An animation is a sequence of images that create the illusion of movement when viewed in rapid succession. In Flash, these images are formed by content that's placed in frames on the Timeline. You might use drawings, photos, or even ActionScript-generated graphics to create an animation in your FLA files.
There are several different ways to create animations using Macromedia Flash 8. Additionally, there are several different types of animations that you can make use of. You can create motion tweens, shape tweens, or frame-by-frame animations. The term tween may be new to you. It's actually a carryover from traditional animation, in which a master animator draws all the animation cells where some change takes place, big or small. Assistant animators then draw all the "in-between" steps from cell to cell. Because human beings hate having to pronounce extra words and syllables, the process was referred to simply as tweening. Scout's honor. In Flash, the concept behind the process holds true. You define the areas in which an animation changes, and Flash draws the in-between steps, or tweens, for you. Isn't that lovely?
You define the beginning points (points where changes are going to occur) and end points in keyframes. When you apply a motion tween betwixt keyframes, Flash fills in the frames between the starting keyframe and the next keyframe it encounters on the Timeline. Likewise with shape tweens, although the goal of a shape tween is not motion, but the physical changing of an object's shape. You will create both motion and shape tweens in this lesson.
A frame-by-frame animation is a more traditional way of creating animation. Instead of having Flash create a tween for you, you draw each frame of the animation yourself in many, many keyframes, thereby allowing you to create more-complicated effects. Automatically produced tweens just can't do everything, after all. Frame-by-frame animations are usually more time-intensive to create, though, and they generally add more file size to the final SWF file.
You can also create animation using ActionScript and (typically) movie clips. Although it goes beyond the scope of this book, it is definitely worth looking into, if and when you choose to learn more about ActionScript.