cairo_set_line_width (cr, 1.0);
cairo_set_line_cap (cr, CAIRO_LINE_CAP_SQUARE);
cairo_move_to (cr, x + 0.5, min_y);
cairo_line_to (cr, x + 0.5, max_y - min_y - 0.5);
cairo_stroke (cr);
cairo_set_line_width (cr, 1.0);
cairo_set_line_cap (cr, CAIRO_LINE_CAP_SQUARE);
cairo_move_to (cr, x + 0.5, min_y);
cairo_line_to (cr, x + 0.5, max_y - min_y - 0.5);
cairo_stroke (cr);