2009

History-Independent (HI) IK Solver
The HI (History-Independent) Solver does not rely on IK solutions calculated
in previous keyframes in the timeline, so it is just as fast to use at frame 2000
as it is at frame 20.
The HI Solver uses a goal to animate a chain. You animate the goal and the
IK solver attempts to move the end effector (the pivot point of the last joint
of the chain) to match the position of the goal. Often the goal is parented to
other control objects such as points or dummies, splines or bones, and these
control objects in turn are wired to viewport or rollout sliders.
The IK solution takes place in a plane, known as the solver plane. The angle of
the solver plane in world space is controlled by a parameter called the
swivel
angle
on page 3397. The swivel angle is animatable. You can adjust it directly,
or with a manipulator.
The HI Solver allows for the creation of multiple or overlapping chains. This
allows you to create multiple goals for additional controls. By linking the goals
to points, splines, bones or dummies, you can create simple controls to animate
complex chains or hierarchies. You can also use constraints on these goals or
control objects, as another animation tool.
Applying an HI Solver
To apply an HI Solver to any part of a hierarchy select the bone or object
where you want to the solver to start. Then choose Animation menu > IK
Solvers > HI Solver. In the active viewport move your cursor to the bone where
you want the chain to end. When you click to select that bone, the goal is
drawn at the pivot point of that bone. If you want a goal at the far end of the
bone, refine the bone where you want to goal to be placed. An extra bone will
be added, and then choosing that bone allows you place the goal at the end.
When you create bones, a small "nub" bone is automatically created at the
end of the chain to assist in this process.
Setting Up Multiple Chains
To rig a skeleton for a human leg you could use three chains in one leg, as
follows:
■ The first chain is created from the hip to the ankle. This chain controls
the overall leg motion including bending of the knee.
3392 | Chapter 15 Animation