Before going on to the final character rig, I found it prudent to do a few small tests. I’m planning on doing a layered approach to the face rig, with some basic deformer based (armature/latice/curve/meshdeform/etc) controls for major motions on the ‘bottom’ layer, and more specific facial expressions on top. The latter will probably be blend shapes, but I haven’t decided completely yet.
For the jaw, I wanted the ability to rotate the jaw freely (as well as push it back and forth) where rotating down results in opening the mouth/lips, and rotating up results in squashing the lips/face, no interpenetration. I mulled a few ideas, but finally decided on combining an armature deform (this could get a replacement in the final rig) to open the jaw, and a lattice deform to squash it, blending between the two based on the jaw angle.
The final result is a bit more complicated than that; I couldn’t find an easy way to blend modifier influences, so I settled for having both modifiers always on, but blending the influence of the bones that do the deformation based on the angle of the jaw. There is a slight risk here: two non-multimodifiers in the stack on top of each other might look bad splitting the deform, but the result in this test wasn’t too bad.
I present you with a quick video capture of the result:
Keep in mind this is just a test! for a real rig, a lot of refinement would be needed to create pleasing deformations; more complex rigging than just the jaw and head for deformation, more constraints, better weight painting, more careful placement and design for the bulge lattice, correction shapes, etc. However, for a test, this is showing some promise- though I would be more comfortable if I could use multimodifiers and blend the influence of the modifiers directly.
I’ll post more tests as I go along. If anyone is remotely interested in the .blend file for such a simple thing, let me know, I’ll be happy to upload it.
Last note: If you are on a mac and cannot view the video, download XiphQT. If you are using Windows download the Ogg codecs for windows . Firefox, Opera and chrome users should be able to view the video directly in the browser (as should Safari users with XiphQT installed). If it doesn’t work, just use the download link instead.