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448 Chapter 12: Animation
Creat ing Control Obj ects
To create control objects to animate the goals,
create dummies, points, splines or other objects
near the goal, then link the goa l to the control
object. For example in a human leg, you migh t
have a goal at the ankle, ball of the foot, and the
toe. You then create three splines under the foot,
one for the heel, one for the ball and one for the
toe. Link each goal to each spline, then you can
animatethegoalsusingthesesplines.Youcould
also link the splines together, so that the rotation of
the toe is controlled by the movement of the heel.
Bes ides hierarchical linkage, you can n ow use the
new Constraint system in conjunction with IK
solvers. You could apply any of the constraints to
create a relationship between the goals or bones
and other objects. The goal could be posit ion
constrained to a dummy which is moved. Or
you could create three bone chains that are all in
the same place, and constrain one bone chain to
another, then weight the constraints.
Bone chains constrained toge ther
Using control objects gives you something bigger
to select in the viewport. You can also use control
objects to separate chains, for example in a human
arm one chain could end at the wrist and another
separate chain be created for the hand and fingers.
The control object at the w r ist serves as the root
node for the hand chain, yet that chain would
remain disconnected (hierarchically speaking)
from the arm chain.
You can create viewport sliders using the
manipulator helper, and then u se the viewpor t
sliderstocontrolthetransformsofthecontrol
objects. Use wire parameters (page 2–411) to hook
up the sliders with t he control objects. You c an
also create Custom Att ributes to add these sliders
to the object rollouts.
Mix ing For ward K i nematics with Inverse
Kinematics
The HI IK solv er provides a tool for mixing FK
and IK in a single animation t r ack. T here is an FK
subcontroller beneath the IK controller assigned
by this solver .
When the Enabled button is on, the FK
subcontroller values are preserved but ignored.
When Enabled is turned off, the FK subcontroller
values apply. To access the Enabled button, select
thegoalandgototheMotionpanel,thenturnoff
the Enabled button. This will allow you to animate
using FK rotations of the bones or hierarchy
objects.
IK for F K p ose allows one to turn on IK in middle
of FK manipulation. When the Enabled button is
turned off, and IK for FK Pose is on, then selecting
and mo ving the goal lets you use IK to create the
forward kinematic keyframes. Moving the goal
poses the sk eleton and add rotation keys to all the
objects in the chain when the A uto Key button is
on.
When working with IK and FK together it is
possibletocreateasituationwherethegoalhas
moved away from the end of the chain. Use the
IK/FK snap button to reposition the goal, snapping
it back to the end of the chain. When AutoSnap
is on, the snap happens automatically; when you
touchthegoal,youdon’thavetoclicktheIK/FK
snap button.