Most often, you use envelopes to correct the way skin behaves as the biped moves. However, you can override envelopes by assigning vertex properties manually.
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.