lackofbindings
Been running into an interesting bug relating to vrc constraints. I will be using this avatar as an example: avtr_c32b6dbf-e8f8-46a4-a338-4828d68e307e It uses VRC Constraints for twist bones in many places. For some reason the lower arm twist bones start to drift out of alignment over time in some circumstances. They have only one axis (Y) frozen, but somehow they slowly drift more and more along the other two axis. Once the bug starts, they seem to very very slowly "orbit" around their pivot over time. The furthest I've seen them go is completely backwards (wrist pointing towards elbows), though usually the effect starts quite subtle.
The constraint still appears to function otherwise perfectly, the weight slider even offsets it towards the resting position (though with the bugged rotation it is still in the wrong place). The strangest part is that it only seems to affect these two constraints on the lower arms, despite there being many more very similar constraints all over the avatar. I suspect it has something to do with gimbal lock and floating point precision.
Resetting the avatar or doing anything that reloads the avatar fixes it instantly, until the next time it occurs.
Repro:
  1. Wear this avatar avtr_c32b6dbf-e8f8-46a4-a338-4828d68e307e
  2. Go to this world wrld_66431182-f46c-45c9-9c8e-ba7f47c10177
  3. Sit in any chair on the vehicle.
  4. Wiggle / move around in chair, like your having a convo, or practically anything to move the avatar
  5. After a bit, check to see if the lower arm joints no longer line up at the elbow.
  6. If arms not separated, continue step 4.
September 25, 2024