Introduction to RPC in Godot4

In the dynamic realm of multiplayer game development, effective communication between different components of the game is paramount. Enter Remote Procedure Calls (RPC), a powerful mechanism that facilitates seamless communication between game entities, enabling a shared experience among players in Godot.

Understanding RPC: The Basics

At its core, an RPC is a communication paradigm that allows one part of a program to invoke a procedure (function) on another remote part. In the context of Godot game development, RPCs serve as the bridge between game clients and the server, enabling the exchange of information that keeps the multiplayer experience in sync.

The Essence of RPCs in Godot

In Godot, RPCs are a fundamental building block for creating dynamic and interactive multiplayer games. They empower developers to transmit essential information, such as player positions, actions, and game events, seamlessly between the server and connected clients.

How RPCs Work in Godot

The workflow of RPCs in Godot involves defining special functions in your scripts that are marked with the [Rpc] annotation. These functions are then automatically replicated across the network, allowing clients to call them as if they were local functions. The server and clients synchronize these RPC calls, ensuring that the game state remains consistent for all players.

RPC Modes: Tailoring Communication

When defining a RPC call in your scripts, Godot provides different RPC modes to tailor communication based on your game's requirements:

1. AnyPeer

The default mode. In this mode, the RPC call is executed on all connected peers. This is suitable for actions that need to be performed on other players or the server.

[Rpc(MultiplayerApi.RpcMode.AnyPeer)]
public void SendPlayerInformation(string name, int id){}

2. Authority:

Executes the RPC only on the server. Useful for actions that should be centralized on the server to maintain authoritative control.

[Rpc(MultiplayerApi.RpcMode.Authority)]
public void SendPlayerInformation(string name, int id){}

3. Disabled:

The default mode. Disables the RPC call for all machines.

[Rpc(MultiplayerApi.RpcMode.Disabled)]
public void SendPlayerInformation(string name, int id){}

[Rpc]
public void SendPlayerInformation(string name, int id){}

Transfer Modes and Transfer Channels: Efficient Data Transmission

When dealing with RPCs, you might encounter the need to transfer data efficiently. Godot provides transfer modes to control how arguments are sent across the network:

1. Reliable

Guarantees that the data will be delivered, and in the correct order. Suitable for essential actions where data integrity is crucial.

[Rpc(TransferMode = MultiplayerPeer.TransferModeEnum.Reliable)]
public void SendPlayerInformation(string name, int id){}

2. Unreliable

Sends the data without ensuring delivery or order. Ideal for non-critical, frequent updates.

[Rpc(TransferMode = MultiplayerPeer.TransferModeEnum.Unreliable)]
public void SendPlayerInformation(string name, int id){}

Transfer Channels

In addition to RPC modes and transfer modes, you can use channels to specify a custom network channel for the RPC call. This can help organize and prioritize different types of data transmissions. This allows you to e.g. split the network traffic for game chat and player movement.

[Rpc(TransferChannel = 10)]
public void SendPlayerInformation(string name, int id){}

Call Local

This mode executes the RPC on the calling machine before sending it across the network. Useful for actions that should have an immediate impact on the local player.

[Rpc(CallLocal = true)]
public void SendPlayerInformation(string name, int id){}

The Dance of Synchronization: Player States in Harmony

As you delve deeper into Godot's networking capabilities, RPCs become the choreography of your multiplayer dance. They orchestrate the synchronization of player states, ensuring that every player's actions reverberate across the entire game world.

In our ongoing journey through Godot's multiplayer capabilities, we've explored the basics of RPCs. Stay tuned for our next instalment, where we'll dive into advanced RPC usage, optimization techniques, and handling intricate player interactions.

May your RPCs be swift, your communication seamless, and your multiplayer experiences truly immersive! Happy coding!

Morris Morrison