられるセキュリティ上の問題に常に注意してください。

Mid-level abstraction

ネットワークを介してゲームを同期する方法に入る前に、同期のための基本のネットワークAPIがどのように機能するかを理解しておくと役立ちます。

Godot uses a mid-level object MultiplayerPeer. This object is not meant to be created directly, but is designed so that several C++ implementations can provide it.

このオブジェクトは PacketPeer から継承されるため、データのシリアル化、送信、受信に役立つすべてのメソッドを引き継ぎます。さらに、ピア、転送モードなどを設定するメソッドを追加します。また、ピアが接続または切断したときに通知するシグナルも含まれています。

This class interface can abstract most types of network layers, topologies and libraries. By default, Godot provides an implementation based on ENet (ENetMultiplayerPeer), one based on WebRTC (WebRTCMultiplayerPeer), and one based on WebSocket (WebSocketPeer), but this could be used to implement mobile APIs (for ad hoc WiFi, Bluetooth) or custom device/console-specific networking APIs.

For most common cases, using this object directly is discouraged, as Godot provides even higher level networking facilities. This object is still made available in case a game has specific needs for a lower-level API.

Hosting considerations

When hosting a server, clients on your LAN can connect using the internal IP address which is usually of the form 192.168.*.*. This internal IP address is not reachable by non-LAN/Internet clients.

On Windows, you can find your internal IP address by opening a command prompt and entering ipconfig. On macOS, open a Terminal and enter ifconfig. On Linux, open a terminal and enter ip addr.

If you're hosting a server on your own machine and want non-LAN clients to connect to it, you'll probably have to forward the server port on your router. This is required to make your server reachable from the Internet since most residential connections use a NAT. Godot's high-level multiplayer API only uses UDP, so you must forward the port in UDP, not just TCP.

After forwarding an UDP port and making sure your server uses that port, you can use this website to find your public IP address. Then give this public IP address to any Internet clients that wish to connect to your server.

Godot's high-level multiplayer API uses a modified version of ENet which allows for full IPv6 support.

ネットワークの初期化

High level networking in Godot is managed by the SceneTree.

Each node has a multiplayer property, which is a reference to the MultiplayerAPI instance configured for it by the scene tree. Initially, every node is configured with the same default MultiplayerAPI object.

It is possible to create a new MultiplayerAPI object and assign it to a NodePath in the the scene tree, which will override multiplayer for the node at that path and all of its descendants. This allows sibling nodes to be configured with different peers, which makes it possible to run a server and a client simultaneously in one instance of Godot.

# By default, these expressions are interchangeable.
multiplayer # Get the MultiplayerAPI object configured for this node.
get_tree().get_multiplayer() # Get the default MultiplayerAPI object.

To initialize networking, a MultiplayerPeer object must be created, initialized as a server or client, and passed to the MultiplayerAPI.

# Create client.
var peer = ENetMultiplayerPeer.new()
peer.create_client(IP_ADDRESS, PORT)
multiplayer.multiplayer_peer = peer

# Create server.
var peer = ENetMultiplayerPeer.new()
peer.create_server(PORT, MAX_CLIENTS)
multiplayer.multiplayer_peer = peer

To terminate networking:

multiplayer.multiplayer_peer = null

警告

When exporting to Android, make sure to enable the INTERNET permission in the Android export preset before exporting the project or using one-click deploy. Otherwise, network communication of any kind will be blocked by Android.

接続の管理

Every peer is assigned a unique ID. The server's ID is always 1, and clients are assigned a random positive integer.

Responding to connections or disconnections is possible by connecting to MultiplayerAPI's signals:

  • peer_connected(id: int) This signal is emitted with the newly connected peer's ID on each other peer, and on the new peer multiple times, once with each other peer's ID.

  • peer_disconnected(id: int) This signal is emitted on every remaining peer when one disconnects.

The rest are only emitted on clients:

  • connected_to_server()

  • connection_failed()

  • server_disconnected()

To get the unique ID of the associated peer:

multiplayer.get_unique_id()

To check whether the peer is server or client:

multiplayer.is_server()

Remote procedure calls

Remote procedure calls, or RPCs, are functions that can be called on other peers. To create one, use the @rpc annotation before a function definition. To call an RPC, use Callable's method rpc() to call in every peer, or rpc_id() to call in a specific peer.

func _ready():
    if multiplayer.is_server():
        print_once_per_client.rpc()

@rpc
func print_once_per_client():
    print("I will be printed to the console once per each connected client.")

RPCs will not serialize objects or callables.

For a remote call to be successful, the sending and receiving node need to have the same NodePath, which means they must have the same name. When using add_child() for nodes which are expected to use RPCs, set the argument force_readable_name to true.

警告

If a function is annotated with @rpc on the client script (resp. server script), then this function must also be declared on the server script (resp. client script), and both must have the same signature, even if this function is not currently used.

If these conditions are not fulfilled, the script may print an error or cause unwanted behavior. See further explanation and troubleshooting on this post.

The annotation can take a number of arguments, which have default values. @rpc is equivalent to:

@rpc("authority", "call_remote", "unreliable", 0)

The parameters and their functions are as follows:

mode:

  • "authority": Only the multiplayer authority (the server) can call remotely.

  • "any_peer": Clients are allowed to call remotely. Useful for transferring user input.

sync:

  • "call_remote": The function will not be called on the local peer.

  • "call_local": The function can be called on the local peer. Useful when the server is also a player.

transfer_mode:

  • "unreliable" Packets are not acknowledged, can be lost, and can arrive at any order.

  • "unreliable_ordered" Packets are received in the order they were sent in. This is achieved by ignoring packets that arrive later if another that was sent after them has already been received. Can cause packet loss if used incorrectly.

  • "reliable" Resend attempts are sent until packets are acknowledged, and their order is preserved. Has a significant performance penalty.

transfer_channel is the channel index.

The first 3 can be passed in any order, but transfer_channel must always be last.

The function multiplayer.get_remote_sender_id() can be used to get the unique id of an rpc sender, when used within the function called by rpc.

func _on_some_input(): # Connected to some input.
    transfer_some_input.rpc_id(1) # Send the input only to the server.


# Call local is required if the server is also a player.
@rpc("any_peer", "call_local", "reliable")
func transfer_some_input():
    # The server knows who sent the input.
    var sender_id = multiplayer.get_remote_sender_id()
    # Process the input and affect game logic.

Channels

Modern networking protocols support channels, which are separate connections within the connection. This allows for multiple streams of packets that do not interfere with each other.

For example, game chat related messages and some of the core gameplay messages should all be sent reliably, but a gameplay message should not wait for a chat message to be acknowledged. This can be achieved by using different channels.

Channels are also useful when used with the unreliable ordered transfer mode. Sending packets of variable size with this transfer mode can cause packet loss, since packets which are slower to arrive are ignored. Separating them into multiple streams of homogeneous packets by using channels allows ordered transfer with little packet loss, and without the latency penalty caused by reliable mode.

The default channel with index 0 is actually three different channels - one for each transfer mode.

Example lobby implementation

This is an example lobby that can handle peers joining and leaving, notify UI scenes through signals, and start the game after all clients have loaded the game scene.

extends Node

# Autoload named Lobby

# These signals can be connected to by a UI lobby scene or the game scene.
signal player_connected(peer_id, player_info)
signal player_disconnected(peer_id)
signal server_disconnected

const PORT = 7000
const DEFAULT_SERVER_IP = "127.0.0.1" # IPv4 localhost
const MAX_CONNECTIONS = 20

# This will contain player info for every player,
# with the keys being each player's unique IDs.
var players = {}

# This is the local player info. This should be modified locally
# before the connection is made. It will be passed to every other peer.
# For example, the value of "name" can be set to something the player
# entered in a UI scene.
var player_info = {"name": "Name"}

var players_loaded = 0



func _ready():
    multiplayer.peer_connected.connect(_on_player_connected)
    multiplayer.peer_disconnected.connect(_on_player_disconnected)
    multiplayer.connected_to_server.connect(_on_connected_ok)
    multiplayer.connection_failed.connect(_on_connected_fail)
    multiplayer.server_disconnected.connect(_on_server_disconnected)


func join_game(address = ""):
    if address.is_empty():
        address = DEFAULT_SERVER_IP
    var peer = ENetMultiplayerPeer.new()
    var error = peer.create_client(address, PORT)
    if error:
        return error
    multiplayer.multiplayer_peer = peer


func create_game():
    var peer = ENetMultiplayerPeer.new()
    var error = peer.create_server(PORT, MAX_CONNECTIONS)
    if error:
        return error
    multiplayer.multiplayer_peer = peer

    players[1] = player_info
    player_connected.emit(1, player_info)


func remove_multiplayer_peer():
    multiplayer.multiplayer_peer = null


# When the server decides to start the game from a UI scene,
# do Lobby.load_game.rpc(filepath)
@rpc("call_local", "reliable")
func load_game(game_scene_path):
    get_tree().change_scene_to_file(game_scene_path)


# Every peer will call this when they have loaded the game scene.
@rpc("any_peer", "call_local", "reliable")
func player_loaded():
    if multiplayer.is_server():
        players_loaded += 1
        if players_loaded == players.size():
            $/root/Game.start_game()
            players_loaded = 0


# When a peer connects, send them my player info.
# This allows transfer of all desired data for each player, not only the unique ID.
func _on_player_connected(id):
    _register_player.rpc_id(id, player_info)


@rpc("any_peer", "reliable")
func _register_player(new_player_info):
    var new_player_id = multiplayer.get_remote_sender_id()
    players[new_player_id] = new_player_info
    player_connected.emit(new_player_id, new_player_info)


func _on_player_disconnected(id):
    players.erase(id)
    player_disconnected.emit(id)


func _on_connected_ok():
    var peer_id = multiplayer.get_unique_id()
    players[peer_id] = player_info
    player_connected.emit(peer_id, player_info)


func _on_connected_fail():
    multiplayer.multiplayer_peer = null


func _on_server_disconnected():
    multiplayer.multiplayer_peer = null
    players.clear()
    server_disconnected.emit()

The game scene's root node should be named Game. In the script attached to it:

extends Node3D # Or Node2D.



func _ready():
    # Preconfigure game.

    Lobby.player_loaded.rpc_id(1) # Tell the server that this peer has loaded.


# Called only on the server.
func start_game():
    # All peers are ready to receive RPCs in this scene.

Exporting for dedicated servers

Once you've made a multiplayer game, you may want to export it to run it on a dedicated server with no GPU available. See Exporting for dedicated servers for more information.

注釈

The code samples on this page aren't designed to run on a dedicated server. You'll have to modify them so the server isn't considered to be a player. You'll also have to modify the game starting mechanism so that the first player who joins can start the game.