Matrix4x4.TRS broken with non-identity Scales?

Unity Engine
1

I can’t imagine that something fundamental like this is bugged, so it must be my fault, but I don’t know what it is.

        Matrix4x4 test = Matrix4x4.TRS(Vector3.zero, Quaternion.identity, Vector3.one);
        Debug.Log("trans: " + test.GetPosition());
        Debug.Log("rot: " + test.GetRotation().eulerAngles);
        Debug.Log("scale: " + test.GetScale());

results (correctly) in:
trans: (0.0, 0.0, 0.0)
rot: (0.0, 0.0, 0.0)
scale: (1.0, 1.0, 1.0)

but

        Matrix4x4 test = Matrix4x4.TRS(Vector3.zero, Quaternion.identity, new Vector3(.5f,.5f,.5f));
        Debug.Log("trans: " + test.GetPosition());
        Debug.Log("rot: " + test.GetRotation().eulerAngles);
        Debug.Log("scale: " + test.GetScale());

results in:
trans: (0.0, 0.0, 0.0)
rot: (18.0, 58.3, 58.3) <----- (!!!)
scale: (0.5, 0.5, 0.5)

Am I being dumb here or is this busted?

I’m in Unity 5.5.1f1.

Thanks

2

Those methods you use on the matrix are not built in are they? At least they are not in the online documentation.
As far as I understand it is mathematically impossible to extract the rotation without knowing the scale from a matrix and vice versa, so I’m guessing the rotation extraction method assumes a uniform scale of 1.

3

Huh, that’s interesting. They (GetPosition/Rotation/Scale) seem built in to me - I did not add them. I don’t know what method they are using but if there are no non-uniform scales/skews I think it should be mathematically possible to extract the rotation.

In any case I will have to doublecheck my code to see if my original failure case (before I created the test case I posted) relied on GetRotation not.