Inverse kinematics (IK) lets you create life-like animation by linking parts so they move in relation to one another in a realistic manner.

For example, using IK you can move a leg to a certain position by articulating the movements of the joints in the leg required to achieve the desired pose. IK uses a framework of bones chained together in a structure called an IK armature. The fl.ik package helps you create animations resembling natural motion. It lets you animate multiple IK armatures seamlessly without having to know a lot about the physics behind the IK algorithms.

Create the IK armature with its ancillary bones and joints with Flash. Then you can access the IK classes to animate them at runtime.

See the Using inverse kinematics section in Using Flash CS4 Professional for detailed instructions on how to create an IK armature.

Your ActionScript code to initiate and control the movement of an IK armature at runtime typically does the following:

The following reference list contains important terms that you will encounter in this chapter:

• Armature: A kinematic chain, consisting of bones and joints, used in computer animation to simulate realistic motion

• Bone: A rigid segment in an armature, analogous to a bone in an animal skeleton

• Inverse Kinematics (IK): Process of determining the parameters of a jointed flexible object called a kinematic chain or armature

• Joint: The location at which two bones make contact, constructed to enable movement of the bones; analogous to a joint in an animal