9

474 Chapter 12: Animation
You can move and animate the spline vert ices
to change the curvature of the spline. Usually,
a helper is placed at each vertex to assist in
animating the spline. The spline curvature is then
passed on to the entire linked structure. The bones
themselves do not change shape.
Normallythenumberofsplineverticesandbones
are the same, but you can use fewer vertices for
easier posing and animating a long multiple-bone
structure with just a few nodes, as opposed to
animating each bone individually.
SplineIKprovidesamoreflexibleanimation
system than other IK solvers. You can position
vertices/helpers anywhere in 3D space, s o the
linked structure can assume any shape you want
to give it.
A helper object is automatically placed at each
vertex when Spline IK is assigned. Each vertex is
linked to its corresponding helper, so a vertex can
be moved by moving the helper.
UnliketheHISolver,theSplineIKsystemdoes
not use a goal. The positions of helpers/vertices
in 3D space is the only factor that determines the
shape of the linked structure.
Note: MovingtheSplineIKhelperstocurlthe
spline can sometimes cause b ones to rotate or
flip unexpectedly. If this happens, you can try
choosing a different upnode object with the IK
chain’sPickUpnodeoptionintheIKSolver
Properties rollout (see Spline IK Solver Rollouts
(page 2–478) ), or use a different I K method for
your hierarchy.
Apply ing a Spli ne I K S olver
The Spline IK solver can be applied at the time
bones are created, or after the bone structure has
already been made.
To apply a spline IK solver when bones are cr eated:
1.
Choose Create panel > Systems > B ones.
2. On the IK C hain Assignment rollout, set IK
Solver to SplineIKSolver, and turn on both
check b oxes: Assign To Children and Assign
To Ro ot.
By default, Assign To Root is on automatically
when you turn on Assign To Children.
3. Drawthebonestructureasusual.Whenyou
right-clicktoendthebonecreationprocess,the
Spline IK Solver dialog (page 2–477) appears.
Set parameters and click OK.