cairo_rotate (cr, position_angle - (width_angle/2.0));
cairo_move_to (cr, 0, 0);
cairo_arc_negative (cr, 0, 0, radius, width_angle, 0.0);
cairo_rotate (cr, position_angle - (width_angle/2.0));
cairo_move_to (cr, 0, 0);
cairo_arc_negative (cr, 0, 0, radius, width_angle, 0.0);