UIBezierPath of a circle and rectangle intersection for a mask - objective-c

Question

I am trying to create a mask region of the intersection of a circle and a rectangle.
I am starting with this code that seems to create an XOR of the circle and rectangle for the mask region but I want just a plain old AND:
- (void)addMaskToHoleViewAtX:(CGFloat) x AtY:(CGFloat) y Radius:(CGFloat) kRadius {
CGRect bounds = holeView.bounds;
CAShapeLayer *maskLayer = [CAShapeLayer layer];
maskLayer.frame = bounds;
maskLayer.fillColor = [UIColor blackColor].CGColor;
CGRect const rect = CGRectMake(CGRectGetMidX(bounds) - kRadius/2,
CGRectGetMidY(bounds) - kRadius,
kRadius,
2 * kRadius);
UIBezierPath *pathrect = [UIBezierPath bezierPathWithRect:rect];
CGRect const circ = CGRectMake(CGRectGetMidX(bounds) - kRadius,
CGRectGetMidY(bounds) - kRadius,
2 * kRadius,
2 * kRadius);
UIBezierPath *pathcirc= [UIBezierPath bezierPathWithOvalInRect:circ];
UIBezierPath *allPaths= [[UIBezierPath alloc] init];
[allPaths appendPath:pathrect];
[allPaths appendPath:pathcirc];
[allPaths appendPath:[UIBezierPath bezierPathWithRect:bounds]];
maskLayer.path = allPaths.CGPath;
maskLayer.fillRule = kCAFillRuleEvenOdd;
holeView.layer.mask = maskLayer;
holeView.center = CGPointMake(x, y);
}
Could someone help me with the syntax to do the AND, I think I might need to use addClip but it is not obvious to me how to do that with the above code?
MY SOLUTION: It appears to me that if I were able to figure how to use addClip to solve this problem in one manner, I would not actually end up with the closed NSBezierPath of the intersection. I prefer not to do it that way as having the intersection NSBezierPath is also needed to easily determine if a point is inside the path. SOOOO, I just created the NSBezierPath of the intersection through calculations and used my derived path to append to the masklayer bounds path. It sure would be nice to have a way of actually obtaining the intersection NSBezierPath without calculations but I just had to move on. Thanks for trying.
Thanks,
Carmen
EDIT : Here is the routine I am calling to put the 'intersection' mask over my _map View. Change _map to your view if you want to try this:
- (void)addHoleSubview {
holeView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 10000, 10000)];
holeView.backgroundColor = [UIColor colorWithRed:255 green:0 blue:0 alpha:0.2];
holeView.autoresizingMask = 0;
[_map addSubview:holeView];
[self addMaskToHoleViewAtX:100 AtY:100 Radius:50];
}

Answer 1

If you aim for the intersection of two paths you should not create a compound path. Appending a path to another path will
result in a union of both paths if using the non-zero winding number rule and both paths have the same direction - or in other words it will have the effect of an AND
result in a shape that contains only the parts of the areas surrounded by the two paths that do not overlap if using the even-odd rule - or in other words it will have the effect of an XOR.
Instead I suggest you first add the first path pathrect to your graphics context and clip
[pathrect addClip];
and then you add the second path pathcirc to your context and clip again:
[pathcirc addClip];
You can now use any filling rule within that context and it will fill the intersection (the AND) of the two paths.