Reading accelerometer in iOS app

In XCode, start with File-New-Project: Game. This will create a demo project, but we will delete most of it. Delete GameScene.sks and Actions.sks. Since the Spaceship image is included in the Assets, we will just use it. Move the Spaceship image to the 2x box. We will deal with GameViewController.swift and GameScene.swift only.

GameViewController.swift

This is all we have for the GameViewController class in GameViewController.swift This sets up the Sprite Kit View, show the frame counts, hides status bar.

class GameViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let scene = GameScene(size: view.bounds.size)
        scene .scaleMode = .resizeFill
        
        let skView = view as! SKView
        skView.showsFPS = true
        skView.ignoresSiblingOrder = true
        skView.presentScene(scene)
    }
    
    override var prefersStatusBarHidden: Bool {
        return true
    }
}

GameScene.swift

Initializing SKScene

Delete all the content of GameScene class. First we want to define the sprite and motion manager to read the accelerometer.

let player = SKSpriteNode(imageNamed: "Spaceship")
let motionManager = CMMotionManager()

We also want to define the variables which stores the x and y position of the sprite. It is of type CGFloat, because that’s the type that’s used to update the position of the sprite, not Int or Double.

var posx:CGFloat = 0
var posy:CGFloat = 0

To put on the sprite on the screen, we call addChild in didMove. We also specify the initial position of the sprite. This is called (once) when the scene is presented into the SKView.

override func didMove(to view: SKView) {
    backgroundColor = SKColor.black
    posx = size.width/2
    posy = size.height/2
    player.position = CGPoint(x: posx, y: posy)
    addChild(player)
}

Handling accelerometer updates

In the same function, we want to connect the data updates from the motion manager to a function which crunches it. We need to check if the device has accelerometer. We then ask the motion manager to start sending the updates and put it in a queue. The updates are put into the deviceMotion variable. If there is no error, the updates will trigger the function handleDeviceMotionUpdate, which we define below.

if motionManager.isDeviceMotionAvailable {
    motionManager.startDeviceMotionUpdates(to: OperationQueue.current!, withHandler: {
        (deviceMotion, error) -> Void in
        if(error == nil) {
            self.handleDeviceMotionUpdate(deviceMotion: deviceMotion!)
        }
    })
}

This function below will be called each time there is an update in the accelerometer values. It receives the deviceMotion. The roll, pitch, yaw values can be accessed by deviceMotion.attitude.roll and so on.

//handle accelerometer values updates
func handleDeviceMotionUpdate(deviceMotion:CMDeviceMotion) {
    let attitude = deviceMotion.attitude
    //saves attitude.roll as roll, etc.
    movePlayer(roll: roll, pitch: pitch)
}

Another function handles how we want to move the sprite. After updating the positions, we finally set the position of the sprite by setting its position to a CGPoint(x: Double, y:Double).

func movePlayer(roll: Double, pitch: Double) {
     if(roll < 0) {
         posx -= 5
     }
     //do more position updates

     //sets the sprite position
     player.position = CGPoint(x: posx, y: posy)
}

That’s it! The sprite will be refreshed accordingly in the new frame! I put the whole project in my git.

source: forestgiant and ioscreator