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flash components, flash animation, web development

One of the coolest features in Flash, beside Flash components,  is its ability to utilize alpha-channel transparency for video. This allows you to do clever things like have a person, complete with drop shadow, walk right across your dynamic website content. Being the creative genius you are, we’re sure you can come up with tons of even more imaginative things to do with video transparency and compositing, so let’s review just how its done. First, you’ll need to shoot your subject against a background of solid color to create an alpha channel or a transparency layer in your video file. You have a choice when filming to use either a green screen or a blue screen as a background. How do you choose? The green screen is preferable for digital video whereas the blue screen is preferable for film. Also keep in mind the colors of the subjects you’re filming. For example, if you’re filming a person dressed as a frog, you may want to use a blue screen; if you’re filming a man painted blue, you may want to use a green screen. Generally, either color will work, but since the green channel in digital video has the highest sampling rate, you’ll want to stick with green in most cases to get a better-quality alpha channel.

I imagine some readers might have no idea what a class or the term “object oriented” means, while others have been using classes in ActionScript (or other languages) for years. So as to not lose anyone, I’m going to try to cover all the basics. AS 2 OOP experts might want to at least skim this section, too, as there are quite a few changes in the way things work in AS 3. If you think you do not have any familiarity with classes, you may be wrong. If you’ve written any code in Flash, chances are you used several classes. A class simply refers to a type of object. MovieClip is a class referring to—you guessed it—movie clips. Text fields, movie clips, buttons, strings, and numbers all have classes.

We’ve already discussed display objects. They are essentially any graphic element. Themost versatile of all display objects is the movie clip, which is a full graphic elementthat includes any number of other display objects, plus a timeline for animation. A simpler version of the movie clip is a sprite. A sprite is essentially a movie clip withonly one frame. When we create display objects from scratch in ActionScript, we’ll usuallybe making sprites. They are naturally more efficient than movie clips because theydon’t have the overhead of multiple frames of animation.Other display objects include things such as text fields, bitmaps, and video.Some display objects, movie clips, and sprites can have other display objects in them.For instance, you can have a sprite that contains several other sprites, as well as sometext fields and bitmaps.Nesting display objects provides you a way to organize your graphic elements. Forinstance, you could create a single game sprite to hold all the game elements you createwith ActionScript. Then, you could have a background sprite inside of it that containsseveral background sprite elements. A game pieces sprite could sit on top of that andcontain moveable game pieces.Because movie clips and sprites can contain multiple objects, they will each maintain alist of these items to determine the order in which they are displayed. This is called adisplay list. We can modify this display list to place objects in front of or in back ofother objects.