1. Artificial Intelligence in Game Design
Terrain Analysis

2. Terrain Analysis
Features of terrain have good/bad influence over map areas
Good locations  Possible goals to move to
Bad locations  Places to avoid when moving
Cover = good
High ground = good
Open space = bad
Slow to travel through = bad

3. Terrain Analysis
Must be based on realistic estimates of how terrain affects play
Game engine based
Example: Engine reduces hit probability by 50% when target > 100 feet above
Factor into NPC deciding to move to high ground
Most likely for “overhead perspective” combat games
Visibility based
Relevant for FPS games
Example: NPCs in shadow not visible to player
NPC should move to such areas

4. Terrain Analysis “Dangerous” terrain elements
Things that can damage character
Terrain that might expose character to attack
Areas that force character to move slowly
Areas where character has chance of getting stuck
Often related to edge costs, but not always
Some slow terrain offers cover
Forrest, darkness, etc.
GASOLINE

5. Terrain Example -1 -2 -3
GASOLINE

6. Terrain and Influence Areas have influence over other areas Examples:
High ground
Shadow
Cover
Influence over
Influence over
Influence over
Influence over

7. Levels of Influence
Amount of influence may depend on relative values between areas
Influence of area i over area j for some property P = f (P(i), P(j))
May be simple difference k × (P(i) – P(j)) Example: height(i ) = height(j ) = k = Influence_Strength (i, j ) = 8
Must be based on how game engine defines advantage of area i over area j
High influence over
Low influence over

8. Influence and Distance
Usual assumption: Influence of terrain decreases with distance
Linear dropoff out to some “range” R
Influence_Strength (i, j ) treated like “strength”
Given distance D (i, j )
Influence (i, j ) = Influence_Strength (i, j ) × (R – D(i, j ) )/R
Influence over other areas 40 feet below this one at distances 1 - 4
Influence over area 3 units away and 40 feet lower = 2.0 5 4 3 2 1 1 2 3 4 5

9. Influence Example B Height = 50 A Height = 40 D Height = 30 C
Influence Over A B C D -
20 * 0.2 * 0.5 = 2.0
10 * 0.2 * 0.25 = 0.5
10 * 0.2 * 0.75 = 1.5
30 * 0.2 * 0.75 = 4.5

10. Total Influence Influence over others – influence others have over it
Total influence of area i = Σ influcence (i, j) – Σ influcence (j, i) j j B
Height = 50 A
Height = 40 D
Height = 30 C
Height = 20
Total Influence A B C D
– 1.5 = 1.0
= 8.0
= -8.0
= -1.0

11. Combined Influences Total influence may involve many factors
A is lower ground than B
A has cover while B does not
Influence of cover = 4.0
Influence of B over A from height = 1.5
Influence of A over B from cover = 4
A has total influence over B of 2.5 B
Height = 50 A
Height = 40

12. Combined Influences Must also factor in unit-based influence maps
Good location controlled by enemy is bad place to move to!
Example:
Influence of B over D from height = 2.0
Influence of D over B from cannon = 3.0
Total influence of D over B = 1.0
B no longer a good place to move to!
May not know that until you move there! B
Height = 50 D
Height = 30 C
Height = 20

13. Map Analysis Complex analysis of crucial map areas Goals:
Crucial for randomly generated terrain
Example: Leaders: Clash of Nations
Goals:
Identify chokepoints between different game zones
Identify hotspots that have influence over chokepoints

14. Map Analysis
Smoothing (image analysis) used to remove small areas of impassible objects
Area around impassible tile T passible  T removed from analysis

15. Map Analysis Random path generation often used
For large number of examples:
Select two random waypoints
Use Dijkstra/A* to find shortest path between them
Keep track of waypoints on path
Store waypoints, path for each
Waypoints with large number of paths are candidate chokepoints

16. Map Analysis Verify chokepoints
For each candidate chokepoint rerun tests that passed through it
If resulting paths significantly longer (or infinite!) chokepoint confirmed

17. Tactical Waypoints in Dungeons
More difficult for dungeon world
Tile centers may not give all good tactical locations
Best tactical location based on cover
Best tactical location based on shadow

18. Tactical Waypoints in Dungeons
Automatic creation
Subdivide area into smaller tiles
Find tiles with highest influences over other tiles
Create new waypoints there
Computationally intensive, but only need to do once
Influence over other points, few points with influence over it