CEFoldAnimationController.m

//
//  CEAccordionAnimationController.m
//  TransitionsDemo
//
//  Created by Colin Eberhardt on 12/09/2013.
//  Copyright (c) 2013 Colin Eberhardt. All rights reserved.
//

#import "CEFoldAnimationController.h"

@implementation CEFoldAnimationController

- (id)init {
    if (self = [super init]) {
        self.folds = 2;
    }
    return self;
}

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext fromVC:(UIViewController *)fromVC toVC:(UIViewController *)toVC fromView:(UIView *)fromView toView:(UIView *)toView {
    
    // Add the toView to the container
    UIView* containerView = [transitionContext containerView];

    // move offscreen
    toView.frame = CGRectOffset(toView.frame, toView.frame.size.width, 0);
    [containerView addSubview:toView];
    
    // Add a perspective transform
    CATransform3D transform = CATransform3DIdentity;
    transform.m34 = -0.005;
    containerView.layer.sublayerTransform = transform;
    
    CGSize size = toView.frame.size;
    
    float foldWidth = size.width * 0.5 / (float)self.folds ;
    
    // arrays that hold the snapshot views
    NSMutableArray* fromViewFolds = [NSMutableArray new];
    NSMutableArray* toViewFolds = [NSMutableArray new];
    
    // create the folds for the form- and to- views
    for (int i=0 ;i<self.folds; i++){
        float offset = (float)i * foldWidth * 2;
        
        // the left and right side of the fold for the from- view, with identity transform and 0.0 alpha
        // on the shadow, with each view at its initial position
        UIView *leftFromViewFold = [self createSnapshotFromView:fromView afterUpdates:NO location:offset left:YES];
        leftFromViewFold.layer.position = CGPointMake(offset, size.height/2);
        [fromViewFolds addObject:leftFromViewFold];
        [leftFromViewFold.subviews[1] setAlpha:0.0];
        
        UIView *rightFromViewFold = [self createSnapshotFromView:fromView afterUpdates:NO location:offset + foldWidth left:NO];
        rightFromViewFold.layer.position = CGPointMake(offset + foldWidth * 2, size.height/2);
        [fromViewFolds addObject:rightFromViewFold];
        [rightFromViewFold.subviews[1] setAlpha:0.0];
        
        // the left and right side of the fold for the to- view, with a 90-degree transform and 1.0 alpha
        // on the shadow, with each view positioned at the very edge of the screen
        UIView *leftToViewFold = [self createSnapshotFromView:toView afterUpdates:YES location:offset left:YES];
        leftToViewFold.layer.position = CGPointMake(self.reverse ? size.width : 0.0, size.height/2);
        leftToViewFold.layer.transform = CATransform3DMakeRotation(M_PI_2, 0.0, 1.0, 0.0);
        [toViewFolds addObject:leftToViewFold];
        
        UIView *rightToViewFold = [self createSnapshotFromView:toView afterUpdates:YES location:offset + foldWidth left:NO];
        rightToViewFold.layer.position = CGPointMake(self.reverse ? size.width : 0.0, size.height/2);
        rightToViewFold.layer.transform = CATransform3DMakeRotation(-M_PI_2, 0.0, 1.0, 0.0);
        [toViewFolds addObject:rightToViewFold];
    }
    
    // move the from- view off screen
    fromView.frame = CGRectOffset(fromView.frame, fromView.frame.size.width, 0);

    // create the animation
    NSTimeInterval duration = [self transitionDuration:transitionContext];
    [UIView animateWithDuration:duration animations:^{
        // set the final state for each fold
        for (int i=0; i<self.folds; i++){
            
            float offset = (float)i * foldWidth * 2;
            
            // the left and right side of the fold for the from- view, with 90 degree transform and 1.0 alpha
            // on the shadow, with each view positioned at the edge of thw screen.
            UIView* leftFromView = fromViewFolds[i*2];
            leftFromView.layer.position = CGPointMake(self.reverse ? 0.0 : size.width, size.height/2);
            leftFromView.layer.transform = CATransform3DRotate(transform, M_PI_2, 0.0, 1.0, 0);
            [leftFromView.subviews[1] setAlpha:1.0];
            
            UIView* rightFromView = fromViewFolds[i*2+1];
            rightFromView.layer.position = CGPointMake(self.reverse ? 0.0 : size.width, size.height/2);
            rightFromView.layer.transform = CATransform3DRotate(transform, -M_PI_2, 0.0, 1.0, 0);
            [rightFromView.subviews[1] setAlpha:1.0];
            
            // the left and right side of the fold for the to- view, with identity transform and 0.0 alpha
            // on the shadow, with each view at its final position
            UIView* leftToView = toViewFolds[i*2];
            leftToView.layer.position = CGPointMake(offset, size.height/2);
            leftToView.layer.transform = CATransform3DIdentity;
            [leftToView.subviews[1] setAlpha:0.0];
            
            UIView* rightToView = toViewFolds[i*2+1];
            rightToView.layer.position = CGPointMake(offset + foldWidth * 2, size.height/2);
            rightToView.layer.transform = CATransform3DIdentity;
            [rightToView.subviews[1] setAlpha:0.0];
         
            
        }
    }  completion:^(BOOL finished) {
        // remove the snapshot views
        for (UIView *view in toViewFolds) {
            [view removeFromSuperview];
        }
        for (UIView *view in fromViewFolds) {
            [view removeFromSuperview];
        }
        // restore the to- and from- to the initial location
        toView.frame = containerView.bounds;
        fromView.frame = containerView.bounds;
        [transitionContext completeTransition:![transitionContext transitionWasCancelled]];
    }];

    
}

// creates a snapshot for the gives view
-(UIView*) createSnapshotFromView:(UIView *)view afterUpdates:(BOOL)afterUpdates location:(CGFloat)offset left:(BOOL)left {
    
    CGSize size = view.frame.size;
    UIView *containerView = view.superview;
    float foldWidth = size.width * 0.5 / (float)self.folds ;
    
    UIView* snapshotView;
    
    if (!afterUpdates) {
        // create a regular snapshot
        CGRect snapshotRegion = CGRectMake(offset, 0.0, foldWidth, size.height);
        snapshotView = [view resizableSnapshotViewFromRect:snapshotRegion  afterScreenUpdates:afterUpdates withCapInsets:UIEdgeInsetsZero];
        
    } else {
        // for the to- view for some reason the snapshot takes a while to create. Here we place the snapshot within
        // another view, with the same bckground color, so that it is less noticeable when the snapshot initially renders
        snapshotView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, foldWidth, size.height)];
        snapshotView.backgroundColor = view.backgroundColor;
        CGRect snapshotRegion = CGRectMake(offset, 0.0, foldWidth, size.height);
        UIView* snapshotView2 = [view resizableSnapshotViewFromRect:snapshotRegion  afterScreenUpdates:afterUpdates withCapInsets:UIEdgeInsetsZero];
        [snapshotView addSubview:snapshotView2];
        
    }
    
    // create a shadow
    UIView* snapshotWithShadowView = [self addShadowToView:snapshotView reverse:left];
    
    // add to the container
    [containerView addSubview:snapshotWithShadowView];
    
    // set the anchor to the left or right edge of the view
    snapshotWithShadowView.layer.anchorPoint = CGPointMake( left ? 0.0 : 1.0, 0.5);
    
    return snapshotWithShadowView;
}


// adds a gradient to an image by creating a containing UIView with both the given view
// and the gradient as subviews
- (UIView*)addShadowToView:(UIView*)view reverse:(BOOL)reverse {
    
    // create a view with the same frame
    UIView* viewWithShadow = [[UIView alloc] initWithFrame:view.frame];
    
    // create a shadow
    UIView* shadowView = [[UIView alloc] initWithFrame:viewWithShadow.bounds];
    CAGradientLayer *gradient = [CAGradientLayer layer];
    gradient.frame = shadowView.bounds;
    gradient.colors = @[(id)[UIColor colorWithWhite:0.0 alpha:0.0].CGColor,
                        (id)[UIColor colorWithWhite:0.0 alpha:1.0].CGColor];
    gradient.startPoint = CGPointMake(reverse ? 0.0 : 1.0, reverse ? 0.2 : 0.0);
    gradient.endPoint = CGPointMake(reverse ? 1.0 : 0.0, reverse ? 0.0 : 1.0);
    [shadowView.layer insertSublayer:gradient atIndex:1];
    
    // add the original view into our new view
    view.frame = view.bounds;
    [viewWithShadow addSubview:view];
    
    // place the shadow on top
    [viewWithShadow addSubview:shadowView];
    
    return viewWithShadow;
}


@end