Animated Shadow on UICollectionViewCell

gistfile1.m

/**
 *  Code to add an animated shadow to a UICollectionViewCell
 */

//
//  HAIMainMenuCollectionViewCell.m
//  app-haikudeck
//
//  Created by Kevin Leneway

// definitions for shadow values for main menu
#define kMainMenuImageShadowOpacity 0.08f
#define kMainMenuCellShadowOpacity 0.0f
#define kMainMenuImageShadowOffsetY 2.0f

-(void)setupShadow {
    // set up the initial soft grey shadow directly under the cells
    self.imageView.layer.shadowColor = [UIColor blackColor].CGColor;
    self.imageView.layer.shadowOpacity = kMainMenuImageShadowOpacity;
    self.imageView.layer.shadowOffset = CGSizeMake(0.0f, 0.0f);
    self.imageView.layer.shadowRadius = 3.0f;
    self.imageView.layer.masksToBounds = NO;

    CGSize size = self.imageView.bounds.size;
    CGRect ovalRect = CGRectMake(5.0f, size.height, size.width-15.0f, 10.0f);
    UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:ovalRect];
    self.imageView.layer.shadowPath = path.CGPath;
}

-(void)applyLayoutAttributes:(UICollectionViewLayoutAttributes *)layoutAttributes
{
    [super applyLayoutAttributes:layoutAttributes];
    
    self.layer.shouldRasterize = YES;
    if ([layoutAttributes isKindOfClass:[HAIMainMenuCollectionViewLayoutAttributes class]])
    {
        self.imageView.layer.shadowOpacity = [(HAIMainMenuCollectionViewLayoutAttributes *)layoutAttributes imageShadowOpacity];
        self.imageView.layer.shadowOffset = CGSizeMake(0.0f, [(HAIMainMenuCollectionViewLayoutAttributes *)layoutAttributes imageShadowOffsetY]);
    }
}

//
//  HAIMainMenuCollectionViewFlowLayout.m
//  app-haikudeck

-(void)applyLayoutAttributes:(UICollectionViewLayoutAttributes *)attributes forVisibleRect:(CGRect)visibleRect
{
    // Skip supplementary views
    if (attributes.representedElementKind) {
        return;
    }
    CGFloat imageShadowOffsetY = kMainMenuImageShadowOffsetY;
    CGFloat imageShadowOpacity = kMainMenuImageShadowOpacity;
    CGFloat distanceFromVisibleRectToItem = CGRectGetMidX(visibleRect) - attributes.center.x;
    CGFloat normalizedDistance = distanceFromVisibleRectToItem / (kMainMenuCellWidth*.25);
    CGAffineTransform transform = CGAffineTransformIdentity;
    
    // calculate the zoom and shadow properties for the selected item
    if (fabsf(distanceFromVisibleRectToItem) < kMainMenuCellWidth * .25) {
        CGFloat zoom = 1 + .2*(1 - ABS(normalizedDistance));
        transform = CGAffineTransformScale(CGAffineTransformIdentity, zoom, zoom);
        imageShadowOffsetY = kMainMenuImageShadowOffsetY + 15.0f*(1 - ABS(normalizedDistance));
        imageShadowOpacity = kMainMenuImageShadowOpacity + 0.15f*(1 - ABS(normalizedDistance));
    }
    
    attributes.transform = transform;
    [(HAIMainMenuCollectionViewLayoutAttributes *)attributes setImageShadowOffsetY:imageShadowOffsetY];
    [(HAIMainMenuCollectionViewLayoutAttributes *)attributes setImageShadowOpacity:imageShadowOpacity];
}

//
//  HAIMainMenuCollectionViewLayoutAttributes.h
//  app-haikudeck
//


@interface HAIMainMenuCollectionViewLayoutAttributes : UICollectionViewLayoutAttributes

@property (nonatomic) CGFloat imageShadowOpacity;
@property (nonatomic) CGFloat imageShadowOffsetY;

@end