Graphics Reference
In-Depth Information
to it naturally, all with only three controls.
Because they are weight-bearing limbs, the
legs are rigged with inverse kinematics.
In the reverse foot rig, the bone that
extends through the majority of the foot
(FOOT in Figure 9.10) begins at the base
of the toe bone and ends at the base of the
lower leg bone. Both the toe bone and this
reverse foot bone are offset children of the
LEG CONTROL bone. All translations
and rotations around theY- and Z-axis have
been locked so that a user cannot directly
manipulate the bones. Movement of the
foot is accomplished by translating and
rotating the LEG CONTROL bone so
that both children (the foot and toe) move
together. The nice thing about the reverse
foot, though, is that you can still rotate the
FOOT bone along the X-axis, letting you
raise the heel off the ground, while keeping
the toe bone anchored, as in Figure 9.11.
Extruded from the end of the foot bone
is an ankle bone (ANKLE in Figure 9.10),
which acts as the target of the leg's IK chain.
And so, moving the LEG CONTROL
moves FOOT, which in turn moves
ANKLE, which drives the IK chain of the
legs. To the animator, though, it's as sim-
ple as manipulating the LEG CONTROL
bone. The rest of the action is hidden.
The toe bone has freedom to rotate along
the X-axis, just like the foot bone, so that
the toes can be curled in either direction.
KNEE
ANKLE
FOOT
LEG
CONTROL
TOE
Figure 9.10
Lower leg and foot controls, demonstrating the “reverse foot” rig
Figure 9.11
You can rotate the foot bone to raise the heel without affecting
the toe placement
NOTE
Consider how much of a rig you need. Even though the mother's toes are individually visible, they
will never move independently. A bone structure for each toe would be overkill, so a single con-
trol is used and the toes are treated as a part of the shoe for animation purposes. The Beast's toes
are sometimes posed expressively, more like a hand, so each toe gets its own control in that case.
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