Question by Lairinus · Aug 20, 2017 at 12:52 PM · c#rotation rigidbody lerp

Quaternion.Lerp finishing before "t" parameter hits 1

The Problem:

I wish to rotate a cube to 180 degrees from 0 degrees. Although this is being completed, I do not have any way to track this because the "t" parameter (lerpTime) is only 0.3-0.5 instead of 1 when the rotation is 180.

To break this down more simply, "Test" is being debugged to my console way after the rotation is completed.

The Code:

     Rigidbody rbdy = null;
     IEnumerator RotateTest(bool reset)
     {
         float speed = 2f;
         Quaternion oldRot = rbdy.rotation;
         Quaternion newRot = rbdy.rotation * Quaternion.Euler(180, 0, 0);
         float lerpTime = 0;
         while (lerpTime < 1)
         {
             yield return new WaitForSeconds(Time.fixedDeltaTime);
             Quaternion nextRot = Quaternion.Lerp(rbdy.rotation, newRot, lerpTime);
             lerpTime += Time.fixedDeltaTime * speed;
             rbdy.MoveRotation(nextRot);
             Debug.Log(lerpTime);
         }
 
         rbdy.rotation = newRot;
 
         Debug.LogWarning("Test");
         yield break;
     }

Further

I have tried setting the "newRot" value to just the Quaternion.Euler(180,0,0) without multiplying the object's rotation with the same exact result.
This rotation is incredibly quick (compared to similar Vector3.Lerps I have implemented). At a speed of 1 it takes maybe a second for the rotation to complete.

Question

How do I properly rotate an object using Quaternion.Lerp and properly track when the rotation ended?

Add comment · Show 5

tanoshimi · Aug 20, 2017 at 12:58 PM 0

"This rotation is incredibly quick (compared to similar Vector3.Lerps I have implemented). At a speed of 1 it takes maybe a second for the rotation to complete."

At a speed of 1, it should take exactly one second to complete. Because you're doing this:

 lerpTime += Time.fixedDeltaTime * speed;

If you want it to take longer, reduce speed.

Lairinus tanoshimi · Aug 20, 2017 at 01:10 PM 0

Thanks for the comment.

At a speed less than 1 (around 0.5) the rotation finishes over a longer period of time as expected, but the "t" parameter is then 0.1 or 0.2 when the rotation finishes. For instance, it takes about 2 or 3 seconds to finish the rotation with a speed of 0.5, but even after the rotation ends it takes another 15 or so seconds to be marked as complete.

tanoshimi · Aug 20, 2017 at 01:16 PM 0

To be honest, I'm not entirely sure why you're using

 yield return new WaitForSeconds(Time.fixedDeltaTime);

at all. Why not simply use:

 yield return null;

Lairinus tanoshimi · Aug 20, 2017 at 01:31 PM 0

I am using Time.fixedDeltaTime because I am moving a rigidbody inside of a coroutine, so it should be close to (if not exactly) on-par with FixedUpdate().

In any event, I tried both yield return null and Time.deltaTime ins$$anonymous$$d with the same result at a speed of 0.5F. I updated the lerpTime to use Time.deltaTime ins$$anonymous$$d of FixedDeltaTime as well.

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