One Way Lerp

Scripting
1

Hello,

I am trying to get smoothly from one value to another (from A to B) like Lerp() function does. But if I am correct, Lerp() continuously loops from A to B and than back from B to A and so on… I would like just one time change from A to B and than stop changing the value. I haven’t found any useful functions yet. Do you recommend any ?

Regards, L

2

Lerp gives a value between A and B. The third parameter is a number between 0 and 1 indicating the mixing ratio of A and B. That’s it. There is no loop, no continuous changing (and no back and forth). However if you want to make a progressive change in time, that is, you want to change continuously from A to B. You need to change the third parameter progressively from 0 to 1.

3

Lerp or Linear Interpelation uses this formula

public static float Lerp(float A, float B, float lerpValue)
{
    lerpValue = Mathf.Clamp(0,1,lerpValue);
    result = A * (1-lerpValue) + B * lerpValue;

    return result;
}

LerpUnclamped is basically the same thing but without the clamp.
Neither of those two functions have the value oscillate back and forth.

What your thinking of is more like Mathf.PingPong()

4

Lerp does what you want. You’re just passing bad t into it.

a = 0
b = 10
Lerp(a, b, t)

If t is 0 then the value is 0. If t is 1 then the value is 10. If t is 0.5 then the value would be 5.

5

Required knowledge: IEnumerator Coroutines (frankly required for Unity, lol)

Here are all the variables you need to interpolate a thing. Interpolation takes a lot more than just “a Lerp”:

-A reference to a thing you want to ultimately move.

-The place it starts moving from.
-The place you want it to finish.

-The amount of time it moves.
-The amount of time that has passed.
-The position of the interpolation at a given percentage of that time passed.

You then assign the thing you want to move to the position at a given percent. Those last two can be confusing, because that’s where the curve comes in. The percent will always progress in a linear fashion. The position may not, but always begins and ends with the percent.

EXAMPLE TIEM - This is an academic example. For instance, in practice the startPosition would often be copied from a supplied movingFloat at the beginning of such a function.

IEnumerator Interpolation()
{   
    float startPosition = 0;
    float endPosition = 100;

    float movingFloat = 0;
    float currentPosition = 0;
    float percentComplete = 0;
    float totalDuration = 5; // 5 seconds

    for (float timePassed = 0;  timePassed < totalDuration; timePassed += Time.deltaTime)
    {
         percentComplete = timePassed / totalDuration;

         // percentComplete = percentComplete * percentComplete; // exponential curve

         currentPosition = Mathf.Lerp(startPosition, endPosition, percentComplete);
         movingFloat = currentPosition;

        Debug.Log(movingFloat);
        yield return 0;
    }
}

Though I am a strong proponent of book learning, a few singular online articles have been indispensable to the advancement of my understanding- so much so that I save them into my library.

Furthermore, I do recommend you initially write your own interpolations. This will eventually encourage you to learn advanced C# concepts as you look for ways to stop writing so much repeat code. Ultimately the plugin DOTween will let you interpolate any variable or even a Transform through space using any curve; with one line of code.

Challenge: Can you make the interpolation perfectly accurate? (hint: use a while() loop and one if() statement)

fucking sweet I got it right in the comment box on the first try

6

@lukagril

Hi, I think more experienced people have already given good answers, but I might add that there is also MoveTowards, which is pretty straightforward to use, and it’s similar to lerp:

7

That’s a great suggestion!

Notice there’s a version of MoveTowards in the .Mathf class also, in case you don’t need a vector.

(also I’m not experienced, just focused on learning first before creating… though I think I named the first project I’m going to finish publicly today!)

8

Thank you guys for your help! Found a solution. I had to rotate object smoothly to have it faced to a ceratin point on map. Instead of changing only one value (rotation.y), I used Quaternion.Lerp() method, and it works perfectly.

Regards, L