code: def _add_freeform_sp(self, origin_x, origin_y):
          
          spTree = self._shapes._spTree
          return spTree.add_freeform_sp(
              origin_x + self._left,
              origin_y + self._top,
              self._width,
              self._height
          )
docs: Add a freeform `p:sp` element having no drawing elements.
  
          *origin_x* and *origin_y* are specified in slide coordinates, and
          represent the location of the local coordinates origin on the slide.