A spinning disabled overlay, akin to ones you'd find on action bars in MMOs.

gistfile1.m

//
//  SDTimedDisableOverlayView.m
//  TimedDisabledAnimation
//
//  Created by Tyrone Trevorrow on 15-05-13.
//  Copyright (c) 2013 Sudeium. All rights reserved.
//

#import "SDTimedDisableOverlayView.h"

static const NSTimeInterval kTargetFramerate = 1.0/60.0;

@interface SDTimedDisableOverlayView ()
@property (nonatomic, strong) NSTimer *timer;
@property (nonatomic, copy) void(^animationCompletion)(BOOL);
@end

@implementation SDTimedDisableOverlayView {
    double _currentAngle;
    double _deltaAnglePerTick;
}

- (UIBezierPath*) disabledAreaPath
{
    UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect: self.bounds
                                                    cornerRadius: self.bounds.size.height / 2];
    return path;
}

- (void) beginAnimationWithCompletion:(CGFloat)completion duration:(NSTimeInterval)duration completionHandler:(void (^)(BOOL))completionHandler
{
    if (self.animationCompletion != NULL) {
        self.animationCompletion(NO);
    }
    self.animationCompletion = completionHandler;
    
    _currentAngle = completion * M_PI * 2;
    double angleToCover = (M_PI * 2) - _currentAngle;
    _deltaAnglePerTick = angleToCover / duration * kTargetFramerate;
    
    if (self.timer != nil) {
        [self.timer invalidate];
    }
    self.timer = [NSTimer timerWithTimeInterval: kTargetFramerate
                                         target: self
                                       selector: @selector(_tick)
                                       userInfo: nil
                                        repeats: YES];
    [[NSRunLoop currentRunLoop] addTimer: self.timer
                                 forMode: NSRunLoopCommonModes];
}

- (void) _tick
{
    _currentAngle += _deltaAnglePerTick;
    if (_currentAngle >= 2*M_PI) {
        [self.timer invalidate];
        self.timer = nil;
        if (self.animationCompletion != NULL) {
            self.animationCompletion(YES);
        }
    }
    [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect
{
    UIBezierPath *shape = [self disabledAreaPath];
    [[UIColor colorWithWhite: 0 alpha: 0.5] set];
    [shape fill];
    
    CGFloat radius = rect.size.height / 2.0;
    if (rect.size.width > rect.size.height) {
        radius = rect.size.width / 2.0;
    }
    
    CGPoint center = CGPointMake(CGRectGetMidX(rect), CGRectGetMidY(rect));
    UIBezierPath *cutOut = [UIBezierPath new];
    [cutOut moveToPoint: center];
    [cutOut addLineToPoint: CGPointMake(center.x, center.y - radius)];
    [cutOut addArcWithCenter: center radius: radius startAngle: -M_PI_2 endAngle: (_currentAngle - M_PI_2) clockwise: YES];
    [cutOut addLineToPoint: center];
    [[UIColor whiteColor] set];
    [cutOut fillWithBlendMode: kCGBlendModeClear alpha: 1];
}


@end