Making Sense of Multiplayer Netcode
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In this presentation, we'll explore the unique concerns of a system that supports dozens of concurrent players in real time. We'll use a mobile game written in JavaScript to test different implementation options and you'll leave ready to go home and design your own multiplayer experience.
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Making Sense of Multiplayer Netcode
- 1. @hunterloftis Making Sense of Multiplayer Hunter Loftis Engineering Manager, Heroku @ Connect.Tech 2018
- 3. 1962
- 4. 1987
- 5. 1996
- 6. 1998
- 7. 2004
- 8. Pre-2011 "Netcode" experts C++, TCP, UDP, ICMP, routing @hunterloftis
- 9. 2011 Renaissance WebSocket protocol (+Node.js) @hunterloftis
- 10. Shared Spaces
- 11. Shared Spaces
- 12. Shared Spaces
- 13. Shared Spaces
- 14. Shared Spaces
- 16. @hunterloftis Most people fail the first time.
- 17. @hunterloftis Most people fail the first time. I did!
- 18. @hunterloftis Most people fail the first time. I did! ... and the second, third, and fourth times too.
- 20. @hunterloftis Common issues • Choppy updates
- 21. @hunterloftis Common issues • Choppy updates • Laggy controls
- 22. @hunterloftis Common issues • Choppy updates • Laggy controls • Changes being applied and then un-applied
- 23. @hunterloftis Common issues • Choppy updates • Laggy controls • Changes being applied and then un-applied • Inconsistent client behavior
- 24. @hunterloftis Common issues • Choppy updates • Laggy controls • Changes being applied and then un-applied • Inconsistent client behavior • Rule breaking
- 25. @hunterloftis We're ignoring decades of experience!
- 27. @hunterloftis What is real-time multiplayer?
- 28. @hunterloftis What is real-time multiplayer? A Lie.
- 29. "It turns out it’s all an illusion. A massive sleight-of-hand." - Glenn Fiedler, Networking for Game Programmers @hunterloftis
- 30. @hunterloftis 100% Scientific bandwidth / $ compute / $ speed of light / $ Time
- 31. @hunterloftis bandwidth / $ compute / $ speed of light / $ Time
- 32. @hunterloftis Sharing an environment over thousands of miles is impossible.
- 33. @hunterloftis Instead, create an illusion:
- 34. @hunterloftis Instead, create an illusion: 1. Input gives feedback immediately.
- 35. @hunterloftis Instead, create an illusion: 1. Input gives feedback immediately. 2. Players believe they are sharing an environment.
- 36. @hunterloftis Instead, create an illusion: 1. Input gives feedback immediately. 2. Players believe they are sharing an environment. 3. Everyone eventually ends up in the same state.
- 37. @hunterloftis How? Entities + Stacked State
- 38. @hunterloftis How? Entities + Stacked State View
- 39. @hunterloftis How? Entities + Stacked State View Predicted
- 40. @hunterloftis How? Entities + Stacked State View Predicted Interpolated
- 41. @hunterloftis How? Entities + Stacked State View Predicted Interpolated Authoritative
- 42. @hunterloftis How? Entities + Stacked State View Predicted Interpolated Authoritative
- 45. @hunterloftis Entities • Have a unique ID.
- 46. @hunterloftis Entities • Have a unique ID. • Belong to an owner.
- 47. @hunterloftis Entities • Have a unique ID. • Belong to an owner. • Belong to a timeline.
- 48. Entities provide a way to partition state { id: 4, x: 50, y: 22, angle: 0, health: 0.7, firing: false }
- 49. @hunterloftis Entities from different timelines can coexist. time = 1.5s time = 1.75s
- 50. @hunterloftis Divergence sacrifices accuracy for smoothness.
- 52. sendToServer({ hit: true })
- 53. @hunterloftis Input In - State Out Server { leftKey: true } [{ id: 1, x: -10, y: 0 } { id: 2, x: 10, y: 0 }] { rightKey: true }
- 55. @hunterloftis Authoritative Server • Prevents cheating
- 56. @hunterloftis Authoritative Server • Prevents cheating • Ensures eventual consistency
- 57. @hunterloftis Authoritative Server • Prevents cheating • Ensures eventual consistency • Allows secrets
- 59. @hunterloftis "Update Rate" How frequently the server sends updates to clients. (eg, 10 Hz)
- 62. @hunterloftis Interpolation • Stores the last two authoritative states in history.
- 63. @hunterloftis Interpolation • Stores the last two authoritative states in history. • Animates from history[0] to history[1].
- 64. @hunterloftis Interpolation • Stores the last two authoritative states in history. • Animates from history[0] to history[1]. • Extrapolates if new data doesn't arrive on time.
- 69. @hunterloftis Client-Side Prediction • Records a buffer of local input.
- 70. @hunterloftis Client-Side Prediction • Records a buffer of local input. • Applies the buffer over the most recent authoritative state.
- 71. @hunterloftis Client-Side Prediction • Records a buffer of local input. • Applies the buffer over the most recent authoritative state. • Only simulates a subset of the rules.
- 72. @hunterloftis Local input stacks on top of authoritative history to push local entities further in time. history[0] history[1] input inputinput
- 76. @hunterloftis View State • Isn't propagated across the network.
- 77. @hunterloftis View State • Isn't propagated across the network. • May be different per-client.
- 78. @hunterloftis View State • Isn't propagated across the network. • May be different per-client. • Adds details to authoritative state.
- 80. @hunterloftis Putting it all together
- 81. @hunterloftis A moment in time Server input 45input 46input 47 state (43)state (42) state (41) input 44 state (40)
- 82. @hunterloftis Player B Sees himself start moving up immediately, then sees Player A start moving up. Player A Sees herself start moving up immediately, then sees Player B start moving up. Both players press UP at the same time.
- 83. @hunterloftis Player B Sees himself stop moving immediately, then sees Player A stop moving at the same height. Player A Sees herself stop moving immediately, then sees Player B stop moving at the same height. Both players release UP at the same time.
- 84. @hunterloftis The illusion has limits Latency Fighters/Sports Twitchy shooters Today's demo Real-time strategy Chess
- 92. @hunterloftis Questions? https://github.com/hunterloftis/dogfight http://www.pages.drexel.edu/~ecb44/print.html https://www.pcgamer.com/netcode-explained/ http://www.gabrielgambetta.com/client-server-game-architecture.html https://developer.valvesoftware.com/wiki/Source_Multiplayer_Networking http://www.gamasutra.com/view/news/128323/Seven_Years_Of_World_Of_Warcraft.php https://gafferongames.com/post/what_every_programmer_needs_to_know_about_game_networking https://stackoverflow.com/questions/11436311/realtime-multiplayer-game-principles-for-tcp-and-node-js "250 Handdrawn Textures" art by Daniel Cook Plane sprites by Sujit Yadav Particle sprites by Kenney