Lets Play Together
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This document discusses network multiplayer game design. It begins with an introduction to the speaker and their past games. The bulk of the document then discusses various topics relating to network game programming at both low and high levels, including network architectures, data transfer methods, latency compensation techniques, and optimization strategies. Example techniques and popular games are referenced throughout.
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Lets Play Together
- 1. “Let’s Play Together” Networked Mul-player Games Amir H. Fassihi Fanafzar
- 2. Background Garshasp: The Monster Slayer, PC 2011 Garshasp: Temple of the Dragon, PC 2012 Shadow Blade, iOS, Android Fall, 2013
- 3. Current Game • Coopera-ve Mul-player Game
- 4. Mul-player Games • Co-‐op/PvP • Local/LAN/Internet • Real-‐-me/Asynchronous
- 5. This Talk • LAN/Internet • Co-‐op/PvP • Real-me
- 6. Game Networking Gameplay Code High Level Network Code Low Level Network Code
- 7. Low Level Networking • Sockets • Transfer Protocols • NAT (Network Address Transla9on)
- 8. Sockets • Socket – IP – Port • OS Support – BSD Sockets – WinSock – …
- 9. Transfer Protocols • UDP – Unreliable – Un-‐ordered – Connec-on-‐less using Datagrams (1400 bytes) • TCP – Reliable – Ordered – Stream Based
- 10. Game Networking UDP + reliability + order
- 11. NAT • Network Address Transla-on • Connec-on Problem with NAT Box – Server Listening on Port – Client changing port • NAT Punch-‐through with Facilitator Server
- 12. High Level Networking • Architecture • Data to Transfer • Lag Compensa-on
- 13. Network Architecture • Peer to Peer • Client Server • Mixed
- 14. Peer to Peer Client 1 Client 2 Client 3 Client 4
- 15. Client-‐Server Client 1 Client 2 Client 3 Server
- 16. Data Transfer How To Share The Same Experience?
- 17. What to Send? 1. Share Inputs 2. Share Input and State (Authorita-ve Server) 3. Share Input and State (Mixed Authority)
- 18. Game Loop (Simplified) 1. Read User Input 2. Do Simula-on 1. Logic 2. AI 3. Physics … 3. Output 1. Render Graphics 2. Play Sound/Music 3. Update UI …
- 19. Sharing Input Client 1 Client 2 User 1 Input User 2 Input
- 20. Shared Input P2P Main Requirement: Determinis=c Simula=on
- 21. Shared Input P2P Constraint (for Lockstep): Lag Effect On Clients No mid-‐game join!
- 22. Shared Input P2P Risk: Chea=ng
- 23. Shared Input P2P Advantage: Low Bandwidth Requirements
- 24. Shared Input P2P Used for: Strategy Games (Starcra', Age of Empires, …)
- 25. 1500 Archers • 1500 Archers on a 28.8: Network Programming in Age of Empires and Beyond, Gamasutra
- 26. Shared State Server Client 1 Client 2 Input 1 Input 2 Game State Game State
- 27. Shared State Main Requirement: Simula=on Only On Server
- 28. Shared State Constraint: High Bandwidth (Especially the Server!)
- 29. Shared State • Cheat Proof • Non-‐determinis-c simula-on is ok • Different client lag will not stall • Mid-‐game joining possible
- 30. Shared State Good For: Ac=on Games Compe==ve Games (eSports)
- 31. Main Challenge Biggest Challenge in Game Networking is:
- 32. Lag!!!
- 33. Lag in Client-‐Server Client Server Press Buaon Press Buaon Fire Fire
- 34. Lag in Client-‐Server Client Server Press Buaon Press Buaon Fire Fire Lag
- 35. Solu-on #1 Client Side Predic=on
- 36. Client-‐side Predic-on Client Server Press Buaon Press Buaon Fire Fire Check Validity
- 37. Client-‐side Predic-on • Fix Client State if different • State History on Client • Useful for player state • Can be used for other objects (extrapola-on)
- 39. Solu-on #2 Input Latency
- 40. Input Latency • Input marked for future • 50-‐100ms • Client will interpolate
- 41. Input Latency Client Server Move Forward T = +100ms Move Forward Find posi-on for: +100 Pos: +100ms Current t: +70ms Interpolate between previous pos and pos at +100ms for +70ms
- 42. Client Interpola-on -me = 1200 -me = 1300 pos = 1, 1, 1 pos = 2, 2, 1 9me = 1250 pos = 1.5, 1.5, 1 Interpolated State
- 43. Solu-on #3 Server-‐side Lag Compensa=on
- 44. Server-‐side Lag Compensa-on • Rewind simula-on on server based on client lag. • Re-‐simulate game.
- 45. Source Engine Lag Compensa-on
- 46. Gameplay Inconsistencies • Wrong posi-on (no compensa9on) • Late Hits (with compensa9on)
- 47. Problem with Lag Compensa-on A B High Lag Low Lag
- 48. Problem with Lag Compensa-on A B High Lag Low Lag B
- 49. Design Lag Compensa=on Strategy can be a “Game Design” decision.
- 50. Doom III Solu-on Player Extrapola=on
- 51. Player Extrapola-on • A kind of Predic-on • Assume controls don’t change • Simulate fully (with Physics) like the server • AKA Dead Reckoning
- 52. Mixed Authority • Clients with Authority over some objects. • Example: Sync Host in FUSE (Overstrike), Game Developer Magazine, Feb 2012
- 53. Network Op-miza-on • High Level – Architecture Selec-on – Update Frequency – Data Relevancy – Priori-za-on
- 54. Network Op-miza-on • Low Level – Bitpacking (bitstreams) – Compression – Delta Values
- 55. Delta Compression in Quake (1996)
- 57. Delta + Reliable UDP
- 59. Doom (1993) • Doom used P2P Lockstep Model. Good for LAN only.
- 64. Cloud Gaming Main Challenge: Lag!
- 65. Figh-ng Game Networking • Peer to Peer – Input Latency – Rollback Technique Example: GGPO Networking Library
- 66. Networking Libraries • Enet • RakNet • Ice • PocoProject • Torque Network Library • ZeroMQ • Boost ASIO
- 67. Conclusion • Networking is a tradeoff between: – Consistency – Responsiveness – Bandwidth – Latency
- 68. References 1 • Robust Efficient Networking, Ben Garney, GDC 2008 • Torque Networking Library (opentnl.org) • Video Game Op-miza-on, Ben Garney • “I Shot You First”, Halo Reach Networking, David Aldridge, GDC 2011
- 69. References 2 • QuakeWorld hap://en.wikipedia.org/wiki/QuakeWorld • Network Systems in Insomniac Games’ Overstrike (FUSE), Game Developer Magazine, Feb 2012 • 1500 Archers on a 28.8, hap://www.gamasutra.com/view/feature/ 131503/1500_archers_on_a_288_network_.php?page=1
- 70. References 3 • “The TRIBES Engine Networking Model”, Frohnmayer and Gis, GDC 1999 • Understanding Figh-ng Game Networking, hap://mauve.mizuumi.net/2012/07/05/understanding-‐figh-ng-‐game-‐ networking/ • GGOP Networking Library, hap://ggpo.net/ • The Doom III Network Architecture hap://mrelusive.com/publica-ons/papers/The-‐DOOM-‐III-‐Network-‐ Architecture.pdf
- 71. References 4 • The Quake 3 Networking Model, Brian Hook, hap://trac.bookouook.com/bookouook/trac.cgi/wiki/ Quake3Networking • What Every Programmer Needs To Know About Game Networking, Glenn Fiedler, hap://gafferongames.com/networking-‐for-‐game-‐programmers/what-‐ every-‐programmer-‐needs-‐to-‐know-‐about-‐game-‐networking/ • Unreal Networking Architectures hap://udn.epicgames.com/Three/NetworkingOverview.html
- 72. References 5 • “Latency Compensa-ng Methods in Client/Server in-‐game Protocol Design”, Yahn Bernier, Valve haps://developer.valvesosware.com/wiki/ Latency_Compensa-ng_Methods_in_Client/Server_In-‐ game_Protocol_Design_and_Op-miza-on#Lag_Compensa-on • Believable Dead Reckoning for Networked Games, Cur-ss Murphy, Game Engine Gems 2 • Choosing a Game Network Library, Patrick Wyaa, hap://www.codeouonor.com/blog/choosing-‐a-‐game-‐network-‐lib
- 73. References 6 • Dead Reckoning: Latency Hiding for Networked games hap://www.gamasutra.com/view/feature/3230/ dead_reckoning_latency_hiding_for_.php
- 74. Special Thanks • Yaser Zhian • Hojjat Jafary • Ashkan Saeidi
- 75. Ques-ons? fassihi@fanafzar.com