How to get collision point when using onTriggerEnter

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I have a number of colliders attached to isKinematic=true rigidbodies as I do not want physics to affect my objects. I am using triggers to detect collisions between the colliders and this works fine. I was wondering if it is possible to determine the collision point (Vector3) and normal using triggers? onTriggerEnter takes a Collider instead of a Collision as a parameter. If this is not possible what would be the best way to have my objects not being affected by physics in anyway yet be able to detect collisions and the point of collision as well?

Answer 1

Answer by shacharoz · Dec 09, 2014 at 09:08 AM

i accomplished this task using a Raycast upon collision (or colliderEnter) event.

 OnTriggerEnter(Collider other){
 
      RaycastHit hit;
         if (Physics.Raycast(transform.position, transform.forward, out hit))
         {
             Debug.Log("Point of contact: "+hit.point);
         }
 }

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kalibcrone · May 25, 2017 at 05:46 PM 1

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This is the method I would use, but this will give you the hit point in world space. You can also get the local point of contact for a specific object by doing the following:

 Vector3 locPos = Vector3.zero;
 RaycastHit hit = default(RaycastHit);
 Ray raycast = new Ray (drawWithObject.position, drawWithObject.transform.forward);
  
 //using a mask so that I can ignore objects I don't want the raycast to hit
  if (Physics.Raycast (raycast, out hit, 1000f, hittable$$anonymous$$ask)) 
          {
              //if pointing at the object you want to get collision point for
              if (hit.transform.gameObject == myObject.gameObject)
              {
                  //have locPos = the local position of the hit point
                  locPos = transform.InverseTransformPoint(hit.point); 
              }
          }

EarthHobbit · Jan 28 at 07:39 AM 0

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In my case, the transform.forward gave the object behind the one hit. I had to update the following code: Physics.Raycast(other.transform.position-other.transform.forward, other.transform.forward, out hit)

Answer 2

Answer by PiFLYON · Mar 17, 2017 at 10:04 PM

On this topic because of google, hope this will help future users. I used the @Sdgd method, but there is no need to use radius to me, the following code is applied on a "shield" objet. I instantiante an impact prefab (containing particles) at the collision point and tell the bullet to die.

This code is in Monobehaviour of my object, having SphereCollider Component, without Rigidbody as player bullets already have kinematic ones. This can work with any kind of collider I guess (sphere or box). This code is for whom wants to use kinematic rigidbodies with trigger colliders (as OnCollisionEnter() doesn't care about them).

The only part that is doing the job are these two lines (all Vector3s) : tmpDirection = (col.transform.position - myTransf.position); tmpContactPoint = myTransf.position + tmpDirection;

The rest of the code is for context...

     private Vector3 tmpContactPoint;
     private Vector3 tmpDirection;
     private GameObject tmpGamob;
     private Transform myTransf;
 
 void Start() {
         myTransf = transform;
     }
 void OnTriggerEnter(Collider col) {
         if (col.tag !="PlayerBullet") return;
         tmpDirection = (col.transform.position - myTransf.position);
         tmpContactPoint = myTransf.position + tmpDirection;
         col.GetComponent<BulletControl> ().Die ();
         tmpGamob= (GameObject)Instantiate(impactBouclier, tmpContactPoint,Quaternion.identity);
         Destroy (tmpGamob, 0.3f);
     }

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CrymX · May 27, 2017 at 10:52 PM 5

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This is totaly wrong

christougher · Nov 04, 2017 at 12:51 AM 0

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This totally worked great for me! :)

PiFLYON christougher · Nov 04, 2017 at 01:40 AM 0

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Nice ! :-) $$anonymous$$aybe you can upvote my answer :))

GuardHei · Jun 15, 2018 at 11:54 AM 2

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It seems that tempContactPoint is just col.transform.position. Could you please explain more details?

DageLV · Jan 22, 2020 at 02:52 PM 1

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Has errors, undefined values and just doesnt work overall, move along people.

dev_cwj · Jul 16, 2020 at 06:24 AM 1

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This is Completely wrong code.

"A + (B-A) == B"

You should know this:

In Vector3, (A - B) equals (Direction from B to A)
(A + 'Direction from B to A') equals (B)

Therefore 'myTransf.position + tmpDirection' is equals 'col.transform.position'

Check Gizmos or Debug.Log

(RTF$$anonymous$$: https://docs.unity3d.com/$$anonymous$$anual/DirectionDistanceFromOneObjectToAnother.html)

Answer 3

Answer by graham20 · Feb 16, 2015 at 01:16 PM

Depending on how big your objects are, you might get away with just using other.transform.position. I use this for playing a splash particle effect when my player hits water and it looks pretty good.

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KarlKarl2000 · Aug 12, 2021 at 02:53 AM 0

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I totally forgot about this simple solution.. slaps forehead .. thanks for re$$anonymous$$ding me. This is totally it chief

In my case I needed a detection point of contact for OnTriggerEnter2D, then spawn something at that vector3 position.

Answer 4

Here's my solution. Only works with a box collider.

localCollider.ClosestPointOnBounds(target.transform.position) does an okay job but is AABB based.

         void OnTriggerEnter(Collider target)
         {
             //print("TouchDamage trigger with " + collider.name);
 
             var damageable = target.gameObject.GetComponent<Damageable>();
             if (damageable != null)
             {
                 var localCollider = GetComponent<BoxCollider>();
                 if (localCollider != null)
                 {
                     if (CheckEdge(target, damageable, BottomRightEdge(localCollider)))
                         return;
                     if (CheckEdge(target, damageable, TopRightEdge(localCollider)))
                         return;
                     if (CheckEdge(target, damageable, BottomLeftEdge(localCollider)))
                         return;
                     if (CheckEdge(target, damageable, TopLeftEdge(localCollider)))
                         return;
 
                     CollideWith(target, localCollider.ClosestPointOnBounds(target.transform.position), damageable);
                 }
                 else
                     CollideWith(target, transform.position, damageable);
             }
         }
 
         bool CheckEdge(Collider target, Damageable damageable, Ray edge)
         {
             foreach (var hit in Physics.RaycastAll(edge, edge.direction.magnitude))
             {
                 if (hit.collider == target)
                 {
                     CollideWith(target, hit.point, damageable);
                     return true;
                 }
             }
             return false;
         }
 
         Ray BottomRightEdge(BoxCollider collider)
         {
             var bottomRight = transform.TransformPoint(collider.center + new Vector3(collider.size.x, -collider.size.y, collider.size.z) * 0.5f);
             var topRight = transform.TransformPoint(collider.center + new Vector3(collider.size.x, collider.size.y, collider.size.z) * 0.5f);
             return new Ray(bottomRight, topRight - bottomRight);
         }
 
         Ray TopRightEdge(BoxCollider collider)
         {
             var bottomRight = transform.TransformPoint(collider.center + new Vector3(collider.size.x, -collider.size.y, -collider.size.z) * 0.5f);
             var topRight = transform.TransformPoint(collider.center + new Vector3(collider.size.x, collider.size.y, -collider.size.z) * 0.5f);
             return new Ray(bottomRight, topRight - bottomRight);
         }
 
         Ray BottomLeftEdge(BoxCollider collider)
         {
             var bottomLeft = transform.TransformPoint(collider.center + new Vector3(-collider.size.x, -collider.size.y, collider.size.z) * 0.5f);
             var topLeft = transform.TransformPoint(collider.center + new Vector3(-collider.size.x, collider.size.y, collider.size.z) * 0.5f);
             return new Ray(bottomLeft, topLeft - bottomLeft);
         }
 
         Ray TopLeftEdge(BoxCollider collider)
         {
             var bottomLeft = transform.TransformPoint(collider.center + new Vector3(-collider.size.x, -collider.size.y, -collider.size.z) * 0.5f);
             var topLeft = transform.TransformPoint(collider.center + new Vector3(-collider.size.x, collider.size.y, -collider.size.z) * 0.5f);
             return new Ray(bottomLeft, topLeft - bottomLeft);
         }
 
         void OnDrawGizmosSelected()
         {
             BoxCollider b = GetComponent<BoxCollider>();
             if (b != null)
             {
                 Gizmos.color = Color.red;
                 Gizmos.DrawRay(BottomRightEdge(b));
                 Gizmos.DrawRay(TopRightEdge(b));
                 Gizmos.DrawRay(BottomLeftEdge(b));
                 Gizmos.DrawRay(TopLeftEdge(b));
             }
         }

Answer 5

Answer by triangle4studios · Jul 11, 2021 at 09:24 PM

Surely col.gameObject.transform.position is the simplest solution for the hit point.

To get the normal, Surely these will work for you:

2D -col.gameObject.transform.up

3D -col.gameObject.transform.forward

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dev_cwj · Jul 12, 2021 at 09:02 AM 0

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The hit point in OnTriggerEnter is not equal col.transform.position(col.gameObject.transform.position). Probably you think of a small object with a collider.

Think about it.. If the sphere collider is very large, then the transform.position of the sphere collider will not touch other collider let alone hit point when OnTriggerEnter situation.

So, hit point in OnTriggerEnter, OnCollisionEnter are not equal col.transform.position The real hit point is myCollider, otherCollider's contact point.

How to get collision point when using onTriggerEnter

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