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840 Chapter 14: character studio
at the parent and child ends of links. Vertices
w ithin overlapping envelopes are blended to
create smooth skin deformation over joints a s
the charac ter moves.
Adjus t Skin B ehav ior
Adjust Physique parameters and introduce
skin behavior effects to achieve the desired
characterization.
• Change default envelope shapes by adding cross
sections and control points to isolate a more
specific volume of vertices for each bone. Use
exclusion lists or per-vertex weighting to apply
fine-tuning control over individual vertices.
• Introduce bulge angles to change muscle shape
based on the ang le of a particular joint. Create
tendons to simulate the motion of tendons
under the skin, based on link movements.
• Adjust lin k parameters to change skin twisting,
sliding, and creasing as t he biped moves.
Sliding allows the skin to compress at the biceps
and forearm as the elbow is bent. Twisting
controlstheamountofskintwistingacrossa
joint intersection.
• Create extra links using 3ds Max bones and
dummy objects for added control. Links can
be added to the abdominal area to control
compression, for example, or to create a link
to animate the chest rising and falling as the
character breathes. If a character has extra
appendages, 3ds Max b ones can be added to
animatethem.Onecommonusageistoadda
bone to animate the jaw.
For further detail, see Physique (page 2–1076).
Animate the B iped Sk eleton
OncetheskinisattachedtoaBipedstructure,you
can freely animate the Biped character and see
then skin behavior update automatically , based on
the c urrent po se.
Tip: SincePhysiqueskindeformationcanslow
visual pla yback of your Biped animation, you
can temporari ly hide the skin object or reduce
itsresolutioninthemodifierstacktoimprove
performance.
You can also choose to develop Biped animations
in a separate scene entirely, and apply them to your
final skinned character when you are satisfied with
your final motion.
A biped (page 2–843) character is essentially an
integrated hierarchy of bones that you can position
freely using keyframes, IK goals, and footsteps.
You can position a biped character using al l
the rotation and transformation tools found in
3ds Max.
Manyofthe3dsMaxcoordinatesystemscanbe
used to position the biped. Local coordinates are
useful to move a limb along its axis (the local X
axis is always the axis along the biped limb); world
coordinates are handy when there is any confusion
regarding which way is up. You can use world
coordinatesasahomebase.In3dsMax,theworld
Zaxisisalwaysup.
Note: Rotationsalwaysoccuraboutthelocalaxis.
Use Freefor m Techniques
Biped provides a variety of methods for creating
character motion e asi ly. You can use a purely
traditional approach by m anually creating
keyframes in freeform mode for different poses,
letting the computer interpolate between joint
positions and IK goals.
Use a Footstep-Driv en Technique
You can also choose a partially assisted approach
by using footsteps and Biped dynamics to help
you create a default walk, run, or jump cycle, and
then adjust the biped keyframes and footsteps
individually.