Parallax NSImageView for OS X

BFParallaxImageView.h

//
//  BFParallaxImageView.h
//  bout-osx
//
//  Created by Jesse Curry on 8/26/14.
//  Copyright (c) 2014 Bout Fitness, LLC. All rights reserved.
//

#import <Cocoa/Cocoa.h>

@interface BFParallaxImageView : NSView
- (void)setImage: (NSImage*)image;
@end

BFParallaxImageView.m

//
//  BFParallaxImageView.m
//  bout-osx
//
//  Created by Jesse Curry on 8/26/14.
//  Copyright (c) 2014 Bout Fitness, LLC. All rights reserved.
//

#import "BFParallaxImageView.h"

#define USE_POP_FOR_ANIMATION 1

#if USE_POP_FOR_ANIMATION
#import <pop/POP.h>
#endif

static const CGFloat kImageOverscan = 1.2; // 20% larger image

@interface BFParallaxImageView ()
@property (nonatomic, weak) NSTrackingArea* trackingArea;
@property (nonatomic, weak) NSImageView* imageView;
@end

////////////////////////////////////////////////////////////////////////////////////////////////////
@implementation BFParallaxImageView
- (instancetype)initWithFrame: (NSRect)frameRect
{
  self = [super initWithFrame: frameRect];
  if ( self )
  {
    [self setupView];
  }
  
  return self;
}

- (instancetype)initWithCoder: (NSCoder*)coder
{
  self = [super initWithCoder: coder];
  if ( self )
  {
    [self setupView];
  }
  
  return self;
}

- (void)setupView
{
  self.wantsLayer = YES;
  
  // Add Image View
  NSImageView* imageView = [[NSImageView alloc] initWithFrame: self.bounds];
  imageView.imageScaling = NSImageScaleProportionallyUpOrDown;
  [self addSubview: imageView];
  self.imageView = imageView;
  
  // Start Tracking
  NSTrackingAreaOptions options = (NSTrackingMouseMoved | NSTrackingActiveInActiveApp);
  NSTrackingArea* trackingArea = [[NSTrackingArea alloc] initWithRect: self.bounds
                                                              options: options
                                                                owner: self
                                                             userInfo: nil];
  [self addTrackingArea: trackingArea];
  self.trackingArea = trackingArea;
}

#pragma mark -
- (void)setImage: (NSImage*)image
{
  CGSize viewSize = self.bounds.size;
  NSSize imageSize = image.size;
  
  if ( imageSize.height > 0 && imageSize.width > 0 )
  {
    CGFloat wRatio = (viewSize.width / imageSize.width);
    CGFloat hRatio = (viewSize.height / imageSize.height);
    CGFloat scale = MAX(wRatio, hRatio);
    scale *= kImageOverscan; // image should be 20% larger than this view to allow parallax
    CGSize scaledSize = CGSizeMake(imageSize.width * scale, imageSize.height * scale);
    
    CGFloat dX = (scaledSize.width - viewSize.width);
    CGFloat dY = (scaledSize.height - viewSize.height);
    
    self.imageView.frame = CGRectMake(-0.5 * dX, -0.5 * dY, scaledSize.width, scaledSize.height);
    self.imageView.image = image;
  }
  else
  {
    self.imageView.bounds = CGRectMake(0, 0, viewSize.width, viewSize.height);
    self.imageView.image = nil;
  }
}

#pragma mark - Tracking
- (void)mouseMoved: (NSEvent*)theEvent
{
  NSPoint eyeCenter = [self convertPoint: [theEvent locationInWindow]
                                fromView: nil];
  CGSize viewSize = self.bounds.size;
  CGSize imageSize = self.imageView.bounds.size;
  
  CGFloat wR = MIN(1.0, (eyeCenter.x / viewSize.width));
  CGFloat hR = MIN(1.0, (eyeCenter.y / viewSize.height));
  
  CGFloat dX = (imageSize.width - viewSize.width);
  CGFloat dY = (imageSize.height - viewSize.height);
  
  CGFloat x = -(wR * dX);
  CGFloat y = -(hR * dY);
  
#if USE_POP_FOR_ANIMATION
  static NSString* const kPosAnimKey = @"positionAnimation";
  POPSpringAnimation* posAnim = [self.imageView.layer pop_animationForKey: kPosAnimKey];
  if ( posAnim == nil )
  {
    posAnim = [POPSpringAnimation animationWithPropertyNamed: kPOPLayerPosition];
    posAnim.springBounciness = 10;
    posAnim.springSpeed = 15;
    posAnim.fromValue = [NSValue valueWithCGPoint: self.imageView.layer.position];
    [self.imageView.layer pop_addAnimation: posAnim
                                    forKey: kPosAnimKey];
  }
  posAnim.toValue = [NSValue valueWithCGPoint: CGPointMake(x, y)];
#else
  self.imageView.layer.position = CGPointMake(x, y);
#endif
}

@end

Demo Video: http://vimeo.com/jessecurry/bfparallaximageview