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Envelopes 1085
Envelopes and Ver tex
Assignments
Envelopes
Envelopes a re Physique’s primary tool to control
skin deformation. Envelopes define an area of
influence about a single link in the hierarchy
and can be set to overlap adjacent links. Vertices
that fall in the overlap area of the envelopes are
weighted to prod uce smooth blending at joint
intersections. Each envelope comprises a pair
of inner and outer bounds, each with four cross
sections.
Envelopes
Deformable and R igid Envelopes
There are two envelope types: deformable and
rigid.
• Deformable envelopes influence vertices they
encompass to follow the deformation spline
created through the hierarchy. Only the vertices
encompassed by deformable envelopes can be
affected by bulge angles or tendons.
• Vertices in a rigid envelope are linked to the
node (the bone) and move in an immobile
relationship to the link. Vert ices in a r igid
envelope, however, are deformed (blended) in
the ove rlap area of other envelopes. There is a
tw ist parameter in Link Sub-Object that can
be enabled in a rigid envelope. This allows the
rigid envelope to twist a long t he length of the
link.
Deformable envelopes (above); Rigid envelopes (below)
Typically, you use deformable envelopes when
you attach a mesh to the biped pelvis to produce
a s of t, flexible skin. Later you reassign certain
links, such as the character’s head, to the ri gid
envelope to minimize the deformation. For special
cases, you can tur n on both deformable and r igid
envelopesforthesamelink.Thisadvancedfeature
allows you to average the effect of the two types of
skin deformation for additional firmness in the
skin. The forearms and legs are sometimes good
candidates for this.