有时候我们需要判断自己所触摸的区域是否是透明的，这时就需要调用glReadPixels函数来进行rgb色值的提取了

白白原创，手游专栏http://blog.csdn.net/u010229677

Size size = Director::getInstance()->getVisibleSize();
CCRenderTexture* render = RenderTexture::create(size.width,size.height);
render->beginWithClear(0,0);
node->visit(); //白白原创
GLubyte pColor[4];
Point location = this ->convertTouchToNodeSpace(touch); 
glReadPixels(location.x,location.y,1,GL_RGBA,GL_UNSIGNED_BYTE,&pColor[0]);			
render->end();
log("r %d g %d b %d a %d",pColor[0],pColor[1],pColor[2],pColor[3]);
if (!pColor[0]&&!pColor[1]&&!pColor[2])
{
	log("tou ming");
}
else
{
	log("bu tou ming");
}