Page 1025 - Kitab3DsMax

After the Skin modifier is applied and bound to the skin mesh, every bone includes an area of influence
called an envelope that defines the skin vertices that it controls. If any of the skin mesh vertices are outside
of the bone’s envelope or are included in an envelope for the wrong bone, then the vertices are left behind
when the bone is moved. This causes an odd stretching of the skin that is easy to identify.
To check the envelopes, select and rotate several of the skeleton’s key bones. If any envelope problems
exist, they are easy to spot, as shown in Figure 40.3. The incorrect stretching of the vertices for the boot
simply means that the envelopes need to be adjusted.
FIGURE 40.3 Chapter 40: Skinning Characters
If the envelopes are off for any of the skin vertices, the skin stretches incorrectly.

Editing envelopes
When the Skin modifier is selected, the Parameters rollout includes an Edit Envelopes button that places
you in a special mode that lets you edit the envelope for the selected bone in the bone list. This mode is also
enabled by selecting the Envelope subobject under the Skin modifier at the top of the Modifier Stack.
When the Edit Envelopes mode is enabled, the entire skin mesh is colored with a gradient of colors to visu-
ally show the influence of the envelope. Areas of red are completely inside the envelope’s influence, areas of
green are somewhat affected by the bone, and areas of gray are completely outside the envelope’s influence.
Figure 40.4 shows a simple loft object surrounding three bone objects with a Skin modifier applied. The
Add Bone button was used to include the three bones within the Skin modifier list. The skin has been set to
See Through in the Properties dialog box, so the bones are visible. The first bone was selected in the bone
list, and the Edit Envelope button was clicked, revealing the envelope for the first bone.

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