cocos2d-js ,精灵不能渲染至画板

Cocos2d-x JavaScript
#1 
    //通过pRTex实现橡皮擦,创建了一个画布
    this.pRTex = new cc.RenderTexture(size.width,size.height);
    this.pRTex.setPosition(size.width/2, size.height/2);
    this.addChild(this.pRTex, 0);

    //加载等待被擦除的图片，渲染到画布上
    var pBg =new cc.Sprite("res/247204.png");
    pBg.x=size.width/2;
    pBg.y=size.height/2;
    pBg.scale=0.4;
    this.pRTex.begin();
    pBg.visit();
    this.pRTex.end();