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Racing Game A.I.

Racing Game A.I. By Austin Borden, Qihan Long, and Jim Pratt. Defining the Racetrack. Sectors Define on-track areas Interfaces Leading and trailing edges of a sector. Interfaces. Right/left edge Driving line nodes: Racing line Overtaking line. Overtaking.

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Racing Game A.I.

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  1. Racing Game A.I. By Austin Borden, Qihan Long, and Jim Pratt

  2. Defining the Racetrack • Sectors • Define on-track areas • Interfaces • Leading and trailing edges of a sector

  3. Interfaces • Right/left edge • Driving line nodes: • Racing line • Overtaking line

  4. Overtaking • When the A.I. car gets close to an opponent, it will change its driving line from racing to overtaking • Multiple overtaking lines possible • Burnout 1:15

  5. Sectors • Stores its distance from start, to finish line, and to other vehicles. • Path types • Terrain types • Walls • Hairpin turns • Brake-Throttle

  6. Path Types • Defines the type of route ahead • Normal • Shortcut • Long route • Weapon pick-up route • Winding road • Drag strip • A.I. chooses route depending on current situation

  7. Terrain Types • Adds another variable for A.I. to deal with • Rugged terrain • Slick • If a route is a shortcut and also rugged, only vehicles capable of traversing will choose this route • Terrain Traversing

  8. Racetrack Definition Conclusion • The more information we provide, the less complex the A.I. system has to be

  9. Racing A.I. Logic • Vehicles do not follow driving lines exactly, only guided by them • A.I. is supposed to emulate human input • Done by creating an A.I. controller

  10. Basic A.I. Framework • Finite State Machines • Allows decision making • Fixed Time-Step • Ensures that AI reacts quickly always • Controls • float dx; //-1.0 to 1.0 for left to right steering • float dy; //-1.0 to 1.0 for max brake to max acceleration

  11. Looking Ahead • Cars look ahead for obstacles and turns • The faster it’s moving, the further it looks to smooth path

  12. Wall Avoidance • Position is predicted by using the current velocity and scaled by how far in the future we are predicting (seconds) • Correction amount is then applied to steering depending on which wall car is closest to • If predicted position is outside of sector, brakes are applied

  13. Hairpin Turns • Looking too far ahead during a sharp turn will cause A.I. to cut corners • To fix this, car looks for hairpin flags and shortens the look ahead distance if flags are found

  14. Under/Over-Steer • With simple physics cars can spin out due to over steering • Cars can also miss turns due to under steering • Based on sideways velocities of wheels

  15. Steer Correction • Depending on over or under-steering, a correction value is added to the current steer value • Overcorrection is prevented by the understeer/oversteer range • Colin McRae Dirt 2

  16. Catch-Up Logic • If A.I. is winning… • Limit A.I.’s top speed in proportion to distance leading • Brake early for corners, accelerate slowly out of turns • Take long routes/ unstable terrain routes • Get worse weapons/ only target other A.I. • Opposite can be used if A.I. is trailing • Good way of making a race challenging for all skill levels • Diddy Kong Racing 1:45 • Shadows of the Empire 5:50

  17. Catch Up Logic Case Study:Pure

  18. The Rubber Band System

  19. Racing Grouping in Pure

  20. Difficulty Regulation • Powerful items • Intelligence modification • Similar Placing

  21. Tuning the Car Handling • If each car has different characteristics, tuning the code can be time consuming.

  22. Adjusting the Parameters • Assign each parameter with a minimum and maximum value. • Modify the parameter depending on whether the lap time decreases or increases. • Time for this process can be reduced by running the game as fast as possible.

  23. Real Time Editing • Real Time Track Modification • An important tool in AI creation is the ability the change the track in real time. • Allows problems in the track to be quickly modified and tested. • User Control Overriding AI • Allows tester to take control when AI becomes stuck or incapable of navigating a certain part of the track. • Can be used to test the AI on specific parts of the track.

  24. Layer Behavior • Reactionary system • Modular approach makes it easy • Multiple inputs for one output • Output contention system ultimately determines output • Layer Interactions: • Overriding • Internal states • Altering input for other layers

  25. Example of Layers

  26. Path Following Layer • Turning and speed dealt with separately • Attempt to keep car on line • Cornering regulation monitors speed • Corners and apex determined • Formulate max speed and braking zone distance • Dynamic according to current speed • Braking, cruise, full throttle

  27. Tactical Racing Layer • Makes competitive racing choices (driver into a racer) • Analyzes situation and races accordingly • Find optimum road position • Generates new paths • Safe guards in place

  28. Visual Perception • 8 eyes, 4 pairs • Determines speed and position of cars and environment • Determines desirability of current position based on environment and position of other cars

  29. Fine Grain Avoidance Layer • Priority • Needed when cars want to occupy same space • Relative car position determines who yields • Prevents collisions by overriding • For passing, steering is moderated • For linear, speed is moderated

  30. Determining Racing Lines • Problems with user made content • Track detail hard to take into account • Lines of minimum curvature are limiting, boring • Midway points across track • Forces used to smooth out sharp turns • Safe guards

  31. Competitive AI Racing Under Open Street Conditions • Allows an AI controlled vehicle to traverse an random network of roads. • Finding the correct route to destination. • Calculating steering brake and throttle values.

  32. Library Interface • RegisterRoute Interface • Holds a list of intersections and roads • Registers the path through the map • Called when entering a new route • DriveRoute Interface • Used on a lower level than the RegisterRoute interface • Calculates steering, throttle, and brakes • Used for driving forward, backing up, colliding, and stopping.

  33. Navigating the City • Find the current location • Update the road cache • When a road is fully traversed, loads a new road into the cache. • Emulate all possible routes • Finds possible routes through the road

  34. Avoiding obstacles • Check for obstacles after the route is calculated.

  35. References • Champandard, Alex J. "Paris Game AI Conference '09: Highlights, Photos & Slides." Game AI for Developers. Web. 24 Mar. 2010. <http://aigamedev.com/open/coverage/paris09-report/#session13>. • "Gamasutra - Features - The Pure Advantage: Advanced Racing Game AI." Gamasutra - The Art & Business of Making Games. Web. 24 Mar. 2010. <http://www.gamasutra.com/view/feature/3920/the_pure_advantage_advanced_.php>. • "Mario Kart Wii: Those Damn Powerups." GamerBunny Speaks. Web. 24 Mar. 2010. <http://gamerbunny.wordpress.com/2008/05/19/mario-kart-wii-those-damn-powerups/>. • Rabin, Steve. AI Game Programming Wisdom 2. Hingham, MA: Charles River Media, 2004. Print. • Rabin, Steve. AI Game Programming Wisdom. Hingham, Mass.: Charles River Media, 2007. Print. • Youtube. Web. 24 Mar. 2010. <http://youtube.com>.

  36. Questions?

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