So, here’s what I did. I created a custom UIView
subclass called BlackoutView
, like so:
BlackoutView.h
#import <UIKit/UIKit.h>
@interface BlackoutView : UIView
@property (nonatomic, retain) UIColor *fillColor;
@property (nonatomic, retain) NSArray *framesToCutOut;
@end
BlackoutView.m
#import "BlackoutView.h"
@implementation BlackoutView
- (void)drawRect:(CGRect)rect
{
[self.fillColor setFill];
UIRectFill(rect);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetBlendMode(context, kCGBlendModeDestinationOut);
for (NSValue *value in self.framesToCutOut) {
CGRect pathRect = [value CGRectValue];
UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:pathRect];
[path fill];
}
CGContextSetBlendMode(context, kCGBlendModeNormal);
}
@end
I then instantiate it as normal, and set the properties to the colour of the mask I want to use, and the frames to be cut out of the mask:
[blackMask setFillColor:[UIColor colorWithWhite:0.0f alpha:0.8f]];
[blackMask setFramesToCutOut:@[[NSValue valueWithCGRect:buttonCircleA.frame],
[NSValue valueWithCGRect:buttonCircleB.frame]]];
This could be improved by allowing me to cut out other shapes besides ovals, but it’s fine for my purposes here and would be easily adapted to do so later. Hopefully this helps others!