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Applying Gaussian Blur to UIViews with Swift Protocol Extensions

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Applying Gaussian Blur to UIViews with Swift Protocol Extensions

· Mobile Zone ·
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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:

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)


    let image = UIGraphicsGetImageFromCurrentImageContext()


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




    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 }


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

            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.blur(blurRadius: 2)

Source Code

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

swift ,blur

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