I get this code from Googling but XCode display error: "Property 'backingScaleFactor' not found on object type 'NSScreen *'"
CGFloat displayScale = 1.0f;
if ([[NSScreen mainScreen] respondsToSelector:@selector(backingScaleFactor)])
{
displayScale = [NSScreen mainScreen].backingScaleFactor;
}
Use [[NSScreen mainScreen] backingScaleFactor]
and make sure that you are building for the OS X 10.7 SDK, with the deployment target set to 10.6.