void OnTriggerExit(Collider other)    // remove text popping up for itemName.
 {
     if (other.tag == "weapon")
     {
         ItemPickup pickup = other.gameObject.transform.Find("ItemText").GetComponent <ItemPickup>();
         pickup.SetTextActive(false);
     }
 }
 void OnTriggerEnter(Collider other)   // for popping up text for itemName.
 {
     if (other.tag == "weapon")
     {
         ItemPickup pickup = other.gameObject.transform.Find("ItemText").GetComponent <ItemPickup>();
         pickup.SetTextActive(true);
     }
 }