How to efficiently create a multi-row photo collage from an array of images in Swift

Question

Problem

I am building a collage of photos from an array of images that I am placing onto a tableview. I want to make the images wrap when the number

Answer 1

Building on alternative 2 provided by Tommie C above I created a function that

• Always fills the total rectangle, without spaces in the collage
• determines the number of rows and columns automatically (maximum 1 more nrOfColumns than nrOfRows)
• To prevent the spaces mentioned above all individual pics are drawn with "Aspect Fill" (so for some pics this means that parts will be cropped)

Here's the function:

func collageImage(rect: CGRect, images: [UIImage]) -> UIImage {
    if images.count == 1 {
        return images[0]
    }

    UIGraphicsBeginImageContextWithOptions(rect.size, false,  UIScreen.mainScreen().scale)

    let nrofColumns: Int = max(2, Int(sqrt(Double(images.count-1)))+1)
    let nrOfRows: Int = (images.count)/nrofColumns
    let remaindingPics: Int = (images.count) % nrofColumns
    print("columns: \(nrofColumns) rows: \(nrOfRows) first \(remaindingPics) columns will have 1 pic extra")

    let w: CGFloat = rect.width/CGFloat(nrofColumns)
    var hForColumn = [CGFloat]()
    for var c=1;c<=nrofColumns;++c {
        if remaindingPics >= c {
            hForColumn.append(rect.height/CGFloat(nrOfRows+1))
        }
        else {
            hForColumn.append(rect.height/CGFloat(nrOfRows))
        }
    }
    var colNr = 0
    var rowNr = 0
    for var i=1; i nrofColumns) {
            ++rowNr
            colNr = 0
        }
        else {
            ++colNr
        }
    }

    let outputImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return outputImage
}

This uses the UIImage extension drawInRectAspectFill:

extension UIImage {
    func drawInRectAspectFill(rect: CGRect, opacity: CGFloat = 1.0) {
        let targetSize = rect.size
        let scaledImage: UIImage
        if targetSize == CGSizeZero {
            scaledImage = self
        } else {
            let scalingFactor = targetSize.width / self.size.width > targetSize.height / self.size.height ? targetSize.width / self.size.width : targetSize.height / self.size.height
            let newSize = CGSize(width: self.size.width * scalingFactor, height: self.size.height * scalingFactor)
            UIGraphicsBeginImageContext(targetSize)
            self.drawInRect(CGRect(origin: CGPoint(x: (targetSize.width - newSize.width) / 2, y: (targetSize.height - newSize.height) / 2), size: newSize), blendMode: CGBlendMode.Normal, alpha: opacity)
            scaledImage = UIGraphicsGetImageFromCurrentImageContext()
            UIGraphicsEndImageContext()
        }
        scaledImage.drawInRect(rect)
    }
}