If origin is given, then it should be one of the character
strings "centroid", "midpoint" or "bottomleft".
The argument vec will be ignored; instead the shift will be performed
so that the specified geometric location is shifted to the origin.
If origin="centroid" then the centroid of the window will be
shifted to the origin. If origin="midpoint" then the centre of
the bounding rectangle of the window will be shifted to the origin.
If origin="bottomleft" then the bottom left corner of the
bounding rectangle of the window will be shifted to the origin.