Determine the direction of "gaze" of the device in any orientation. (Swift 3.2)

CMDeviceMotion.swift

extension CMDeviceMotion {
    
    func gaze(atOrientation orientation: UIInterfaceOrientation) -> SCNVector4 {
        
        let attitude = self.attitude.quaternion
        let aq = GLKQuaternionMake(Float(attitude.x), Float(attitude.y), Float(attitude.z), Float(attitude.w))
        
        let final: SCNVector4
        
        switch UIApplication.shared.statusBarOrientation {
            
        case .landscapeRight:
            
            let cq = GLKQuaternionMakeWithAngleAndAxis(.pi / 2, 0, 1, 0)
            let q = GLKQuaternionMultiply(cq, aq)
            
            final = SCNVector4(x: -q.y, y: q.x, z: q.z, w: q.w)
            
        case .landscapeLeft:
            
            let cq = GLKQuaternionMakeWithAngleAndAxis(.pi / -2, 0, 1, 0)
            let q = GLKQuaternionMultiply(cq, aq)
            
            final = SCNVector4(x: q.y, y: -q.x, z: q.z, w: q.w)
            
        case .portraitUpsideDown:
            
            let cq = GLKQuaternionMakeWithAngleAndAxis(.pi / 2, 1, 0, 0)
            let q = GLKQuaternionMultiply(cq, aq)
            
            final = SCNVector4(x: -q.x, y: -q.y, z: q.z, w: q.w)
            
        case .unknown:
            
            fallthrough
            
        case .portrait:
            
            let cq = GLKQuaternionMakeWithAngleAndAxis(.pi / -2, 1, 0, 0)
            let q = GLKQuaternionMultiply(cq, aq)
            
            final = SCNVector4(x: q.x, y: q.y, z: q.z, w: q.w)
        }
        
        return final
    }
}