线条flash代码在flash画板中，怎样用代码设置画出的线条是平滑的？

package{
import flash.display.Sprite;
import flash.events.MouseEvent;
public class Main extends Sprite{
private var ceng:Sprite;
private var isdown:Boolean = false;
private var linesize:uint = 2;
private var oldx:Number;
private var oldy:Number;
public function Main():void{
init();
}
private function init():void
{
ceng new Sprite();
addChild(ceng);
stage.addEventListener(MouseEvent.MOUSE_DOWN,ondown);
stage.addEventListener(MouseEvent.MOUSE_MOVE,onmove);
stage.addEventListener(MouseEvent.MOUSE_UP,onup);
}
private function ondown(evt:MouseEvent):void
{
isdown = true;
oldx = stage.mouseX;
oldy = stage.mouseY;
}
private function onmove(evt:MouseEvent):void
{
if(isdown){
ceng.graphics.lineStyle(linesize,0x000000);
ceng.graphics.moveTo(