Detect from what direction a shere collider was hit

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I've read a few posts on a similar question but most seem to talk about box colliders and sides. in my case the collider would be a sphere.

Would using raycast tell me what direction the hit occurred on the sphere collider. is this even possible?

Answer 1

Answer by Killhatch · Apr 11, 2015 at 07:11 PM

The collision object you are passed in OnCollisionEnter contains a field called Contacts. A ContactPoint class has a Point field (of type Vector3). To find the incoming direction of the hit, subtract the contact point's position from the that of the colliding object.

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_Gkxd · Apr 11, 2015 at 08:34 PM 0

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Every contact point contains a normal vector, which already gives you the direction from which an object is hit, so there is no need to subtract two positions. (Also, the position of a collider isn't necessarily its center for some objects, but that's not something most people have to worry about.)

RaycastHit has a similar normal vector too.

Killhatch · Apr 11, 2015 at 09:18 PM 0

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That is incorrect. The normal field contains the normal vector of the triangle that was hit. alt text

I would not call that "the direction from which an object is hit". The RaycastHit returns the same thing.

We can agree that the position of the collider isn't necessarily accurate but as you say yourself it is not something most people have to worry about.

contactnormal.png (105.1 kB)

_Gkxd · Apr 12, 2015 at 04:43 AM 0

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I guess it's just a difference between how we define what "direction hit" is. When I look at that picture, the sphere is being hit in the direction of the red arrow.

In this case, "direction hit" can also be defined as the velocity that the black line is travelling in right before it hits the sphere. It really depends on context and what effect you want to create.

Killhatch · Apr 12, 2015 at 09:52 AM 0

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OP has not specified it clearly but it might very well be what you mean. We will have to ask for an elaboration.

Answer 2

Answer by lordlycastle · Apr 11, 2015 at 09:28 PM

You can find the direction the sphere was hit from, by finding out the direction of the velocity of the projectile that hit it. Simply implement OnCollisionEnter method in the collider that is going to get hit, and find the velocity of the colliding object using it’s rigid body. Remember you’ll have to inverse that vector to get the absolute direction, but that depends on what you plan on doing with it.

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I_Am_Gamer · Apr 13, 2015 at 12:24 PM 0

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Hopefully this will help any confusion due to my description lol.

alt text

Green arrow is the player object and its direction. Circle is the sphere which is child object. Red arrow points to the position at which the sphere was hit.

alt text

I need to know the position the hit occurred so I can instantiate something at (near to the sphere) in that direction.

spherecollision2.png (2.4 kB)

spherecollision.png (2.5 kB)

lordlycastle · Apr 18, 2015 at 01:59 AM 1

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@I_Am_Gamer The Collision class has a variable Contacts, that contains all the contact points. Read up the scripting API. It also has relative velocity, and you cal always find the absolute velocity if you need it.

 void OnCollisionEnter(Collision collision) {
     ContactPoint contact = collision.contacts[0];
     Quaternion rot = Quaternion.FromToRotation(Vector3.up, contact.normal);
     Vector3 pos = contact.point;
     Instantiate(explosionPrefab, pos, rot) as Transform;
     Destroy(gameObject);
 }

Detect from what direction a shere collider was hit

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