So I'm learning kineFX in Houdini, not new to the software at all, but I have only two days of "experience" in all this rigging stuff.

I already created the skeleton and oriented the bones properly. The issue is that I keep encountering a very annoying bug. When I try to unparent a bone, fix its orientation, and reparent it again, the rig pose suddenly starts to glitch, and all the handles shift to weird pivot offsets, becoming deformed.
By simply selecting the joint, the pose shifts. It moves with all transform parms to 0.
I fixed that by simply not using the parent thing and working on the orientation by eye, but then I tried to create twist joints on the arm, and the bug happened again. I have no idea why, and I have no idea how to fix it, because I need a way to create those joints.

This was recorded on H 20.5.487 btw, but I updated the H v21.0.440 (the latest version) and the bug remains the same.

Thanks so much if somebody has already had this issue and knows how to fix it )

I'm not sure what the exact cause is, but here Rig Pose SOP is telling you something is wrong. What does the warning say in the node info panel?

raincole

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I'm not sure what the exact cause is, but here Rig Pose SOP is telling you something is wrong. What does the warning say in the node info panel?

Thank you, man! I didn’t see the warning — what an amazing eye you have! The warning says: “Discarding shears on group0.”

As far as I’ve discovered, when you unparent/parent, split, resample, or modify the joint geometry, the transform matrix gets corrupted. It’s no longer orthogonal (only translation, rotation, and scale) after those modifications and ends up with more values than it should. Because of that, the Rig Pose node interprets it as if there’s shear in the matrix and discards it right away.

Once part of the matrix is deleted, the rest of the components break since there’s missing data. Apparently, you can’t really do anything other than deleting the attribute and rebuilding it again. I tried using Orient Joints, reconstructing the matrix with Rig VOP and Attribute VOP… nothing worked.

The only solution I found was: Attribute Delete → Orient Joints.

I even made a tutorial in case anyone else encounters this bug, because it was a real pain to solve.
Thanks again

The problem here is that the Resample SOP is a generic geometry operator so it doesn't know about the data constraints that KineFX requires. So what happens is that the Resample SOP is mostly likely just linearly interpolating the components of the transform matrices (feel free to log an RFE to improve this). My fix here is to just apply a Rig Doctor and then an Orient Joints (make sure you turn on Up Vector). I've attached the file I tried.