"dynamic" blur using layer mask

BlurredView.h

#import <UIKit/UIKit.h>

@interface BlurredView : UIView
-(void)update;
@end

BlurredView.m

//
//  BlurredView.m
//
//  Created by Hellier on 04.10.13.
//  Copyright (c) 2013 void. All rights reserved.
//

#import "BlurredView.h"


@interface UIImage(Blur)
-(UIImage*)blurWithRadius:(float)radius;
@end

@implementation UIImage(Blur)

-(UIImage*)blurWithRadius:(float)radius
{
    CIContext *context = [CIContext contextWithOptions:nil];
    CIImage *imageToBlur = [CIImage imageWithCGImage:self.CGImage];
    CIFilter *gaussianBlurFilter = [CIFilter filterWithName: @"CIGaussianBlur"];
    [gaussianBlurFilter setValue:imageToBlur forKey: @"inputImage"];
    [gaussianBlurFilter setValue:@(radius) forKey: @"inputRadius"];
    CIImage *resultImage = [gaussianBlurFilter valueForKey: @"outputImage"];
    CGImageRef cgImage = [context createCGImage:resultImage fromRect:[imageToBlur extent]];
    return  [[UIImage alloc] initWithCGImage:cgImage];
}

@end

@interface BlurredView()
@property (strong,nonatomic) UIImageView *imageView;
@property (strong,nonatomic) UIView *maskView;
@end

@implementation BlurredView


-(id)initWithCoder:(NSCoder *)aDecoder
{
    self = [super initWithCoder:aDecoder];

    self.maskView = [[UIView alloc] init];
    self.maskView.backgroundColor = [UIColor blackColor];



    self.imageView = [[UIImageView alloc] init];
    self.imageView.clipsToBounds = YES;
    self.imageView.autoresizingMask = UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleHeight|UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleBottomMargin | UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleLeftMargin;

    self.imageView.layer.mask = self.maskView.layer;

    return self;
}

-(void)awakeFromNib
{
    [super awakeFromNib];
    self.clipsToBounds = YES;
}

-(UIImage*)renderToImage:(UIView*)view
{
    float scale = [UIScreen mainScreen].scale;
    CGSize size = view.frame.size;
    size.width*=scale; size.height*=scale;
    UIGraphicsBeginImageContextWithOptions(view.frame.size, NO, scale);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextTranslateCTM(context, 0, 0);
    CALayer *layer = view.layer;
    self.layer.hidden = YES;
    [layer renderInContext:context];
    self.layer.hidden = NO;
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}


-(void)update
{
    self.imageView.image = [[self renderToImage:self.superview] blurWithRadius:6];
}

-(void)setBounds:(CGRect)bounds
{
    self.maskView.bounds = bounds;
    [super setBounds:bounds];
}

-(void)setCenter:(CGPoint)center
{
    self.maskView.center = center;
    [super setCenter:center];
}

-(void)didMoveToSuperview
{
    if (self.superview)
    {
        self.imageView.frame = self.superview.bounds;
        [self.superview insertSubview:self.imageView belowSubview:self];
        self.maskView.frame = self.frame;
        
        double delayInSeconds = 0.01;
        dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
        dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
            [self update];
        });
    } else
    {
        [self.imageView removeFromSuperview];
    }
}

@end