Adobe's Flash Professional provides many ways to animate objects. A highly useful feature for creating lifelike animations of people and animals is the Bone Tool. The Bone Tool allows you to animate body parts at their joints by creating Inverse Kinematic chains, which are chains of bone segments, such as a leg, a knee and a foot. IK chains provide a wide range of motion --- sometimes too wide to appear realistic. You can constrain IK chain movements by creating anchor points at the joints of the chain, making the motions of the animation appear more lifelike.
- Skill level:
- Moderately Challenging
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Things you need
- Flash CS4 or later
Open an existing Flash movie (FLA) in which you want to create an animated body part or start a new movie: Click the "File" menu and choose "New." This opens the New Document dialogue box. Choose "ActionScript 3.0," and click "OK."
Drag the segments of the body part (or parts) that you want to animate from the Library panel to the stage, or use Flash's drawing tools to draw the body parts. IK chains must consist of separate objects. For example, a leg would consist of an upper leg, lower leg and foot, each segment a different object. If you draw the segments with Flash's drawing tools, place Flash in Merge Drawing Mode. The Merge Drawing button is the second button from the bottom of the Tools panel. Merge Drawing is turned on when the button appears depressed.
Select all the segments of your body part, and then select the Bone Tool, which is the bone icon in the Tools panel.
Draw the segments of the IK chain over each segment of the body part. Each IK chain segment has a start joint and an end joint. Start each new segment where you ended the previous segment.
Creating an IK Chain in Flash
Click the IK chain segment you want to constrain to select it. When you select an IK chain segment, the changes that you make to the segment apply to the joint at the top of the segment. If, for example, you select a thigh segment, the setting's changes you make will apply to the hip joint, rather than the knee joint.
Go to the "Joint: Rotation" section of the Properties panel, click "Enable," and then click "Constrain." By default, Flash adds an anchor point with a minimum and maximum constraint setting of 45 degrees each. You can widen and shorten the constraint by adjusting the "Min" and "Max" values. For example, a foot joined at the ankle has a limited range of rotation. You cannot move your foot upward 45 degrees, so you would adjust the "max" setting to constrain the upward movement of the foot to a more natural setting, such as 20 degrees. The "Min" setting constrains the downward movement.
Repeat Step 1 and Step 2 for each IK chain joint you want to constrain. Now, when you manipulate the segments with the Selection tool, the movement of body parts should appear more natural.
Adding Anchor Points to the IK Chain
Tips and warnings
- You can add anchor points to control back and forth, or sideways, movement of the body segments with the "Joint: X Translation" and "Joint: Y Translation" options in the Properties panel. Follow the steps for adding anchor points to the IK chain.
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