How to determine whether the iphone screen is a retina screen in cocos2d

In cocos2d, how does one determine whether the iphone screen is a retina screen? During Iphone game development, it is often necessary to determine whether the screen is a retina Retina screen. cocos provides a way to enable retina display, record whether Retina display is supported here:
The Code is as follows:
Define in AppDelegate:

 bool  m_bRetinaMode;

In AppDelegate

The following code is called in applicationDidFinishLaunching:

    if( ! [director enableRetinaDisplay:YES] ){      m_bRetinaMode=false;      CCLOG(@"Retina Display Not supported");}       else{      m_bRetinaMode=true;}

It is better to define another function for external calls:

+ (Bool) isRetinaMode;

IsRetinaMode implementation:

+ (Bool) isRetinaMode
{
Return m_bRetinaMode;
}