Advanced Racing Game AI in PURE

1. Iain Gilfeather Advanced Racing Game AI in PURE

3. Race Management • What happens if we don't manage the race? • AI either too good or too bad • AI won't react to the player's mistakes • Necessity of race management mechanisms • Make it challenging for anyone • Adapt to different situations • Fun

4. Rubber Band • Big rubber band around the player forcing the AI players to be around him • (Usually) Using any means necessary • Rubber Band: • Pros: • Works almost always • Removes completely the ‘lonely racing syndrome’ • Cons: • Usually needs cheating • It’s easy to spot, so it breaks the illusion of fairness

5. Skills • Represent how well a player performs on a particular behaviour/gameplay aspect. • 1 Skill per player per behaviour • Eventually all behaviors have the same skill value • Skills are normalized (to the [0..1] range)‏ • They could also be used to represent personality • Original approach to difficulty: static skills

6. Skill Porperties • Broad Range: if not broad enough we won’t be able to cover all the user cases • Responsiveness: using small increases normally so we want it to have small steps too

7. Skills Video

8. Dynamic Competition Balancing • Static skills during the race didn’t work well • Either too hard or too easy • Lonely racing • Dynamic Competition Balancing (DCB) is a system that modifies the skills dynamically during the race according to some rules • Tries to match the player's skill

9. Dynamic Competition Balancing • The first approach tried to match the player index with the leaderboard position • Way too inflexible • Didn’t work that well • We then introduced the concept of groups • Divided in group heads and members • Members follow the head/heads in order • Didn't work neither • Groups too loose or no groups at all • Lonely racing

10. Race Script: Summary • It’s the final method we used in the game • This Race Script concept includes not only the definition of the script itself but part of the implementation • Fixed the lonely racing sensation, the groups mechanism and it didn’t feel the AI was cheating.

11. Race Script: Definition • This is the part implemented by designers • It'll be a document explaining how the race should ideally develop under different circumstances: • The different player abilities must be reflected in the document • It's important for designers to understand that the race depends heavily on the player's performance • It’s not a strict script, just some guidelines for the race

12. Race Script: Example • Example from Pure: the ideal case • 3 groups: head, middle, back • Head and middle group leave the player behind at the start • Player goes progressing and jumping from one group to another • Some AI riders will jump with the player • At the middle of the last lap the player is in head position and the AI will be more forgiving from now on with his errors

13. Race Script: Implementation • The main idea is to use distance as the main rule for the DCB. • Every rider is aiming to be at a point X meters in front of or behind the human player • The skills of the rider will vary according to the distance to the aiming point, not to the player • Grouping players is achieved by giving them similar aiming points • The point may also move during the race • Thus we can have groups that progress during the race

14. Race Script: Implementation • From the player’s perspective it’s him who progresses through the groups • He doesn’t know we are making it easier for him • It’s subtle and rewarding • Main 2 differenciation points from Rubber Band: • Skills limited to a certain range • Follow the Race Script (not all around the player)‏

17. Race Script: Other mechanisms • Other mechanisms were used to ensure the game worked as desired • AI will have 1 skill at the beginning of the race • They need to make some distance from the player to ensure the initial groups • It's a complicated a very crucial moment for the AI • Too many cars/bykes • Some difficulty modifier based on the lap • Some people found it too easy at the beginning • Each lap is a bit easier than the previous one • This is very small (0 at the end)‏

18. Race Script: Other mechanisms • An 80% of the race is used to interpolate between the initial and end aiming positions, the 20% final uses the last positions. • Is consistent with the script • Otherwise it may be too difficult and unforgiving at the end • The AI riders will stop to improve their skills in the last meters to give make the first position even more accessible to players • Even with previous measures the AI was sometimes hard and unforgiving in the last meters

19. Other genres • I think this mechanism could be used in other genres • More control to the designers over the difficulty • You only need 2 key elements • Skills • Script • And an idea of how to implement it

20. Conclussions • I think we achieved our initial goals: • Have challenging, fun races • No lonely racing • Subtle and rewarding • Coherent groups throughout the race • This method may be easily adapted to any other kind of racing game

21. Thank you