Chop a rectangle from another rectangle on iOS

gistfile1.m

static
void divide_rect_from_rects(CGRect rect1, CGRect rect2, CGRect *slice, CGRect *remainder, CGRectEdge edge)
{
    NSCParameterAssert(slice);
    NSCParameterAssert(remainder);
    
    CGRect intersected = CGRectIntersection(rect1, rect2);
    if (CGRectIsEmpty(intersected)) {
        *slice = CGRectNull;
        return;
    }
    
    CGFloat chop;
    switch (edge) {
        case CGRectMinYEdge: chop = fabs(CGRectGetMinY(intersected) - CGRectGetMinY(rect1)); break;
        case CGRectMaxYEdge: chop = fabs(CGRectGetMaxY(rect1) - CGRectGetMaxY(intersected)); break;
        case CGRectMinXEdge: chop = fabs(CGRectGetMinX(intersected) - CGRectGetMinX(rect1)); break;
        case CGRectMaxXEdge: chop = fabs(CGRectGetMaxX(rect1) - CGRectGetMaxX(intersected)); break;
        default: NSCAssert(0, @"invalid CGRectEdge value"); break;
    }

    CGRectDivide(rect1, slice, remainder, chop, edge);
    return;
}

- (NSArray *)rectsFromRect:(CGRect)rect1 chopRect:(CGRect)rect2
{
    if (CGRectIsEmpty(rect1))
        return @[];

    CGRect intersected = CGRectIntersection(rect1, rect2);
    if (CGRectIsEmpty(intersected))
        return [NSArray arrayWithObject:NSStringFromCGRect(rect1)];

    NSMutableArray *rects = [NSMutableArray array];
    CGRect slice, remainder;
    slice = remainder = CGRectNull;
    divide_rect_from_rects(rect1, intersected, &slice, &remainder, CGRectMinYEdge);
    if (!CGRectIsEmpty(slice))
        [rects addObject:NSStringFromCGRect(slice)];

    divide_rect_from_rects(remainder, intersected, &slice, &remainder, CGRectMaxYEdge);
    if (!CGRectIsEmpty(slice))
        [rects addObject:NSStringFromCGRect(slice)];

    divide_rect_from_rects(remainder, intersected, &slice, &remainder, CGRectMinXEdge);
    if (!CGRectIsEmpty(slice))
        [rects addObject:NSStringFromCGRect(slice)];

    divide_rect_from_rects(remainder, intersected, &slice, &remainder, CGRectMaxXEdge);
    if (!CGRectIsEmpty(slice))
        [rects addObject:NSStringFromCGRect(slice)];

    return rects;
}