public void invalidate_drill_pages(ShapeTile p_shape){
  drill_page_array.invalidate(p_shape);
}

public void invalidate_drill_pages ( ShapeTile p_shape ) { drill_page_array . invalidate ( p_shape ) ; }
invalidates all drill pages intersecting with p_shape , so the they must be recalculated at the next call of get_ddrills ( )
