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Flash, at its core, is an animation machine. From the very earliest versions, Flash has supported animation through tweens—where you create a couple of keyframes that are different and let Flash fill in what is in between. However, this book is not about tweens. This book is about the powerful language built into Flash, called ActionScript. This book covers programming, math, and physics techniques used to make things move with ActionScript. As you’ll see, this gives you levels of power, control, and interactivity that you could never hope to match with tweening.

If the first chapter was a somewhat philosophical overview of animation, this one is a sort of technical overview of what it takes to animate with ActionScript, and in particular, ActionScript 3.0 (AS 3). This chapter covers the essentials of loops for animation, movie clips and sprites, classes, and user interaction. It gives you the majority of the information you need to understand the ActionScript techniques used in the rest of the book.

I wanted to put this chapter near the beginning of the book, as you’ll be using trigonometry extensively for animation techniques, starting with the examples in Chapter 5. In fact, I’ll even touch on it in the next chapter on rendering techniques. However, feel free to jump ahead if you already know basic trig or are just anxious to get into animating things. You can always come back here when you come across something you don’t understand.

The graphics in the sample programs in the book so far have been drawn using a few simple drawing commands, and I’ve alluded to this mythical “drawing API” a few times. But for the most part I’ve just thrown the code at you without much explanation.

Well, congratulations! You’ve made it to the point in the book where the action really starts. This means that (a) you’ve persevered through all the chapters so far, (b) you skimmed over the previous chapters and felt like you knew enough of it to get by, or (c) you got bored and jumped ahead. However it happened, here you are. Just remember, if you start having trouble, you can probably find help in an earlier chapter.

You’ve covered a lot of ground in the preceding chapters; you can now get some kind of graphic into a sprite and use all kinds of forces to move it around the screen. However, you’ve probably already run into a small annoyance with many of the examples you’ve created so far: When you move the object off the screen, bang—it’s gone. Sometimes, if it’s moving fast at some angle, you have no way of knowing how to get it back. Your only option is to restart the movie.

It’s likely that a primary goal of your animation is to allow smooth user interaction, and a lot of this interaction will be through the mouse. I talked about mouse events back in Chapter 2, but you haven’t really done much with them yet. Now, you’ll get some hands-on practice with them.

It’s hard to believe that it took seven chapters to get through “the basics,” but here you are at Chapter 8, the beginning of the advanced stuff. Or, as I prefer to think of it, the point where things start to get interesting. Up to now, each chapter covered more general techniques and concepts. Beginning with this chapter, I’ll be concentrating on one or two specialized types of motion per chapter.

As you’ve progressed through the book to this point, you’ve seen how to make objects move and make them interact with the space they occupy. Now, you’re going to delve into making these objects interact with each other. For the most part, this will involve determining when two objects have touched each other. This is a subject known as or .

This chapter covers a particular technique known as . As its name implies, this technique involves rotating a coordinate around a point. While useful all by itself, coordinate rotation is indispensable for several very interesting effects. One of those is the answer to a question that has continuously been asked on all the Flash boards for years: “How do I bounce something off an angled surface?” I’ll cover how to do that in this chapter.