1 The FreeCiv AI Zack Ives Steve Wolfman CSE 590AG April 20, 1999

2 Cheesy Heuristics!  Mostly a series of rules with weights and randomness  Different options are evaluated for desirability  Roulette-wheel-style ai_fuzzy function decides whether AI will follow heuristics  Mostly a peer-model agent structure with a bit of hierarchy, mostly re-evaluating at each turn  Different AI’s to control cities, tech advances, units, etc.  (Though military AI is somewhat hierarchical; both coordinator to assign roles and a unit-level AI)  Each AI gets “votes” weighting decisions

3 The AI Files  aihand - main AI routines  aicity - city-level AI  aitech - tech goal AI  aitools - utility routines (choose wonders, govt)  aiunit - unit-level AI; settlers - settler AI (in server)  advdomestic - intra-city advisor (worker placement, valuation of improvements)  advisland, advscience, advtrade, advattitude - blank  advmilitary - offense & defense for units  server/citytools - city/worker reasoning functions

4 General AI Components  In aihand, several important functions:  ai_manage_units - control units, assess defense & offense & needs  ai_manage_cities - control city building, spending  ai_manage_taxes - set tax/science/luxury rate  ai_manage_government - set government style  ai_manage_tech - tech advances  No coordinating AI, but inter-module communication

5 Interesting Ideas  Bodyguard  if city already defended, defensive unit will try to find a low- defense “charge” and AI will coordinate movement  Urgency and value  Cities and domestic and military advisors collaboratively determine how valuable improvements, reinforcements, or new technologies will be, and how urgently they’re needed  Tech is valued according to needs noticed throughout movement, building, …  Sacrifice  If city is ready to be conquered, try to sell what you can

6 What the AI Emphasizes  Wonders and caravans  Diplomats If opponent’s diplomat or spy is nearby, builds diplomat for defense  Builds up money to buy improvements  If troops not serving purpose, AI brings them home  Transports try to land near destination  Republic and “We love the consul day”

7 Cheats Apparently not as many as we’d think!  AI has knowledge of full map and enemy unit locations  AI has no penalty for changing what’s being built  At higher difficulty levels, AI not constrained by maximum rates on tax, science, etc.  Civil disorder - last-second fix for unhappy city (though does suffer effects if unable to make city happy)  AI changes government for free (no Anarchy)

8 The Unit AI - Structure  In aiunit and advmilitary  Main function ai_manage_units  ai_manage_settler  ai_manage_caravan  ai_manage_ferryboat  ai_manage_explorer  ai_manage_military: based on role, auto-settle, build city, defend home, attack, fortify, run, escort, explore  Can ask for units (ai_wants_role_unit) and get closest possible match (due to tech limitations)

9 The Unit AI - What It Does  Settlers - auto_settler_findwork  Check terrain for value as city  Rate usefulness of mining, roads, irrigation, detox, etc.  Exploration  Top priority = huts  Then randomly explore  Caravan  Find city building wonder not near completion, send caravan

10 Unit AI - Military  Calculate belligerence (offensive rating), vulnerability (defensive rating) of units  Military finds victim based on attack power vs. vulnerability  Bodyguard - extra defensive unit finds vulnerable unit, becomes its bodyguard; AI synchronizes movement  Assigns roles to units (auto-settle, build city, defend home, attack, fortify, run, escore, explore)  find_something_to_kill - main controlling function for coordinating attacks  generate_warmap - assessment of distances, possibilities, & costs of moving & attacking  Choose most appealing targets, send forces to eradicate

11 Military Advisor  Assess danger due to opposing forces  Assess city defenses  If city in danger, may specify desire for coastal fortress, SAM, SDI  Based on this, may want prerequisite new technologies  Assess offensive capability and desires  May wish to build new units, acquire new technologies  Decide what to kill

12 The City AI - structure  In aicity and advdomestic  Main function in aicity is ai_manage_cities  ai_manage_city - arrange workers  ai_manage_buildings - globally important bldgs (palace & wonders)  ai_city_choose_build - locally evaluate buildings (calls domestic advisor)  Main function in advdomestic is ai_eval_buildings  individually rates each type of building according to food/prod/gold/bulb  considers luxury result in terms of new available workers

13 Money Management in the City AI  Money spent based on collaborative needs (“votes”)  Considers cities in order of greatest need  Tries to buy something for every city  Becomes frugal with remaining money if ever it cannot afford something “important” (highly desired)  Some heuristics restrict buying  Don’t spend too much at once (except for high want)  Don’t build Wonder in threatened city

14 Taxes, Luxury, and Sciency (oh my!)  Handled in ai_manage_taxes (in aihand )  Luxuries considered first  Only if government is Republic  Try to maximize population gain from “we love the consul”  Sacrifice if leaves insufficient tax rate to acquire needed funds or if unable to reach optimal celebration point  Taxes next  Gathers enough money to cover expenses plus population dependent “spare change” requirements  Science gets leftovers

15 Government changes  Simple module (partly because AI cheats!)  Different possible goal governments define track  Change as soon as next government on track becomes available  No backtracking to earlier government  Current AI hardwired to Republic track

16 Useful code  AI code is hard to reuse  AI uses many server structures unavailable to client (e.g., warmap)  Shared structures (such as tech_want ) are hard to disentangle from code  Smallest functions most useful  City calculations in advdomestic such as pollution caused/ameliorated by an improvement  Danger assessments?

17 Bonus: FreeCiv AI Fun!  “hhjj” is a structure used to calculate celebration levels in cities at various luxury levels… what does hhjj stand for?

18 Technology  tech_want structure maintains desire levels for various techs  Each component can up tech requirements  Military wants better units/transports  Missing wonder/governments cause want for enabling techs  Global AI adds hardwired want for Republic track techs  Cities want enabling techs for buildings  Global AI fudges philosophy want upward (if not developed yet)  Prerequisites of desired tech weighted  Weights reduced according to time to reach tech