limitting the number of collisions a collider per fixedUpdate in Physing2D

Unity Engine
1

TLDR: Is there a way to limit number of collisions a rigidbody/collider can enter per fixedUpdate?

I am building a 2D simulator where thousands of rigidbodies continously collide with one another. I do not have to be deterministic but I have to maximize the number of rigidbodies. However FPS drops significantly at about 500 rigidbodies.
two biggest responsible parties are:
Physics2D.CompileContactCallbacks 17%
Physics2D.Step 15%

Each rigidbody has an OnCollisitonStay2D() method. I found I can minimize the impact of the code inside with a counter as below;

int totalCollisionsThisFrame =0;

    private void LateUpdate()
    {
        totalCollisionsThisFrame = 0;
    }

    private void OnCollisionStay2D(Collision2D collision)
    {
        if (totalCollisionsThisFrame < 2)
        {
            animal.Collide(collision.collider);
            totalCollisionsThisFrame++;
        } else {
                //Reserved
        }
    }

However, since the OnCollisionStay2D is still called, it impacts unncessarily.

So to remove the rigidbody from collisions after the first 2 collision detection, I tried the following;

A). changing the layer once the number of total collisions are above 2 and chaning it back in the LateUpdate() so it wont be part of collision calculations…
This was very inefficient.

B). Putting the rigidbody to sleep using rigidbody2D.Sleep() once the number of total collisions are above 2 and Wake() in LateUpdate()… also very inefficient.

C). IgnoreCollision() doesn’t help either. It is not just in efficient, because I don’t keep the data (for efficiency purposes) there is no way of reverting it back. There is no method to undo all ignoreCollisions with one go.

D) I considered ECS for improving efficiency however I can not find any tutorial that uses both ECS, colliders and joints. If you know any it would be appreciated.

Long story short; my question is;

  1. Is there a way to limit number of collisions a rigidbody/collider can enter per fixedUpdate?

Thanks in advance

2

in 3D the duration of a collision is

1 * Time.fixedDeltaTime OnCollisionEnter(Collision collision)
n * Time.fixedDeltaTime OnCollisionStay(Collision collision)

3

I am sorry. I failed to understand how this could be useful in my case.

4

Oh i was suggesting to use collision duration but i think it will give the same result.
Anyway, with the code above you should have a better behaviour if you set totalCollisionsThisFrame
to Zero in OnCollisionExit2D() instead of LateUpdate().

And its normal that OnCollisionStay2D() keep sending messages as you are stuck in the same collision…
If you want a single execution, so use OnCollisionEnter2D.

1 Like
5

Wow thanks, Using onCollisionExit2D instead of LateUpdate actually improved Physics2D.CompileContactCallbacks from 16% to 12%. I am not sure about how gameplay is affected but I didnt notice anything as of yet.

However OnCollisionEnter2D instead of OnCollisionStay2D would not work for me as somethings need to have extended affect as the contact is remained.

However, the question still remains: I still wonder if Unity Physics Engine has a way of limiting number of collisions (or collision callbacks) of a rigidbody for each fixedUpdate.