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Artificial Intelligence in Game Design Map Representation and Path Finding.

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Presentation on theme: "Artificial Intelligence in Game Design Map Representation and Path Finding."— Presentation transcript:

1 Artificial Intelligence in Game Design Map Representation and Path Finding

2 Path Creation StrategyMovement Path Planning Where to move toHow to get thereGet there Current location Idea: Specify goal location and let AI find path from current position to goal

3 Waypoints Path = graph structure Vertices = waypoints on path Edges between waypoints directly reachable from one another Current location

4 Waypoints and Costs Goals: –Provide waypoints that let characters reach all locations on level Can SEEK any location from some waypoint –Minimize number of waypoints Cost of path planning = O(number of waypoints) 2 Key idea: –Waypoint creation done offline (during game design) –Path planning done many times during gameplay

5 Defining Waypoints Defining waypoints manually –Usually at points where direction change necessary Corners Intersections Doors –Character must be able to directly seek waypoint from any adjacent waypoint –Character must be able to directly seek all points in map from some waypoint

6 Defining Waypoints Manually

7 Defining Waypoints Convenient to generate waypoints automatically Simplest case: simple 2D grid (square or hex) –Some points impassible (water, mountains, etc.)

8 Defining Waypoints Automatically Can often use floor tiles –Used by level designer to create level –Used to define visibility, lighting areas, where sounds can be heard, etc. –Usually triangular or rectangular

9 Defining Waypoints Automatically One waypoint per tile –Usually in center Link waypoints in adjacent tiles May still need to tweak manually –Make sure all points directly reachable from a waypoint –Add strategic waypoints (cover, shadow, etc.) –Make special waypoints for door entry, exit, etc.

10 Triangular Mesh Generation Automatically generating triangular tiles that cover level –Connect some two adjacent walls to form a triangle –Continue connecting adjacent walls and/or adjacent borders –Continue until all walls are part of some triangle

11 Waypoint Cleanup Can automatically remove some redundant waypoints –Not an endpoint (degree > 1) –All adjacent points can directly reach each other without using that waypoint –Often based on visibility (ray tracing)

12 Path Creation Path = list of adjacent waypoints Move along path using FollowPath steering –Seek close enough to next path waypoint Desired path

13 Path Creation Initial waypoint = –Waypoint in same tile as character –Closest waypoint to character May need to test each –Avoid going backward initially –Less of a problem with small tiles Seek that first waypoint Should seek this first Goal: ATM

14 Path Creation Reaching goal = –Character in same tile as goal –Character at waypoint nearest goal Arrive at goal from that last waypoint

15 Hierarchical Paths Simple maps at different levels of detail –Better than single map with thousands of points –Single best solution to minimizing pathfinding costs Connect points on high-level maps to entrances/exits on low level maps

16 Hierarchical Paths Requires hierarchical representation of location Under seat D001 Computer Lab Kilcawley Center Holy Grail At podium Room 301 Meshel Hall Me Path to room 301 exit Path from 301 exit to Meshel Hall exit Path from Meshel Hall exit to Kilcawley Center entrance Path from Kilcawley Center entrance to Computer Lab entrance Path from Computer Lab entrance to seat D001

17 Path Planning May have several possible paths from current location to goal Need to find best path –Otherwise character does not look intelligent! Goal Good path Bad path

18 Edge Costs Best path defined by edge costs –Time to travel path –Distance, etc. Best path = path with smallest total cost Goal Good path Cost = 22 Bad path Cost =

19 Terrain-based Costs Can base cost on terrain type –Grass = 1 –Desert = 2 –Forest = 3 –River = 20 Often multiply by edge distance –5 miles of desert = cost of 10 –8 miles of grass with ¼ mile river = cost of = 13

20 Other Edge Costs Danger –Cost of traveling through enemy territory = 5 * normal cost –Important part of tactical movement

21 Other Edge Costs Visibility –Dark = factor of 3 –Fog = factor of 2 –Can also add to danger Long path now best

22 Character Edge Costs Different characters may have different edge costs –Grass = 2 –Desert = 2 –Forest = 10 –River = 30 –Grass = 1 –Desert = 3 –Forest = 2 –River = 10 Squad cost = max(individual costs)

23 Non-Symmetric Edge Costs Often harder to go one direction than another –Stairs –Jumping from one level to lower level Will have different costs in each direction –Two directed edges instead of one directed edge –No second edge in one way path 42 1

24 Some characters require time to realistically make a direction change –Part of edge cost –Separate edge from location to same location Turning Costs Arrive Align Seek 5 3 4

25 Inflection Points Waypoints often near convex corners –Shortest path in wide areas –Better than putting waypoint in center of area Path given by floor tiles Faster path

26 Inflection Points Put waypoint at each convex corner Move out some safeRadius from corner Connect waypoints visible from one another safeRadius

27 Inflection Points Potential problem: jagged areas could create too many waypoints Solution: Only add waypoints for obstacles between critical areas (such as doors) –Recursively add waypoints until critical areas connected Irrelevant inflection points

28 Inflection Points Automatic creation of waypoints on arbitrary racing track

29 Path Smoothing Problem: Grid-based floor tiles with waypoints at center –Jagged paths –Too many unnecessary turns –Better to create path using non adjacent nodes

30 Path Smoothing Recursive algorithm: –Draw line between start and goal –Stop at obstacle –Continue

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