8

582 Chapter 12: Animation
the motion flow system (page 2–878) .The
optimization feature can automat ically find
the best timing for a t r a nsition between two
clips. When you ma ke a transition between
foot-based clips (clips where IK constraints
keep the feet planted at certain times), you can
cause the transition to focus on one foot or
the other. See
Working with Transitions (page
2–592)
.
• In biped animation, if a transition between
foot-basedclipscausesthefoottoslideor
pop slightly during the transition, you can fix
this problem with a
mixdow n (page 3–1067)
(flattening all tracks into one t rack). See
Exporting Animation to the Biped (page
2–601)
.
• You can change the
weight (page 2–596) of clips
or tracks so they affect the animation more at
some times than others. See
Adjusting Track
Weight (page 2–596)
.
• You can use only the part of a clip’s motion that
affects specified body parts. See
Filtering Mixer
Tr acks (page 2–589)
.
• When motions applied to a biped’s upper
body vary greatly from motions on its lower
body, the Mixer a utomatically compensates for
discrepancies in ba lance. See
Adjusting Biped
Balance in the Mixer (page 2–599)
.
Note: Balance parameters are available only
when mixing biped objects.
Tra nsi tions Bet ween Foot-B ased Clips
The Motion Mixer excels in its ability to maintain
smoothness of motion over transitions between
foot-based clips. Foot-based clips use IK
constraints to keep one or b oth feet locked down
overthecourseofthemotion.
For bipeds, the Mixer provides tools for
maintaining foot positions during transitions:
• Computing the influence of balance from the
uppertothelowerbody.Withoutthis,layered
motion t racks w i ll appear to be art ificially
combined since out since the resulting motion
will be plagued by the isolation of dynamics
and improper b alance.
• Mixdowns allow for precise eliminat ion of
the foot sliding with the aid of knee limit
filtering to u nnatural knee poppimg art ifacts.
In short, the goal of the mixer is to assemble
seamless, coherent character motion using
building blocks composed from other motion
fragments.
For non-biped rigs and other 3ds Max objects,
the Mixer provides velocity blends and sub-blends
to maintain smooth and coordinated motion.
Compar ing the Moti on M ix er a nd M otion
Flow
Both the Motion Mixer and Motion Flow (page
2–878)
canbeusedtocreatetransitionsbetween
a consecutive series of BIP files. However, there
are a few signific ant differences between the two
features:
•WiththeMotionMixer,severalBIPfilescanbe
usedatthesametimetoaffectbipedmotion.
Compare with Motion Flow, where only one
BIP f ile, or a transition between two consecutive
BIP files, affects the biped at any given time.
• With the Motion Mixer, you can sp ecify that a
BIP file w ill affec t only one part of the body.
This feature is not available in Motion Flow.
•IntheMotionMixer,youcanuseamixdown
to automatically lock feet during transitions
between biped foot-based mot ions. Motion
Flow does not perform this function.
• A M otion Flow network can be used in
conjunction with the Crowd feature, giving the
bipeds a choice of motions over the course of