Question

I’m animating a bunch of words in AS3. Because I’m going to be using this on a mobile device, I want to use bitmaps rather than Sprites. So I’ve created WordObjects, which have a .bitmap property that I can access.

I have the following code, which fires on the click event and loops through an array inside an enterframe event. This is probably a bad idea, but I’m not sure how to do it better. (What is surprising is that it runs just fine in Flashbuilder, but slows to a crawl in Flash CS5.)

Is there some better way to do this? I just want an efficient way to animate the array of bitmaps.

    private function clickhandler (e:MouseEvent){

        this.addEventListener(Event.ENTER_FRAME, blowemup);
    }
    private function blowemup(e:Event){
        var newPosition:Number;
        for(var i:int=0; i<arrWordObjects.length; i++)
        {
            newPosition = updatePosition(arrWordObjects[i].bitmap);
            arrWordObjects[i].bitmap.x += newPosition;
            arrWordObjects[i].bitmap.y += getRandomNumber();

        }
    }

Answer 1

Something that will make a huge difference is using for each(Object in Array) rather than the standard for loop.

private function blowemup(e:Event):void
{
    var newPosition:Number;

    var i:ArrWordsObjectClass; // <-- don't know what the class for this is, just replace
    for each(i in arrWordObjects)
    {
        newPosition = updatePosition(i.bitmap);
        i.bitmap.x += newPosition;
        i.bitmap.y += getRandomNumber();
    }
}

A for each loop is typed, meaning a lot of time is saved where normally it’d be trying to work out what arrWordObjects[i] is every iteration.

Also, side note: using one ENTER_FRAME driven function and looping through everything in your application that you want to handle each frame is much more efficient than applying hundreds of listeners for objects.

I normally create a handler class that contains the ENTER_FRAME and an array storing my objects, like so:

package
{
    import flash.events.Event;
    import flash.display.Sprite;

    public class Handler extends Sprite
    {
        // vars
        public var elements:Array = [];

        /**
         * Constructor
         */
        public function Handler()
        {
            addEventListener(Event.ENTER_FRAME, _handle);
        }

        /**
         * Called on each dispatch of Event.ENTER_FRAME
         */
        private function _handle(e:Event):void
        {
            var i:Element;
            for each(i in elements)
            {
                i.step();
            }
        }
    }
}

Then I create a base class for all the objects that I want to handle, containing the step() function called above.

package
{
    import flash.display.DisplayObject;

    public class Element extends Object
    {
        // vars
        public var skin:DisplayObject;

        /**
         * Called on each dispatch of Event.ENTER_FRAME at Handler
         */
        public function step():void
        {
            // override me
        }
    }
}

Now just extend Element with your objects:

package
{
    import flash.display.Sprite;

    public class MyThing extends Element
    {
        /**
         * Constructor
         */
        public function MyThing()
        {
            skin = new Sprite();

            skin.graphics.beginFill(0);
            skin.graphics.drawCircle(0,0,40);
            skin.graphics.endFill();
        }

        /**
         * Override step
         */
        override public function step():void
        {
            skin.x += 4;
        }
    }
}

And get it all going!:

var handler:Handler = new Handler();

var m:MyThing;
var i:uint = 0;
for(i; i<10; i++)
{
    m = new MyThing();
    m.y = Math.random()*stage.stageHeight;

    handler.elements.push(m);
    addChild(m.skin);
}