Multiplayer Deterministic 2D Strategy Game

A production-quality Rust project implementing a multiplayer deterministic 2D strategy game with authoritative server architecture.

Architecture

• Authoritative Server: Maintains full game state, processes commands deterministically
• Client-Side Prediction: Smooth gameplay with rollback reconciliation
• Fixed Timestep Simulation: 60 ticks per second for deterministic behavior
• Custom Binary Protocol: Compact serialization without JSON overhead

Project Structure

├── shared/          # Shared library crate
│   ├── math.rs      # Fixed-point math for determinism
│   ├── protocol.rs  # Binary protocol definitions
│   └── tick.rs      # Tick timing utilities
├── server/          # Server binary
│   ├── main.rs      # Entry point
│   ├── net.rs       # Tokio-based networking
│   ├── simulation.rs# Deterministic game simulation
│   ├── world.rs     # World state management
│   └── protocol.rs  # Protocol re-export
└── client/          # Client binary
    ├── main.rs      # Entry point with Bevy
    ├── net.rs       # TCP networking
    ├── render.rs    # Bevy rendering
    ├── input.rs     # Input handling
    └── protocol.rs  # Protocol re-export

Features

• Fixed-Point Math: Deterministic arithmetic using integer-based fixed-point numbers
• State Snapshots: Full state synchronization every 10 ticks
• Delta Updates: Efficient per-tick incremental updates
• Command Buffering: Per-tick command queuing for deterministic replay
• Checksum Verification: Desync detection via state checksums
• Client Prediction: Local simulation with server reconciliation

Protocol Messages

Type	Description
Handshake	Client authentication
HandshakeAck	Server acknowledgment with player ID
InputCommand	Player movement/stop commands
StateSnapshot	Full world state
DeltaUpdate	Incremental state changes
Ping/Pong	Latency measurement

Building

cargo build --release

Running

Terminal 1 - Start server:

./target/release/server

Terminal 2 - Start client:

./target/release/client

Controls

• Right Click: Move selected units to cursor position
• S: Stop all units
• A: Clear selection

Configuration

Server address: 127.0.0.1:7777 (configurable in client/src/main.rs)

Technical Details

Determinism

• All simulation uses fixed-point arithmetic (1000 scale factor)
• No floating-point operations in game logic
• Identical tick processing on server and client

Networking

• TCP-based reliable communication
• Length-prefixed binary packets
• Non-blocking client I/O with threaded networking

Simulation

• 60 ticks per second (16.67ms per tick)
• Unit speed: 100 units/second
• World size: 800x600