Activity 6


Inverse kinematics (IK) is a way of animating objects using bones chained into linear or branched armatures in parent-child relationships. When one bone moves, connected bones move in relation to it.

Inverse kinematics lets you easily create natural motion. To animate using inverse kinematics, you simply specify the start and end positions of bones on the Timeline. Flash automatically interpolates the positions of the bones in the armature between the starting and ending frames.

You can use IK in 2 ways:

  • By using a shape as a container for multiple bones. For example, you can add bones to a drawing of a snake so that it slithers realistically. You can draw these shapes in Object Drawing mode.
  • By chaining symbol instances. For example, you can link movie clips showing a torso, arm, lower arm, and hand so that they move realistically in relation to each other. Each instance has only one bone.

Note: You can animate armatures not only in the Timeline but also with ActionScript 3.0. For more information, see the

fl.ikclasses in the ActionScript 3.0 Language and Components Reference.

A shape with an IK bone armature added. Note that the head of each bone is round and the tail is pointed. The first bone added, the root bone, has a circle at the head.

A group of several symbols with an IK bone armature attached. The shoulders and hips of the figure are branch points in the armature. The default transformation points are the head of the root bone, interior joints, and the tail of last bone in a branch.
Note: To use inverse kinematics, your FLA file must specify ActionScript 3.0 as the Script setting in the Flash tab of the Publish Settings dialog box.

Bone styles

There are 4 ways that Flash can draw bones on the Stage:

  • Solid. This is the default style.
  • Wired. Useful when the solid style obscures too much of the artwork beneath the bone.
  • Line. Useful for smaller armatures.
  • None. Hides the bones to show only the artwork beneath them.

To set the Bone Style, select the IK span in the Timeline and then select the style from the Style menu in the Options section of the Properties panel.

Note: If you save a document with the Bone Style set to None, Flash automatically changes bone style to Line the next time you open the document.

Pose Layers

When you add bones to symbol instances or shapes, Flash creates a new layer for them in the Timeline. This new layer is called the pose layer. Flash adds the pose layer to the Timeline between existing layers to maintain the previous stacking order of objects on the Stage.

In Flash Pro CS5, each pose layer can contain only one armature and its associated instances or shape. In Flash CS5.5, the pose layer can contain other objects in addition to one or more bone armatures.