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System Design - MMOG - Game

System design: Design Multiplayer game

Game Loop​

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while (true) {
check_input()
update_game_state()
render_screen()
}

Physics Engines​

  • Unity
  • Unreal Engine

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  1. Strategic games
  2. Slow turn games
  3. First person games

Authoritative Server​

  • Holds all the state information and validates each state information with it's own state
  • No one can hack the client and run mod commands
  • Therefore can't have peer to peer connection between players

Networking​

  • Deterministic Lock Step
  • Sends only input only and not the new state of game character
  • Encode each bit for each input thereby saving more bandwidth
  • Using this other side can simulate their own environment
  • Sampling size - 60 / sec

  1. TCP (Head of line blocking), therefore can't use TCP

  2. Playout Buffer (keep 5 sec in buffer like in youtube, netflix, that keeps preloaded some data beforehand, so intermittent network can be smoothened)

  3. Can have a buffer space (park space) of 50 ms so the overall experience is smooth

  4. Therefore instead of TCP use UDP,

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  • Send previous inputs in all packets
  • Add timestamps for replay- State Synchronization
    • Sync state of the environments object
      • Object State
        • Position
        • Orientation
        • Linear Velocity
        • Angular Velocity
  • Jitters and lagging
    • Prediction
      • Linear Interpolation
      • Polar Interpolation
      • Hermite Interpolation

Handling states, corner cases, rules for objects​

  • Via if-else statement
    • Not maintainable
    • Not scalable
    • No design pattern

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  • World Server
  • Game /Area Server
  • Data Structure - Map Template

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Patch Servers​

  • Everyone should be in same version in MMOG
  • Real time updates

Game State Backup​

  1. Important bits
  2. Only if changed
  3. Individual
  4. Async

CDN​

Game Sprites

Database​

  • SQL
  • Sharded SQL
  • NoSQL