[Rigging] Tri-joint shadow weighting

A skinning technique to fake deforming layers using Linear Blend Skinning (i.e. a unique skin cluster in Maya), useful for instance, for characters with overlapping geometry layers (e.g., body + clothing). The requires 3 joints under a common parent:

• Primary deformer joint - Influences both mesh layers simultaneously, skin weights are identical, preventing interpenetration during shared deformation
• Inner layer joint - Controls the inner mesh only
• Outer layer joint - Controls the outer mesh only

The key to avoid self-penetration resides in:

• The inner and outer joints position is unchanged while the primary joint animates.
• Inner and outer joint share the same skin weight pattern ("shadow weight")

Notes

A proper way to deform multiple layers is to apply multiple deformers, for instance, several skin clusters (Maya), or some post process lattice deformation etc. Those are usually not supported in game engines though.

 

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