Similar method to Unity's Quaternion.FromToRotation?

Spectrix · January 31, 2022, 5:36pm

Is there a method that gives similar results to Unity’s Quaternion.FromToRotation() in Flax Engine? So far I can’t find any.

stefnotch · January 31, 2022, 7:07pm

Last time I checked, there wasn’t one. So here is an implementation. Feel free to just copy it, I’m hereby releasing those functions under CC0.

But more importantly, would you have a name suggestion for them? They are certainly useful enough to warrant being added into Flax.

github.com

stefnotch/anime-rendering-experiments/blob/00f6da2b911374f52835f8299829d0e1e718b243/Source/Game/InverseKinematics.cs#L16-L52

    
      
          // Terrible name, suggest better one plez:
          public static Quaternion FromVectors(ref Vector3 from, ref Vector3 to)
          {
              // See https://web.archive.org/web/20210224054602/lolengine.net/blog/2014/02/24/quaternion-from-two-vectors-final
              float normUV = Mathf.Sqrt(from.LengthSquared * to.LengthSquared);
              Vector3.Dot(ref from, ref to, out var realPart);
              realPart += normUV;
          
          
    Vector3 normal;
          
          
    if (realPart < Mathf.Epsilon * normUV)
              {
                  realPart = 0.0f;
                  normal = Mathf.Abs(from.X) > Mathf.Abs(from.Z) ?
                      new Vector3(-from.Y, from.X, 0.0f) :
                      new Vector3(0.0f, -from.Z, from.Y);
              }
              else
              {
                  Vector3.Cross(ref from, ref to, out normal);

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Spectrix · January 31, 2022, 7:45pm

Thank you very much! Maybe VectorFromTo as a name?

stefnotch · February 1, 2022, 8:00am

Interesting. How about being more specific and calling it

DirectionFromTo
FromDirections
FromToDirection

After all, one gives the function direction-vectors.

Spectrix · February 1, 2022, 2:48pm

That’s definitely a better idea. I liked FromToDirection the moment I saw it.

Spectrix · February 19, 2022, 7:50pm

Maybe they can get added in time for the Flax 1.3 release.