Unreal Engine Multiplayer for Gameplay Systems: Replication Basics for Chat, Cameras and Hiding
Multiplayer gets easier once you apply one rule everywhere: the server decides, clients ask. Here is how that plays out for three common features.
1. The server owns the truth
Clients send requests through Server RPCs ("I want to open this door", "I want to say this"). The server checks the request and changes the state. State that everyone needs is replicated through variables, and RepNotify functions let clients react when a value changes (play a sound, update a widget).
2. Chat
The client sends the text to the server with a Server RPC. The server trims and limits the length, adds the player's name from the Player State, and forwards the message to every player (a Client RPC to each controller, or a Multicast). Keep messages short, add a small rate limit, and let the UI only display what the server confirmed.
3. Security cameras
Scene Capture components render on each machine and are not something to replicate. Replicate only which camera a player is viewing. Scene captures are expensive, so lower the resolution, limit how often they update and only capture while somebody is actually looking at the monitor.
4. Hiding spots
Store "is hidden" and "which spot" as replicated state. The server validates entering and leaving (is the spot free, is the player in range), and the camera or peek view stays local to the hiding player. Make sure your AI respects the state, for example by skipping hidden players in perception checks.
5. Test early, with lag
In the editor, play with two or more players and a dedicated or listen server, and turn on Network Emulation to simulate latency and packet loss. Most replication bugs only show up with lag.
Common mistakes
- Putting game state in widgets instead of replicated actors or the Player State.
- Calling a Multicast from a client (it only works from the server).
- Using Get Player Controller (0) for per-player logic on the server: index 0 is not "the player who asked".
- Replicating everything "just in case". Replicate what others need to see.
Want working examples?
The Simple Multiplayer Chat System, the Simple CCTV System (Cameras) and the Simple Hide system are 100% Blueprint and built with replication in mind. See them below.
