AI Wander how to weight wander to return to spawn point

Question

I have a function that returns a random wander force for an enemy AI using perlin noise but I want to know how I can 'weight' it so if it gets too far away from its original spawn point, it will gradually turn around and return.

private Vector2 wanderForce() {
    perlinPos += inc;
    float tempAngle = (float) (SimplexNoise.noise(perlinPos, 100.213) * wanderPower) + startAngle;
    float dist = origPos.cpy().sub(pos).len();// distance from spawn point
    wanderForce = AngVecTools.angleToVect(tempAngle);
    return wanderForce;
}

Answer 1

If you want wandering then your perlin function that dictates motion should be based from the starting position offset i.e. xOffset AND time, and yOffset AND time. This will give true random coherent wandering. Perlin functions are deterministic so you have to have time. If you were using the above to directly establish position there would be no problem and the enemy would wander around the starting position. However, because you use this to provide a wanderforce then the link to the original starting position is broken. From that, to provide a bias to return to the original starting position (or wander back I should say) then consider if the wandering force function is towards the starting position or away. If away multiply by .9 or some such. This function could also be a function of distance i.e. over a certain distance reduction becomes higher.

This is one way. Another way that fits with using angles is to grab the difference between the wanderingAngle and the angleToOrigin and reduce that by 0.9 etc in the same way so there is a bias in direction.

EDIT Although its a bit different from above I think this is better. This code is for perlin wandering -location- around the spawn point (yes square not circle as the limit)

float xSpawnOffset = SimplexNoise.noise(spawnX+(System.currentTimeInMillis() % 1000/1000f))* wanderMaxDistance;

float ySpawnOffset = SimplexNoise.noise(spawnY+(System.currentTimeInMillis() % 1000/1000f))* wanderMaxDistance;

You need different spawn positions in there to make sure you don't get the same wander on both axis, and also so its a different wander for all enemies. This gives you a non-escaping wander. You may need to put a random into this as well in the case you have xSpawn and ySpawn being exactly the same.

Create targetWanderPosition from the original spawn position plus offsets. Then the enemy simply heads towards this point.

Vector2 wanderForce = (currentPosition.sub(targetWanderPosition)).scl(movementStrength);

So basically the enemy -continuously heads- to the ideal wanderPoint, which will itself be a wander around the spawn point.