Unity Issue: AI Ally Twitching (Top down shooter)

Kilgore__Trout

Hi guys, posted this on unity answers. Thought i'd try it here to see if anyone can figure it out.



I've encountered a problem with an AI ally (armed with a gun) twitching (rotating rapidly side to side on the Y axis) when enemies get close. I think it's either caused by the ally and enemy rigidbodies bumping off one another, or the ally trying to keep its weapon pointed at an up close enemy.


I tried changing some of the properties of the rigidbody (mass, drag, angular) to no avail. Also commented out the code which rotates the ally toward the enemy. This prevents the twitching, but the ally isn't much use if it doesn't aim at enemies.


Update 1: Increasing the radius of the ally's capsule collider from 0.3 to 0.6 seems to have solved the problem. The enemies can't get so close now. This might suggest that the targetting/rotation code for the ally doesn't handle close up calculations very well, rather than it being a problem with collisions between rigidbodies. Using a oversize collider isn't a very good solution though, so an alternate one would be nice.

I've included the code the ally uses to rotate/track targets. If you need any more info, please ask. Thanks!

1. public void RotateToTarget()
2. {
3. // Predict time it will take a bullet to reach enemy
4. float secsFlightTime = (targetPosition - centreBulletSpawn.transform.position).magnitude / bulletSpeed;
6. // Get current velocity of target
7. Vector3 targetMovePerSec = target.rigidbody.velocity;
8. targetMovePerSec.y=0;
10. // Predict the future position of the target
11. Vector3 estHitPos = targetPosition + targetMovePerSec * secsFlightTime;
13. // Get the rotation needed to hit the enemy
14. Vector3 aimDirection = estHitPos - centreBulletSpawn.transform.position;
16. // Rotate turret to face that position
17. Quaternion neededRotation = Quaternion.LookRotation(aimDirection);
18. transform.rotation = Quaternion.Slerp(transform.rotation, neededRotation, rotationSpeed * Time.deltaTime);
20. //transform.rotation = neededRotation;
21. }

Kilgore__Trout

Just after I posted, I remembered I'd thought of a possible solution last night, but hadn't tried it yet. Can't delete the post, so may as well bring closure. Figured it might have something to do with trying to estimate the future position of an enemy who is already really close, so I added a distance check and only estimated the future position of the target if it was more than 2 units away.

Here's the new code:

// Estimates the target's position when the bullet will hit, and rotates toward it
public void RotateToTarget()
{
// Do a distance check to see how far away the enemy is
float distToEnemy = Vector3.Distance(position, targetPosition);

// If the enemy is more than 2 units away
if(distToEnemy > 2)
{
// Predict time it will take a bullet to reach enemy
float secsFlightTime = (targetPosition - centreBulletSpawn.transform.position).magnitude / bulletSpeed;

// Get current velocity of target
Vector3 targetMovePerSec = target.rigidbody.velocity;
targetMovePerSec.y=0;

// Predict the future position of the target
Vector3 estHitPos = targetPosition + targetMovePerSec * secsFlightTime;

// Get the rotation needed to hit the enemy
Vector3 aimDirection = (estHitPos - centreBulletSpawn.transform.position).normalized;

// Rotate turret to face that position
Quaternion neededRotation = Quaternion.LookRotation(aimDirection);
transform.rotation = Quaternion.Slerp(transform.rotation, neededRotation, rotationSpeed * Time.deltaTime);
}

// Else, the enemy is less than 2 units away
else
{
// Get the rotation needed to hit the enemy
Vector3 aimDirection = (targetPosition - position).normalized;

// Rotate turret to face that position
Quaternion neededRotation = Quaternion.LookRotation(aimDirection);
transform.rotation = Quaternion.Slerp(transform.rotation, neededRotation, rotationSpeed * Time.deltaTime);
}
}