Freitag, 2. April 2010

Behavior - Mirco vs. Macro

As we saw in the last video, the AI already behaves somehow reasonable for most of the time. However it is obvious that we can't let our AI behave determinsitc. A determinstic AI is likely to behave "stupid", e.g. our hitherto implemented AI would chase a player forever if he drives around a long wall.

It is a good idea to add some fuzziness to the AI's behavior. Our AI decides to hunt a player down if his health goes below a quarter of maximum. We could instead say that it does only do so in 80% of the time.

Or, to prevent the pitfall from above (and similar cases) let's say that whenever a certain objevtive has been pursued for more than 1 minute without success, try something else. Or every second let there be a chance of 1% to do something else. Or define a curve with the Curve Editor for a more differentiated way to determine the chance to abort your present task.

However before we finally add fuzzines to our behavior let's try and make the behavior as good as possible without.

What will be our next step?

A) One idea would be to implement a bunch of "micro behaviors" that simulate human player tactics. In a team shooter like battlefield or counterstrike, that would be something like hide & snipe, or use a tank to attack.

In Squar, the micro behaviors significantly depend on the currently available power-ups. In fact, we have until now implemented some kind of micro behavior for an enemy that has collected no power-up at all. Once it has collected a tank power-up it could activate the grenades and start destroying enemy towers. To define the micro behavior for using grenades we could consider again a priortiy chain which target to attack first. It makes no sense to attack the enemy tank because we probably won't hit it with grenades. So we could start with converters as primary targets and proceed to towers as secondary targets. It is straightforward to define a routine that let's the AI activate the grenades at once when it picks up a tank power-up and starts firing according to this priorization.

But should we keep building (and collecting) and fire at targets within range only,
or should we give priority to destroying enemy towers? This brings us to the second way of proceeding with the AI implementation.

B) While one could call A the bottom-up approach, we will now consider the top-down approach. Instead of implementing micro-behaviors and determining which to choose when later, we could try and specifiy more abstract guidelines at first.

The advantage of developing the AI bottom-up is that we can think about every plan of action the AI could take before we have to put them together. That way, we may have certain ideas of when it is advantageous to, e.g., activate a certain upgrade and when it is not.

The advantage of developing the AI top-down is that this approach makes it less likely that we have to modify our micro behaviors later when we find out that we should organize things differently (e.g., integrate or separate movement and shooting in a micro behavior).

=> I would suggest to start top-down, especially if its your own game you are developping the AI for, because you should already have quite a good idea of your micro behaviors should look like in this case.
Whenever you feel like you don't get ahead this way, switch to implementation of micro-behaviors, test them and try when it is advantageous to activate which of them. I will henceforth refer to this question by macro behavior.

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