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Ch 7.1: Using a Spatial Database for Runtime Spatial Analysis

Ch 7.1: Using a Spatial Database for Runtime Spatial Analysis. Purpose. Dynamic environment – player’s actions are unpredictable, player can change environment (i.e. game has a physics engine) High levels of interactivity, coupled with dynamic environments, require sophisticated AI

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Ch 7.1: Using a Spatial Database for Runtime Spatial Analysis

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  1. Ch 7.1: Using a Spatial Database for Runtime Spatial Analysis

  2. Purpose • Dynamic environment – player’s actions are unpredictable, player can change environment (i.e. game has a physics engine) • High levels of interactivity, coupled with dynamic environments, require sophisticated AI • AI needs way to process information in environment

  3. Example

  4. Possible Representations • Static • Place “hints” in the game world • Analyze world and build a data structure • Dynamic • Influence maps (establishes implicit boundaries between opposing forces) • Want a solution that represents all relevant data

  5. Spatial Database • 2D grid overlaid on top of the game world • Multiple independent layers superimposed on the same grid • Most useful layers: • Openness • Area occupancy • Area search • Line-of-fire • Light level

  6. Use of Spatial Database • Combine multiple layers to compute composite desirability values • AI examines nearby cells, moves accordingly • Implicitly coordinates behavior of multiple AIs

  7. Openness Layer • Needed for tactics which require certain amount of open space (ex – “Circle of Death”) • Cells contain values that indicate how close it is to a wall/object • If blocked, value = 0; else, value = 1 • Propagate influence of 0-value cells to neighbors

  8. Example Propagation

  9. Uses of Openness Layer • Can determine the direction of increasing/decreasing openness • Can use this gradient to find the middle of the room (high openness) and the walls (low openness)

  10. Area Occupancy Layer • More for RTS games, “fog of war” • Each unit propagates an area of influence around itself • Cells with nonzero values are visible • Units update grid values when moving (or created/destroyed) • Used in other genres for AIs to know how populated an area of the world is

  11. Uses of Area of Occupancy Layer • Higher values if cells are closer to more agents • Avoid moving into occupied areas when maneuvering • Difference between “fog of war” and occupancy – values depend on distance between AI units for occupancy, not “fog of war”

  12. Area Search Layer • Games with stealth components, AI needs to search for player • Scouts in RTS games, uncovering the map • Initialize the layer to zero values • Increment cell values as they enter AI agent’s view arc

  13. Implementation for Stealth Games • Guard considers surrounding area a “hidden map” • Has clues to aid search; knows where to begin and where to look • Store database of evidence, bias search towards it • Decay database over time (randomly?) • Automatically coordinates multiple NPCs

  14. Thief 3

  15. Line-of-Fire Layer • For game genres with ranged weapons • Want to ensure that AIs don’t block each others’ shots • Each cell starts as zero • When AI aims, propagates values in its viewing arc • Each AI ignores its own contribution (temporarily subtract value before reading)

  16. Light Level Layer • Needed for games with dynamic lighting • Stealthy characters/vampires would avoid light, guards would prefer light • Initialize to 0s • Each light source propagates values based on current radius, lighting type, intensity, etc.

  17. Handling 3D Environments • Single 2D grid can’t represent vertically overlapping areas • Solution: transform grid into one of sub-grids • Assign a sub-grid to each different height • Works well for human environments

  18. Potential Issues • Spatial database system could be a performance nightmare • Large grid + high resolution + large # of AIs + frequent updates = • Updating certain areas constantly is a waste of time/memory

  19. Optimizations • Pare size of the grid (make cells represent larger areas of environment) • Don’t recalculate static layers • Decompress sub-grids as needed • Combine cells if all values are the same • Use short-circuit evaluation • Update cells only when used

  20. Sources • Tozour, Paul, “Using a Spatial Database for Runtime Spatial Analysis,” AI Game Programming Wisdom 2. • HL2 video - http://www.zippyvideos.com/212120745294215.html • Thief 3 video - http://media.pc.ign.com/media/015/015244/vids_4.html • BSOD image - www.palindrom.agava.ru/en.intro.bsod.html

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