8

Animation Constraints 375
Select tracks in the dialog that you want to include
in a Block. Valid tracks are darker.
Inter face
Can ce lExits the Track View Pick dialog with no
changes.
If tracks are highlighted in the Hierarchy list,
then the
Block Parameters dia log (page 2–372)
is
displayed when you click OK, to allow you to set
the duration for the Block.
Animation Constraints
Animation constraints are used to help automate
the animation process. They can b e used to control
an object’s position, rotation, or scale through a
binding relationship with another object.
A constraint requires one object and at least one
target object. The target imposes specific limits on
the constrained object.
For example, if you want to quickly animate an
airplane flying a predefined path, you could use a
path constraint to restrict the airplane’s motion to
asplinepath.
The constraint’s binding relationship with its
targets can be animated on or off ov er a period of
time.
Common uses for constraints:
Linking one object to another over a period
of time, such as a character’s hand picking up
abaseballbat
Linking an object’s position or rotation to one
or several objects
Keeping an object’s position between two or
more objects
Constraining an object along a path or b etween
multiple paths
•Constraininganobjectalongasurface
Making an object point toward another object’s
pivot point
Controlling the look at” direction of a
character’s eyes
Keeping an object’s orientation in relation to
another
There are seven types of constraints:
Attachment constraint (page 2–376)
attaches
an object’s position to a face on another object
Surface constraint (p age 2–379)
restricts an
object’s position along the surface of another
object
Path constraint (page 2–380)
restricts an
object’s movement along a path
Position const raint (page 2–384)
causes the
constrained object to follow the position of
another object
Link constraint (page 2–386)
links the
constrained object from one object to another