There are 4 resolution ios devices currently: iphone, iphone 4(s), ipad1/2, new ipad, feel painful about this? don't tell your feeling to android developers.
in cocos2d, just use suffix to the image files or atlas as below rules:
static NSString *__suffixiPhoneRetinaDisplay =@"-hd"; // for iphone 4/s
static NSString *__suffixiPad =@"-ipad"; // for ipad 1, 2
static NSString *__suffixiPadRetinaDisplay =@"-ipadhd"; //for new pad
no suffix for iphone 1, 3g, 3gs
if we have a texture named dog.png. you got a chance to draw 4 files to support 4 kinds of ios devices in a single project like this way:
dog.png ->iphone
dog-hd.png ->iphone 4/s
dog-ipad.png -> ipad 1, 2
dog-hdipad.png -> new ipad
and in your codes just use the name "dog.png", cocos2d can pick the right file with suffix for you.
what's a fun!