MathUtils: Added .inverseLerp().

[Hoodgail]

Description

Calculates the linear parameter t that produces the interpolant value within the range [a, b]. The a and b values define the start and end of the line.
https://www.gamedev.net/tutorials/programming/general-and-gameplay-programming/inverse-lerp-a-super-useful-yet-often-overlooked-function-r5230/ for more information and to why its useful

This contribution is funded by Hoodgail.

[Mugen87]

We should consider to implement the method like in Unity. If you do this:

const t = MathUtils.inverseLerp( 2, 2, 2 );

The method returns NaN because of the zero divide. I would use:

inverseLerp: function ( a, b, value ) {

    if ( a !== b ) {

        return MathUtils.clamp( ( value - a ) / ( b - a ) );

    } else {

        return 0;

    }

}

[Hoodgail]

Resolved

[Mugen87]

@mrdoob This looks good to me.

I can enhance the docs and unit tests with a subsequent PR.

[mrdoob]

@mrdoob Do you consider three.js a gaming engine?

I think it's a valid use case.

I wouldn't want it to focus too much on games but I'm interested in making it easier for people to do games with it:

https://threejs.org/examples/?q=game#games_fps

[mrdoob]

Thanks!