AWRParallaxAnimationController.h

@interface AWRParallaxAnimationController : ECSlidingAnimationController <ECSlidingViewControllerLayout>

@property (nonatomic) CGFloat parallaxFactor;

@end

AWRParallaxAnimationController.m

@implementation AWRParallaxAnimationController

#pragma mark - ECSlidingViewControllerLayout

- (CGRect)slidingViewController:(ECSlidingViewController*)slidingViewController
         frameForViewController:(UIViewController*)viewController
                topViewPosition:(ECSlidingViewControllerTopViewPosition)topViewPosition
{
	CGRect frame = slidingViewController.view.bounds;
	
	if (viewController == slidingViewController.topViewController) {
		if (topViewPosition == ECSlidingViewControllerTopViewPositionAnchoredRight) {
			frame.origin.x = slidingViewController.anchorRightRevealAmount;
		} else if (topViewPosition == ECSlidingViewControllerTopViewPositionAnchoredLeft) {
			frame.origin.x = -slidingViewController.anchorLeftRevealAmount;
		}
	} else if (viewController == slidingViewController.underLeftViewController) {
		if (topViewPosition != ECSlidingViewControllerTopViewPositionAnchoredRight) {
			frame.origin.x = -slidingViewController.anchorRightRevealAmount * self.parallaxFactor;
		}
	} else if (viewController == slidingViewController.underRightViewController) {
		if (topViewPosition != ECSlidingViewControllerTopViewPositionAnchoredLeft) {
			frame.origin.x = slidingViewController.anchorLeftRevealAmount * self.parallaxFactor;
		}
	}
	
	return frame;
}

#pragma mark - UIViewControllerAnimatedTransitioning

- (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext {
	return 0.25;
}

- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext {
	UIViewController* fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
	CGRect fromViewInitialFrame = [transitionContext initialFrameForViewController:fromViewController];
	CGRect fromViewFinalFrame = [transitionContext finalFrameForViewController:fromViewController];
	
	UIViewController* toViewController  = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
	CGRect toViewInitialFrame = [transitionContext initialFrameForViewController:toViewController];
	CGRect toViewFinalFrame = [transitionContext finalFrameForViewController:toViewController];
	
	UIView* containerView = [transitionContext containerView];
	fromViewController.view.frame = fromViewInitialFrame;
	toViewController.view.frame = toViewInitialFrame;
	
	UIViewController* topViewController = [transitionContext viewControllerForKey:ECTransitionContextTopViewControllerKey];
	if (toViewController != topViewController) {
		[containerView insertSubview:toViewController.view belowSubview:fromViewController.view];
	}
	
	NSTimeInterval duration = [self transitionDuration:transitionContext];
	[UIView animateWithDuration:duration animations:^{
		[UIView setAnimationCurve:UIViewAnimationCurveLinear];
		fromViewController.view.frame = fromViewFinalFrame;
		toViewController.view.frame = toViewFinalFrame;
	completion:^(BOOL finished) {
		if ([transitionContext transitionWasCancelled]) {
			fromViewController.view.frame = fromViewInitialFrame;
			toViewController.view.frame = toViewInitialFrame;
		} else if (toViewController == topViewController) {
			[fromViewController.view removeFromSuperview];
		}
        
		[transitionContext completeTransition:finished];
	}];
}

@end