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Multijugador de alto nivel

API de alto nivel vs bajo nivel

A continuación se explican las diferencias de redes de alto y bajo nivel en Godot, así como algunos aspectos fundamentales. Si deseas saltar de cabeza y agregar redes a tus primeros nodos, salta a Inicializando la red a continuación. ¡Pero asegúrate de leer el resto más tarde!

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.

Esto se debe a las limitaciones inherentes de los protocolos de bajo nivel:

  • TCP asegura que los paquetes siempre llegarán de manera confiable y en orden, pero la latencia generalmente es más alta debido a la corrección de errores. También es un protocolo bastante complejo porque entiende lo que es una "conexión" y se optimiza para los objetivos que a menudo no se adaptan a aplicaciones como los juegos multijugador. Los paquetes se almacenan en el búfer para enviarlos en lotes más grandes, intercambiando menos sobrecarga por paquete para una mayor latencia. Esto puede ser útil para cosas como HTTP, pero generalmente no para juegos. Parte de esto se puede configurar y desactivar (por ejemplo, desactivando el "algoritmo de Nagle" para la conexión TCP).

  • UDP es un protocolo más simple que solo envía paquetes (y no tiene ningún concepto de "conexión"). No poseer corrección de errores lo hace bastante rápido (baja latencia), pero los paquetes pueden perderse en el camino o ser recibidos en el orden incorrecto. Además de eso, el MTU (tamaño máximo de paquete) para UDP es generalmente baja (solo unos pocos cientos de bytes), por lo que la transmisión de paquetes más grandes significa dividirlos, reorganizarlos y volver a intentar si una pieza falla.

En general, se puede pensar que TCP es confiable, ordenado y lento; UDP como no confiable, no ordenado y rápido. Debido a la gran diferencia en el rendimiento, a menudo tiene sentido volver a construir las partes de TCP deseadas para los juegos (confiabilidad opcional y orden de paquetes) mientras se evitan las partes no deseadas (funciones de congestión/control de tráfico, algoritmo de Nagle, etc.). Debido a esto, la mayoría de los motores de juegos vienen con una implementación así, y Godot no es una excepción.

En resumen, puedes usar la API de red de bajo nivel para obtener el máximo control e implementar todo encima de los protocolos de red puros o usar la API de alto nivel basada en SceneTree que hace la mayor parte del trabajo pesado detrás de las escenas de una manera generalmente optimizada.

Nota

La mayoría de las plataformas compatibles con Godot ofrecen todas o la mayoría de las funciones de red de alto y bajo nivel mencionadas. Sin embargo, como las redes siempre dependen en gran medida del hardware y del sistema operativo, algunas funciones pueden cambiar o no estar disponibles en algunas plataformas de destino. En particular, la plataforma HTML5 actualmente ofrece compatibilidad con WebSocket y con WebRTC pero, carece de algunas de las características de mayor nivel, así como del acceso sin formato a protocolos de bajo nivel como TCP y UDP.

Nota

Más sobre TCP/IP, UDP y redes: https://gafferongames.com/post/udp_vs_tcp/

Gaffer On Games tiene muchos artículos útiles (en inglés) sobre la creación de redes en Juegos (aquí), incluida la exhaustiva introduction to networking models in games (introducción a modelos de redes en juegos).

Si deseas utilizar tu biblioteca de redes de bajo nivel preferida en lugar de la red integrada de Godot, consulta aquí un ejemplo: https://github.com/PerduGames/gdnet3

Advertencia

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.

Este es siempre el caso cuando se trata de redes y no tiene nada que ver con Godot. Por supuesto, puedes experimentar, pero cuando liberes una aplicación en red, siempre ocúpate de cualquier posible problema de seguridad.

Mid-level abstraction

Antes de entrar en cómo nos gustaría sincronizar un juego en la red, puede ser útil entender cómo funciona la base de la API de red para la sincronización.

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.

Este objeto se extiende de PacketPeer, por lo que hereda todos los métodos útiles para serializar, enviar y recibir datos. Encima de eso, agrega métodos para configurar un peer, modo de transferencia, etc. También incluye señales que le permitirán saber cuándo se conectan o desconectan los peers.

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.

Inicializando la red

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

Advertencia

Cuando exportes a Android, asegúrate de habilitar el permiso INTERNET en la configuración de exportación de Android antes de exportar el proyecto o utilizar el despliegue de un solo clic. De lo contrario, la comunicación de red de cualquier tipo será bloqueada por Android.

Administrar conexiones

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()

Llamadas a procedimientos remotos

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.

Advertencia

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). Both RPCs must have the same signature which is evaluated with a checksum of all RPCs. All RPCs in a script are checked at once, and all RPCs must be declared on both the client scripts and the server scripts, even functions that are currently not in use.

The signature of the RPC includes the @rpc() declaration, the function, return type, AND the nodepath. If an RPC resides in a script attached to /root/Main/Node1, then it must reside in precisely the same path and node on both the client script and the server script. Function arguments (example: func sendstuff(): and func sendstuff(arg1, arg2): will pass signature matching).

If these conditions are not met (if all RPCs do not pass signature matching), the script may print an error or cause unwanted behavior. The error message may be unrelated to the RPC function you are currently building and testing.

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.

Exportando para servidores dedicados

Una vez que hayas hecho un juego multijugador, tal vez quieras exportarlo para ejecutarlo en un servidor dedicado sin GPU disponible. Ver Exportando para servidores dedicados para más información.

Nota

Los ejemplos de código de esta página no están diseñados para funcionar en un servidor dedicado. Tendrás que modificarlos para que el servidor no sea considerado como un jugador. También tendrás que modificar el mecanismo de inicio del juego para que el primer jugador que se una pueda iniciar el juego.