Looping—replaying a section of your animation over and over again—is an efficient way to create long-playing effects for a modest investment of effort and file size.
Say, for example, you want to create a repetitive background effect such as sunlight glinting off water, palm fronds waving in the breeze, or flickering lights. You can create the frames necessary to show the effect briefly (a couple seconds' worth or so), save the frames as a movie clip, and place an instance of that movie clip in one of the layers of your animation so that the effect spans your entire animation. Flash automatically replays the movie clip until you tell it otherwise, so you get an extended effect for a just a few frames' worth of work—and just a few frames' worth of file size, too. Such a deal. (For a more in-depth look at movie clip symbols, check out Chapter 7.)
You've seen this kind of looping background effect in action if you've ever watched The Flintstones—or just about any other production cartoon, for that matter. Remember seeing the same two caves shoot past in the background over and over again as Fred chased Barney around Bedrock?
To loop a series of frames using a movie clip symbol:
Open the file loop_no_mc.fla, which you can download from the "Missing CD" page.
On the Stage, you see a sprinkling of white stars on a blue background. In the Library, you see four symbols, including the blink_lights movie clip symbol (Figure 10-14).
Since you've never seen this ...