gistfile1.txt

//
//  UIView+OBJSnapshot.m
//  NavigationTransitionTest
//
//  Created by Chris Eidhof on 9/27/13.
//  Copyright (c) 2013 Chris Eidhof. All rights reserved.
//

#import "UIView+OBJSnapshot.h"

@implementation UIView (OBJSnapshot)

- (UIImage*)objc_snapshot
{
    UIGraphicsBeginImageContextWithOptions(self.bounds.size, NO, 0);
    [self.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *i = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return i;

}

@end

GPUImageAnimator.h

//
//  GPUImageAnimator.h
//  NavigationTransitionTest
//
//  Created by Chris Eidhof on 9/28/13.
//  Copyright (c) 2013 Chris Eidhof. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "Animator.h"

@class GPUImageDissolveBlendFilter;
@class GPUImagePicture;
@class GPUImagePixellateFilter;
@class GPUImageView;



@interface GPUImageAnimator : NSObject
  <UIViewControllerAnimatedTransitioning,
   UIViewControllerInteractiveTransitioning>

@property (nonatomic) BOOL interactive;
@property (nonatomic) CGFloat progress;

- (void)finishInteractiveTransition;
- (void)cancelInteractiveTransition;

@end

GPUImageAnimator.m

//
//  GPUImageAnimator.m
//  NavigationTransitionTest
//
//  Created by Chris Eidhof on 9/28/13.
//  Copyright (c) 2013 Chris Eidhof. All rights reserved.
//

#import "GPUImageAnimator.h"
#import "GPUImage.h"
#import "GPUImagePicture.h"
#import "GPUImagePixellateFilter.h"
#import "UIView+OBJSnapshot.h"
#import "GPUImageView.h"

static const float duration = 1;

@interface GPUImageAnimator ()

@property (nonatomic, strong) GPUImageDissolveBlendFilter* blend;
@property (nonatomic, strong) GPUImagePicture* sourceImage;
@property (nonatomic, strong) GPUImagePixellateFilter* sourcePixellateFilter;
@property (nonatomic, strong) GPUImagePicture* targetImage;
@property (nonatomic, strong) GPUImagePixellateFilter* targetPixellateFilter;
@property (nonatomic, strong) GPUImageView* imageView;
@property (nonatomic, strong) id <UIViewControllerContextTransitioning> context;
@property (nonatomic) NSTimeInterval startTime;
@property (nonatomic, strong) CADisplayLink* displayLink;
@end

@implementation GPUImageAnimator

- (id)init
{
    self = [super init];
    if (self) {
        [self setup];
    }

    return self;
}

- (void)setup
{
    self.imageView = [[GPUImageView alloc] init];
    self.imageView.alpha = 0;
    self.imageView.opaque = NO;

    self.blend = [[GPUImageDissolveBlendFilter alloc] init];
    self.blend.mix = 0;

    self.sourcePixellateFilter = [[GPUImagePixellateFilter alloc] init];
    self.sourcePixellateFilter.fractionalWidthOfAPixel = 0;

    self.targetPixellateFilter = [[GPUImagePixellateFilter alloc] init];
    self.targetPixellateFilter.fractionalWidthOfAPixel = 0;

    [self.sourcePixellateFilter addTarget:self.blend];
    [self.targetPixellateFilter addTarget:self.blend];

    [self.blend addTarget:self.imageView];

    self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(frame:)];
    [self.displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
    self.displayLink.paused = YES;
}


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

- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
{
    self.context = transitionContext;
    UIViewController* toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    UIViewController* fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];

    UIView* toView = toViewController.view;
    UIView* fromView = fromViewController.view;

    UIView* container = [transitionContext containerView];
    [container addSubview:toView];
    [container sendSubviewToBack:toView];

    self.imageView.frame = container.bounds;
    [container addSubview:self.imageView];

    self.sourceImage = [[GPUImagePicture alloc] initWithImage:fromView.objc_snapshot];
    [self.sourceImage addTarget:self.sourcePixellateFilter];

    self.targetImage = [[GPUImagePicture alloc] initWithImage:toView.objc_snapshot];
    [self.targetImage addTarget:self.targetPixellateFilter];

    [self triggerRenderOfNextFrame];
    
    toView.alpha = 0;
    self.imageView.alpha = 1;
    self.startTime = 0;
    self.displayLink.paused = NO;

}

- (void)triggerRenderOfNextFrame
{
    [self.sourceImage processImage];
    [self.targetImage processImage];
}

- (void)startInteractiveTransition:(id <UIViewControllerContextTransitioning>)transitionContext {
    [self animateTransition:transitionContext];
}

- (void)frame:(CADisplayLink*)link
{
    [self updateProgress:link];
    self.blend.mix = self.progress;
    self.sourcePixellateFilter.fractionalWidthOfAPixel = self.progress *0.1;
    self.targetPixellateFilter.fractionalWidthOfAPixel = (1- self.progress)*0.1;
    [self triggerRenderOfNextFrame];

    if (self.progress == 1 && !self.interactive) {
        [self finishInteractiveTransition];
    }
}

- (void)updateProgress:(CADisplayLink*)link
{
    if (self.interactive) return;

    if (self.startTime == 0) {
        self.startTime = link.timestamp;
    }
    self.progress = MAX(0, MIN((link.timestamp - self.startTime) / duration, 1));
}

- (void)setProgress:(CGFloat)progress
{
    _progress = progress;
    if (self.interactive) {
        [self.context updateInteractiveTransition:progress];
    }
}

- (void)finishInteractiveTransition
{
    self.displayLink.paused = YES;
    [self.imageView removeFromSuperview];
    [self.context viewControllerForKey:UITransitionContextFromViewControllerKey].view.alpha = 1;
    [self.context viewControllerForKey:UITransitionContextToViewControllerKey].view.alpha = 1;
    if (self.interactive) {
        [self.context finishInteractiveTransition];
    }
    [self.context completeTransition:YES];
}

- (void)cancelInteractiveTransition
{
    // TODO
}

@end

UIView+OBJSnapshot.h

//
//  UIView+OBJSnapshot.h
//  NavigationTransitionTest
//
//  Created by Chris Eidhof on 9/27/13.
//  Copyright (c) 2013 Chris Eidhof. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface UIView (OBJSnapshot)
- (UIImage*)objc_snapshot;
@end