As there are many ways to approach facial rigging, I have been speaking with riggers working at different studios to learn about their methods. Some take a more conservative approach, relying mostly on shape keys for deformation. Others prefer a more hybrid method, starting with bone-based deformation and adding corrective shape keys to achieve expressive and appealing shape changes.

Due to the current limitation of Blender's dependency graph, which cannot handle rivets properly, I wanted to create a setup that uses a ribbon system, similar to the one used for eyes.

The ribbon setup involves a guide mesh extracted from an inner lip edge loop. The lip bones are oriented to point toward each vertex on the ribbon mesh. The ribbon mesh is controlled by control bones that are weighted with a smooth falloff. This allows us to generate clean and appealing shapes using simple bone deformation, while maintaining smooth transitions between neighboring points thanks to the ribbon guide.

I am quite pleased with how easy it is to set this up. It provides a straightforward solution for creating a lip zipper and offers comprehensive control over the lips. It allows for the design of extreme shapes such as lip curls and puckers, while still offering the flexibility to move, rotate, and scale individual bones for detailed control over the final shape.