9

Understanding Physique 835
Envelopes and Weighted Vertices
EnvelopesarethePhysiquemodifier’sprimary
tool for controlling skin deformation; tendons
and bulge ang les are used to fine tune mesh
deformation after envelopes are adjusted. All
envelopes have an inner and outer bound
(boundar y). Vert ices 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 between the inner and outer bounds receive
a weight between 0 and 1.
Ver tices 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 weighting
from multiple links is considered blending.Itis
possible that weights assigned to some vertices
don’t reach a total weight of 1.0 or greater. Rather
than leaving these vertices b ehind, Physique by
default normalizes them to a val ue of 1.0.
Adjusting falloff, overlap, sca le, and other envelope
parameters changes vertex weight distribution
across links. This, in turn, 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 will be to adjust envelopes.
Deformable and R igid Envelopes
TherearetwoEnvelopetypesperlink,deform able
(page 3–927) and rigid (page 2–1085).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 p arameters. Rig id 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 rigid envelopes exclusively. B oth
rigid and deformable envelopes can be turned on
for the same lin k. For example, by scaling b oth
envelopes, you could deform the shoulder with a
rigid envelope and the armpit with a deformable
envelope.
The Number of Links T hat Can Affect a
Vertex
Any number of overlapping envelopes (NLinks
(page 3–978))caninfluencevertices.Normally,N
Links are preferred. For special purposes 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, al ign the biped to the
mesh in Figure mode (page 2–982).Useapose
w ith the arms outstretched so the hands are away
from the torso. Sa v e 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. Tur n on Attach to Node and select the
root node in the hierarchy (biped Pelvis or root
node in a bones hierarchy, not the C OM). In the
Physique Initialization dialog, click Initialize to
create default envelopes based on the links 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