question: public ShapeTileBox surrounding_box ( ) { if ( is_clear ( ) ) return null ; int llx = Integer . MAX_VALUE ; int lly = Integer . MAX_VALUE ; int urx = Integer . MIN_VALUE ; int ury = Integer . MIN_VALUE ; for ( int layer_idx = 0 ; layer_idx < layer_count ; ++ layer_idx ) { OctagonMutable curr = octa_arr [ layer_idx ] ; llx = Math . min ( llx , ( int ) Math . floor ( curr . lx ) ) ; lly = Math . min ( lly , ( int ) Math . floor ( curr . ly ) ) ; urx = Math . max ( urx , ( int ) Math . ceil ( curr . rx ) ) ; ury = Math . max ( ury , ( int ) Math . ceil ( curr . uy ) ) ; } if ( llx > urx || lly > ury ) { return ShapeTileBox . EMPTY ; } return new ShapeTileBox ( llx , lly , urx , ury ) ; }
target:  Merge all info on all layers so you can update the gdi