var bm:BitmapData=new BitmapData(img_mc.width, img_mc.height);
var disp:DisplacementMapFilter = new DisplacementMapFilter(bm,new Point(0,0),1,2,20,25, DisplacementMapFilterMode.CLAMP);
var offsets:Array = [new Point(0, 0), new Point(0, 0)];
 
addEventListener(Event.ENTER_FRAME, doUpdate);
function doUpdate(evt:Event):void
{
  offsets[0].x -=4;
  offsets[1].y -=1;
  bm.perlinNoise(45, 20, 2 ,50, true, false, 7, true, offsets);
  img_mc.filters=[disp];
}