1. Burnout 3: Case Study (Outline) What is Burnout 3? What is Burnout 3? What does this mean? What does this mean? How did we satisfy these constraints? How did we satisfy these constraints? Racecars Racecars Traffic system Traffic system Aggressive driving Aggressive driving What did we learn? What did we learn?

2. What is Burnout 3? Racing Racing Aggressive driving Aggressive driving Crashing Crashing Traffic Traffic Fast paced, twitch gaming Fast paced, twitch gaming

3. What does this mean? Racing Racing Cars must be in the right position, travelling at the right speed Cars must be in the right position, travelling at the right speed Car movement should be as smooth and similar to offline as possible Car movement should be as smooth and similar to offline as possible Cars will only change speed/direction gradually Cars will only change speed/direction gradually Aggressive driving Aggressive driving Cars really, really must be in the right position, travelling at the right speed Cars really, really must be in the right position, travelling at the right speed Important events must be the same on all consoles (slam/shunt/takedown) Important events must be the same on all consoles (slam/shunt/takedown)

4. What does this mean? Crashing Crashing Cars must be in the right position, travelling at the right speed Cars must be in the right position, travelling at the right speed Cars must be able to change velocity sharply Cars must be able to change velocity sharply Traffic Traffic Traffic system must handle up to 254 cars without maxing out bandwidth (10kB/s) Traffic system must handle up to 254 cars without maxing out bandwidth (10kB/s) Fast paced, twitch gaming Fast paced, twitch gaming Client must be authoritative Client must be authoritative

5. Racecars Client owns their own position Client owns their own position Your car doesn’t jump or move unexpectedly Your car doesn’t jump or move unexpectedly Open to cheating Open to cheating

6. Racecars version 0.1 Send matrix and velocity in update packet Send matrix and velocity in update packet Put the racecar where the packet says, when it arrives Put the racecar where the packet says, when it arrives Cars are seen in the past Cars are seen in the past Cars jump when latency varies (and it does!) Cars jump when latency varies (and it does!) Simple and cheap (memory + CPU) Simple and cheap (memory + CPU)

7. Racecars version 0.5 Buffer message Buffer message Apply it when its time has come Apply it when its time has come Cars are smoother Cars are smoother Cars are even more ‘in the past’ because buffering adds latency Cars are even more ‘in the past’ because buffering adds latency If you don’t apply packets you receive ‘late’ you are artificially increasing packet loss too If you don’t apply packets you receive ‘late’ you are artificially increasing packet loss too Uses slightly more memory, but still cheap in terms of CPU Uses slightly more memory, but still cheap in terms of CPU More complicated, and applying ‘late’ messages makes it even more complicated More complicated, and applying ‘late’ messages makes it even more complicated

8. Racecars final version When message arrives extrapolate position forwards in time When message arrives extrapolate position forwards in time First attempt: extrapolating position using velocity First attempt: extrapolating position using velocity Second attempt: Lightweight version of physics Second attempt: Lightweight version of physics Cars are seen in the present Cars are seen in the present Not as smooth as version 0.5 Not as smooth as version 0.5 Expensive in CPU Expensive in CPU

9. Traffic System Size of traffic ID/position/orientation 10 bytes Size of traffic ID/position/orientation 10 bytes Traffic system is updating up to 254 cars at once Traffic system is updating up to 254 cars at once So total packet size to send position and orientation of all traffic is 2540 bytes! So total packet size to send position and orientation of all traffic is 2540 bytes! Traffic system must be deterministic Traffic system must be deterministic

10. Traffic System Based on lanes Based on lanes Traffic cars follow a param along a lane Traffic cars follow a param along a lane Traffic cars stop at traffic lights Traffic cars stop at traffic lights Traffic cars change lane at certain points (splitters) Traffic cars change lane at certain points (splitters) Divergence detection Divergence detection In game replays helped lots! In game replays helped lots!

11. Crashing traffic If a car crashes you can’t remove it from the traffic system If a car crashes you can’t remove it from the traffic system It becomes invisible, and ignored by physics It becomes invisible, and ignored by physics Traffic ownership Traffic ownership You detect that an unowned traffic car has crashed You detect that an unowned traffic car has crashed You start sending out updates (you own it) You start sending out updates (you own it) Other people apply your updates Other people apply your updates Is possible for more than one player to own a traffic car Is possible for more than one player to own a traffic car Can’t afford to extrapolate, so run in the past (racecar version 0.5) Can’t afford to extrapolate, so run in the past (racecar version 0.5) Change to past masked by smoke and particles! Change to past masked by smoke and particles!

12. Aggressive Driving Send extra info in updates (slam/shunt/takedown) Send extra info in updates (slam/shunt/takedown) Send multiple times in case of packet loss, but only for about half a second Send multiple times in case of packet loss, but only for about half a second

13. Pickups Similar to aggressive driving Similar to aggressive driving Two players can get the same pickup Two players can get the same pickup

14. End of race Send results packet Send results packet Race time Race time Fastest lap Fastest lap Crash damage Crash damage Pickups Pickups Susceptible to cheating Susceptible to cheating

15. What we learnt Plan to network from the outset Plan to network from the outset Traffic system Traffic system Try anything unknown in prototype Try anything unknown in prototype Racecars Racecars Crashing traffic Crashing traffic Networking strategy is game-specific Networking strategy is game-specific Reassess if game design changes Reassess if game design changes Develop and test in real world conditions Develop and test in real world conditions