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...

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).

The resulting deformation
will be *w1*l1 + w2*l2 + w3*l3 + wf*root*.
The root portion of this deformation is essentially an undeformed
portion that simply follows the root of the skeleton.

In Cases where Some Envelopes Use Partial Blending and Some Do Not

The vertex weight fill-in in overlap areas will be based on the percentage of partial and non partial weights. For example, If the total weight of non partial links is 80% of the total summed partial and non partial weight, then 80% of the fill-in will be more of the non partial deformation. The remaining 20% fill-in will come from the root.

Example: If 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.

Let's assume *l1* and *l2* are
nonpartial, and *l3* is partial. The nonpartial
weight is *w1 + w2* = 0.5; the partial weight
is *w3* = 0.4; the nonpartial weight
is 0.5/(0.5+0.4) = .555555, or 56%; and the fill-in weight is still
(1.0 - .9) or *wf* = 0.1.

Physique fills in with
56% of *wf* with more of the nonpartial
blended links. The remaining 44% of *wf* is filled
in with the root as in the partial blended case. This provides a
smooth transition between the partial and nonpartial links.