ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Working with inverse kinematics
Using Springs
Flash Player 10 and later, Adobe AIR 1.5 and later, requires Flash CS5 or later
Inverse kinematics in Flash Professional CS5 supports bone spring. Bone spring can be set during authoring, and bone
spring attributes can be added or modified at runtime. Spring is a property of a bone and its joints. It has two attributes:
IKJoint.springStrength, which sets the amount of spring, and IKJoint.springDamping, which adds resistance
to the strength value and changes the rate of decay of the spring.
Spring strength is a percent value from the default 0 (completely rigid) to 100 (very loose and controlled by physics).
Bones with spring react to the movement of their joint. If no other translation (rotation, x, or y) is enabled, the spring
settings have no effect.
Spring damping is a percent value from the default 0 (no resistance) to 100 (heavily damped). Damping changes the
amount of time between a bone’s initial movement and its return to a rest position.
You can check to see if springs are enabled for an IKArmature object by checking its IKArmature.springsEnabled
property. The other spring properties and methods belong to individual IKJoint objects. A joint can be enabled for
angular rotation and translation along the x- and y-axes. You can position a rotational joint’s spring angle with
IKJoint.setSpringAngle and a translational joint’s spring position with IKJoint.setSpringPt.
This example selects a bone by name and identifies its tailJoint. The code tests the parent armature to see if springs are
enabled and then sets spring properties for the joint.
var arm:IKArmature = IKManager.getArmatureAt(0);
var bone:IKBone = arm.getBoneByName("c");
var joint:IKJoint = bone.tailJoint;
if (arm.springsEnabled) {
joint.springStrength = 50; //medium spring strength
joint.springDamping = 10; //light damping resistance
if (joint.hasSpringAngle) {
joint.setSpringAngle(30); //set angle for rotational spring
}
}
Using IK Events
Flash Player 10 and later, Adobe AIR 1.5 and later, requires Flash CS4 or later
The IKEvent class lets you create an event object that contains information about IK Events. IKEvent information
describes motion that has terminated because the specified time, distance, or iteration limit was exceeded.
The following code shows an event listener and handler for tracking time limit events. This event handler reports on
the time, distance, iteration count, and joint properties of an event that fires when the time limit of the IKMover is
exceeded.
Last updated 6/6/2012
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