e.g. When I rotate the character's upper shin bone, the vertices behave as if her lower thigh bone is also rotating. enter image description here

The vertices around the lower thigh are not weighted to anything else but the thigh bones and I only have one armature modifier. I'm fairly certain it's reacting to that unmoving lower thigh bone but just don't know why. I don't even know what to google for this problem! enter image description here enter image description here I have used many many bone constraints on this rig but as far as I can tell no constraint should result in a mesh deformation without the bone actually moving. Does Blender just become glitchy when you use too many bone constraints?

[edit] I also want to add that this problem is absent when I import the model and animation into Unreal Engine 4 so it's looking more and more like a bug or a Blender feature that I'm not aware of.

  • $\begingroup$ I actually dont see much of a problem there. (usually you want the knee to stretch instead of just clasping in on its self.) However, try unchecking preserve bone volume. $\endgroup$ – David May 1 '16 at 17:18
  • $\begingroup$ The problem is the bulge on the front of the thigh that only appears when the knee bends. The bones that are moving have no weights touching that part of the leg so it shouldn't be moving. Preserve volume also has no effect on the problem, unfortunately. $\endgroup$ – GearSting May 1 '16 at 17:31
  • $\begingroup$ Consider showing images in [weight paint] mode for the bones you believe are defectively affecting the mesh. $\endgroup$ – atomicbezierslinger May 1 '16 at 17:50
  • $\begingroup$ I could only post two out of the three pictures I had due to being new. Should I just post the weight paint pic as an answer? $\endgroup$ – GearSting May 1 '16 at 17:54
  • $\begingroup$ Okay I just edited the question's second picture. Should be more helpful but now you'll just have to take my word for it when I say that those vertices around the lower thigh are not weighted towards anything but the thigh bones and the little bit of the shin you can see. $\endgroup$ – GearSting May 1 '16 at 18:06

Okay so I fixed it, I think. I just dissolved the lower thigh bone and subdivided the upper one and gave the new one the same name as the old lower thigh bone so the weights would sync up.

I still have no idea what the problem was but it's gone now.

  • $\begingroup$ An answer should give the root cause. $\endgroup$ – ideasman42 May 3 '16 at 3:37
  • $\begingroup$ Weights. Try to set Show Zero Weights = Active instead of None (in options tab of the weight paint mode). I can bet, you'll be surprised. :-) The cure - using Clean button of weight tools with low threshold, and then normalize all the deforming groups. Or select and remove verts from groups by hand in edit mode. $\endgroup$ – Mechanic Nov 24 '18 at 15:46

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