http://stackoverflow.com/questions/41202823/filter-on-calayer-except-for-a-shape-which-is-an-union-of-non-necessarily-disti

HolyView.swift

import Cocoa

@IBDesignable
class HolyView: NSView {
    
    override func draw(_ dirtyRect: NSRect) {
        super.draw(dirtyRect)
        
        let center1 = NSPoint(x: bounds.size.width * 0.3 + bounds.origin.x, y: bounds.size.height / 2 + bounds.origin.y)
        let radius1 = bounds.size.width / 6
        
        let center2 = NSPoint(x: bounds.size.width * 0.7 + bounds.origin.x, y: bounds.size.height / 2 + bounds.origin.y)
        let radius2 = bounds.size.width / 6
        
        let path = NSBezierPath()
        path.move(to: NSPoint(x: center1.x, y: center1.y - radius1))
        path.appendArc(withCenter: center1, radius: radius1, startAngle: -90, endAngle: 270)
        path.move(to: NSPoint(x: center2.x, y: center2.y - radius2))
        path.appendArc(withCenter: center2, radius: radius2, startAngle: -90, endAngle: 270)
        path.move(to: bounds.origin)
        path.appendRect(NSInsetRect(bounds, 10, 10))
        path.close()
        
        path.windingRule = .evenOddWindingRule
        
        NSColor.blue.setFill()
        path.fill()
        
        NSColor.black.setStroke()
        path.lineWidth = 5
        path.stroke()
    }
    
}

This illustrates move(to:) to avoid lines between the various subpaths:

Clearly, you're probably not drawing the paths, so it's not necessary, but it's useful when drawing boundaries like this.