Vector3.Lerp inside a Coroutine is not working as it should on Unity3D

Question

I am having a strange issue when using a Vector3.Lerp inside a coroutine and it makes no sense because I have many Coroutines in my game and they are all working fine.

WHAT I AM TRYING TO ACHIEVE

I am simply trying to move an object from a starting height to a final height with a coroutine called InVolo() and a simple Vector3.Lerp to change the position of the object.

MY CODE

float elapsedTime = 0f;

    while (elapsedTime < TempoSalita)
    {


        transform.position = Vector3.Lerp(transform.position, 
            new Vector3(transform.position.x, maxHight, transform.position.z), (elapsedTime / TempoSalita));


        elapsedTime += Time.deltaTime;

        yield return null;
    }

    transform.position = new Vector3(transform.position.x, maxHight, transform.position.z);
    yield return null;

The maxHight is simply 4f and TempoSalita is 2f. The coroutine is started in an OnTriggerEnter and it is working fine, the object is reaching the y of 4f and it exits the while in 2 seconds.

THE PROBLEM

Basically, elapsedTime / TempoSalita is becoming 1 after 2 seconds, as it should be, but the object reaches the ending position after like 0.3 seconds, when elapsed/TempoSalita is 0.2 and it makes no sense to me. Vector3.Lerp should go from startpos to endpos in the time of the t value to go from 0 to 1. But it goes to the final position in 0.2 seconds and I don't have a clue why.

WHAT I TRIED

I have tried to Debug.Log the elapsedTime and it is changing fine, tried to use only Mathf.Lerp between the y values and it does the same thing. There is nothing else in that script that can affect it, this is how the Coroutine starts:

 void OnTriggerEnter(Collider other)
{
    if(other.CompareTag("Saltino"))
    {
        StartCoroutine(InVolo());
        
    }
}

It starts only one time. Do you know what can cause this strange problem?

Answer 1

It could be the condition you are using which seems a bit suspect to me.

Generally I would write this a bit differently, something like..

var t = 0f;
var start = transform.position;
var target = new Vector3(transform.position.x, maxHight, transform.position.z);

while (t < 1)
{
    t += Time.deltaTime / TempoSalita;

    if (t > 1) t = 1;

    transform.position = Vector3.Lerp(start, target, t);

    yield return null;
}

First you have your start and target values created before altering the position. The t value will increase until it reaches (or passes) 1. Since we do not want t to go beyond 1 we do a check before applying the lerp. Our t value is calculated outside of the lerp to make it clear and easy to read/modify.

The above will run for time specified and does not require the extra lines at the end since t will eventually be exactly 1.