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320 Chapter 12: Animation
• position extents for sliding drawers
•camerafield-of-view
• limiting patch resolution to that supported by
thegameengine
Character riggers can use limits to create complex
relationships or shortcuts in rigs. Examples
include:
• Wire wrist-twist bones to t he rotation of the
hand, but limit the rotation of the wrist-twist or
hand to stop short of any flipping that might
occur.
• Prevent unnatural translation of a spline IK
helper by causing limit values for its local
position tracks to react to the ang le or distance
of the helper from surrounding helpers.
• React to when IK is disabled, and match the
limits of the solver in FK .
• Limit the position of the IK chain s wivel-angle
target for the k nee so that it can never go behind
the charac ter. T hat i s, the target is linked to
character’s root.
Use Cases
Followingisabrieflistofexamplesofspecificuses
for the Limit controller:
• Select the Y Rotation tracks of all finger bones
in a character’s hands and assign a Limit
controller. Use Set Key mode to pose the fingers
at the extremes of their ranges of motion and
then use the
rig ht-click menu (page 2–325) >
Set Upper/Lower Limit commands to limit the
fingers’ motion.
Note: Limits are included for Set Key via the
Other category.
• You apply a Noise controller to the X Rotation
track of a w indow shutter object to m ake it
rattle, but the object intersects the building
at the lower end of its motion range. Apply a
Limit controller to the track and s et the L ower
Limit value to prevent the intersection.
• Following from the previous example, say
the wind tears the window shutter from the
building at frame 100. If the Noise controller
isinaFloatListwithaBezierFloat,youcan
weight the noise to 0 at frame 100, when
the s hutter is torn from the building by the
wind, at which point the animator will key the
animation. Limits are unnecessary after frame
100. At frame 99, you’d use Set Lower Limit.
Then, at frame 100, you’d edit the Lower Limit
value to set the limit to much lower, essential ly
remo ving the limit. Finally, you would set
keyframestoanimateitsmovementpastframe
100.
Limita tions of the Limit Contr oller
It’s important to be aware of the following
limitations of Limit controllers:
• Limit controllers do not limit IK joints. All IK
solvers use their own limits, and ignore Limit
cont rollers. Interactive IK uses t he cur rent
controllers,butitalsohasitsownlimits,so
using Limit cont rollers with interactive IK w il l
produce unpredictable results.
• The Limit controller currently supports only
Float controllers. Thus, the Limit controller is
currently available only under the name Float
Limit.
• Upper and lower limits values are expressed
inthesameunitsorcoordinatesasthoseused
by the limited controller. Thus, for example,
Float limits on an X Position track are in local
coordinates, not in global coordinates.
Procedure
Example: To use the Limit controller:
1.
Startwithananimatedobject,andopenCurve
Editor.