Add MathUtils.pingpong()

[marcofugaro]

Related issue: -

Description

One function I find useful is the pingPong function. It alternates between two values, you can use it to alternate between two colors for example.
It also can be combined with the in-out eases from Robert Penner's Easing Functions to create a differently shaped alternating function.

Here is how the function looks like:
https://www.desmos.com/calculator/vcsjnyz7x4

[gkjohnson]

It looks like the current implementation doesn't work as expected with negative numbers:

MathUtils.pingPong( - 1.5 ); // - 1.5
MathUtils.pingPong( - 2.5 ); // - 0.5

[marcofugaro]

@gkjohnson missed that, thanks for testing. It is fixed by using the euclideanModulo instead of the javascript modulo.

I added the correct negative case to the unit test.

[Mugen87]

The same function also exists in Unity, see

https://docs.unity3d.com/ScriptReference/Mathf.PingPong.html

Reference implementation:

https://github.com/Unity-Technologies/UnityCsReference/blob/61f92bd79ae862c4465d35270f9d1d57befd1761/Runtime/Export/Math/Mathf.cs#L361-L366

[marcofugaro]

Thanks, I was aware, I put the unity link in the description.

From the unity implementation, I renamed the parameter t to x to better match the rest of the MathUtils functions.

[Mugen87]

Thanks, I was aware, I put the unity link in the description.

Sorry, did not realize that^^. I know the method from Unity and I think it's a useful addition to MathUtils.

[mrdoob]

Maybe pingpong instead of pingPong in this case? We have smoothstep and smootherstep ...

[marcofugaro]

Sure, it makes sense. Done!

[mrdoob]

Thanks!