Hello fellow devs,
we encountered a weird issue with scaling spine bones and cannot figure out if this is a longly hidden engine bug or simply a misunderstanding on our side.
We try to set pelvis, spine_01, spine_02, etc. to fixed values to make an obese Control Rig “template” of our skeleton, where the belly is big. This Control Rig then shall be inserted in an Anim Blueprint and be controlled by its Alpha pin from 0.0 (normal) to 1.0 (obese).
But as soon as we control its Alpha in the Anim Blueprint, there is a weird behavior that child bones from pelvis upwards scale incorrectly. Form 0.0 to 0.5 all child bones increase in size, proportional to the scaled bones in the Control Rig, and from 0.5 to 1.0 the child bones scale back to their original scale. Actually, we expect the child bones to always keep their original scale no matter which value Alpha has.
We tried offsetting the scale, setting it directly, counter-calculating scale from child bones, etc.
Please see the video, since it is hard to explain by text:
We reproduced the identical behavior in UE 5.0, 5.1, 5.2 source-built and 5.0, 5.1 binary. In all versions:
- Custom Control Rig
- Bungee Man Control Rig from Epic’s Samples Pack (only UE 5.1)
- Transform (Modify) Bone nodes (since we thought Control Rigs were not capable of scaling in such a way)
@Jeremiah3D can you give us a hint what might go wrong?
We hope you can help!
Sincerely,
Polyphoria
