vala out argument question

    public override void get_size(Gtk.Widget widget, Gdk.Rectangle? cell_area,
                                   out int x_offset, out int y_offset,
                                   out int width, out int height) {
        x_offset = 0;
        y_offset = 0;
        width = this.MIN_CELL_WIDTH;
        height = this.MIN_CELL_HEIGHT;
    }