Synchronizing States & Events
Introduction
Netcode for GameObjects (Netcode) includes three options for synchronizing game states and/or events:
- Messaging System
- Remote Procedure Calls (RPCs)
- Custom Messages
- NetworkVariables
- Handled by the "internal" messaging system and categorized under "Networking".
While each of the above options can be used for the same thing, synchronizing states or events, they all have specific use cases and limitations.
Messaging System
The Netcode messaging system provides you with the ability to handle sending and receiving messages or events. The entire messaging system supports the serialization of most primitive value types as well as any classes and/or structures that implement the INetworkSerializable interface.
Remote Procedure Calls
RPCs can be viewed as a way to send an event notification as well as a way to handle direct communication between a server and a client (or vice versa). This is sometimes useful when the ownership scope of the NetworkBehavior, that the remote procedure call is declared within, belongs to the server but you still want one or more clients to be able to communicate with the associated NetworkObject.
Some Usage Examples:
- A ServerRpc can be used by a client to notify the server that the player is trying to use a world object (that is, a door, a vehicle, etc.)
- A ClientRpc can be used by a server to notify a specific client of a special reconnection key or some other player specific information that doesn't require its state to be synchronized with all current and any future late joining client(s).
The are two types of RPC methods:
- ServerRpc: A client invoked remote procedure call received by and executed on the server-side.
- ClientRpc: A server invoked remote procedure call received by and executed on one or more clients.
Custom Messages
Custom messages provide you with the ability to create your own "netcode message type" to handle scenarios where you might just need to create your own custom message. Read More About Custom Messages
NetworkVariable System
A NetworkVariable is most commonly used to synchronize state between both connected and late joining clients. The NetworkVariable system only supports non-nullable value types, but also provides support for INetworkSerializable implementations as well you can create your own NetworkVariable class by deriving from the NetworkVariableBase abstract class. If you want something to always be synchronized with current and late-joining clients, then it's likely a good NetworkVariable candidate.