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So I'm trying to learn rigging/armatures and I've been dissecting the rigify rig to get a better understanding. But some bones seemingly don't have any children parented to them, yet they still deform the mesh. For example, the torso bone moves the entire torso, but none of the spine bones are parented to it. Also I see no drivers or bone constraints that point to it. Any insight?

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The deform bones are the only bones that actually deform the mesh. Their name begins with DEF- and they are on layer 30. Almost all of them are green-colored. This means they have constraints. The spine deform bones have Copy Transform and Stretch To constraints with the tweak spine bones (layer 5) as their target.

The torso control (layer 4) has some children and grandchildren. If you follow the hierarchy in the outliner, you will find the tweak bone (tweak_spine.003). The neck controller is the parent of the other tweak bone (tweak_spine.004).

Conclusion: the control bones (torso & neck) move the tweak bones, and the deform spine bones follow the tweak bones due to constraints.

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  • $\begingroup$ thank you! I noticed there is actually a MCHTorso.parent bone as a parent to the torso and also the torso is not a child to the root, yet the root still moves the torso bone? $\endgroup$
    – Blith
    Aug 1 at 12:55
  • $\begingroup$ You're welcome. I just took a quick look at how the MCHTorso.parent bone works. Not 100% sure but this bone has a Armature contraint called SWITCH_PARENT. The influence is controlled by a driver that uses a property (torso_parent) assign to the torso bone. This switch is visible in the N-panel in the Rig Main Properties section, called Torso Parent (0/1). Select torso or hips to see it. If it's set to 0 you can move the legs for a jump & the upper body stays in place. Hope that helps :-) $\endgroup$
    – Blunder
    Aug 2 at 10:26
  • $\begingroup$ Just to clarify, it's the Armature constraint (a relationship constraint) that makes the MCHTorso bone a child of the root bone and move along with it. But that is not immediately obvious from the documentation. $\endgroup$
    – Blunder
    Aug 2 at 10:37

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