Why is my Mathf.Lerp not lasting for the intended duration, even though I'm not using Time.time as the t variable?

Question

just figured this out myself but hadn't found a direct answer here so I thought I'd share for other people making the same mistake. I'll post the answer myself if it gets approved in the moderation queue.*

Why is my Lerp not lasting the intended duration?

 using UnityEngine;
 using System.Collections;
 
 public class TestingLerpScript : MonoBehaviour {
 
     void Start(){
         StartCoroutine(LerpCoroutine(10f, 5f, 0.05f));
     }
     
 
     IEnumerator LerpCoroutine(float finalX, float duration, float marginOfError){
 
         Debug.Log (duration);
 
         float startTime = Time.time;
         float currentX = 0f;
 
         while( (currentX != finalX) && (Mathf.Abs(finalX-currentX))>marginOfError)
         {
             float localTime = Time.time-Time.deltaTime - startTime;
             float percentCovered = localTime/duration;
 
             currentX = Mathf.Lerp (currentX, finalX, percentCovered);
 
             yield return null;
         }
 
         Debug.Log(Time.time-startTime);
         
     }
 }

Thank You.

Answer 1

Best Answer

Answer by Lucanio · Jan 02, 2014 at 05:35 AM

The problem is you're using currentX as a starting position each time the Lerp is called, but the starting position should remain the same. This is what it should be instead:

        float startTime = Time.time;
         float startX = 0f;
         float currentX = startX;
 
         while( (currentX != finalX) && (Mathf.Abs(finalX-currentX))>marginOfError)
         {
             float localTime = Time.time-Time.deltaTime - startTime;
             float percentCovered = localTime/duration;
 
             //currentX = Mathf.Lerp (currentX, finalX, percentCovered);
             currentX = Mathf.Lerp (startX, finalX, percentCovered);
 
             yield return null;
         }

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Lucanio · Jan 02, 2014 at 05:31 AM 0

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I'm not sure if the -Time.deltaTime is correct.

Why is my Mathf.Lerp not lasting for the intended duration, even though I'm not using Time.time as the t variable?

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