For github.com/Keithbsmiley/swift.vim/pull/30

after.swift

// MARK: NHBalancedFlowLayoutDelegate

func collectionView(collectionView: UICollectionView!,
                    layout collectionViewLayout: NHBalancedFlowLayout!,
                    preferredSizeForItemAtIndexPath indexPath: NSIndexPath!) -> CGSize {
                        if UIScreen.mainScreen().scale == 1.0 {
            var size = photos[indexPath.item].size
            size.width /= 2
            size.height /= 2
            return size
                        }
        return photos[indexPath.item].size
                    }

                    // MARK: UICollectionViewDataSource

                    override func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
                        return 1
                    }

                    override func collectionView(collectionView: UICollectionView,
                                                 numberOfItemsInSection section: Int) -> Int {
                    return photos.count
                                                 }

                                                 override func collectionView(collectionView: UICollectionView,
                                                                              cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
                                                 let cell = collectionView.dequeueReusableCellWithReuseIdentifier(photoCellID,
                                                                                                                  forIndexPath: indexPath) as PhotoCell
        if let highResPhoto = highResPhotos[indexPath.item] {
            cell.imageButton.setBackgroundImage(highResPhoto, forState: .Normal)
        } else {
            cell.imageButton.setBackgroundImage(photos[indexPath.item], forState: .Normal)
        }
        cell.imageButton.tag = indexPath.item
        return cell
                                                                              }

before.swift

// MARK: NHBalancedFlowLayoutDelegate

func collectionView(collectionView: UICollectionView!,
    layout collectionViewLayout: NHBalancedFlowLayout!,
    preferredSizeForItemAtIndexPath indexPath: NSIndexPath!) -> CGSize {
        if UIScreen.mainScreen().scale == 1.0 {
            var size = photos[indexPath.item].size
            size.width /= 2
            size.height /= 2
            return size
        }
        return photos[indexPath.item].size
}

// MARK: UICollectionViewDataSource

override func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
    return 1
}

override func collectionView(collectionView: UICollectionView,
    numberOfItemsInSection section: Int) -> Int {
    return photos.count
}

override func collectionView(collectionView: UICollectionView,
    cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier(photoCellID,
            forIndexPath: indexPath) as PhotoCell
        if let highResPhoto = highResPhotos[indexPath.item] {
            cell.imageButton.setBackgroundImage(highResPhoto, forState: .Normal)
        } else {
            cell.imageButton.setBackgroundImage(photos[indexPath.item], forState: .Normal)
        }
        cell.imageButton.tag = indexPath.item
        return cell
}