19-05-2003 23:54									#1
	Strategies Increase the size of your Attachments

Strategies

It's good to be back. Old Nellie gave up the ghost and has gone to computer heaven someplace out there in cyberspace.

Ahenobarb wrote in another thread:

quote: I created my own strategy, but cannot figure out how to make the AI use it.

The short answer is that you have to use the SetStrategicState and/or ConsiderStrategicState functions, but this isn't at all helpful. MrOgre's explanation in the AI Customization doc is really quite good as far as it goes. It's just, er umm, a bit abbreviated.

I started to write this before my computer broke down. I've got a back up computer - but it's modem doesn't work. So,
I broke down and got an ASDL connection, and it's finally come through. In the meantime, rather than wasting time lurking around the other forums, I've been doing a lot of programming and writing. Here's the long answer.

	19-05-2003 23:56									#2
	Lose 30 kilos (of popups)

1: Personalities and Civilizations

In Civ2 and Civ3 an AI civ's strategy is determined by the civ itself, i.e, there are a few flags which are set on a civ by civ basis and determine that civ's strategy. In CTP it's a bit more complicated:

quote: [MrOwl] We also have AI personalities. ... So different opponents will "feel" different because their play styles will be so different. ... Each civ comes with two distinct personalities that are randomly chosen.

(MrOwl is Steve Mariotti, the lead programmer for Civ:CTP; the quote is from a Poly chat on Oct 3, 1998.) Once the civ's leader is chosen by the computer, it's the flags in his personality structure that determine that civ's base strategic and diplomatic states. For example, if you're playing against the Irish and the computer has given them Brian Boru (who has the Stalin personality) as a leader, the relevent data is:

code:

PERSONALITY_STALIN {
  Exploration: Minimal
  Expansion: Average
  Discovery: Military
  Conquest: Agressive
  Trustworthiness: Chaotic
  Alignment: Evil
}

	19-05-2003 23:57									#3
	Support Apolyton or Terrorists Win

2: Strategic States

So, first, what's a strategic state? Essentially, a strategic state is given by the data contained in a STRATEGY_XXX_DEFAULT strategy. If you look at, say, STRATEGY_MILITARIST_DEFAULT and imagine removing any of the data that can be changed, you're left with a sort of template. A strategic state can then be thought of as any acceptable set of data that can be used to fill in this template. (Actually, this isn't completely accurate because you can add new GoalElements and BuildListSequenceElements. Also, there's some data in STRATEGY_ATTACK and STRATEGY_LAUNCH_NUKES that's not in any of the default strategies, but it's a good approximation.)

Next, what is it for a strategic state to be initialized? There is a SLIC event, InitStrategicState(int_t), that occurs on turn 0 (and, IIRC, only on turn 0). When it occurs, the computer loads the correct default strategy for player[0]. If you've written your own default strategy, you can initialize it along these lines:

code:

HandleEvent(InitStrategicState) 'Example_InitAtStart' post {

    if (player[0].owner == 2){
         SetStrategicState(player[0].owner, StrategyDB(STRATEGY_AHENOBARB_DEFAULT));
    }
}

	19-05-2003 23:58									#4
	Got spare money?

3: Developing Personalities

What about all those other little strategies in strategies.txt? After the InitStrategicState event has occured, on turn 0 (and on every succeeding turn) the NextStrategicState event occurs. This is used to transition from the player's initial strategic state to what might be called his base personality strategic state and also to patch in partial strategies that allow the AI to react to different game dependent situations.

Just as the Discovery flag in the player's personality structure determines what DEFAULT strategy is initialized, so also the Exploration and Expansion flags determine which of the EXPLORE_XXX, SETTLE_XXX, and XXX_START strategies are used. The relevent data here is:

code:

STRATEGY_EXPLORE_NEAR  
 Loaded for players with personality that has Exploration:Minimal.

STRATEGY_EXPLORE_FAR 
 Loaded for players with personality that has Exploration:Medium.

STRATEGY_EXPLORE_WIDE  
 Loaded for players with personality that has Exploration:Wide.

----------

STRATEGY_AGRESSIVE_START 
 Loaded for players with personality that has Exploration:Wide or Exploration: Medium.

STRATEGY_CAREFUL_START  
 Loaded for players with personality that has Exploration:Minimal.

----------

STRATEGY_SETTLE_COMPACT 
 Loaded for players with personality that has Expansion:Minimum. 

STRATEGY_SETTLE_COMPACT 
 Loaded for players with personality that has Expansion:Average.

STRATEGY_SETTLE_LARGE 
 Loaded for players with personality that has Expansion:Maximum.

Last edited by Peter Triggs on 20-05-2003 at 00:07

	19-05-2003 23:59									#5
	Enter the AD-FREE zone

4: Priority Based List Processing

In the chat mentioned above, MrOwl remarked that the AI used an 'established AI principle' which he described as "priority-based list processing (give me the best 15 things to do here)". This must be his own terminology because I haven't been able to find out anything about it through Google. However, you can see priorities all over the place and one place they're used is in:

quote: VOID ConsiderStrategicState(player, priority, dbIndex) Merge the Strategy whose StrategyDB index is 'dbIndex' into the player's initial (default) strategic state with a priority of 'priority'.

MrOgre describes this operation as follows:

quote: When a new strategy is “considered” using ConsiderStrategicState, parameters defined by the new strategy record overwrite the values defined in the base strategy (set by SetStrategicState). As strategies are merged in values are overwritten in an order determined by their priority; lower priority strategic state records being overwritten by records that were considered with a higher priority. In this way you can have two handlers fire that load strategy records that modify the same parameter. The changes caused by the strategy record with the higher priority will be the one used.

This is how the AI adjusts to changing game situations. I just described how some of the strategies in strategies.txt are determined by the AI civ leader's personality. The others are loaded under circumstances that we largely don't know about. But here's an example in a reply by Richard Myers to a question of WesW's:

quote: WW: Finally, at the bottom of the file, there is a list of Defense Strategies. What triggers these? I know nothing about when they come into effect, or how long they last. RM: At the beginning of each turn, the Maximum Threat for an AI is computed, and as the threat increases, the minimum garrison in each city increases. Essentially this is a way to make sure the AI protects its cities with more units when things get more dangereous later in the game. If you add a new strategic state that is triggered every turn (with a priority > 1000 or so) which redefines the garrison counts, then you can use your own system.

The war strategies (STRATEGY_SEIGE, STRATEGY_ATTACK, STRATEGY_DEFEND, and STRATEGY_LAUNCH_NUKES) may be (in fact, I suspect must be) handled in some special way. I have my own system for building units and while developing it found myself in a situation where an AI civ should have been building cruise missiles but was building infantry units instead. They were coming from the data in STRATEGY_SEIGE, which I thought I had overridden. So I whipped out the offending data and my system is working fine (fingers crossed).

But, anyway, this is where things really do begin to be fun. You can write your own strategies (which can be almost any subset of the data in a default strategy) and then use the ConsiderStrategicState function in a NextStrategicState handler to get an AI civ to use them in whatever circumstances you care to define.

For example, it's the GOALS section of a strategy that determines how the AI moves it's units around the map. The priority field in each GoalElement sets a base priority for how much it would like to make a move of that kind. If it's an attacking move, however, the data in the FORCE MATCHING structures determine how strong the army has to be before it will actually make the move (which may be suicidal). So, if you wanted an AI civ to attack sort of like the Barbs, you could define a strategy like this:

code:

STRATEGY_BANZAI {

      GoalElement { Goal GOAL_ATTACK	    
	      Priority   800000  MaxEval  25 MaxExec  25 }

	GoalElement { Goal GOAL_HARASS_CITY 
	      Priority   800000  MaxEval  25 MaxExec  25 }

	GoalElement { Goal GOAL_HARASS      
	      Priority   800000  MaxEval  25 MaxExec  25 }

	GoalElement { Goal GOAL_PILLAGE	    
	      Priority   800000  MaxEval  10 MaxExec   5 }

	GoalElement { Goal GOAL_SEIGE	    
	      Priority   790000  MaxEval  25 MaxExec  10 }
    
        Offensive {
		AttackMatch   0.0
		DefenseMatch  0.0
		RangedMatch   0.0
		BombardMatch  0.0
		ValueMatch    0.0
         }

        Defensive {
		AttackMatch   0.0
		DefenseMatch  0.0
		RangedMatch   0.0
		BombardMatch  0.0
		ValueMatch    0.0
	}

        Harass {
	      AttackMatch   0.0
		DefenseMatch  0.0
		RangedMatch   0.0
		BombardMatch  0.0
		ValueMatch    0.0
        }
}

	20-05-2003 00:32									#6
	Support Apolyton buy from Amazon

Here's that file I've been looking for:

Attachment: strategyexample.slc
This has been downloaded 9 time(s).