Unity Netcode

Unity Netcode for GameObjects

Architecture

┌────────────┐         ┌───────────┐
│   Client   │  RPCs   │  Server   │  authoritative
│            │◀───────▶│ (or Host) │  state — broadcasts via
│ predicts   │  Vars   │           │  NetworkVariable + RPC
└────────────┘         └───────────┘

Use server-authoritative: never trust the client for damage, currency, or movement validation.

NetworkBehaviour basics

public class PlayerController : NetworkBehaviour {
    public NetworkVariable<int> Health = new(100,
        NetworkVariableReadPermission.Everyone,
        NetworkVariableWritePermission.Server);

    [Rpc(SendTo.Server)]
    public void FireRpc(Vector3 origin, Vector3 dir) {
        if (!IsServer) return;
        // server-side validation + spawn projectile
        SpawnProjectileServerSide(origin, dir, OwnerClientId);
    }

    [Rpc(SendTo.NotMe)]
    public void OnHitEffectRpc(Vector3 pos) {
        // VFX on every client except sender
    }
}

RPC targets (Unity 6 attribute syntax)

Client-side prediction

1. Client samples input → applies move locally + sends to server.
2. Server validates → broadcasts authoritative state.
3. Client reconciles: if server state diverges from prediction, replay inputs from divergence frame.

NGO doesn't ship a prediction system out-of-the-box — you build one with NetworkTransform.AuthoritativeMode = Owner + custom interpolation, or move to NetCode for Entities for first-class prediction.

Lag compensation (hit-scan)

When server processes a fire RPC:

1. Read client RTT → rewind world state to now - rtt/2.
2. Raycast against rewound colliders.
3. Apply damage as if the shot landed at that historical state.

Implement via a ring buffer of past Transform/Collider snapshots (e.g. 1s @ 20Hz).

Unity Gaming Services integration

• Relay — NAT punchthrough; host gets a Join Code that clients use.
• Lobby — pre-game rooms with metadata; passes Relay Join Code to clients.
• Matchmaker — skill/region-based queue; spins up Multiplay servers.
• Multiplay — dedicated server hosting; build Linux server build, deploy via UGS dashboard.

Anti-patterns

Production checklist

• [ ] All damage / economy / inventory mutations server-side only
• [ ] Lag compensation for hit-scan weapons
• [ ] NetworkObject pools for projectiles / spawned entities
• [ ] Relay + Lobby tested on real network (cellular, restrictive NAT)
• [ ] Server build CI pipeline (Linux IL2CPP) → Multiplay deploy
• [ ] Client/server version negotiation on connect — reject mismatches
• [ ] Anti-cheat: server validates inputs, throttles RPC rate