Rigidbody2d Collision Breaks Quaternion.Slerp

Question

I am trying to use the following function during every update to rotate a rigidbody2d sprite (spaces$$anonymous$$p) towards the mouse using rotateTorque as a speed. T$$anonymous$$s works perfectly until I use the other controls to drive the object into another rigidbody2d collider (planet) w$$anonymous$$ch causes the spaces$$anonymous$$p to get left upside down w$$anonymous$$le my mouse is still pointing up. At t$$anonymous$$s point the Slerp function seems to slow down the rotation such that it is barely rotating towards my mouse anymore. It seems as though colliding with objects through the physics engine somehow breaks the interpolation of the slerp.

How do I fix t$$anonymous$$s?

It works perfectly before colliding with anyt$$anonymous$$ng and even sometimes after but depends on the final rotation of the spaces$$anonymous$$p. Not$$anonymous$$ng else is interfering with the spaces$$anonymous$$ps rotation.

     void HandleRotation() {
         Vector2 direction = Camera.main.ScreenToWorldPoint(Input.mousePosition) - transform.position;
         float angle = Mathf.Atan2(direction.y, direction.x) * Mathf.Rad2Deg;
         Quaternion to = Quaternion.AngleAxis(angle, Vector3.forward);
         Debug.Log("from " + transform.rotation.eulerAngles + " to " + to.eulerAngles + " mouse " + Camera.main.ScreenToWorldPoint(Input.mousePosition));
         transform.rotation = Quaternion.Slerp(transform.rotation, to, rotateTorque * Time.fixedDeltaTime);
         Debug.Log("new " + transform.rotation.eulerAngles + " time " + (rotateTorque * Time.fixedDeltaTime));
     }

Here is a log of when it gets stuck. It seems somehow somet$$anonymous$$ng is reverting the rotation, but I have checked all my code and not$$anonymous$$ng else changes the transform and the object is no longer touc$$anonymous$$ng any other rigidbody2d/colliders

 from (0.0, 0.0, 48.6) to (0.0, 0.0, 89.8) mouse (-0.3, 1.1, -10.0)
 UnityEngine.Debug:Log(Object)
 BaseS$$anonymous$$p:HandleRotation3() (at Assets/BaseS$$anonymous$$p.cs:140)
 BaseS$$anonymous$$p:Update() (at Assets/BaseS$$anonymous$$p.cs:210)
 new (0.0, 0.0, 50.1) time 0.03580748
 UnityEngine.Debug:Log(Object)
 BaseS$$anonymous$$p:HandleRotation3() (at Assets/BaseS$$anonymous$$p.cs:142)
 BaseS$$anonymous$$p:Update() (at Assets/BaseS$$anonymous$$p.cs:210)
 from (0.0, 0.0, 48.4) to (0.0, 0.0, 89.8) mouse (-0.3, 1.1, -10.0)
 UnityEngine.Debug:Log(Object)
 BaseS$$anonymous$$p:HandleRotation3() (at Assets/BaseS$$anonymous$$p.cs:140)
 BaseS$$anonymous$$p:Update() (at Assets/BaseS$$anonymous$$p.cs:210)
 new (0.0, 0.0, 49.9) time 0.03610305
 UnityEngine.Debug:Log(Object)
 BaseS$$anonymous$$p:HandleRotation3() (at Assets/BaseS$$anonymous$$p.cs:142)
 BaseS$$anonymous$$p:Update() (at Assets/BaseS$$anonymous$$p.cs:210)

Answer 1

Best Answer

Answer by simonpushelberg · Dec 09, 2019 at 02:59 PM

I was able to find a fix! I needed to use RigidBody2D.MoveRotation() instead of setting transform.rotation. T$$anonymous$$s allows the player input and physics engine to both control the rotation properly without interfering with each other. I probably should also put t$$anonymous$$s inside of a FixedUpdate call instead of Update, but Update seems to be fine for now.

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Answer 2

Answer by Ermiq · Dec 09, 2019 at 07:10 AM

Don't know why you actually have the issue with collisions, but I see one suspicious t$$anonymous$$ng in your code.

Quaternion.AngleAxis() doesn't give you a 'full' resulting rotation. It gives you just a 'partial' rotation w$$anonymous$$ch is not related to anyt$$anonymous$$ng and it just represents some rotation from some (not defined) rotation for given degrees around the given axis.

To get the actual rotation that your transform should rotate to in the end of the Slerp() you need to 'add' the to rotation to the current transform rotation:

 Quaternion to = transform.rotation * Quaternion.AngleAxis(angle, Vector3.forward);

T$$anonymous$$s will be the rotation w$$anonymous$$ch is your current rotation plus the rotation around Z axis for angle degrees.

PS: since I'm not smart enough for Tan's and Sin's, I prefer to use Vector3.SignedAngle() to get the angle between two direction vectors.

 angle = Vector3.SignedAngle(direction, transform.forward, Vector3.forward);

T$$anonymous$$s gives an angle between s$$anonymous$$p-to-mouse direction and current s$$anonymous$$p direction, related to the Z axis, e.g., it will be -90 when the s$$anonymous$$p is looking right and mouse is above the s$$anonymous$$p. Probably the same as your math stuff, I don't know.

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simonpushelberg · Dec 09, 2019 at 02:58 PM 0

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Thanks for the reply.

This did not fix the issue and made the rotation without collision not work.

I was able to find a fix! I needed to use RigidBody2D.MoveRotation() instead of setting transform.rotation. This allows the player input and physics engine to both control the rotation properly without interfering with each other. I probably should also put this inside of a FixedUpdate call instead of Update, but Update seems to be fine for now.

Rigidbody2d Collision Breaks Quaternion.Slerp

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