Maya Rendering Guides

Using Blended Wire Deformers for Facial Rigging

Although blend shapes create a flexible and convincing facial rig, they are often tedious to set up and prone to errors. If you apply the Create Blend Shape tool to curves, however, you can avoid some of these problems. With such a setup, various parts of the face are driven by blended wire deformers. To create a blended wire system for a character's mouth, follow these steps:

1. Create a default primitive NURBS circle. Rotate the circle 90 degrees in the X axis. Move the circle so that it sits in front of the character's mouth. Display the circle's vertices. Move and scale vertices so that the circle mimics the contour of the mouth in the front and side workspace views. The curve should not touch the face geometry but should "float" off of it slightly. As with all facial rigging, the best results are achieved if the character's mouth is modeled slightly open.

A circle is shaped to fit a character's mouth.

Once the circle is shaped, choose Modify ^ Freeze Transformations and Edit ^ Delete By Type ^ History. Rename the circle mouthNeutral.

1. Duplicate mouthNeutral. Make one duplicate for each desired target phoneme or mouth blend shape. Move the duplicated target circles to the left or right so that they can be easily seen and edited. Do not, under any circumstance, freeze the transformations of the target circles or adjust their pivots. Rename the target circles to match their intended shapes (for example, mouthSmile, mouthFrown, mouthO, and so on).
2. Open the Hypergraph Scene Hierarchy window. Parent the mouthNeutral node to the character's neck joint. Switch to the Animation menu set, and choose Deform ^ Wire Tool. The Wire tool steps you through the tool's application by printing messages on the Help line at the bottom of the Maya window. First, select the head geometry and press Enter. Second, select the mouthNeutral circle and press Enter. The tool automatically creates a mouthNeutralBaseWire node, which is parented to the neck joint. As a transform node, mouthNeutralBaseWire must travel with the mouthNeutral circle for the deformation to function. The Wire tool also creates a mouthNeutralBaseWireShape node and a wire1 node, which control the deformation in tandem.
3. As a test, move mouthNeutral forward. The lips should be pulled along with the curve. If not, adjust the strength of the wire deformer by selecting the head, expanding the wire1 section in the INPUTS area of the Channel Box, and raising the Envelope attribute value. If the wire deformer's influence is traveling too far and is affecting too much of the nose or chin, reduce the Dropoff Distance[0] attribute, which is found in the same section. Envelope is a scaling factor, which increases or decreases the overall strength of the deformation. Dropoff Distance[0] represents the world distance the wire deformer's influence travels.
4. Return the mouthNeutral to its start position by zeroing out its Translate values. Select all the target circles, Shift+select mouthNeutral, choose Deform ^ Create Blend Shape ^ □, enter a blend shape name into the BlendShape Node field, and click the Create button.
5. Open the Blend Shape window by choosing Window ^ Animation Editors ^ Blend Shape. A blend slider is created for each target circle. Select the first blend shape slider and move it up to 1. In a workspace view, select the corresponding target circle and display its vertices. Move the vertices into the appropriate target shape (smile, frown, and so on). Since the blend slider is at 1, the face deforms as you massage the vertices. Once the target circle makes a satisfactory deformation, return the slider to 0. Select the next blend slider, push it up to 1, and tweak its corresponding target circle. Repeat this process for each of the blend sliders and target circles.

Although this section uses primitive circles to create wire deformers, you are free to use curves created by the CV Curve and EP Curve tools. As such, the curves do not need to be closed. At the same time, the curves do not need to have an excessive number of vertices. If

Weighting a Head with the Component Editor 9 9

you'd like to add similar wire deformers to other parts of the face, such as the eyes or eyebrows, repeat the steps with new sets or neutral and target circles or curves. A sample scene is included as mouth_wire.mb in the Chapter 5 scene folder on the CD.

(Left) A completed blended wire deformer system. Target circles sit to the right of the face and form an O shape, a frown, and a smile . (Right) The corresponding blend shape sliders.

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