Interval y_extent = Interval (pmin, pmax);
Box line_box (x_extent, y_extent);
Stencil line = Lookup::round_filled_box (line_box, blotdiameter);
Interval y_extent = Interval (pmin, pmax);
Box line_box (x_extent, y_extent);
Stencil line = Lookup::round_filled_box (line_box, blotdiameter);