title: UINavigationController — left and right flip animation between pushes and pops when presented via presentViewController
body: <p>Supposed you've got:</p>
  
  <pre><code>- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
  {
      self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
      // Override point for customization after application launch.
  
      UIViewController *rootViewController = [[UIViewController alloc] init];
      rootViewController.view.backgroundColor = [UIColor whiteColor];
  
      [self.window setRootViewController:rootViewController];
      [self.window makeKeyAndVisible];
  
      UINavigationController *modal = [[UINavigationController alloc] initWithRootViewController:[[PTFrontViewController alloc] init]];
      modal.modalPresentationStyle = UIModalPresentationFormSheet;
      [rootViewController presentViewController:modal animated:YES completion:NULL];
  
      return YES;
  }
  </code></pre>
  
  <p>whereas <code>PTFrontViewController</code> and <code>PTBackViewController</code> view controllers have nothing interesting for sake of this example.</p>
  
  <p>How could you push an instance of <code>PTBackViewController</code> from <code>PTFrontViewController</code> animating as in <code>UIViewAnimationTransitionFlipFromLeft</code> or <code>UIViewAnimationTransitionFlipFromRight</code>?</p>
  
  <p>I am already well aware of these three things:</p>
  
  <ol>
  <li>this is not exactly how you should make use of <code>presentViewController</code></li>
  <li>there is a good reason for <code>UINavigationController</code>'s default animation</li>
  <li>there are several answers how to "customize" <code>UINavigationController</code>'s default animation while pushing and poping, but if you try the code for your self you will notice that when a view controller is presented via <code>presentViewController</code> there are drop shadows and background views that won't get animated correctly</li>
  </ol>
  
  <p>So please answer taking these things in mind. Thank you.</p>