question: @ Override public ShapeTileBox offset ( double p_dist ) { if ( p_dist == 0 || is_empty ( ) ) { return this ; } int dist = ( int ) Math . round ( p_dist ) ; PlaPointInt lower_left = new PlaPointInt ( box_ll . v_x - dist , box_ll . v_y - dist ) ; PlaPointInt upper_right = new PlaPointInt ( box_ur . v_x + dist , box_ur . v_y + dist ) ; return new ShapeTileBox ( lower_left , upper_right ) ; }
target:  Returns the box offseted by p_dist. If p_dist > 0, the offset is to the outside, else to the inside.