Non-static colliders without rigidbody still cost in Unity 5?

Should I make sure a rigidbody is on same GameObject or parent?

 

I don't think so.. anybody?

 

Is it still slower than moving a non-static collider?

 

It's not an issue, I'm just asking out of curiosity and I only had one question.

The profiler used to issue a warning, if I moved a gameobject (by setting the transform.position directly) that had a collider (I'm talking about 3D physics, which I thought was clear, since I quoted you talking about 3D physics), without a kinematic rigid body.

And since this was a thing that a lot of developers did (by mistake, or simply not knowing better), I believe this case was optimized (at least, that's what I remember reading on a Unity blogpost, please correct me if I'm wrong).

So to be more specific:

Is doing GameObject.transform.position = new Vector3(a,b,c); (assume a,b,c are random values) faster on a gameobject that has a collider and a rigidbody set to kinematic, or on a gameobject that just has a collider (at which point, I believe the collider is considered to be "static")?

EDIT:

From this blogpost: https://blogs.unity3d.com/2014/07/08/high-performance-physics-in-unity-5/

Which makes me think that moving a static collider and a rigidbody-less collider is now the same thing, which certainly wasn't the case in Unity 4. Is it? Or are there still differences?

 

There have been tests, they were kinda inconclusive (but it seems they are now roughly in the same ballpark in terms of performance)

I'm adding rigidbodies when I intend to move colliders, so it's not an issue for me personally. It's a bit weird workflow though (which you seem to agree on).

The thing is, on the forums, there was a big push to educate people on this issue, since a lot of people did it wrong (in the Unity 4 era).

Then there was the blog post I posted above, which led people to believe, that for Unity 5, kinematic rigidbody or not, it's the same thing now, at least performance wise.

But then the manual ( https://docs.unity3d.com/Manual/CollidersOverview.html ) says

Which is the opposite. But then again, as a lot of things in the manual, it could just be very outdated.

So you can probably see why people are a bit confused as what the "best practice" is.

 

And to confuse things even further, it seems moving colliders without rigidbodies is actually much faster according to a quick test I just did.

 

Yeah, so, moving 1000 box colliders takes about 2.8ms, and if I attach a Kinematic Rigidbody on the parent object (or to all cubes individually, it makes no difference it seems), it needs around 27ms.

So maybe I'm doing something wrong, or the manual is flat out wrong, or there's a bug?

 

@yant

I submitted a bug report (as a documentation bug, since I really don't know if it's an actual bug, or if the docs are simply outdated). I had a repro scene attached with it. It's case 873057.

 

From the tests I've made, it seems like moving non-rigidbody colliders is now the fastest thing. It's faster than moving kinematic rigidbody colliders or non-kinematic rigidbody colliders.

This surprised me because it was kind of a well-known Unity thing that everytime you had to move colliders, it was better if they had rigidbodies, but apparently this isn't true anymore

 

@yant Any update on this?

 

Which is fine, btw. Having to add a rigidbody just to mark a collider as "non-static" was always kinda weird.

So it's good that it was changed. The thing is we don't know how exactly it was changed and the manual saying the complete opposite of what is happening isn't helping.

I'm not sure there's an actual bug here, the thing needed could be a complete rewrite of that section in the manual.

 

@AcidArrow What Unity version do you've used with your test?

I've tested it myself with 1000 moving cubes and got the same result (kinematic rigidbodies are slower) @ Unity 5.4.

 

Hi
I'm moving thousands of trigger colliders every frame ( using their transform )
I've had a kinematic rigidbody attached to every trigger, but I've tried removing it and the performance changed significantly ( from about 15 fps to 40 fps )
The player ( with a rigidbody ) is still able to collide with the triggers without any issues.

I wanted to know if this might introduce bugs or if some collisions might not be detected ?

 

maybe it can helps https://forum.unity.com/threads/2d-...overhead-if-they-have-animated-parent.635962/

 

@larex39 Thanks, but I think I have the opposite issue
removing the kinematic rigidbodies really enhances performance
Right now i'm just concerned of getting weird physics behavior since unity recommends adding rigidbodies to any trigger collider that moves

 

i found it is always bad idea to move coliders by their transforms, so instead of removing the kinematic rigid bodyes try to move them by rigidbody.movePosition and you should have better performance

 

Considering they are all triggers i think its fine. @slake_it

 

I also thought so but that is not true, if you are moving triggers you are moving coliders that means the physics is always involved, and they behave like static rigid bodyes without collision

 

look at this thread:
https://forum.unity.com/threads/2d-...overhead-if-they-have-animated-parent.635962/
I was also moving lot of triggers and i thought there should be no physics involved, but there always is, but you can make it faster, as i wrote at the end of the thread

 

Cool, I wish things were as clear for 3D physics as well.

 

To use Unity EventSystem with Sprites, as far I know, I need to attach colliders to Sprites in order to receive events like OnDrag, OnDrop, etc...

So, let's say I want to drag and drop Sprites. Then I need to add a 2D collider to get events. And I will move them (they are moving while dragging), so, do I need to add a Rigidbody although I don't need physics?

 

@MelvMay Thank you for the thorough breakdown. In my 2D game, I don't use a single RigidBody, but I do use BoxColliders/PolyColliders/etc. I then use Physics queries like RayCasts/CircleCast/etc, to detect collisions.

Because I don't have a single RigidBody in my scene, would I still see a performance benefit from adding Kinematic RigidBodies to all my moving objects with colliders?

 

Read MelvMay's answers for 2D physics.

For 3D physics it's an unknown, because after multiple threads, bug reports and repro cases, it's impossible to get a clear answer for Unity's 3d Physics.

The manual still says the same things, many years later, which to the best of my understanding, are 100% false.

 

From unity 5 its false, afaik.
Static colliders are very optimized and doesnt require rigidvodies.

 

How long has that been there? I remember reporting this ages ago.

In the meantime, could you please give a breakdown of what we should do in common use cases in 3D physics?

• When should we use a kinematic Rigidbody?
• Should we ever deliberately move a collider which does not have a Rigidbody attached?

Bonus question, since @MelvMay answered an equivalent for 2D:

• Should articulated children of Rigidbodies have a Rigidbody and joint of their own?

 

1) when you want to make a dynamic object static for a little while (assuming*)

2) yes, since Unity 5 its a proper thing to do

3) i think it depends on what your trying to do

 

Well, sure, I also think I know what the answers to those things are. However, my answers are all based on what the documentation says and speculation / informal personal testing after we were told it had changed.

Some confirmation and detail would be great.

 

I've been looking for this all over the entire internet for years. Thank you!