Computer/enemy AI

[Hackmaster]

Hey Guys...

I've got this RPG i'm working on... which you would know if you've read my other recent posts... But i'll re-iterate.

I am using classes for the Items and spells and such, and am having no trouble there. what's really got me hung up is enemy AI.

I have some really small experience with AI. I made a pong for class...(it's kind of the right of passage, now-a-days... it wasn't even a mid-term or a final) and I had various levels of difficulty. All I did was made a procedure that got the ball 100% of the time, and one that missed 100% of the time.
I just did a randint(var, 1, 100) to see which one it would call. something like this:

code:

var hitMiss: int loop randint(hitMiss, 1, 100) if hitMiss =< 25 then      Hit else      Miss end if

that would be easy, medium would be less than or equal to 50, hard would be to 75, and super hard would be 95.

needless to say, it's not a great system. and now, if we talk about enemies in an rpg (which we are), you, at the higher levels, have to determine not only wheather they will attack or defend, but wheater they will use a spell, or just a plain attack, and if it's a spell, what spell... it just goes on and on. I'm sure that there is a better way then spinning like 5 loops with randints specific to the enemy.

this is made easier by objects (everything is) because I could just specify the percent it will succeed in the initializing proc, but is that the only way? anyone with AI experience, I would love your help with this. Thanks!

[Cervantes]

Heh, I think the AI will depend greatly upon the battle system you decide on.

I would advise trying to do it without random choices as much as possible. Try to make a formula to decide what to do, and only go to random when two options are equally probable.

[ericfourfour]

You did mention objects so here is an idea...

I find that polymorphism really helps with AI. What I usually do is have a player class. The player has a deferred procedure called chooseAction (or something similar). Then I have a real player class and an artificial player class. The real player class then has a body procedure called chooseAction which lets the user choose the attack. The artificial player class has a body procedure called chooseAction which decides what action to use based on a series of conditions.

It would look a lot like this:

code:

class Player     deferred proc chooseAction () end Player class RealPlayer     inherit Player     body proc chooseAction         put "Pick an action"         ...     end chooseAction end RealPlayer class ArtificialPlayer     inherit Player     body proc chooseAction         if ...     end chooseAction end ArtificialPlayer

This way you could easily implement ai into your program. You could also derive more ArtificialPlayers if you want different ai.

[Hackmaster]

Yes, Eric, I agree with you.

Objects are the way to go here... but using just straight if statements in that situation can lead to problems... and a really, really big if statement tree. That is my defacto way to do it, I just posted this to see if someone knew a better way.

by the way, since you know about objects and such, tell me your opininon of my stat system:

everyone has certain stats, both computer and player. then, whenever someone would do something to change the other's (or their own) stats, they call a certain function within the other. I've made lots of statprocs, like this:

code:

class PlayerCharacter import blah export blah %% stuff proc change_HP(change : int) HP := HP + change end change_HP end Player_Character

basically, I feed it a negative value if the enemy just attacked me, and a
positive one if I have just healed myself. this prcedure has a replica for all the stats, so I can make stat lowering/raising skills and such. what do you think?

[ericfourfour]

What I like to do is have a stats class. Within that class you could keep all of the stat changing procedures. If ever you need more specialized stats you could just derive another class.

However, when dealing with HP (health) I usually have two separate functions. One called increaseHealth and one called decreaseHealth. The increaseHealth returns true when maximum health is reached while decreaseHealth returns true when minimum health is reached.

How it would look:

code:

class Stats     export increaseHealth, decreaseHealth     fcn increaseHealth (amount : int) : boolean         health += amount         if health > maxHealth then             health := maxHealth         end if         result health = maxHealth     end increaseHealth     fcn decreaseHealth (amount : int) : boolean         health -= amount         if health < 0 then             health := 0         end if         result health = 0     end decreaseHealth end Stats