旋转后努力使节点沿其轴移动（Swift | ARKit | SceneKit）

Question

As the title states, after I rotate my ship node, I would like the "go" button to cause the ship to travel in the direction it is now facing after the rotation. Currently, pressing the "go" button causes the ship to continue moving along the world's z-axis instead of the direction the ship is facing (obviously because I don't have any code in there telling it otherwise).

I have tried using worldTransform and convertPosition:toNode: with no luck currently.

In ViewController:

let ship = SpaceShip();
    let SHIP_SPEED: Float = 3.00;
    let scene = SCNScene();


    var timer = Timer();

    var upPressed = false;
    var rightPressed = false;
    var downPressed = false;
    var leftPressed = false;
    var goPressed = false;
    var stopPressed = false;
    var firePressed = false;

    //initial angles for rotating ship
    //if ship is flipping upside down, it is because of these
   /* var xAngle: SCNMatrix4?
    var yAngle: SCNMatrix4?
    var zAngle: SCNMatrix4? */

    @IBOutlet weak var sceneView: ARSCNView!

    @IBAction func upBtnDown(_ sender: Any) {
        upPressed = true;
    }
    @IBAction func upBtnUp(_ sender: Any) {
        upPressed = false;
        ship.rotateShip(ship.getNode(), x: 180, y: 0, z: 180);
    }

    @IBAction func rightBtnDown(_ sender: Any) {
        rightPressed = true;

    }

    @IBAction func rightBtnUp(_ sender: Any) {
        rightPressed = false;
        ship.rotateShip(ship.getNode(), x: 180, y: 0, z: 180);
    }

    @IBAction func downBtnDown(_ sender: Any) {
        downPressed = true;
    }

    @IBAction func downBtnUp(_ sender: Any) {
        downPressed = false;
        ship.rotateShip(ship.getNode(), x: 180, y: 0, z: 180);
    }

    @IBAction func leftBtnDown(_ sender: Any) {
        leftPressed = true;

    }

    @IBAction func leftBtnUp(_ sender: Any) {
        leftPressed = false;
        //ship.rotateShip(ship.getNode(), x: 180, y: 0, z: 180);
    }

    @IBAction func goBtnDown(_ sender: Any) {

        goPressed = true;
    }

    @IBAction func goBtnUp(_ sender: Any) {
        goPressed = false;
    }

    @IBAction func stopBtnDown(_ sender: Any) {
        stopPressed = true;
    }

    @IBAction func stopBtnUp(_ sender: Any) {
        stopPressed = false;
    }


    @IBAction func fireBtnDown(_ sender: Any) {
        firePressed = true;
    }

    @IBAction func fireBtnUp(_ sender: Any) {
        firePressed = false;
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        //set scene from storyboard to scene variable
        sceneView.scene = scene;
        sceneView.scene.physicsWorld.contactDelegate = self;
        sceneView.delegate = self;

    }

    override func viewWillAppear(_ animated: Bool) {

        super.viewWillAppear(animated);

        let configuration = ARWorldTrackingSessionConfiguration();

        sceneView.session.run(configuration);

        addShip();

    }

    func renderer(_ renderer: SCNSceneRenderer, updateAtTime time: TimeInterval) {

        ship.physicsBody?.velocity = SCNVector3(0,0,0);

        if(upPressed == true) {
            ship.physicsBody?.velocity.y = SHIP_SPEED;
            ship.rotateShip(ship.getNode(), x: 170, y: 0, z: 180);
        } else if (rightPressed == true) {
            ship.physicsBody?.velocity.x = SHIP_SPEED;
            ship.rotateShip(ship.getNode(), x: 180, y: 0, z: 170);
        } else if (downPressed == true) {
            ship.physicsBody?.velocity.y = -SHIP_SPEED;
            ship.rotateShip(ship.getNode(), x: 190, y: 0, z: 180);
        } else if (leftPressed == true) {
            //ship.physicsBody?.velocity.x = -SHIP_SPEED;
           ship.rotateShip(ship.getNode(), x: 180, y: 15, z: 190);
            print(ship.getNode().rotation);

        } else if (goPressed == true) {
            ship.physicsBody?.velocity.z = -SHIP_SPEED;
        } else if (stopPressed == true) {
            ship.physicsBody?.velocity.z = SHIP_SPEED;
        }

    }

    func getZForwards(node: SCNNode) -> SCNVector3{
        return SCNVector3(node.worldTransform.m31, node.worldTransform.m32, node.worldTransform.m33);
    }

    func addShip() {
        ship.loadModel();

        ship.position = SCNVector3(0, 0, -2);

        sceneView.scene.rootNode.addChildNode(ship);
    }

    func degToRad(deg: Float) -> Float{
        return deg / 180 * Float(M_PI)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

In SpaceShip():

class SpaceShip: SCNNode {

    var node = SCNNode();

    func loadModel() {
        guard let virtualObjectScene = SCNScene(named: "art.scnassets/ship.scn") else {return};

        let wrapperNode = SCNNode();

        for child in virtualObjectScene.rootNode.childNodes {
            wrapperNode.addChildNode(child);
        }

        node = wrapperNode.childNodes[0];
        let shape = SCNPhysicsShape(node: node, options: nil);
        self.physicsBody = SCNPhysicsBody(type: .dynamic, shape: shape);
        self.physicsBody?.isAffectedByGravity = false;

        rotateShip(node, x: 180, y: 0, z: 180);

        self.addChildNode(wrapperNode);
    }

    func getNode() -> SCNNode {
        return node;
    }

    func rotateShip(_ node: SCNNode, x: Float, y: Float, z: Float){
        //original angles
        let xAngle = SCNMatrix4MakeRotation(degToRad(deg: x), 1, 0, 0);
        let yAngle = SCNMatrix4MakeRotation(degToRad(deg: y), 0, 1, 0);
        let zAngle = SCNMatrix4MakeRotation(degToRad(deg: z), 0, 0, 1);


        let rotationMatrix = SCNMatrix4Mult(SCNMatrix4Mult(xAngle, yAngle), zAngle);

        node.pivot = SCNMatrix4Mult(rotationMatrix, node.transform);
    }

    func degToRad(deg: Float) -> Float{
        return deg / 180 * Float(M_PI)
    }

}

Thank you

Answer 1

transfomPosition does not work because it transforms a position, but you don't want that, you want to transform a direction . This also is a SCNVector3 but entirely different, because you only want the rotation applied, not the translation .

Either use transformVector or use worldFront directly, which are new in iOS 11.