[ActionScript 3.0] AS3.0 烟雾粒子效果

package {
    import flash.display.Bitmap;
    import flash.display.BitmapData;
    import flash.display.Sprite;
    import flash.events.Event;
    import flash.events.MouseEvent;
    import flash.geom.Point;
    [SWF(width="500",height="400")]
    public class SmokeFog extends Sprite {
        private var vectormap:BitmapData;
        private var bmpdata:BitmapData;
        private var oy:int = 0;
        private var w:int;
        
        public function SmokeFog(){
            w = 200;
            vectormap = new BitmapData(w, w);
            bmpdata = new BitmapData(w, w, false, 0);
            addChild(new Bitmap(bmpdata));
            stage.addEventListener(Event.ENTER_FRAME, reset);
        }
        
        private function reset(e:Event):void {
            vectormap.perlinNoise(w * .5, w * .5, 3, 1, false, true, 7, false, [new Point(0, oy++)]);
            bmpdata.fillRect(bmpdata.rect, 0);
            for (var y:int = 0; y < vectormap.height; y++){
                for (var x:int = 0; x < vectormap.width; x++){
                    var px:uint = vectormap.getPixel(x, y);
                    var r:int = px >> 16 & 0xFF;
                    var g:int = px >> 8 & 0xFF;
                    var b:int = px & 0xFF;
                    var tx:int = x + (g / 0xFF - .5) * w;
                    var ty:int = y + (b / 0xFF - .5) * w;
                    
                    if (ty < 0 || ty >= bmpdata.height || tx < 0 || tx >= bmpdata.width)
                        continue;
                    var col:uint = bmpdata.getPixel(tx, ty);
                    col += 0x010101 * (int)(r * .2);
                    if (col > 0xFFFFFF)
                        col = 0xFFFFFF;
                    bmpdata.setPixel(tx, ty, col);
                }
            }
        }
    }
}