Duple c = item_to_window (Duple (_center.x, _center.y));
context->arc (c.x, c.y, _radius, _start_degrees * (M_PI/180.0), _arc_degrees * (M_PI/180.0));
Duple c = item_to_window (Duple (_center.x, _center.y));
context->arc (c.x, c.y, _radius, _start_degrees * (M_PI/180.0), _arc_degrees * (M_PI/180.0));