Hi all, I’m delving into facial motion capture and the only snafu I’ve encountered so far is a rigging/parenting hierarchy when using Rigify-based rigs. So in a given scene I’ve got:
-the tracking empties (no tracking constraints on them, they’ve been baked to f-curves) aligned with the control bones of the facial rig. In some cases, these bones are deformers themselves (like for the eyebrows, for instance).
-the Rigify-based rig with a facial deformation setup.
-All the facial rig control bones are parented to a face root bone, which is in turn parented to the Rigify ORG-Head bone.
-Copy Location constraints on the control bones, targeting the tracking empties in World Space.
So what I was doing with a much simpler rig was parenting the control bones and the empties to a Head bone, then parenting the Head bone to a Head control bone. This way I was avoiding any cyclic dependencies.
But Rigify isn’t a terribly “simple” rig, and I just can’t wrap my head around how to avoid cyclic dependencies here. Please help! 
I thought the description might be sufficient, but I can upload a .blend if necessary.
