Multiplayer Netcode (NGO)

Overview

Implementation of Unity Netcode for GameObjects (NGO). Covers connection management (Host/Client), state synchronization (NetworkVariables), messaging (RPCs), and object spawning.

When to Use

•Use for CO-OP games
•Use for competitive multiplayer
•Use when state needs to be synced
•Use for lobby systems
•Use for authoritative server logic

Key Concepts

Concept	Description
NetworkManager	Core component handling connections
NetworkBehaviour	MonoBehavior extension for networked scripts
NetworkVariable	Variables synced automatically
ServerRpc	Client asks Server to do something
ClientRpc	Server tells Client to do something

Architecture

code

┌─────────────────────────────────────────────────────────────┐
│                  AUTHORITATIVE SERVER                       │
├─────────────────────────────────────────────────────────────┤
│                                                             │
│   CLIENT A                SERVER (Host)             CLIENT B│
│  ┌──────────────┐        ┌──────────────┐      ┌──────────┐ │
│  │ Input (Move) │───────▶│ Validate     │◀─────│ Input    │ │
│  │              │ Start  │ Update State │      │          │ │
│  │ Present View │◀───────│ Broadcast    │──────▶ Present  │ │
│  └──────────────┘ Server │ State        │      │ View     │ │
│                   RPC    └──────────────┘      └──────────┘ │
│                             ClientRPC                       │
│                         NetworkVariable                     │
│                                                             │
└─────────────────────────────────────────────────────────────┘

Best Practices

•✅ Separate Visuals from Logic
•✅ Use NetworkVariable for state (Health, Ammo)
•✅ Use RPCs for events (Explosions, Emotes)
•✅ Validate all ServerRPCs (Anti-cheat)
•✅ Spawn networked objects via NetworkObject.Spawn()
•❌ NEVER sync input directly (sync results/commands)
•❌ NEVER modify NetworkVariables on the client
•❌ NEVER use Instantiate for networked objects directly

Few-Shot Examples

Example 1: Player Movement (Server Authoritative)

User: "Sync player movement."

Agent:

csharp

public class PlayerNet : NetworkBehaviour
{
    public override void OnNetworkSpawn() { ... }

    [ServerRpc]
    public void MoveServerRpc(Vector3 input)
    {
        // Server validates and moves
        transform.position += input * Speed * Time.deltaTime;
    }
    
    void Update() {
        if (IsOwner) {
            MoveServerRpc(Input.GetAxis("Vertical"));
        }
    }
}

Example 2: Synced Variable (Health)

User: "Sync health across clients."

Agent:

csharp

public class HealthNet : NetworkBehaviour
{
    public NetworkVariable<int> Health = new NetworkVariable<int>(100);

    public override void OnNetworkSpawn()
    {
        Health.OnValueChanged += (oldVal, newVal) => UpdateHealthBar(newVal);
    }
    
    [ServerRpc]
    public void TakeDamageServerRpc(int amount)
    {
        Health.Value -= amount; // Auto-syncs to all clients
    }
}

Example 3: Spawning Objects

User: "Spawn a bullet."

Agent:

csharp

// MUST be run on Server
private void Fire()
{
    var bullet = Instantiate(_bulletPrefab, pos, rot);
    bullet.GetComponent<NetworkObject>().Spawn();
}

Related Skills

•@backend-integration - Lobbies and Relay
•@object-pooling-system - Networked pooling
•@asynchronous-programming - Connection timeouts