2D Top Down Shooter: AI Ally twitching

Question

Hi, and thanks for reading,

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!

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

Answer 1

Sorry to answer my own question, but I just figured it out. Maybe it might be useful to the next guy. I think the problem had to do with estimating the future position of a target that is really close. Solved by adding a distance check, and only predicting future position if the target was over 2 units away. Code below:

 // 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);
         }
     }

Answer 2

Answer by reppiz01 · Aug 22, 2013 at 09:50 AM

Vector3 aimDirection = estHitPos - centreBulletSpawn.transform.position;

try:

Vector3 aimDirection = (estHitPos - centreBulletSpawn.transform.position).normalized;

instead.

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DMCH · Aug 22, 2013 at 12:13 PM 0

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Thanks, but the character is still twitching. Almost certain it has to do with enemies being very close, as opposed to rigidbodies bumping into one another.

reppiz01 · Aug 22, 2013 at 01:59 PM 1

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i thought of that, so my idea was to normalize, to "make" the distance bigger.

but nice that you solved it on your own.

2D Top Down Shooter: AI Ally twitching

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