[Ralith]

Even if you're writing your own engine from scratch, VR runtimes provide orientation information directly to the engine as a 4x4 transform matrix. They would have to ignore all the documentation and go far out of their way to somehow regress to euler angles, and are likely introducing other precision issues in doing so.

[dreamcompiler]

4x4 transform matrices typically represent 3-space transformations with homogeneous coordinates. Rotation matrices in this framework are effectively the same thing as Euler angles. They are not quaternions.

[vvanders]

If you want to get pedantic they're also not euler angles, they're 4x4 transformation matrices.

You can pick out euler angles just as easily as calculating the quaternion by taking the basis vectors through the matrix and extracting it from there.