float ver = [[[UIDevice currentDevice] systemVersion] floatValue];
// You can't detect screen resolutions in pre 3.2 devices, but they are all 320x480
if (ver >= 3.2f)
{
    UIScreen* mainscr = [UIScreen mainScreen];
    w = mainscr.currentMode.size.width;
    h = mainscr.currentMode.size.height;

    if (w == 640 && h == 960) // Retina display detected
    {
        // Set contentScale Factor to 2
        self.contentScaleFactor = 2.0;
        // Also set our glLayer contentScale Factor to 2
        eaglLayer.contentsScale=2; //new line
    }
}