flex 抓图,该怎么解决

flex 抓图
我想用Flex做一个抓图效果，就是图片放在面板上，用鼠标点击后不放图片会跟着鼠标移动的效果。
  利用mouseDown记录移动前的坐标，用mouseMove实现鼠标跟随效果。可是只要我的鼠标在图片上移动图片就会动，我想当鼠标按下不动的时候移动鼠标才调用mouseMove。这样能实现吗？或者应该通过别的方法实现？

[解决办法]

XML code

<?xml version="1.0"?><mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"                layout="absolute"                width="700"                height="410">    <mx:Script>        <![CDATA[            import mx.managers.PopUpManager;            import flash.display.Bitmap;            import flash.events.MouseEvent;                        [Bindable]            private var oldX:Number, oldY:Number;                        protected function image_2_mouseDownHandler(event:MouseEvent):void            {                oldX=event.stageX;                oldY=event.stageY;            }            protected function image_2_mouseMoveHandler(event:MouseEvent):void            {                if (event.buttonDown)                {                    var x:Number=event.stageX - oldX;                    var y:Number=event.stageY - oldY;                    oldX=event.stageX;                    oldY=event.stageY;                    image_2.move(image_2.x + x, image_2.y + y);                }            }        ]]>    </mx:Script>    <mx:Canvas id="canvas_2" width="100%" height="100%">        <mx:Image id="image_2"                  source="img/car.jpg"                  mouseDown="image_2_mouseDownHandler(event)"                  mouseMove="image_2_mouseMoveHandler(event)">        </mx:Image>    </mx:Canvas></mx:Application>