Unity2D object rotation on Mobile device - unity3d

Question

I want to know if there is a way to rotate the object only when the user click and drag on the gameobject. If the user click and drag anywhere else, the gameobject should not rotate.
Object with this script on it is rotating no matter where the user clicks.
void Update()
{
if (Input.touchCount > 0)
{
touch = Input.GetTouch(0);
if (touch.phase == TouchPhase.Moved)
{
Vector2 dir = Camera.main.ScreenToWorldPoint(Input.GetTouch(0).position) - Camera.main.ScreenToWorldPoint(transform.position);
float angle = Mathf.Atan2(dir.y, dir.x) * Mathf.Rad2Deg;
Quaternion rotation = Quaternion.AngleAxis(angle - 90, Vector3.forward);
transform.rotation = rotation;
transform.rotation = rotationZ * transform.rotation;
}
}

Answer 1

Your current code indeed only checks for touches .. it doesn't matter whether these are "hitting" anything or not.
You could e.g. use a Physics.Raycast in order to check if your touch is above an object using
// store the direction from object to touch when the touch started
private Vector2 startDirection;
// store the objects orientation when the touch started
private Quaternion startRotation;
// only process touch moved if the touch actually started above this object
private bool isValidTouch;
// The collider of this object
[SerializeField] Collider _collider;
// The main camera
[SerializeField] Camera _mainCamera;
private void Awake()
{
if(!_collider) _collider = GetComponent<Collider>();
if(!_mainCamera) _mainCamera = Camera.main;
}
void Update()
{
if (Input.touchCount > 0)
{
touch = Input.GetTouch(0);
var touchPosition = touch.position;
switch(touch.phase)
{
case TouchPhase.Began:
// Check if this touch actually is over this object
if(_collider.RayCast(_mainCamera.ScreenPointToRay(touchPosition), out var hit))
{
// Now store initial data
// You want to do ONLY ONE:
// - Either transform the touch into worldspace (more complicated)
// - OR transform the position into screenspace (easier)
// You definitely do not want to do both!
startDirection = (touchPosition - (Vector2)_mainCamera.WorldToScreenPoint(transform.position));
startRotation = transform.rotation;
isValidTouch = true;
}
break;
case TouchPhase.Moved
if(isValidTouch)
{
// Get the current touch direction
var direction = (touchPosition - (Vector2)_mainCamera.WorldToScreenPoint(transform.position));
// Get the angle between them
var differenceAngle = Vector3.SignedAngle(startDirection, direction, Vector3.forward);
// rotate the original rotation according to the current angle
Quaternion rotation = startRotation * Quaternion.AngleAxis(differenceAngle, Vector3.forward);
transform.rotation = rotation;
}
break;
case TouchPhase.Ended
isValidTouch = false;
break;
}
}
}