Restricting body movement withing a specific length while dragging a gameobject in unity

Question

private void OnMouseDrag()
{
    Vector3 screen_sp=new Vector3(Input.mousePosition.x,Input.mousePosition.y,screen_space.z);
    Vector3 cur_pos=Camera.main.ScreenToWorldPoint(screen_sp)+offset;
        if(pendulum_object.gameObject != null && pendulum_object.gameObject.rigidbody!=null)
        {
                transform.position=cur_pos;
                    Debug.Log ("Pendulum is being dragged left"+transform.position);
                    Debug.Log("Mouse position is:"+Input.mousePosition);
                    Debug.Log("Current position is:"+cur_pos);
        }
}

The problem is:The dragging of game object must be restricted to the length of string. The pendulum is joint using hinge joint to the world.

Answer 1

You should proceed in the following way

1) Get the input mouse position convert it to world co-ordinates

Vector3 direction = Camera.main.ScreenToWorldPoint (Input.mousePosition);

2) Now calculate the directional Vector3 form anchor of the hinge joint to the input mouse position.

Vector3 diff = direction - Anchor.transform.position;

3) The last step will be to restrict the Position of the pendulum along this directional vector as per the string length (float) . By normalising we get the direction , then we clamp the magnitude to max String Length.

pendulum_object.transform.position = diff.normalized * Mathf.Clamp (diff.magnitude, 0, StringLength);

Note: If the pendulum is a child of a game object and if the scale and position differs. Then you need to use pendulum_object.transform.localPosition and also take care of the scaling factor.