擦除效果实现，bitmapData数据清除

import flash.display.Sprite;
import flash.display.BlendMode;
import flash.display.BitmapData;
import flash.display.Bitmap;
import flash.events.MouseEvent;
import flash.geom.Matrix;
import flash.geom.ColorTransform;
import flash.text.TextField;
import flash.utils.ByteArray;
import flash.geom.Rectangle;

var mc:Sprite = new mc_link();

var btp:BitmapData = new BitmapData(w, h);
btp.draw(mc);
var bt:Bitmap = new Bitmap(btp);
addChild(bt);

var isDrawing:Boolean;
//定义擦除画笔的宽度
var penW:int = 15;

this.stage.addEventListener(MouseEvent.MOUSE_DOWN, downHandle);
this.stage.addEventListener(MouseEvent.MOUSE_UP, upHandle);
this.stage.addEventListener(MouseEvent.MOUSE_MOVE, moveHandle);

function downHandle(e:MouseEvent):void{
if(bt.hitTestPoint(this.mouseX, this.mouseY)){
isDrawing = true;
}
}
function upHandle(e:MouseEvent):void{
isDrawing = false;
}

function moveHandle(e:MouseEvent):void{
if(!isDrawing)return;

e.updateAfterEvent();

//擦除原理：使用空数据替换
var nullBtp:BitmapData = new BitmapData(penW, penW, true, 0x00000000);
var byteArr:ByteArray = nullBtp.getPixels(nullBtp.rect);
byteArr.position = 0;
btp.setPixels(new Rectangle(bt.mouseX, bt.mouseY, penW, penW), byteArr);

　　　　　　//检测是否完全擦除:btp.getColorBoundsRect(0xFF000000,0x00000000,false);
　　　　　　
}

btp.draw(drawMc, new Matrix(), new ColorTransform(), BlendMode.ERASE);