8

Bulges 945
The resulting deformation wil l be w1*l1 + w2*l2
+w3*l3+wf*root
.Therootportionofthis
deformation is essentially an undeformed portion
that simply follows the root of the skeleton.
InCaseswhereSomeEnvelopesUse
Par tial Blending and S ome Do Not
The vertex weight fill-in in overlap areas will be
based on the percentage of part ial and non partial
weights. Forexample,Ifthetotalweightofnon
partial links is 80% of the tot al summed partial
and non p a rtial weight, then 80% of the fil l-in
will be more of the non partial deformation. The
remaining 20% fill-in will come from the root.
Example: If Vertex
v is assig ned to links l1, l2, and
l3, the weights for these link s a re: w1 =0.2, w2 =
0.3, and
w3 =0.4.
Let’s assume
l1 and l2 are nonpart ial, and l3 is
part ial. 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.
The program fi lls in w ith 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 nonpar t ia l links.
Bulges
For some animations, simply attaching the skin
and correcting its vertex assignments results in an
animated skin you can use in final renderings. For
other animations, you might need to give the skin
more realistic movement, for example, muscles
that bulge.
Physique lets you simulate an underlying
musculature for the skin by adding
tendons (page
2–948)
and bulges:
• Bulges change t he skin’s profile to simulate
bulging muscles. You create the bulge by
establishing bulge ang les, relationships between
cross-sectional slices of the skin and specific
poses of the skeleton joint. Imagine a cross
sectiontobeaslicethroughtheskin’smesh,
perpendicular to the link. By making changes
tocrosssections,youinturndistorttheshape
of the mesh. Bulges in your character can b e
constructed by associating certain poses with
related changes to the cross sections, in other
words by defining
bulge angles .
At any joint angle, you can define a bulge
angle, and you may define as many bulge
angles as needed. T he bulge angle consists of
the current orientation of the joint together
w ith any defined cross sections. In addition,
you can adjust the influence of a bulge angle.
Physique considers all the bulge angles as the
character moves. The resulting bulge is created
byinterpolatingtheeffectsofthevariousbulge
angles having some influence at the current
joint angle.
Forexample,tocreateabulgingbicepsmuscle,
in Bulge sub-object level, on a selected link,
insert a cross section near the center of the
upper arm. Pose the ar m into a flexed position,
w ith the angle between upper and lower arms
at 90 degrees or less. Insert a bulge angle and
adjust the cross section so that it distorts the
mesh appropriately. In the viewports and in the
Bulge Editor (page 2–965) ,youcaneditthe
shapeofthebulgetolooklikeaflexedbiceps
muscle:higherandwiderabovethebone
than below it. Now as the el bow bends f rom a
straig ht orientation up and toward the shoulder,
Physique bulges the biceps appropr iately.
see
Creating Bulges (page 2–946) for more
information about creating bulges.