Looking for something like InverseLerp()

Development Programming & Scripting C++
1

I’m working with a noise function that returns values between -1.0f and 1.0f. I want to Lerp this value into a new coord system from 0 to 1000. In Unity I would use the InverseLerp() like this:

// example values
float x = 0;
float y = 1000;
float xx = 0.3443;
float yy = -0.1743;

Mathf::Lerp(x, y, Mathf::InverseLerp(xx, yy, value));

The above code would basically allow me to “scale up” my values to the new coord system while keeping my ratios the same. UE4 (FMath) does not have this function, so how would I go about doing this?

Thanks

2 

Mathf::InverseLerp(float xx, float yy, float value)
{
    return (value - xx)/(yy - xx);
}
3

I’m not sure why a lerp or inverse anything is required here, it looks like all you want is (value + 1.f) * 500.f?

4

Thanks, this is exactly what I was looking for.

Great question. It’s very possible you are right. I’ll do some experimenting and find out. Thank you.

5 

 
/** Returns Value normalized to the given range.  (e.g. 20 normalized to the range 10->50 would result in 0.25) */
UFUNCTION(BlueprintPure, Category="Math|Float")
float UKismetMathLibrary::NormalizeToRange(float Value, float RangeMin, float RangeMax)
{
    if (RangeMin == RangeMax)
    {
        if (Value < RangeMin)
        {
            return 0.f;
        }
        else
        {
            return 1.f;
        }
    }

    if (RangeMin > RangeMax)
    {
        Swap(RangeMin, RangeMax);
    }
    return (Value - RangeMin) / (RangeMax - RangeMin);
}

6

You probably want FMath::GetMappedRangeValue. There are clamped and unclamped versions.

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7

Very late to this but since I had the same question, the function you want for inverse lerp is FMath::GetRangePct.

FMath::GetMappedRangeValue is effectively the result of an inverse lerp on one range, and a lerp into another range. You can use it by giving it a 0-1 range but that’s a waste since GetRangePctis what it uses internally for the first step.

3 Likes