What is the cheapest way to prevent object A from going through object B

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alt text Both object A and object B have a kinematic rigid body attached; Interpolate: Interpolate, Collision Detection: Continous Speculate.

I'm using onTriggerEnter to detect the collision.

The problem is both object A and object B is moving very fast. And as you probably already know the faster an object moves the greater the travel distance between frames. So in one frame, there is a good amount of distance between object A and objectB and in the next frame object A pass-through object B.

My question is, is there a way to detect collision immediately on the impact between object A and object B? I know about raycasting and based on what I learn it's expensive and it's mostly used for extremely fast moving objects like a bullet.

Answer 1

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Answer by black_sheep · May 30, 2019 at 11:46 PM

Raycasts are only expensive when you use hundreds of them per frame. I'm using =~20 per frame on my project and it does not hurt performance heavily. But what you should use in this case if the collider's bounds. If the closest distance from A to the bounds of B is smaller than the radius of A, than the ball is getting through B. Luckily, unity already has the functions for us. Code would look like:

 Collider ColliderB = B.GetComponent<ColliderB>();
 float distance = colliderB.bounds.sqrDistance;
 if(distance <= A.radius){
     //the direction for going away
     Vector3 vector = A.transform.position - B.transform.position;
     //goes away by the distance to the collider + the radius of the ball
     A.transform.position += vector.normalized * (distance + A.radius)
 }

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Answer 2

Answer by wyatts · May 30, 2019 at 04:17 AM

In 2018.3 Unity introduced Speculative continuous collision detection. That should help with this if you're not already using it.

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xxTheo · May 30, 2019 at 07:16 AM 0

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I may have miss spelled it but I did include "Collision Detection: Continous Speculate"

xxmariofer xxTheo · May 30, 2019 at 08:06 AM 0

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can you share the code of how you move it? probably that way you can fix it

Answer 3

Answer by gaggedegg · May 30, 2019 at 10:09 AM

@xxTheo

In OnTriggerEnter() there is a way to detect which object is colliding with which object by checking the tag of colliding object.

Suppose your ObjectA has tag "ObjA", you can check collision by:

private void OnTriggerEnter(Collider coll) { if(coll.CompareTag("ObjA")) { if(gameObject.name == "ObjectB") { Debug.Log("Collision happned with ObjectB "); } }

gameObject.name will give you the name of the object with which ObjectA is collided.

Hope this help :)

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xxmariofer · May 30, 2019 at 10:17 AM 1

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his issue is objects not colliding because they are really fast

xxTheo xxmariofer · May 30, 2019 at 08:05 PM 0

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Thank you xxmariofer, I'm very grateful for every response I get but do these people actually read what I wrote or did I do a terrible job at explaining the problem.

This is how I'm moving object B alt text

alt text

Object A is move by the character's animation. It parented to the character's right hand. The animation exits once Object A collide with object B. Which is done in a similar manner with on trigger but ins$$anonymous$$d of changing the rotational direction upon impact I ins$$anonymous$$d change an animation parameter from false to true

screen-shot-2019-05-30-at-35408-pm.png (49.8 kB)

screen-shot-2019-05-30-at-35340-pm.png (113.4 kB)

xxmariofer xxTheo · May 30, 2019 at 08:59 PM 1

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you should get better results using forces, try changing the fixedupdate code to this

  rb.angularVelocity = speed * EulerAngleVelocity * Time.deltaTime;
  rb.maxAngularVelocity = 99999999;

this will give you more precise collisions, BUT you need to make the rigidbody not kinematic to be affected by forces

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What is the cheapest way to prevent object A from going through object B

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