Rigidbody2D.position doesn't teleport the object with the interpolation settings on

The description of

Rigidbody2D.MovePosition

seems to be more detailed but then the question arises: whether the differences in the descriptions mutually applicable (to both types of rigidbodies)?

For example, the

Rigidbody.MovePosition

description sounds like it moves only a kinematic rigidbody. It also explicitly states that

MovePosition

complies with the interpolation settings and

position

should be used for teleportation needs. Unfortunately, the last statement does not correspond to reality, at least this is not the case for

Rigidbody2D

. My experiments have shown that both:

Rigidbody2D.MovePosition

and

Rigidbody2D.position

comply with interpolation settings.

The first part of the video demonstrates the movement of two

Rigidbody2D

kinematic objects via

MovePosition

&

position

with the interpolation "on". Then I turn off interpolation and play the same scene. Time is set to

0.01

, so you can easily observe that interpolation works in the first part and does not in the second. Also in the first part you can notice that changing

Rigidbody2D.position

with interpolation settings "on" really teleports the object (as documentation claims) but only in the first

FixedUpdate

, then it is interpolated along with

Rigidbody2D.MovePosition

.

So, my questions are (the most important one is the 3rd):

1. Is the differences in the descriptions mutually applicable (to both types of rigidbodies)?
2. Why does

   Rigidbody2D.position

   interpolate the object after the first

   FixedUpdate

   while it shouldn't?
3. What is the correct way to teleport the kinematic

   Rigidbody2D

   with the interpolation settings "on"?

----------------------
Unity 2021.1.17f

 

Perhaps I didn't formulate the question clearly.

I'm moving a kinematic Rigidbody2D with interpolation "on" via MovePosition in FixedUpdate and I have no problems with this at all.

Then at some event, I need to teleport the object to some position without the visual interpolation effect. I expected that changing Rigidbody2D.position should do the trick, but it moves the object the same way as MovePosition does, i.e. using visual interpolation.

The main question is what is the recommended way to teleport the object without visual interpolation? Since using Rigidbody2D.position doesn't help, are there any other options?

The Rigidbody documentation contains some recommendations for teleportation (to use Rigidbody.position), but the Rigidbody2D documentation does not. So, I expected that it could be the same that's why I tried Rigidbody2D.position (which didn't work).

> If you modify either the Transform or the Rigidbody2D pose, it'll stop interpolation until the next simulation step.
My experiments (in the video) show that Rigidbody2D.position doesn't stop interpolation.

I'm not an English speaker, so if it's not clear this time I'll try again with some code.

 

The problem is that it does not stop interpolation. I would be happy if it did

> Send me your test project and I'll have a look.
Ok, I'll put the link to the project today.

 

In this project (link):
- Press 1 to move the object using Rigidbody2D.MovePosition
- Press 2 to move the object using Rigidbody2D.position

Time is set to 0.05, so you can observe visual interpolation.
You can see that interpolation is not stopped when pressing 2 for using Rigidbody2D.position

Video demo:

 

Thank you for the details and quick fix!

Here is the bug report (Case 1367721) : https://fogbugz.unity3d.com/default.asp?1367721_l3ao7dkdn0r45v6c

It is said here that

Also, my experiments have shown that using Transform.position causes the object to freeze for a moment that almost imperceptible at normal speed but noticeable when Time = 0.05f or less.

So, I tried to avoid using Transform.position and came up with these 2 workarounds that worked smoothly:

Code (CSharp):

1. Rigidbody2D rb = tr.GetComponent<Rigidbody2D>();
2. var tr = transform;

1. Changing Rigidbody2D.position along with Transform.position and turning the object off&on:

Code (CSharp):

1. tr.gameObject.SetActive(false);
2. rb.position += (Vector2)shift;
3. tr.position += shift;
4. tr.gameObject.SetActive(true);

2. Turning interpolation off & on when changing rigidbody position:

Code (CSharp):

1. tr.gameObject.SetActive(false);
2. rb.position += (Vector2)shift;
3. tr.position += shift;
4. tr.gameObject.SetActive(true);

I would also like to ask you to supplement the Rigidbody2D.MovePosition & Rigidbody2D.position sections with the missing information (especially the latter, since it's almost empty).

 

I can create a demo project to demonstrate this "freezing" if you would be interested in looking into it.

 

Yes, that's exactly how I read it and was almost ready to give up.

Okay, I'll add another scene to it and let you know when it's ready.

 

This is exactly what I was going to write and even wrote the correct subtitle,

but then just duplicated the code from the previous example.

The code I intended to write was this:

Code (CSharp):

1. Rigidbody2D rb = player.GetComponent<Rigidbody2D>();
2. RigidbodyInterpolation2D interpolation = rb.interpolation;
3. rb.interpolation = RigidbodyInterpolation2D.None;
4. rb.position += (Vector2)shift;
5. rb.interpolation = interpolation;

 

I received it by email after submitting the bug report from Unity editor

 

Here is my new demo (the last commit in the same project).
The scene name is "FreezeTest".
It contains 3 "Ground" objects, following closely after each other (just 3 clones).



Each "Ground" object contains simple objects (like black pole and green tree) so that the player's (white circle) movement is noticeable. When the player reaches the end of the 2-nd Ground object (marked by black pole) it is teleported to the end of the 1-st Ground, this creates the illusion of an infinite runner. Since teleportation occurs when the player is in the process of moving, it must be smooth so that the movement looks natural, as if there were no teleportation at all.

The Player object has 3 components on it: PlayerMove1, PlayerMove2, and PlayerMove3.
All of them are inherited from the PlayerMoveBase abstract class and override only one method: teleport.
Each overridden method uses a different workaround for teleportation. The scripts move the Player object when pressing keys 1, 2 and 3, respectively.

For this particular demo, only the worst (most expensive) workaround (PlayerMove3) gives a nice movement+teleportation experience:

Code (CSharp):

1. public class PlayerMove3 : PlayerMoveBase
2. {
3.     protected override void teleport(Vector2 pos)
4.     {
5.         gameObject.SetActive(false);
6.         _rigidbody.position = pos;
7.         transform.position = pos;
8.         gameObject.SetActive(true);
9.     }
10. }

2 others cause "freezing" and "interpolation" side effects which are well noticeable even at normal speed.

 

Sorry, I didn't get this, are these fixes already available in any of the Unity versions? It looks they are in a review state now.

This was clearly noticeable on my laptop, so I didn't record a video.
Teleportation occurs as soon as the object goes behind the black pillar, and this is exactly where the object stops for a second when using

transform.position = pos;

for teleportation. The expected movement, however, should be smooth.

I don't quite understand what you mean. I will quote parts I'm confused with:
> the Transform position doesn't change anything when the call returns apart from the Transform
What does it mean: call returns apart from the Transform?
> The body will be updated when the simulation step runs because its first task is to check if Transforms have been manually changed.
Do you mean "rigidbody"? If Transforms have been manually changed the physics system will calculate the next rigidbody position based on the changed

Trasfrom.position

, and not on the

Rigidbody2D.postion

?

I haven't tried it yet. I will check it tomorrow.

 

I have tried setting Simulation Mode = Update and this caused constant intermittent movement (not only when teleportation occurs but every frame). I guess it's because interpolation doesn't work in this mode.

Could you, please, check one more time if you don't really notice any stops of the white circle as in the last video (just after the black poles) when holding key "1" ? I checked this project on another computer and it showed the same: the object stops for a moment after the black poles.
Time Scale should be 0.05 in the Project Settings.

 

I think it is because the TimeScale is set to 0.05 for testing interpolation in FixedUpdate mode. In Update mode it may cause the opposite effect.

 

It looks Ok. I can change it later to using Rigidbody when your fix is released.

Can physics calculations in this mode lead to any other issues or side effects? I mean is it absolutely safe to use Update instead of FixedUpdate for physics?

 

Yes, no issues are noticeable to the eye, although I think this is a bit incorrect logically: it should make a move even when teleportation occurs (in the same update). IOW teleportation is a trick to visualize endless running in a limited range of X coordinates. At the same time, the object is constantly moving regardless of whether the trick was performed or not. So I think this example would be logically more correct:

Code (CSharp):

1. private void Update()
2. {
3.     if (!Input.GetKey(_moveKey))
4.         return;
5.  
6.     if (_rigidbody.position.x > _teleportTriggerX) // teleportation can happen or not...
7.         _rigidbody.position = new Vector2(_rigidbody.position.x - _groundSize.x, _rigidbody.position.y);
8.  
9.     // .. but the object makes a move every step
10.     _rigidbody.MovePosition(_rigidbody.position + (_velocity * Time.deltaTime));
11. }

 

I could go with the previous working example and wouldn't bother you with this, but, well, this example doesn't help with "stopping" when teleporting. This is interesting to me, so I looked into it a little. What happens here is that just after the

transform.position

is changed in the

teleport()

method the

_rigidbody.MovePosition()

doesn't do anything up to the next FixedUpdate. IOW

transform.position

is not being changed up to the next FixedUpdate as it normally is if no teleportation (changing

transform.position

) occurs. The log proves it:

Update: transform.position.x = 14.89941, _rigidbody.position.x = 14.946

Update: transform.position.x = 14.89941, _rigidbody.position.x = 14.946

FixedUpdate: transform.position.x = 14.89941, _rigidbody.position.x = 14.946

// after this

transform.position.x is being interpolated up to the next FixedUpdate:

MovePosition(15.446)

Update: transform.position.x = 14.96772, _rigidbody.position.x = 15.446

Update: transform.position.x = 14.96772, _rigidbody.position.x = 15.446

Update: transform.position.x = 14.96772, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.03236, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.03236, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.03236, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.08148, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.08148, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.08148, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.15591, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.15591, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.15591, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.21049, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.21049, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.21049, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.28232, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.28232, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.28232, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.35494, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.35494, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.35494, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.42184, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.42184, _rigidbody.position.x = 15.446

Update: transform.position.x = 15.42184, _rigidbody.position.x = 15.446

FixedUpdate: transform.position.x = 15.42184, _rigidbody.position.x = 15.446

Teleport!

// after this

transform.position.x is NOT being interpolated up to the next FixedUpdate (because of the Teleport call before it):

MovePosition(5.921839)

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

Update: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

FixedUpdate: transform.position.x = 5.421839, _rigidbody.position.x = 5.421839

// and here it starts working again  (since not teleportation occurs):

MovePosition(5.921839)

Update: transform.position.x = 5.424759, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.424759, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.424759, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.478089, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.478089, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.478089, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.536054, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.536054, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.536054, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.603037, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.603037, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.603037, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.65183, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.65183, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.65183, _rigidbody.position.x = 5.921839

Update: transform.position.x = 5.702931, _rigidbody.position.x = 5.921839

My try to depict this for clarity:



Also I tried to replace

_rigidbody.position

with

transform.position

since we are then changing

transform.position

in the teleportation method, but this didn't help.

Code (CSharp):

1. private bool tryTeleport()
2. {
3.     if (transform.position.x < _teleportTriggerX)
4.         return false;
5.  
6.     teleport(new Vector2(transform.position.x - _groundSize.x, transform.position.y));
7.     return true;
8. }

Maybe this is related to the fixes you've made.