Multiplayer Coin Collector

A real-time multiplayer game with authoritative server and client-side interpolation, designed to handle simulated network latency.

Requirements

• Python 3.8+
• websockets
• pygame

Install dependencies:

pip install -r requirements.txt

How to Run

1. Start the Server:

   python server.py

   The server will start on ws://localhost:8765.

2. Start Clients: Open two separate terminal windows and run:

   python client.py

   We can specify a custom server URI if needed:

   python client.py ws://localhost:8765

3. Gameplay:

   • The game starts automatically when 2 players connect.
   • Use WASD or Arrow Keys to move.
   • Collect coins to score points.
   • The server simulates 200ms latency for all network traffic (Bidirectional: 200ms Uplink + 200ms Downlink).
   • Clients use Snapshot Interpolation to ensure smooth movement despite the latency.

Architecture

Server (server.py)

• Authoritative: Manages all game state (player positions, scores, coins).
• Latency Simulation:
  • Downlink: Delays state broadcasts by 200ms.
  • Uplink: Delays processing client inputs by 200ms.
• Tick Rate: Runs at 120 ticks per second for high-precision simulation.
• Coin Logic: Spawns 5 coins on start. New coins spawn every 5 seconds.
• Auto-Shutdown: Server automatically closes when all players disconnect.
• Protocol: Uses WebSockets for communication. JSON messages for state updates.

Client (client.py)

• Rendering: Uses Pygame for visualization. Runs at 120 FPS.
• Interpolation: Implements a history buffer (350ms) to store past server states. Renders entities delayed by the buffer amount to interpolate smoothly between known states.
• Prediction: Does not use client-side prediction (per requirements), relying purely on interpolation of authoritative server state.

Implementation Details

• Interpolation: The client maintains a buffer of state snapshots. It renders the game state from current_time - interpolation_delay. It finds the two snapshots surrounding this render time and linearly interpolates between them.
• Collision: All collision detection happens on the server.
• Security: Clients only send input vectors (WASD/Arrows). They cannot report scores or positions directly.