Cut Out Shape with Animation

Question

I want to do something similar to the following:

How to mask an image in IOS sdk?

I want to cover the entire screen with translucent black. Then, I want to c

Answer 1

I've been struggling with this same problem and found some great help here on SO so I thought I'd share my solution combining a few different ideas I found online. One additional feature I added was for the cut-out to have a gradient effect. The added benefit to this solution is that it works with any UIView and not just with images.

First subclass UIView to black out everything except the frames you want cut out:

// BlackOutView.h
@interface BlackOutView : UIView

@property (nonatomic, retain) UIColor *fillColor;
@property (nonatomic, retain) NSArray *framesToCutOut;

@end

// BlackOutView.m
@implementation BlackOutView

- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetBlendMode(context, kCGBlendModeDestinationOut);

    for (NSValue *value in self.framesToCutOut) {
        CGRect pathRect = [value CGRectValue];
        UIBezierPath *path = [UIBezierPath bezierPathWithRect:pathRect];

        // change to this path for a circular cutout if you don't want a gradient 
        // UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:pathRect];

        [path fill];
    }

    CGContextSetBlendMode(context, kCGBlendModeNormal);
}
@end

If you don't want the blur effect, then you can swap paths to the oval one and skip the blur mask below. Otherwise, the cutout will be square and filled with a circular gradient.

Create a gradient shape with the center transparent and slowly fading in black:

// BlurFilterMask.h
@interface BlurFilterMask : CAShapeLayer

@property (assign) CGPoint origin;
@property (assign) CGFloat diameter;
@property (assign) CGFloat gradient;

@end

// BlurFilterMask.m
@implementation CRBlurFilterMask

- (void)drawInContext:(CGContextRef)context
{
    CGFloat gradientWidth = self.diameter * 0.5f;
    CGFloat clearRegionRadius = self.diameter * 0.25f;
    CGFloat blurRegionRadius = clearRegionRadius + gradientWidth;

    CGColorSpaceRef baseColorSpace = CGColorSpaceCreateDeviceRGB();
    CGFloat colors[8] = { 0.0f, 0.0f, 0.0f, 0.0f,     // Clear region colour.
        0.0f, 0.0f, 0.0f, self.gradient };   // Blur region colour.
    CGFloat colorLocations[2] = { 0.0f, 0.4f };
    CGGradientRef gradient = CGGradientCreateWithColorComponents (baseColorSpace, colors,     colorLocations, 2);

    CGContextDrawRadialGradient(context, gradient, self.origin, clearRegionRadius, self.origin, blurRegionRadius, kCGGradientDrawsAfterEndLocation);

    CGColorSpaceRelease(baseColorSpace);
    CGGradientRelease(gradient);
}

@end

Now you just need to call these two together and pass in the UIViews that you want cutout

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];

    [self addMaskInViews:@[self.viewCutout1, self.viewCutout2]];
}

- (void) addMaskInViews:(NSArray *)viewsToCutOut
{
    NSMutableArray *frames = [NSMutableArray new];
    for (UIView *view in viewsToCutOut) {
        view.hidden = YES; // hide the view since we only use their bounds
        [frames addObject:[NSValue valueWithCGRect:view.frame]];
    }

    // Create the overlay passing in the frames we want to cut out
    BlackOutView *overlay = [[BlackOutView alloc] initWithFrame:self.view.frame];
    overlay.backgroundColor = [UIColor colorWithWhite:0.0 alpha:0.8];
    overlay.framesToCutOut = frames;
    [self.view insertSubview:overlay atIndex:0];

    // add a circular gradients inside each view
    for (UIView *maskView in viewsToCutOut)
    {
        BlurFilterMask *blurFilterMask = [BlurFilterMask layer];
        blurFilterMask.frame = maskView.frame;
        blurFilterMask.gradient = 0.8f;
        blurFilterMask.diameter = MIN(maskView.frame.size.width, maskView.frame.size.height);
        blurFilterMask.origin = CGPointMake(maskView.frame.size.width / 2, maskView.frame.size.height / 2);
        [self.view.layer addSublayer:blurFilterMask];
        [blurFilterMask setNeedsDisplay];
    }
}