IntendedEndpoint.swift

func intendedEndpoint(with velocity: CGVector, from currentPosition: CGPoint) -> Endpoint {
    var velocity = velocity

    // We want to reduce movement along the secondary axis of the gesture.
    if velocity.dx != 0 || velocity.dy != 0 {
        let velocityInPrimaryDirection = fmax(fabs(velocity.dx), fabs(velocity.dy))

        velocity.dx *= fabs(velocity.dx / velocityInPrimaryDirection)
        velocity.dy *= fabs(velocity.dy / velocityInPrimaryDirection)
    }

    let projectedPosition = UIGestureRecognizer.project(velocity, onto: currentPosition)
    let endpoint = self.endpoint(closestTo: projectedPosition)

    return endpoint
}