CGPoint+perpedicular.swift

extension CGPoint {
    func midBetween(_ other: CGPoint) -> CGPoint {
        return CGPoint(x: (self.x + other.x) / 2.0,
                       y: (self.y + other.y) / 2.0)
    }

    func perpedicularTo(_ other: CGPoint, distance: CGFloat) -> (CGPoint, CGPoint) {
        // Vector from p to p1;
        var diff = CGPoint(x: other.x - self.x, y: other.y - self.y);
        // Distance from p to p1:
        let length = CGFloat(hypotf(Float(diff.x), Float(diff.y)))
        // Normalize difference vector to length 1:
        diff.x /= length;
        diff.y /= length;
        // Compute perpendicular vector:
        let perp = CGPoint(x: -diff.y, y: diff.x)

        //let markLength = 3.0; // Whatever you need ...
        let a = CGPoint(x: self.x + perp.x * distance/2, y: self.y + perp.y * distance/2)
        let b = CGPoint(x: self.x - perp.x * distance/2, y: self.y - perp.y * distance/2)

        return (a, b)
    }
}