Rotating an object at which I am looking (ARFoundation)

Question

2 items are placed in AR. i would like to rotate 1 of those items while its in the middle of the screen (using touch controls and Raycast).

I would like all the rotation part of the code to be executed when the camera is looking at the object.

this is the script i use on an object placed in the scene, the Move function works since that is only activated when you tap on the screen where the object is and drag it away (Raycast to a Collider). however my rotation works on all objects in the scene when i swipe anywhere because if i swipe on the collider i move the object, so for rotation i have to stay outside that collider.

public class MoveObject : MonoBehaviour
{
    public bool holding;
    private Component rotator;
    int doubleTap = 0;

    void Start()
    {
        holding = false;
    }

    void Update()
    {
        if (holding)
        {
            Move();
        }

        // One finger
        if (Input.touchCount == 1)
        {
            // Tap on Object
            if (Input.GetTouch(0).phase == TouchPhase.Began)
            {
                Ray ray = Camera.main.ScreenPointToRay(Input.GetTouch(0).position);
                RaycastHit hitTouch;

                if (Physics.Raycast(ray, out hitTouch, 100f))
                {
                    if (hitTouch.transform == transform)
                    {
                        holding = true;
                    }
                }
            }
            // Release
            if (Input.GetTouch(0).phase == TouchPhase.Ended)
            {
                holding = false;
            }
        }

        if (Input.touchCount == 1 && !holding) //THIS is the rotation part
        {
            // GET TOUCH 0
            Touch touch0 = Input.GetTouch(0);

            // APPLY ROTATION
            if (touch0.phase == TouchPhase.Moved)
            {
                transform.Rotate(0f, touch0.deltaPosition.x * 0.5f, 0f);
            }
        }
    }

    void Move()
    {
        RaycastHit hit;
        Ray ray = Camera.main.ScreenPointToRay(Input.GetTouch(0).position);
        // The GameObject this script attached should be on layer "Surface"
        if (Physics.Raycast(ray, out hit, 30.0f, 
        LayerMask.GetMask("Surface")))
        {
            transform.position = new Vector3(hit.point.x,
                                             transform.position.y,
                                             hit.point.z);
        }
    }
}

Answer 1

You'll probably want another flag similar to holding to make sure that you don't rotate an object the center of the screen passes over during a swipe, such as when the camera is moving and the object passes through the center of the screen.

You can use Camera.ViewportPointToRay with input of new Vector3(0.5f, 0.5f, 0) to create a ray coming from the center of the screen. From there, the process is similar to your holding code.

Also, with a little rearranging, you can re-use the raycast that is already used to check if this object was touched because it also checks if any object was touched. Only checking to start rotating when the first raycast touches nothing avoids rotating (and raycasting unnecessarily) in the situation where this object is in the center of the screen but another object was touched.

As a sidenote, it's recommended to cache the result of Camera.main because it does a FindGameObjectsWithTag internally every time you reference it and that can add up to extra computation time.

Altogether, it could look like this:

private bool rotating;
private Camera cam;

void Start()
{
    holding = false;
    rotating = false;
    cam = Camera.main;
}

void Update()
{
    // One finger
    if (Input.touchCount == 1)
    {
        Touch touch0 = Input.GetTouch(0);

        if (touch0.phase == TouchPhase.Began)
        {
            Ray ray;
            RaycastHit hitTouch;

            // test hold start
            ray = cam.ScreenPointToRay(touch0.position);
            if (Physics.Raycast(ray, out hitTouch, 100f))
            {
                if (hitTouch.transform == transform)
                {
                    holding = true;
                }
            }
            else  // avoid rotating/raycasting again in situation 
                  // where this object may be in center of screen 
                  // but this or other object was touched.
            {
                // test rotate start
                ray = cam.ViewportPointToRay(new Vector3(0.5f, 0.5f, 0));
                if (Physics.Raycast(ray, out hitTouch, 100f)))
                {
                    if (hitTouch.transform == transform)
                    {
                        rotating = true;
                    }
                }
            } 
        }
        else if (touch0.phase == TouchPhase.Moved)
        {
            if (holding)
            {
                Move();
            }
            else if (rotating)
            {
                transform.Rotate(0f, touch0.deltaPosition.x * 0.5f, 0f);
            }
        }
        // Release
        else if (touch0.phase == TouchPhase.Ended)
        {
            holding = false;
            rotating = false;
        }
    }
}