Morph Amature flips Face Bone Rotation

[Maneki]

For some reason, when I turn on “auto morph armatures” to adjust the rig to the morph, it seems that it flips the rotation direction of face bones, at least the eye bones are flipped and the character starts looking down while the morph is turned on to go up.

Edit: It permanently flips the rotation, even if I turn “auto morph armatures” off, save the project and reload Blender, it keeps being broken. IMPORTANT: It only breaks after the bones actually have to get adjusted. If you just turn on “auto morph armature” on a base mesh which doesn’t need bone movement adjustment, it keeps working.

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[Thomas Larsson]

I can confirm this behaviour, but I’m not sure what to do about it. The problem arises for bones that are aligned with the Y axis, where a very small change in the head and tail locations apparently can change the local axes a lot.

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[Maneki]

My current solution would be custom eye bones but that’s just a patch at best. From the daz importers perspective that would be maybe auto-generate some eye bones which just follow the location of the original bones but aren’t impacted on the rotation by ERC data?

[Alessandro Padovani]

I’m out of my area of expertise here so it’s just a comment hoping it helps. May the various coordinate systems help with this ? I mean using XYZ or XZY changes the evaluation order of the axis rotation so getting different gimbal locks. Also daz studio has equivalent eulers and when we convert from daz to blender this should be taken into account to get the same gimbal lock for fk poses.

There’s also a “axis angle” in blender 3.1.2 that I never noticed before.

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[Thomas Larsson]

Fixed in last commit. The rotation part of the editbone matrix is now preserved when the armature is morphed, only the bone head and length are changed. In particular, bones that are parallel to the y axis remain so after morphing.

Alessandro, no, that is how the posebone matrix is presented. The editbone matrix depends on the head, tail and roll angle.

[Maneki]

It seems to be fixed at first glance, thanks Thomas!

[Maneki]

Bone rotation issue seems to be fixed.