Before and after question

programming flash
1

I’m new in Flash, now I want to make a before and after photo gallery, and each set of photo have a bar in it, so user can click on the bar and slide left and right to see the effect before and after, but the problem is I only know the AC for moving the bar but not with the mask, so did any one know how to make the mask move with the bar? Thanks a lot!

Below is the code I have and the SWF file, please help and thanks!

slider_mc.addEventListener(MouseEvent.MOUSE_DOWN, drag);
stage.addEventListener(MouseEvent.MOUSE_UP, drop);


function drag(e:MouseEvent):void
{
     e.target.startDrag(false, new Rectangle(0,300,800,0));
}


function drop(e:MouseEvent):void
{
     stopDrag();
}

4shared.com/document/HgJSIDce/Before_and_After.html