查看了很多的文章(C++,JS),试了很多方法,但是都没有成功,希望万能的网友能够指出问题所在,谢谢 
var HelloWorldLayer = cc.Layer.extend({
sprite: null ,
pEraser: null ,
pRTex: null ,
ctor: function () {
// ////////////////////////////
// 1. super init first
this ._super();
var size = cc.winSize;
// hello world背景图片
this .sprite = new cc.Sprite("res/shopping_mall_background.png");
this .sprite.attr({
x: size.width / 2 ,
y: size.height / 2
});
this .addChild( this .sprite, 0 );
// 橡皮擦
this .pEraser = new cc.DrawNode();
this .pEraser.drawDot(cc.p(0, 0), 20, cc.color(255, 255, 255, 0));
this .pEraser. retain();
// 通过pRTex实现橡皮擦
this.pRTex = new cc.RenderTexture(size.width,size.height,cc.Texture2D.PIXEL_FORMAT_RGBA8888);
this.pRTex.setPosition(cc.p(size.width/2, size.height/2 ));
this.addChild(this.pRTex,10);
// 加载等待被擦除的图片
var pBg = new cc.Sprite("res/shopping_mall_title.png");
pBg.setPosition(cc.p(size.width /2, size.height/2 ));
this.pRTex.begin();
pBg.visit(this.pRTex);
this.pRTex.end();
cc.eventManager.addListener({
event: cc.EventListener.TOUCH_ONE_BY_ONE,
onTouchBegan: function (touches, event){
cc.log( "start" );
return true ;
},
onTouchMoved: function (touch, event) {
var target = event.getCurrentTarget();
target.pEraser.setPosition(touch.getLocation());
target.eraseByBlend();
}
}, this );
},
eraseByBlend : function ()
{
this .pEraser.setBlendFunc(cc.ONE_MINUS_SRC_ALPHA, cc.ZERO);
this .pRTex.begin();
this .pEraser.visit();
this .pRTex.end();
}
});
var TestScene = cc.Scene.extend({
onEnter: function () {
this._super();
var layer = new HelloWorldLayer();
this.addChild(layer);
}
});