Standalone rendering

If you want a visualization on its own, without an enclosing Image, call its render(width, height, unit=diagram_unit) and add the picture yourself. This is the one place you render explicitly.

RelationDiagram diagram = RelationDiagram();
diagram.add_set(new string[] {"1", "2"}, "A");
diagram.add_set(new string[] {"a", "b"}, "B");
diagram.add_relation(0, 1, new pair[] {(0,0), (1,1)});

picture p = diagram.render(8, 6);   // width, height (cm) — unit defaults to the theme's diagram_unit
add(currentpicture, p);

Every visualization implements the same render(width, height, unit=diagram_unit) contract and lays itself out to fill the given width x height. unit is only there to override the scale for this one call — pass it explicitly (e.g. render(8, 6, 2cm)) if you need a picture at a different scale than the rest of your figures; otherwise there’s nothing to specify.