Prevent two game objects from moving each other

Hello everyone,

I have the following situation - I have two game objects, both have a rigidbody attachted to them. Now I would like to find a way that those those two objects can't push each other around, but they should still collide, so that one object can't pass the other one.

Is there a simple way to archieve this behaviour...?

Best
Verdemis

 

"can't push each other around"...."still collide"

Those two statements seem like a contradiction. Collisions involve two objects overlapping, which causes the physics system to literally push them away from each other until they are no longer overlapping. So what you're trying to do sounds like it will be complicated because it seems like you're trying to defy the way physics works.

Can you give some description of the general case you're trying to solve? My best guess about your situation is that maybe you're trying to have multiple players running around bumping into things, but where players can't push other players around? Let's say that was what you were doing, which sounds sort of feasible at first. It raises two kind of complex questions: 1) What if player A pushes some other rigidbody (a box) into player B? Would player B move? They're not directly being pushes by player A (they're being pushed by a box) so what should happen? and 2) Let's say Player A is pushed by some other force into Player B, perhaps by an explosion. Would Player B move in that case? Or would Player A just hitPlayer B and come to a dead stop?

Your situation probably isn't what I'm describing, but I think you'll still run into issues with the two objects indirectly interacting, which would be complex. Anyway, maybe you can describe your specific situation, and other approaches might come to mind.

 

@dgoyette Thank you for your explanation. In my case I have two characters... which can move only on the x axis. They should not be able to walk past the other character, but they also should not push another around... but I still need physics for them.

But at the moment it's seems like pushing each other around is not such a big problem as I thought at first. But knowing a way to prevent that would be nice.

 

Because of how specific your case is (single-axis movement), there's probably a reasonable workaround. Here's an approach that might work. I'm assuming you have some kind of Player Controller that accepts inputs and moves the player in the appropriate direction. What I'd do is detect when another player is immediately left or right of you (either via a raycast or via a trigger collider), and disable the player's left or right movement ability. In other words, if the other player is directly right of me, don't allow me to move right.

This approach, however, would still allow normal physics forces to be transferred between players. For example, if Player A got pushed very fast into Player B, Player B would still move due to that collision. That may or may not be reasonable in your case.

 

You can use a couple of trigger zones around the players: when they meet, they can't go further.

 

When they collide, modify the velocity to cancel against the direction toward the other object:

• get direction from source to destination, normalized
• rb.velocity = Vector3.ProjectOnPlane(rb.velocity, direction)

When they collide, their velocity is removed in the direction of the other.

 

Make a child on both objects give both the same collider as their parents have and a static rigidbody give the give them a different layer then the parents have use the collision matrix so the parents layers only collide with the children layers then make a script in which u use Physics or Physics2D.IgnoreCollision(Parent collider, child collider)