drawing ellipses

["Amadeus W. M." <amadeus84 verizon net>]

How do I draw an ellipse (or rectangle, for that matter), rotated by some
angle? I know about Drawable::draw_arc() and draw_rectangle(), but these
only draw the objects with the semiaxes parallel to the image axes. I
imagine I have to set up some transformation matrix, and I don't know what
to look for. Thanks!