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Partial Blending and Weight Assignments
Most often, you will want to use envelopes to correct the way skin behaves
as the biped moves. However, you can override envelopes by manually
assigning vertex properties. For example, you can remove the influence of
inappropriate links from selected vertices. You can also change the weight
distribution between links for a single vertex by using type-in weights.
In Cases where No Envelopes Use Partial Blending (the Default)
Vertex v is assigned to links l1, l2, and l3, and the weights for these links are:
w1 = 0.2, w2 = 0.3, and w3 = 0.4.
In a non-partial blended case, the sum of these vertex weights is w1 + w2 +
w3 = 0.9 (less than 1.0).
With partial blending off, Physique will normalize the weights so they sum
to 1.0. For example:
w1' = w1 / w1+w2+w3 = 0.2/0.9 = .2222222...
w2' = w2 / w1+w2+w3 = 0.3/0.9 = .3333333...
w3' = w3 / w1+w2+w3 = 0.4/0.9 = .4444444...
so
w1'+w2'+w3' = 1.0
In Cases where All Envelopes Use Partial Blending
The weight fill-in for vertices with a weight less than 1 will always fill with
the weight of the root. Whenever a vertex is assigned to a group of links, all
of which are partially blended, then the remaining weight will be assigned
and blended with the root link.
This works well for a case where you want partial deformation falling off to
no deformation. An example would be a static head, where you are deforming
the head for facial expressions, but the head itself remains in place.
For example: vertex v is assigned to links l1, l2, and l3. The weights for these
links are: w1 = 0.2, w2 = 0.3, and w3 = 0.4.
The sum of these vertex weights is w1 + w2 + w3 = 0.9 (less than 1.0). We need
an additional fill-in weight (wf). The fill-in weight is determined by 1.0 -
(w1+w2+w3) = 0.1, or 10%. Physique fills in with weight wf from the root
(leaving the vertex partially undeformed).
4646 | Chapter 17 character studio