8

422 Chapter 12: Animation
Bones system with HI IK solver applied
Each type of IK solver has its own behavior and
workflow, as well as its own specialized controls
and tools that display in the Hierarchy and Motion
panels. IK solvers are plug-ins, so programmers
can expand the software’s capabilities by
customizing or writing their own IK solvers.
3dsMaxshipswithfourdifferentIKsolvers.
How Does a n I K Sol ver Work?
AnIKsolvergenerallyoperatesinthisway:an
inverse kinematic chain is defined on part of the
hierarchy, say from the h ip to the heel, or the
shoulder to the wrist of a character. At the end of
the IK chain is a g izmo, called the goal. The goal
can be repositioned or animated over time in a
variety of ways, often using linkage, parameter
wiring or
constraints (page 2–375) .Nomatter
how the goal is moved, the IK s olver attempts to
move the pivot of the last joint in the chain (also
called the end effector) to meet the goal. The IK
solverrotatesthepartsofthechaintostretchout
and reposition the end effector to coincide with
the goal.
Using an IK solver to animate an arm
Frequently, t he end effector is constrained to the
ground plane. For example, you might "pin" the
toes as the heels lif t in a character walk cycle. Then
the movement of the root of the chain poses the
legs up from the toes.
Four plug-in IK solvers ship with 3ds Max:
•
HI (History-Independent) Solver (page 2–427)
The HI Solver is the preferred method for
character animation, and for any IK animation
in long sequences. With HI Solvers, you can set
up multiple chains in a hierarchy. For example,
a character’s leg might have one chain from hip
to ankle, and another from heel to toe.
Because this solver’s algorithm is
history-independent, it is fast to use
regardless of how many frames of animation are
involved. Its speed is the same on frame 2000
as it is on frame 1 0. It is stable and jitter-free in
viewports. This solver creates a goal and an end
effector (although the display of end effector
is off by default). It uses a
swivel ang le (page
2–430)
to adjust the solver plane to position the
elbow or the knee. You can display the swivel
angle manipulator as a handle in the viewpor t,
and adjust it. HI IK also uses a preferred angle