SWIFT 2 UIBezierPath wont draw vertically

I am trying to build a lock screen app.

I have managed to get the path to draw from one point and update when drawing the line from one point to another. I am now trying to build a "snap to" function where the line "snaps to" the dot and then that dot's mid point will be the next "point from" to use for the next line.

The issue is that the line will only draw horizontally when using the snap to function, when I try to draw it vertically, the line disappears and does not draw between the last dot and the vertical or diagonal dot.

what I mean is this:

when I draw horizontal:

when I try to draw from the bottom right to the top left:

This is my code:

TOUCHES BEGAN:

override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
    process_touch(touches)

    drawPath = UIBezierPath()
    drawPath.moveToPoint((touches.first?.locationInView(self.superview))!)

    shapeLayer = CAShapeLayer()
    shapeLayer.strokeColor = UIColor.blackColor().CGColor
    shapeLayer.fillColor = UIColor.clearColor().CGColor
    shapeLayer.lineWidth = 4.0
    self.superview!.layer.addSublayer(shapeLayer)

    last_x = (touches.first?.locationInView(self.superview).x)!
    last_y = (touches.first?.locationInView(self.superview).y)!

}

TOUCHES MOVED (This also draws the line before the snap):

override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent!) {
    process_touch(touches)

    if(shapeLayer != nil) {
        shapeLayer.removeFromSuperlayer()
        shapeLayer =  nil
        drawPath.removeAllPoints()
        drawPath = nil
    }

    if(drawPath == nil) {
        drawPath = UIBezierPath()
    drawPath.moveToPoint((touches.first?.locationInView(self.superview))!)

        shapeLayer = CAShapeLayer()
        shapeLayer.strokeColor = UIColor.blackColor().CGColor
        shapeLayer.fillColor = UIColor.clearColor().CGColor
        shapeLayer.lineWidth = 8.0
        self.superview!.layer.addSublayer(shapeLayer)
    }

    drawPath.moveToPoint(CGPoint(x: last_x, y: last_y))
    drawPath.addLineToPoint((touches.first?.locationInView(self.superview))!)
    shapeLayer.path = drawPath.CGPath

    setNeedsDisplay()

}

TOUCHES ENDED:

override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
    Globals.alreadySnapped = []
    Globals.snappedPoints = []

    last_x = (touches.first?.locationInView(self.superview).x)!
    last_y = (touches.first?.locationInView(self.superview).y)!

    if(shapeLayer != nil) {
        shapeLayer.removeFromSuperlayer()
        shapeLayer =  nil
    }

    if(drawPath != nil) {
        drawPath.removeAllPoints()
        drawPath = nil
    }

    if(main_shapeLayer != nil) {
        main_shapeLayer.removeFromSuperlayer()
        main_shapeLayer =  nil
    }

    if(main_drawPath != nil) {
        main_drawPath.removeAllPoints()
        main_drawPath = nil
    }


}

DRAWING THE LINE (after the snap):

func draw_line_to(last_location:CGPoint, new_location: CGPoint) {

    if(main_drawPath == nil) {
        main_drawPath = UIBezierPath()
        main_drawPath.moveToPoint(CGPoint(x: last_location.x, y: last_location.y))

        main_shapeLayer = CAShapeLayer()
        main_shapeLayer.strokeColor = UIColor.blackColor().CGColor
        main_shapeLayer.fillColor = UIColor.clearColor().CGColor
        main_shapeLayer.lineWidth = 8.0
        self.superview!.layer.addSublayer(main_shapeLayer)
    }

    main_drawPath.moveToPoint(CGPoint(x: last_location.x, y: last_location.y))
    main_drawPath.addLineToPoint(CGPoint(x: new_location.x, y: last_location.y))
    main_shapeLayer.path = main_drawPath.CGPath

    last_x = new_location.x
    last_y = new_location.y

    setNeedsDisplay()

}

SNAP TO:

func append_point(obstacle_view: HoverButtonView, touch_location: CGPoint) {

    Globals.snappedPoints.append(touch_location)

    if(main_shapeLayer != nil) {
        main_shapeLayer.removeFromSuperlayer()
        main_shapeLayer =  nil
    }

    if(main_drawPath != nil) {
        main_drawPath.removeAllPoints()
        main_drawPath = nil
    }

    var count = 0
    var last_point: CGPoint = CGPoint(x: 0.0, y: 0.0)

    for point in Globals.snappedPoints {

        print("point (point)")

        if(count > 0) {
            draw_line_to(last_point, new_location: point)
        } else {
            draw_line_to(point, new_location: point)
        }

        last_point = point
        count+=1
    }

}

Deal with the touch

func process_touch(touches: NSSet!) {
    // Get the first touch and its location in this view controller's view coordinate system
    let touch = touches.allObjects[0] as! UITouch
    let touchLocation = touch.locationInView(self.superview)

    obstacleViews = Globals.obstacleViews

    for obstacleView in obstacleViews {
        // Convert the location of the obstacle view to this view controller's view coordinate system
        let obstacleViewFrame = self.superview!.convertRect(obstacleView.frame, fromView: self.superview)

        // Check if the touch is inside the obstacle view
        if CGRectContainsPoint(obstacleViewFrame, touchLocation) {

            if(!Globals.alreadySnapped.contains(obstacleView)) {
                Globals.alreadySnapped.append(obstacleView)

                var touch_loc = CGPoint(x: obstacleViewFrame.midX, y: obstacleViewFrame.midY)
                append_point(obstacleView, touch_location: touch_loc)
            }
        }
    }
}

What changes should I make to the above code to allow horizontal, vertical and diagonal lines to snap to the dots?