1. Simple Soccer
GAM 376
Robin Burke
Fall 2006

2. Outline
Game Implementation
Project #1

3. Admin Homework #3 Grading Upcoming due today I am behind
but no other homework due for awhile
Upcoming
10/9: Design phase of Soccer project
10/11: Midterm
10/17: Soccer project

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

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

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

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

8. SoccerBall embeds some of the physics of its motion FuturePosition
Δx = v Δt + ½ af Δt2
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?

9. 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

10. Simple Soccer 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"

11. Team state kickoff offense defense 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

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

13. Team Behaviors Tracks passes Tracks ball Controlling player
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

14. 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

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

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

17. State Machine Global state Wait ReceiveBall KickBall Dribble ChaseBall
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

18. SupportAttacker ReceiveBall ChaseBall Dribble ReturnToHR KickBall Wait
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

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

20. Key Calculations Is a pass safe? Is it possible to shoot?
predict trajectory of ball
predict closest intercept of each opponent
Is it possible to shoot?
test positions along the goal mouth
does this randomly
Who to pass to?
tests all of the teammates for validity and nearness to goal
Where to place the pass?
out of opponents range
within receivers range

21. Demo

22. SteeringSoccerLab Not the same as Buckland's
Allows multiple team implementations
Records the CPU time used by each AI implementation
Don't use Buckland's code

23. Abstract class AbstSoccerTeam Abstract functions
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

24. 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

25. AbstractFactory

26. 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)

27. 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

28. Project #1 Two parts Design (10/6) Implementation (5 pm, 10/17)
tell me what you want to do to create a better team
Implementation (5 pm, 10/17)
deliver implementation
I will compile and check compatibility
Tournament (10/18)
In class
Last minute changes OK

29. Tournament rules Round-robin Scoring
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

30. Monday
Lab using SimpleSoccer