Blurable

###Apply a Gaussian Blur to any UIView with Swift Protocol Extensions

Work in progress: adds blur() and unBlur() methods to UIView components which applies a Core Image Gaussian blur filter to the contents.

######Companion project to this blog post: http://flexmonkey.blogspot.co.uk/2015/09/applying-gaussian-blur-to-uiviews-with.html

Here's a fun little experiment showing the power of Swift's Protocol Extensions to apply a CIGaussianBlur Core Image filter to any UIView with no developer overhead. The code could be extended to apply any Core Image filter such as a half tone screen or colour adjustment.

Blurable is a simple protocol that borrows some of the methods and variables from a UIView:

var layer: CALayer { get }
var subviews: [UIView] { get }
var frame: CGRect { get }

func addSubview(view: UIView)

func bringSubviewToFront(view: UIView)

...and adds a few of its own:

func blur(blurRadius blurRadius: CGFloat)
func unBlur()

var isBlurred: Bool { get }

Obviously, just being a protocol, it doesn't do much on its own. However, by adding an extension, I can introduce default functionality. Furthermore, by extending UIView to implement Blurable, every component from a segmented control to a horizontal slider can be blurred:

extension UIView: Blurable
{

}

##The Mechanics of Blurable

Getting a blurred representation of a UIView is pretty simple: I need to begin an image context, use the view's layer's renderInContext method to render into the context and then get a UIImage from the context:

UIGraphicsBeginImageContextWithOptions(CGSize(width: frame.width, height: frame.height), false, 1)

layer.renderInContext(UIGraphicsGetCurrentContext()!)

let image = UIGraphicsGetImageFromCurrentImageContext()

UIGraphicsEndImageContext();

Once I have the image populated, it's a fairly standard workflow to apply a Gaussian blur to it:

guard let blur = CIFilter(name: "CIGaussianBlur") else
{
    return
}

blur.setValue(CIImage(image: image), forKey: kCIInputImageKey)
blur.setValue(blurRadius, forKey: kCIInputRadiusKey)

let ciContext  = CIContext(options: nil)

let result = blur.valueForKey(kCIOutputImageKey) as! CIImage!

let boundingRect = CGRect(x: -blurRadius * 4,
    y: -blurRadius * 4,
    width: frame.width + (blurRadius * 8),
    height: frame.height + (blurRadius * 8))

let cgImage = ciContext.createCGImage(result, fromRect: boundingRect)

let filteredImage = UIImage(CGImage: cgImage)

A blurred image will be larger than its input image, so I need to be explicit about the size I require in createCGImage.

The next step is to add a UIImageView to my view and hide all the other views. I've subclassed UIImageView to BlurOverlay so that when it comes to removing it, I can be sure I'm not removing an existing UIImageView:

let blurOverlay = BlurOverlay()
blurOverlay.frame = boundingRect

blurOverlay.image = filteredImage

subviews.forEach{ $0.hidden = true }


addSubview(blurOverlay)

When it comes to de-blurring, I want to ensure the last subview is one of my BlurOverlay remove it and unhide the existing views:

func unBlur()
{
    if let blurOverlay = subviews.last as? BlurOverlay
    {
        blurOverlay.removeFromSuperview()
        
        subviews.forEach{ $0.hidden = false }
    }

}

Finally, to see if a UIView is currently blurred, I just need to see if its last subview is a BlurOverlay:

var isBlurred: Bool
{
    return subviews.last is BlurOverlay
}

##Blurring a UIView

To blur and de-blur, just invoke blur() and unBlur() on an UIView:

segmentedControl.unBlur()
segmentedControl.blur(blurRadius: 2)

##Source Code

As always, the source code for this project is available at my GitHub repository here. Enjoy!