void OnMouseTranslation()
{
Vector3 mousePos= Camera.main.WorldToScreenPoint(transform.position);
float z_pos = transform.position.z;
mousePos.x = Input.mousePosition.x;
mousePos.y = Input.mousePosition.y;
Vector3 point = Camera.main.ScreenToWorldPoint(mousePos);
point.z = z_pos;
transform.position = point;
}