Actions abstraction in Goal Oriented AI

Question

I am back with another question about Goal Oriented AIs.

To explain my problem, I will use a specific example.

In my game, population nodes are spawned on a world map, and important characters called "Migration leaders" can spawn, take in migrants, lead them to a good spot, and then establish a new population node there and finally despawn as they have served their one-time purpose.

What I want to achieve is having only one action called "MoveToTarget" which has no pre-conditions apart from having a target location, and has the effect of setting the fact "Reached target location" to true, which itself is the precondition for other actions. Not sure this is the right way to structure that in the GOAP but that's not exactly my problem, at least I do not think so.

My problem is that, since you can't work with actions that take in an argument, I have little notion of how the AI should determine the location which it will move to when the "MoveToTarget" action triggers, for the following reasons :

• Depending on the character type and generally what is happening, each character will think differently about where they're interested in going. Furthermore, what happens when I have to interrupt the AI's "plan" for some reason ? The original target location for, say, transporting migrants is lost !

• I do not which to make different actions like "MoveToMigrationTarget" because then I'll have to make many MANY more actions, like "MoveToCombatTarget" or "MoveToRessources" and I do not think that will work as that will make me have to keep a "Migration target", a "Combat target".. in memory even for characters that have nothing to do with either of those.

So my question exactly is, where is the AI supposed to do the "practical thinking" in a GOAP ? The Actions themselves must be abstract, and can't take in any argument so I have to somehow have target location(s) in memory and have the GOAP planner know which target corresponds to which action.

I could also extend that question to basically any action that need a specific target / object to work.

Answer 1

You could have a universal method (public static void MoveToTarget(Transform targetLocation, GameObject objectThatNeedsMoving) {/.../}) that can be reused, regardless of the goal location, as long as you intend for their pattern of movement towards the path to be the same. For instance, you may intend to simply lerp to that location, regardless of character type.

If you need a variety of path patterns, you could inspect the GameObject to determine what kind of object it is, and what pattern you would choose to follow. For instance, perhaps a GameObject has a script called Monster attached to it, so I can see if the passed in Object has a Monster script, and if it is not null, tell it to follow a parabolic curve rather than a straight line. From there, forward the targetLocation and gameObject to your method for moving in that special pattern, perhaps you would have named it MoveToTargetParabolic(Transform targetLocation, GameObject objectThatNeedsMoving) or MoveToTargetMonster(Transform targetLocation, GameObject objectThatNeedsMoving).

Answer 2

Generally your problem seems to be focusing on actions more than goals. Your migrant characters have the goal of establishing a new population center, not going to point a. This goal can remain unchanged, even if the target location becomes unavailable, or if a better location becomes available.

Establishing a population center can be broken down into prerequisites: having migrants and being at the location. Since being at the location is a prerequisite for the goal, the character should search for a good location, and then initiate an attempt to move there (this would initiate the moveToTarget action.) When the current action of a character no longer favors their goal, they will stop perusing it (ie: if they arrive at a good location along the way, the prerequisite is met, no need to keep moving). As for if the location becomes unavailable, moveToTarget should fail/become impossible to initiate. The character will have to look for other means to satisfy the "good location" prerequisite.

You can continue breaking down prerequisites into less abstract levels until you get something you can implement. For example a good location could be broken down into having food, water, ect.

The practical thinking occurs by characters selecting the "best" action available, when one action becomes infeasible/impossible, it is no longer a candidate for the best action, and something else must be selected as a means to satisfy the goal prerequisites.