onCollisionStay called on contact?

[Fox-Handler]

I have a simple question that I hope an experienced unity user can help me with. I have read that onCollisionStay is called whenever rigid body is in contact with something. But when I for instance, make a ball jump in the air and it hits a platform above it, it does nothing. So when is it called exactly?

     private var onGround = false;
     
    if(Input.GetKeyDown(KeyCode.W)  OnGround == True)
    {
    rigidbody.velocity.y = jumpHeight;
    }
     
    onGround = false;
     
    function OnCollisionStay ()
    {
    onGround = true;
    }

[3agle]

So a quick look at the documentation:

Unity - Scripting API: MonoBehaviour.OnCollisionStay(Collision)

Shows that OnCollisionStay requires a parameter, so your code should look like this:

     private var onGround = false;
     
    if(Input.GetKeyDown(KeyCode.W)  OnGround == True)
    {
    rigidbody.velocity.y = jumpHeight;
    }

    onGround = false;

    function OnCollisionStay (collisionInfo : Collision)
    {
    onGround = true;
    }

Edit:

Of course you should (and probably are?) wrap the input if code in the Update function…
Update() and OnCollisionStay() should be defined side-by-side.

[Patico]

If you don’t use collisionInfo in the function, leave out the collisionInfo parameter as this avoids unneccessary calculations. (Unity - Scripting API: Collider.OnCollisionStay(Collision))

So, OnCollisionStay () is ok and more preferable in this case.
And also:

Note that collision events are only sent if one of the colliders also has a non-kinematic rigidbody attached.

[Fox-Handler]

I read this

OnCollisionEnter is called when this collider/rigidbody has begun touching another rigidbody/collider.

and onCollisionStay is this

OnCollisionStay is called once per frame for every collider/rigidbody that is touching rigidbody/collider.

It’s just somewhat confusing the way its written. I’ve also noticed that if I were to jump and hit the side of a platform it still jumps. So it is called everytime it touches a collider? So since it hits the bottom of the platform above it and isn’t called why is this.

http://docs.unity3d.com/Documentation/Components/RigidbodySleeping.html

Here it says that when the rigid body falls to rest it starts sleeping, but if its still up in the air when it hits the above platform is it still “awake” . Sry if im abusing the terminology. It’s just hard to tell why it does what it does.

[3agle]

@Patico

So, OnCollisionStay () is ok and more preferable in this case.

Ah yeah, I guess it would help if I read the entirety of my own link

[Fox-Handler]

Thought about it for a while and the best I could come up with is that right after the ball makes impact, it falls asleep

Rigidbody sleeping happens completely automatically. Whenever a rigidbody is slower than the sleepAngularVelocity and sleepVelocity it will start falling asleep. After a few frames of resting it will then be set to sleep. When the body is sleeping, no collision detection or simulation will be performed anymore. This saves a lot of CPU cycles.

So I guess that its “asleep” right after it hits an object because all its velocity is lost. Any opinions or interest? Please feel free to correct me if I missed something. I’m only interested in how the mechanics work.

[Fox-Handler]

as a quick note I just wanted to add that when I was experimenting with sound with onCollisionStay, I noticed that the ball would jump and then fall and make a sound upon impact. However When it hits a wall overhead, it still makes a sound, but when it lands it does not.

Rigidbody sleeping happens completely automatically. Whenever a rigidbody is slower than the sleepAngularVelocity and sleepVelocity it will start falling asleep. After a few frames of resting it will then be set to sleep. When the body is sleeping, no collision detection or simulation will be performed anymore. This saves a lot of CPU cycles.

I was thinking this had to do with it losing all velocity upon impact and “sleeping”, as opposed to it jumping going into a rest period and picking its velocity back up while falling so that it is still “awake”. I’m not too sure how velocity works but as I said if I’m missing anything or understanding this completely wrong, please feel free to jump in.

[Fox-Handler]

I just wanted to correct myself really fast and state that onCollisionStay Should get called continously while in contact with an object that has a rigidbody/collider. furthermore, I believe it was the way I was implementing my code that gave me the results I had. In fact If you wanted you could actually use the (Input.GetKey()) and actually have the ball stick to the ceiling or run up the side of a wall. So that could probably be a neat idea for a game.