1. Embracing Emergent Behavior with Goal-Based AI
Kevin Dill

2. Blue Fang Games
“To create compelling, emotionally engaging games, focused on the animal kingdom, that set the benchmark for broad-based family entertainment.”

4. The Plan Motivation Kohan 2 Demo Common AI Techniques Goal-based AI
Boxy-dog Demo
Questions

5. The Plan What I Want: Or, more generally: Cunning Opponents
Responsive Allies
Replayability
Organic Credibility
Emotional Appeal
Compelling Performances
Or, more generally:
Situational Awareness
Emergent Behavior

6. Motivation, cont. Declarative AI (vs. Procedural AI)
Wikipedia: A program is “declarative” if it describes what something is like, rather than how to create it.
Developers role: not to tell the AI what to do, but to tell the AI how to decide for itself.

8. Techniques – Scripted AI
AI Follows a script, much like a movie
Script specifies exactly what will happen, when it will happen, where it will happen
Advantages:
Gives designers explicit control
Easy to write
Easy to balance
Disadvantages
Repetitive and predictable

9. Techniques – State Machines
A “state” is defined for every high-level action the AI can take
Transitions are defined to move from one state to another state
Each state has custom code to control the character while in that state

10. First Person Shooter Example
Search For Enemy
Got Ammo
Get Ammo
Got Health
Enemy Found
Enemy Lost
Get Health
Attack
Got Away, Low on Health
Got Away, Low on Ammo
Low on Health
Low on Ammo
Run Away

11. Techniques – State Machines
Advantages:
Easy to conceptualize
Easy to implement
Middleware tools exist
Disadvantages:
Complexity scales poorly as AI grows
Rampant duplication of code
Can only do one thing at a time

12. Techniques – Goal Based AI
A “goal” is defined for every high-level action that the AI can take
Each goal is assigned a priority:
Base priority (evaluate current situation)
Allocate resources
Optimize resources and calculate final priority
Highest priority goal(s) are executed

13. Goal Types Some common RTS goals: Attack – Construct Building
Defend – Repair Building
Explore – Upgrade Building
Recruit Unit – Sell Building
Recover Health – Give Resources To Ally
Research

14. Techniques – Goal Based AI
Advantages
Flexible and powerful
Complexity scales fairly well as AI grows
Can execute more than one goal at a time
Emergent behavior
Disadvantages:
Priority calculations (“Bucket of Floats”)

15. Goal Selection Basics WWHD (What Would a Human Do?)
Write down a list of the factors you would consider if you were playing the game
Some common tricks:
Bonuses – Repeat Penalties
Multipliers – One-Time Bonuses
Exponents – Actor Categories
Fuzzy Factors – Templates

16. Example: Attack Goal Base priority:
Actor value for the most desirable building or unit in the area (taking into account enemy’s economy if appropriate)
Travel Distance
Intervening targets (attack goals only)

17. Attack Goal, cont. Priority Curve: Other considerations
My CV / Enemy CV
1.2
3.0
Multiplier 1x 2x
Target CV Ratio
Priority Curve:
Target CV ratio
Min CV to assign
Low CV exponent
Max advantage
Max multiplier
Other considerations
Combined arms
Wall strength
Adjusting builder CV
* CV = Combat Value

18. Loose Ends Goal Commitment Goal Inertia Locked Goals
IF: you can’t afford something now
BUT: you will be able to soon
THEN: don’t perform lower priority goals that use the same resource
Goal Inertia
Bonus to keep doing what you’re doing
Locked Goals
Disable all other goals until current goal is complete

19. Jack the Terrier