Simple Soccer

1. Simple Soccer GAM 376 Robin Burke Winter 2008

2. Outline • Game Implementation • Project #1

3. Admin • Homework #3 • due today • Grading • I am behind • but no other homework due for awhile • Upcoming • 1/31: Design phase of Soccer project • 1/29: Midterm • 2/12: Soccer project

4. Simple Soccer • A 2D sports game • 5 agents per team • 4 field players • 1 goal keeper • 1 ball • 1 field • 2 goals

5. Issues for Sports AI • Perfection • player agents cannot be perfect • unrealistic, unbeatable • Roles • in team sports, players usually have well-defined roles • Stats • player performance is usually governed by stats • abstract quantities standing in for physical abilities • categories: defense, speed, etc. • interactions between players calculated based on stat comparisons and random factors

6. Architecture • Main loop • Update SoccerPitch • Redraw • SoccerPitch • responsible for updating what is on the field

7. SoccerPitch • Walls on all four sides • no throw-ins or goal kicks • Regions • 18 rectangular regions • for positioning players • Goals • each tracks number of goals scored

8. MovingEntity • Abstract class for all moving objects • has steering behaviors • Subclasses • SoccerBall • FieldPlayer

9. SoccerBall • embeds some of the physics of its motion • FuturePosition • Δx = v Δt + ½ afΔt2 • where af is the deceleration due to friction • TimeToCoverDistance • Δt = (v' – v) / af • but what is v' • issues • what if inner part is negative? • then the ball won't get that far • what is the initial velocity, v?

10. Velocity Reset • What really happens? • a player swings a foot • moment of interaction with ball • impulse • new velocity results • really it is a foot/ball collision • But not necessary to model it this way • assume that the ball is stopped before a kick • players can't add to existing velocity • OK, because it looks OK • much easier to model • Initial velocity • equals impulse acceleration • equals F / m • So we can calculate TimeToCoverDistance • given two points and a force

11. Soccer Players • Implementation of a 5-player soccer team • Two state machines • "Team state" • "Player state" • Tiered state machines • common in tactical FPS games • teams have a tactical state • "flanking" • and each member has its own role • "covering fire"

12. Team states • kickoff • everybody go to default position • not true soccer kickoff • offense • look for opportunities to get a pass upfield from the player with the ball • defense • go to defensive position • closest player chases ball

13. Offense other team possession goal scored our team possession Kickoff Defense goal scored play starts

14. Problems?

15. Team Behaviors • Tracks passes • receiving player of a pass • set when a pass is made • Tracks ball • closest player to the ball • constantly updated • Controlling player • the player with the ball • Supporting player • a player that will get into position for a pass

16. Support Spot • Considers 30 positions on the opponent's half of the field • Calculates which position can • receive a pass and • can shoot a goal and • are close enough to ball • Supporting player will try to go to the best support spot

17. Player state • defense • chase ball if you're the closest • offense • move toward goal with ball • pass if possible • without ball (if supporting player) • move to support spot • ask for pass • otherwise • do nothing

18. Steering behaviors • tracking the ball "visually" • chasing the ball • steering to support position • goalie has special behavior to get in blocking position

19. State Machine • Global state • routes messages • Wait • ReceiveBall • accept a pass • KickBall • make a pass • Dribble • try to move the ball downfield • ChaseBall • try to take possession of the ball • ReturnToHomeRegion • go home for kickoff • SupportAttacker • go to supporting position

20. MSG: Support MSG: Receive_Ball SupportAttacker ReceiveBall MSG: Go_Home not closest in receiving range ChaseBall Dribble kicked ReturnToHR in range can't shoot or pass can't kick KickBall closest at home Wait goal or pass attempt

21. Goal Keeper • Different states • TendGoal • interpose self between ball and goal midpoint • InterceptBall • if within tending range • PutBallBackIntoPlay • passes to nearest player

22. Issues for Player AI • Passing • when is it effective to pass? • when is it safe to pass? • Shooting • when is it possible to shoot? • where to aim a shot?

23. Passing B U A

24. Tests • Create target positions • player himself • to points on a circle around the player • Ignore • opponents behind passer • opponents farther away than the target • Calculate • time for ball to arrive at intercept position • test whether opponent can reach the position before the ball • Prefer targets closer to the goal • also considers target position near target player

25. Shooting U

26. Test • Examine a few random locations across the goal mouth • treat like pass targets • can opponents intercept?

27. Demo • What don’t the players do?

28. SoccerLab • Not the same as Buckland's • Allows multiple team implementations • Records the CPU time used by each AI implementation • Do not use Buckland's code

29. Abstract class • AbstSoccerTeam • all soccer teams must subclass • Abstract functions • CreatePlayers • teams can have different player setups • InitStateMachine • for team state machine • teams can have different team FSMs • InitPlayers • Name

30. How to allow different opponents? • Need students to make their own soccer teams • need to run tournament in which teams compete • don't want to recompile when adding a team • How to make extensible code that doesn't need recompilation? • In particular • how can I create an instance if I don't know the name of the class

31. Factory pattern • Basic idea • have a class whose job it is to create other objects • Get around the need to compile a call to new • a call to new requires a class name at compile time • A factory class • calls new • but we can use polymorphism • we can have a bunch of different factories • Result • what gets created is a function of which factory we choose • a decision that can be made at run time

32. AbstractFactory

33. Registration • How to know which factory object to use? • Static instance that registers a name on instantiation • Table associating factories with names • Result • dynamic object creation • (A bit easier in Java using reflection)

34. Implementation • TeamMaker class • includes a static "registry" member • table of name, class pairs • has a newTeam method • looks up the factory class in the table • calls its makeTeam method • The class stored here is a subclass of TeamMaker • must implement makeTeam • makes an instance of the right team object • must include a static member with an instance of itself • when that instance is created • it calls the TeamMaker constructor with a name • the factory class is then registered under that name

35. Abstract Code • SoccerTeamFactory.h class SoccerTeamFactory {public: MakeSoccerTeam(std::stringteam_id, Goal* home_goal,Goal* opponents_goal, SoccerPitch* pitch, team_colorcolor); }; • TeamMaker.h class TeamMaker { public: static AbstSoccerTeam* newTeam(string name, Goal* home_goal, Goal* opponents_goal, SoccerPitch* pitch, AbstSoccerTeam::team_colorcolor); } TeamMaker::TeamMaker (std::string className) { if (registry == NULL) registry = new MakerMap(); registry->insert( std::make_pair(className, this) ); }

36. Team Code • SoccerTeamMaker const SoccerTeamMakerSoccerTeamMaker::registerThis; SoccerTeamMaker::SoccerTeamMaker() : TeamMaker("BucklandTeam") {} SoccerTeam* SoccerTeamMaker::makeTeam(Goal* home_goal, Goal* opponents_goal, SoccerPitch* pitch, SoccerTeam::team_colorcolor) const { return new SoccerTeam(home_goal, opponents_goal, pitch, color); }

37. Project #1 • Two parts • Design (1/31) • tell me what you want to do to create a better team • Implementation (5 pm, 2/11) • deliver implementation • I will compile and check compatibility • Tournament (2/12) • In class • Last minute changes OK

38. Teams • Team A • Allen / Irsheid • Team B • Bandes / Wit • Team C • Beasley / O'Brien • Team D • Dalbke /Lopardo • Team E • Gittens / Loane • Team F • Horst /Kuhlenschmidt • Team G • Koharcheck / Kruse • Team H • Perez

39. Tournament rules • Round-robin • 1 game matches • 5 minutes / match • Scoring • Lower scoring team • get a bonus if they used less CPU time • 20% less CPU = 1 point • Ties go to the most efficient team • Degenerate strategies disqualified • Randomized elements must stay

40. Getting Started • Download my SoccerLab code • Requires (but does not include) • Buckland’s Common directory • Read the Simple Soccer chapter • consider possible improvements that Buckland suggests

41. Demo • Where is the stupidity? • Possible fixes

42. Thursday • Begin discussion of graphs / pathfinding • Tuesday • Lab using SimpleSoccer