flash as3 控制图片缩放和平移，刚开始平移还行，但放大或缩小图片在点击移动就变成放大功能，哪里出错了
mport flash.events.MouseEvent;
import flash.events.Event;
var speed:Number=5;
var a:int=0;
var b:int=0;
var scale:Number=0.05;
var sd:int=0;
addEventListener(MouseEvent.MOUSE_DOWN,onDown);
addEventListener(MouseEvent.MOUSE_UP,onUp);
function onDown(e:MouseEvent):void{
switch (e.target.name){
case "up_btn":
a=-1;
b=0;
break;
case "down_btn":
a=1;
b=0;
break;
case "left_btn":
b=-1;
a=0;
break;
case "right_btn":
b=1;
a=0;
break;
case "d_btn":
sd=1;
a=0;
b=0;
break;
case "x_btn":
sd=-1;
a=0;
b=0;
break;
default:
break;
}
addEventListener(Event.ENTER_FRAME,onEnter);
}
function onUp(e:MouseEvent):void{
removeEventListener(Event.ENTER_FRAME,onEnter);
}
function onEnter(e:Event):void{
mc.x+=speed*b;
mc.y+=speed*a;
mc.scaleX=mc.scaleY+=scale*sd;
}