8
Understanding Physique 693
Envelopes and Weighted Vertices
EnvelopesarethePhysiquemodifier’sprimary
tool for controlling skin deformation; tendons
and bulge angles are used to fine tune mesh
deformation after envelopes are adjusted. Al l
envelopes have an inner and outer bound
(boundar y). Vertices falling within the inner
bound of a single link receive a full weight of 1.0
from that link. Those falling outside the outer
bound receive no weight from that link. Vertices
falling b etween the inner and outer bounds receive
a weight between 0 and 1.
Vertices move together with the link that influences
them. Where multiple envelopes encompass
a vertex, that vertex receives weight from each
envelope and follows each link to an average
position based on these weights. This weig hting
frommultiplelinksisconsidered
blending
.Itis
possible that weights assigned to some ver tices
don’t reach a total weight of 1.0 or greater. Rather
than leaving these vertices behind, Physique by
default normalizes them to a value of 1.0.
Adjusting falloff, overlap, scale, and other envelope
parameters changes vertex weight distribution
across links. This, in tu rn, changes the way sk in
behaves as the biped moves. Much of the work
you’ll do to correct the way skin deforms on a
character wil l be to adjust envelopes.
Deformable and Rigid Envelopes
There are two Envelope t ypes per link,
deformable
(page 3–1021)
and
rig id (page 2–936)
.Deformable
envelopes follow the Physique deformation spline
that runs through the joints in the hierarchy,
and can be deformed using bulge angles,
tendons, and link parameters. Rigid envelopes
determine vertex-link assignment based upon
the linear 3ds Max link and move in an immobile
relationship to the link. Vertices in a rigid
envelope, however, are deformed (blended) in the
overlap area of other envelopes.
Typically you use deformable envelopes; however,
game developers with game-engine restrictions
may want to use r ig id envelopes exclusively. Both
rigid and deformable envelopes can be turned on
for the same link. For example, by scaling both
envelopes, you could deform the shoulder with a
rigid envelope and the armpit with a deformable
envelope.
The Number of Links That Can Affect a
Vertex
Any number of overlapping envelopes (
NLinks
(page 3–1072)
)caninfluencevertices.Normally,
N Links are preferred. For special pur poses such as
games requirements, you can limit the number of
links (envelopes) that can affect a vertex. The No
Blending parameter is similar to the method used
in version 1 of the software; a vertex is assigned to
only one link.
Physique Work flow
Before Physique is applied, align the biped to the
mesh in
Figure mode (page 2–835)
.Useapose
w ith the ar ms outstretched so the hands are away
from the torso. Save a figure file, so it’s easy to
return to this pose whenever you need. Select
the mesh and choose Physique in the Modify
panel. Turn on Attach to Node and select the
root node in the hierarchy (biped Pelvis or root
node in a bones hierarchy, not the COM). In the
Physique Initialization dialog, click Initialize to
create default envelopes based on the li nks in the
hierarchy. The remainder of the work is adjusting
envelopes and optionally adding bulge angles and
tendons.
Envelope size, overlap, and other parameters
are adjusted with the character in an animated
position (with Figure mode turned off). By
scrubbing the time slider back and forth, you
can spot problem areas and adjust the envelopes
affecting the problem areas. In Place mode is