Physics - how do I set the following:

1) Define the movement for a rigid body's velocity
2) If two rigidbody's colliders collide, the rigid bodies stop and do not pass through each other
3) When scenario #2 occurs involving a non-moving, but not static rigidbody, NO PUSHING OCCURS.

Basically, I want to control my own movement and use Unity's physics to *prevent* movement, but NEVER to trigger new movement.

I've tried setting the velocity on the objects every frame... but objects still end up pushing each other around.

 

A simple way to do this:

Code (CSharp):

1.  
2. void OnCollisionEnter2D(Collision2D other) {
3.   other.GetComponent<Rigidbody2D>().isKinematic = true;
4.   GetComponent<Rigidbody2D>().isKinematic = true;
5.   other.GetComponent<Rigidbody2D>().isKinematic = false;
6.   GetComponent<Rigidbody2D>().isKinematic = false;
7. }
8.  

Maybe not the most efficient way to do it, but it should work...

 

I don't understand how the above would work. Can you explain? In the end, don't both continue reacting as normal?

 

Darn, turns out it doesn't work with the 2D physics. I did something similar with the 3D physics way back, and just converted that. Unfortunately I didn't test it until now, which was stupid.

What it is supposed to do is turn the colliding objects into kinematic objects (static might have been better), which should turn off movement and rotation. Then they are turned back to non-kinematic and they should be free to react to forces again. But it doesn't seem to work properly with 2D physics. It kinda works, but after some research I see why it doesn't work completely.

So, I'm sorry for that suggestion :-(

 

So, I did some tests. I had a number of boxes moving about and tried to find a way to minimize reactions on collision.

I got the best result when I used a Rigibody2D set to Kinematic, Simulated on and Use Full Kinematic Contacts to on. Then I placed a tiny script on the objects:

Code (CSharp):

1. using UnityEngine;
2.  
3. public class test : MonoBehaviour
4. {
5.     void OnCollisionEnter2D()
6.     {      
7.         GetComponent<Rigidbody2D>().velocity = Vector2.zero;
8.     }
9. }
10.  

WIth low speeds this works perfectly. With higher speeds there might be some slight overlap, since they don't push apart. However, this could be compensated for by making their colliders slightly larger.

 

When I tried this with Kinematic turned on, the objects didn't collide with each other. Did this work for you?

 

Yes, but you have to turn on both Simulated and Use Full Kinematic Contacts.

 

Okay. Nervous, but will try this out.

 

Weird, I did try that and I did get slight overlaps any way. (I guess I shouldn't have delete my test scene, now I have to redo it to try again )

 

Here is a screenshoot of my new test scene:


I did use a pretty fast speed, just to make sure that the overlaps was more visible. However, I do get overlaps at smaller speeds as well. On of the scripts set a start velocity of the Rigidbody2D, nothing more and the other script does set the velocity to zero at OnCollisionEnter2D.

I found it a bit weird that Continuous Collisions didn't get nice, precise intersections.

 

Yes, I did only set an initial velocity. All the brown object started a bit away and got a velocity towards the gray object (which was stationary). Once I did the Rigidbody2D.velocity change I didn't touch it again until the collision. So there shouldn't be anything else but the physics at work.

 

oh thank god, do you think this bug will get fixed by June?

 

Okay, I tried this out.

What happened was the callback was correctly called when I intersected another collider object... but it didn't stop the objects from moving through each other if the velocity is updating during the FixedUpdate() function.

Look, what I want is simple:
If any objects try to push through each other, they stop. They don't move each other. They just stop.

Why can't this be easy? I am angry and frustrated.

I want to set my desired velocity in one place. Then be told if I hit something - and if I'm hitting something NOT move through it. This can't be rocket science.

Instead, it's telling me that I hit something, but continues to push through it. That's because the OnCollisionEnter2D function is only fired once when the first touch happens, not every time.

Now, to get what I want, I need to be doing constant movement checks... keeping track of all of the contact points... F*** THIS.

I just want my objects to not move through each other and not push each other around.

 

@MelvMay here's an abbreviated version of what I'm doing:

Kinematic, Use Full Kinematic Contacts, Simulated, etc. Just like you mentioned in the 2d build thread

Code (csharp):

1.  
2. ... class... MonoBehaviour etc
3. {
4.    
5.     public virtual void OnCollisionEnter2D(Collision2D coll)
6.     {
7.         MyRigidBody.velocity = Vector2.zero;
8.     }
9.  
10.     private Vector3 _lastVelocity;
11.  
12.     void FixedUpdate()
13.     {
14.           // Apply the final velocity
15.         _lastVelocity = GetCurrentVelocity();  // This is off elsewhere in the game scripts. Just trust me, it provides a non zero vector3.
16.         MyRigidBody.velocity = _lastVelocity;
17.  
18.         // I actually want to freeze movement if the body's velocity is almost zero...
19.         if ( _lastVelocity.magnitude <= 0.05f )
20.             MyRigidBody.constraints = RigidbodyConstraints2D.FreezeAll;
21.         else
22.             MyRigidBody.constraints = RigidbodyConstraints2D.FreezeRotation;
23.  
24.         int contactCount = MyRigidBody.GetContacts(contacts);
25.         if ( contactCount > 0 )
26.         {
27.             Debug.LogFormat("Contact count: {0}", contactCount);
28.             MyRigidBody.velocity = Vector3.zero;
29.         }
30. }
31.  

I am getting 6-12 contact point 2d objects.

However, instead of the objects stopping (see https://forum.unity3d.com/threads/physics-how-do-i-set-the-following.449027/) - the two colliders slowly push through each other like molasses.

I. Just. Want. Hard. Stops.

Why is this so complex to achieve.

 

MyRigidBody's velocity is NOT changed anywhere else in the game scripts. It's only set here... and I am setting it to Vector3.zero if the contacts is greater than 0.

THIS THING SHOULD BE IMMOBILE, not pushing through like jelly through a cheap plastic collander.

 

Don't get me wrong, running through walls inconsistently is fun too. -_-

"50% of the time it works everytime"

 

Example of what's happening

 

No effect. I still run through the other object's collider.

 

@MelvMay

I have calmed down now.

I posted this thread in non-experimental land because I wanted to reach an audience for what seemed like a basic need:

"No push back when two objects collide."

When that didn't work, I went back to Experimental land to try to determine if two objects were touching using your new feature - and used that to try to make the velocity zero.

I realize this has to be as confusing for you to follow as it is for me to try to figure out. It feels basic. It's instead a lot of hoops and I don't get why things stop working when I run into them.

 

I have created the following (Experimental 2D) thread for future discussion on this topic:

https://forum.unity3d.com/threads/disabling-physics-pushing-and-demo-scene.452181/

 

I had the same problem, I'll try to dig out the answer for you.

 

but he does say it's not working, or I'm I reading it incorrectly?

 

I see I didn't see the post I thought Xelnath had setup a new thread for it, so I did not select it, it was only when you mentioned the script I selected the new created thread