Wire Deformer Rig for Face Shape Creation
For the purposes of creating a fast way to create blend shapes, I created a wire deformer rig. The wire deformer makes the creation of expressions very quick. By manipulating the points on the curves, I was able to move the surface of the skin in a very elastic, natural way.
Another thing that was working in my favor, in a big way, was that the model being manipulated was a low-resolution cage. This version of the model was very fast to edit, and the smoothed results always looked better than if the model had been edited in high-resolution.
During the process of modeling blend shapes, the animation rig that had the jaw rotation skeleton was used to ensure that the rotation used for the blend shape jaw matched the rotation used by the jaw on the actual animation rig.
Cleanup and Testing
The modeler needs to test and clean up blend shapes after making them. Testing blend shapes is a critical part of the modeling process. Many things can go wrong during the creation of blend shapes. Any time the model is exported from Maya in another format (like .obj) will scramble the order of the polygons in the model. Anything that affects polygon ordering will create many problems.
|[Figure 48] indicates where the curvers were drawn to create the wire deformers used to edit the model for blend shapes.
When testing the model, the modeler should be looking for technical problems as well as aesthetic problems. The technical problems will become evident quickly and require no additional discussion.
The aesthetic problems include the following:
- Does the shape look natural? Does it look like a shape that would normally occur on the face?
- Does the shape cause undesirable stretching and twisting? Most expressions on a real face do not cause too much stretching of the skin, but on a cartoon character, this is not the case. In extreme poses, there will be some stretching that needs to be dealt with, so the modeler needs to determine whether the stretching is acceptable or not.
- Are the polygons distributed as evenly as possible for the blend shape? Uneven distribution of the polygonal topology will cause the geometry and textures to deform unnaturally. The skin in a character is an elastic sheet that covers the bones and muscles, so the modeler has to determine if that sheet is getting stretched too much in one place.
- Test the final blend shapes with the hair, eyes and teeth in place. Are there any intersections of the skin surface with the hair, eyes and teeth?
In order to get the character rendered, the modeler needs to apply UV coordinates to the character. The process of editing UVs has a fairly straightforward goal: Will the texture artist be able to paint textures on this character that will not twist or deform unnaturally?
There are many methods for applying UVs. For this section, the basic application types will not be discussed. In order to texture this model, there were two primary methods employed in the application of UV coordinates. One method was used solely on the head, and the other method was used on the rest of the character.