Facial Motion and Controls - Animating with Blender: How to Create Short Animations from Start to Finish - page 167

eyebrow, have been selected. With that selection made, click the New button in the Vertex Groups sec-
tion of the Links and Materials panel of the Edit buttons , shown in Figure 10.12. Give the vertex group
a descriptive name (such as “right_brow”), and then click the Assign button to actually assign the selected
vertices to the newly created group.

NOTE
Before you enter Edit mode to make your selection, make sure that the Shapes panel is set to
the “Basis” key. Remember that any time you enter Edit mode, you are editing and selecting
based on the currently visible shape. While you could technically build your vertex groups with
the mesh set to any shape, you will probably get a better result when working with the “Basis”
shape.

Create vertex groups in this way for each of the
control zones. Unlike working with weight groups
and the armature deform modifi er, you need to
be very careful how these vertex groups overlap.
Shape keys are additive , meaning that two shape
keys applied to the same area of the mesh will not
blend together—they will reinforce one another.
For example, if you were to create vertex groups
for both the left and right brow areas and have
them share a common seam, the vertices along
that seam will receive twice the amount of shape
keying than they ought to if you were to apply
both shape keys at once. Those vertices would be
moved completely by the one shape control, and
then moved again by the second control, producing
something not very natural, such as in Figure 10.13.

Figure 10.13 The row of vertices between the brows is receiving

shape information from both the left and right brow shapes

To fi x this, you simply reselect only the seam vertices and change their weights to 0.5 in the Vertex Groups
tools. To do this, bring up each group in the panel that the seam vertices are a part of, change the Weight
control to 0.5 , and click Assign . Figure 10.14 shows the border vertices of the right eyebrow group being set
to a weight of 0.5. The weighting on a vertex across all groups needs to add up to 1.0 , indicating that it will
use a total of 100% of the deformation from all shapes combined. In the case of the border between the brows,
0.5 works because there are only two vertex groups affecting those vertices (and 0.5 1.0). If you have

a vertex that is shared by four groups, you would need to give it a weight of 0.25 in each group.

0.5

In reality, though, the notion of discreet, nonoverlapping zones like this will not produce very good results. When a
person moves their right eyebrow, some motion is seen in the surrounding areas. There is no clear delineation of a
stopping point. Something more complex is called for. Figure 10.15 shows the brows as fading, overlapping zones.
This is more diffi cult to accomplish because you will have to set very carefully the weighting to make sure that the