.AS File Format – Movie clips

The timeline model

• A timeline plays from frame 1 at the movie’s frame rate and loops unless stop() is called. Frame scripts run each time their frame is entered.
• Frames are reached by number or label: gotoAndPlay("intro"), gotoAndStop(10), nextFrame(), prevFrame(). Scenes are joined into one timeline in the SWF.
• Clips have the properties of ActionScript 1.0: _x, _y, _xscale, _yscale, _width, _height, _rotation, _alpha, _visible, _name, _currentframe, _totalframes, _framesloaded, _xmouse, _ymouse, _parent, _target, _url, _droptarget, and from Flash Player 6 enabled, useHandCursor, hitArea, tabEnabled, tabIndex, focusEnabled and trackAsMenu.
• Flash Player 7 adds _lockroot and menu, a clip’s own context menu.

Symbols with classes

In a symbol’s linkage properties the author ticks Export for ActionScript, gives an identifier, and enters the full name of an ActionScript 2.0 class, which normally extends MovieClip. Every instance of the symbol, whether placed in the FLA or made by code, is then an instance of that class: its constructor runs, its methods and event methods apply, and the compiler checks code that uses it with that type.

// Symbol "Ball" in the library: linkage identifier "Ball",
// ActionScript 2.0 class com.example.Ball
class com.example.Ball extends MovieClip {
    public var speed:Number;            // given by the init object

    public function onEnterFrame():Void {
        _y += speed;
        if (_y > Stage.height) removeMovieClip();
    }
}

// in a frame script
var b:com.example.Ball = com.example.Ball(
    this.attachMovie("Ball", "ball" + n, this.getNextHighestDepth(), {speed: 3, _x: 100}));

The compiler turns the linkage into a call to Object.registerClass for the symbol, so this is the ActionScript 1.0 mechanism with checked types. Export in First Frame, on by default, puts the symbol in frame 1 so that it can be attached from the start. Instances inside the symbol, such as a text field label_txt, are declared as variables of the class so that the compiler knows their types.

Making clips and managing depths

Depths placed in the FLA start at −16383; code uses 0 to 1048575. The version 2 components’ DepthManager keeps the highest depth, 1048575, and the lowest for itself, so with components on a timeline getNextHighestDepth can give a depth above the range that removeMovieClip accepts.

Loading

loadMovie and loadMovieNum load SWF files and JPEG images, and from Flash Player 8 GIF and PNG images and progressive JPEGs. Flash Player 7’s MovieClipLoader does the same with listener events for start, progress, completion and errors. onLoadInit is the point at which the loaded movie’s first frame has run and its contents can be used. Setting _lockroot on the target keeps _root in the loaded movie pointing at itself.

var loader:MovieClipLoader = new MovieClipLoader();
var watcher:Object = {};
watcher.onLoadProgress = function (t:MovieClip, done:Number, total:Number):Void {
    bar_mc._xscale = 100 * done / total;
};
watcher.onLoadInit = function (t:MovieClip):Void {
    t._x = 20;
};
loader.addListener(watcher);
loader.loadClip("photo.jpg", this.createEmptyMovieClip("photo", 1));

Drawing

The drawing methods of Flash Player 6, lineStyle, beginFill, beginGradientFill, moveTo, lineTo, curveTo, endFill and clear, gain in Flash Player 8 more line options (pixel hinting, scaling, caps, joints and mitre limit), gradient spread and interpolation, lineGradientStyle and beginBitmapFill, which fills with a BitmapData.

Flash Player 8 display features