flash AS3涂鸦板画矩形时,如何实现鼠标提示形状框?

//主要用到了mousemove事件
//鼠标按下时记住按下的点 mouseMove的时候先clear()在画框
//松开时移除mouseMove事件
//以下的代码直接放到FLASH里面
var sp:Sprite;
var p:Point;
stage.addEventListener(MouseEvent.MOUSE_DOWN, mouseDownHandler);
stage.addEventListener(MouseEvent.MOUSE_UP, mouseUpHandler);

function mouseDownHandler(evt:MouseEvent):void {
sp = new Sprite();
stage.addChild(sp);
p = new Point(mouseX, mouseY);
stage.addEventListener(MouseEvent.MOUSE_MOVE, mouseMoveHandler);
}

function mouseMoveHandler(evt:MouseEvent):void {
sp.graphics.clear();
sp.graphics.lineStyle(1, 0xfff000, 1);
sp.graphics.drawRect(p.x, p.y, mouseX - p.x, mouseY - p.y);
}

function mouseUpHandler(evt:MouseEvent):void {
stage.removeEventListener(MouseEvent.MOUSE_MOVE, mouseMoveHandler);
}