Chapter 9. Realistic Animation with IK Bones

Everywhere you look in the real world, you see things that are linked together: a dog and its tail, a ribbon and a bow, a train engine and its caboose. And then, of course, there’s that song about the thigh bone connected to the hip bone. In Flash, you’ve always been able to draw these objects, but starting with CS4, you could link them together so they’d move in your animation as if they were actually connected. Now using the Bone tool, you can link objects, so when you move the hip bone, the thigh bone automatically moves in a realistic manner. The animation tool you use is appropriately called a bone; specifically an IK bone. IK stands for inverse kinematics, which is the type of animation algorithm at work here, but you don’t have to remember that. You can just call them “bones,” and know that you’re using the same technology that computer game developers use to make onscreen characters move realistically.

In this chapter, you’ll learn about the two different ways you can use Flash’s IK Bones tool—with symbols, and with shapes. When you use bones with symbols, you link one symbol to another. For example, suppose you have a train in your animation. Each car is a separate, carefully drawn symbol. Using bones, you can link the engine to the coal car, the coal car to the boxcar, and so on, all the way down to the caboose. The other way you can use bones is with shapes. In the past, if you wanted to draw a snake, you’d have a hard time getting that snake to squirm and slither properly. You had to painstakingly reposition, distort, or even redraw several versions of the snake to make a good animation. Now you can draw a snake, place bones inside that single shape, and then bend the shape into realistic poses, which makes it easy to reposition or pose your snake for some realistic slithering and sliding. Flash Professional CS5.5 adds a new tool to IK bones called pinning. The ability to pin an object to a specific point on the stage makes it much easier to create the proper pose.