断设备是iphone 4的又一方法，这个还是比较简单的

if( UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad )

{

// The device is an iPad running iPhone 3.2 or later.

}

else

{

NSArray *modes = [UIScreen mainScreen].availableModes;

UIScreenMode *mode = [modes objectAtIndex:0];

if( mode.size.width == 640 )

{

// The device is an iPhone 4

[director setContentScaleFactor:2];

}

else

{

// The device is an old school iPhone or iPod touch.

}

}

//-----------------------------------------------------------

#define isRetina ([UIScreen instancesRespondToSelector:@selector(currentMode)] ? CGSizeEqualToSize(CGSizeMake(640, 960), [[UIScreen mainScreen] currentMode].size) : NO)

gDisplayRatio = 1.0;

if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad){

gCurrentDisplayMode = DISP_IPAD;

gDisplayRatio = 2.0;

}

else

{

if (isRetina == YES) {

[director setContentScaleFactor:2.0];

gCurrentDisplayMode = DISP_RETINA;

}else {

gCurrentDisplayMode = DISP_WXVGA;

}

}