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442 Chapter 12: Animation
to define a direction for rotation, so the elbow
or k nees bend correctly. It also allows you to
switch between IK and FK by keyframing IK
Enabling, and it has a special IK for FK pose
function so you can use IK to set FK keys.
• Spline IK Solver (page 2–473)
The Spline IK solver uses a spline to determine
the curvature of a series of bones or other
linked objects.
Vertices on a Spline IK spline are called nodes.
Like vertices, the nodes can be moved and
animated to change the curvature of the spline.
The number of spline nodes c an be fewer than
thenumberofbones. Thisprovidestheease
of posing or animating a long multiple-bone
structure with just a few no des, as opposed to
animating each bone individually.
Spline IK provides a more flexible animation
system than other IK solvers. Nodes can be
moved a nywhere in 3D sp ace, so the linked
structure can be intricately shaped.
A helper object is automatically placed at each
node when Spline IK is assigned. Each node is
linked to its corresponding helper , so a node
canbemovedbymovingthehelper.Unlikethe
HI Solver, the Spline IK system does not use
a goal. The positions of nodes in 3D space is
the only factor that determines the shape of the
linked structure. Rotating or sca ling nodes has
no effect on the spline or structure.
Note: 3ds Max also provides two other methods
of inverse kinematic manipulation of hierarchies,
which don’t depend on a solver: Interactive IK
(page 2–480) and Applied IK (page 2–481).
IK with B ones
While you can apply an IK solver to any hierarchy
of objects, a system of Bones (page 1–404)
combined with an IK solver is a good way to
animate a character.
A bones system is a jointed, hierarchical linkage
of bone objects. Bones are used as an armature
on to which objects are link ed. If you use the
skin modifier (page 1–791),youcan"skin"an
object to the bones, so the animation of the bones
deforms the mesh that models a character. If you
have a jointed character, you can use l in kage or
constraints so the bones animate the mesh.
Animating bon es with skin causes the skin to stretch or shrink.
Turning O ther Objects into Bones
Any object c an be turned into a bone object.
Right-click any object and select Properties from
the quad menu (page 3–694).IntheBonegroup,
choose Bone On /Off. You ca n then choose Show
Links Only to replace the display of the objects
w ith the bones. This can be useful if you have a
geometrically intensive hierarchy to animate. The
interactive viewport response will be much quicker