soojung-kang/multiplayer

Multiplayer Game Development

Networking architecture and synchronization principles.

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1. Architecture Selection

Decision Tree

What type of multiplayer?
│
├── Competitive / Real-time
│   └── Dedicated Server (authoritative)
│
├── Cooperative / Casual
│   └── Host-based (one player is server)
│
├── Turn-based
│   └── Client-server (simple)
│
└── Massive (MMO)
    └── Distributed servers

Comparison

| Architecture | Latency | Cost | Security | |--------------|---------|------|----------| | Dedicated | Low | High | Strong | | P2P | Variable | Low | Weak | | Host-based | Medium | Low | Medium |

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2. Synchronization Principles

State vs Input

| Approach | Sync What | Best For | |----------|-----------|----------| | State Sync | Game state | Simple, few objects | | Input Sync | Player inputs | Action games | | Hybrid | Both | Most games |

Lag Compensation

| Technique | Purpose | |-----------|---------| | Prediction | Client predicts server | | Interpolation | Smooth remote players | | Reconciliation | Fix mispredictions | | Lag compensation | Rewind for hit detection |

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3. Network Optimization

Bandwidth Reduction

| Technique | Savings | |-----------|---------| | Delta compression | Send only changes | | Quantization | Reduce precision | | Priority | Important data first | | Area of interest | Only nearby entities |

Update Rates

| Type | Rate | |------|------| | Position | 20-60 Hz | | Health | On change | | Inventory | On change | | Chat | On send |

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4. Security Principles

Server Authority

Client: "I hit the enemy"
Server: Validate → did projectile actually hit?
         → was player in valid state?
         → was timing possible?

Anti-Cheat

| Cheat | Prevention | |-------|------------| | Speed hack | Server validates movement | | Aimbot | Server validates sight line | | Item dupe | Server owns inventory | | Wall hack | Don't send hidden data |

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5. Matchmaking

Considerations

| Factor | Impact | |--------|--------| | Skill | Fair matches | | Latency | Playable connection | | Wait time | Player patience | | Party size | Group play |

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6. Anti-Patterns

| ❌ Don't | ✅ Do | |----------|-------| | Trust the client | Server is authority | | Send everything | Send only necessary | | Ignore latency | Design for 100-200ms | | Sync exact positions | Interpolate/predict |

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Remember: Never trust the client. The server is the source of truth.

When to Use

This skill is applicable to execute the workflow or actions described in the overview.