gistfile1.m

UIBezierPath *buttonPath = [UIBezierPath bezierPathWithRoundedRect:self.bounds cornerRadius:self.layer.cornerRadius];
			
			CAShapeLayer* shadowLayer = [CAShapeLayer layer];
			//shadowLayer.cornerRadius = 8.0f;
			[shadowLayer setOpacity:1];
			[shadowLayer setBackgroundColor:UIColor.redColor.CGColor];
			
			// Standard shadow stuff
			[shadowLayer setShadowOpacity:1.0f];
			[shadowLayer setShadowColor:[[UIColor colorWithWhite:1 alpha:1] CGColor]];
			[shadowLayer setShadowOffset:CGSizeMake(2.0f, 2.0f)];
			[shadowLayer setShadowRadius:5];
			// Causes the inner region in this example to NOT be filled.
			[shadowLayer setFillRule:kCAFillRuleEvenOdd];
			
			// Create the larger rectangle path.
			CGMutablePathRef path = CGPathCreateMutable();
			CGPathAddRect(path, NULL, CGRectInset(self.bounds, -42.0f, -42.0f));
			// Add the inner path so it's subtracted from the outer path.
			CGPathAddPath(path, NULL, buttonPath.CGPath);
			CGPathCloseSubpath(path);
			
			[shadowLayer setPath:path];
			CGPathRelease(path);
			
			[self.layer addSublayer:shadowLayer];