如何在jsPDF中对齐多行中心？

Question

我找到了此解决方案以使文本居中对齐

string conString = "Data Source = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = XXX.XXX.XX.XX)(PORT = 1521)))(CONNECT_DATA=(SID=XXX))); User Id = XXX; Password = XXX;";

            using (OracleConnection con = new OracleConnection(conString))
            {
                using (OracleCommand cmd = con.CreateCommand())
                {
                    try
                    {
                        con.Open();
                        cmd.BindByName = true;

                        cmd.CommandText = "select doc from archivos where rownum = 1";

                        OracleDataReader reader = cmd.ExecuteReader();

                        while (reader.Read())
                        {
                            await context.Response.WriteAsync("Datos: " + reader.GetString(0) + "\n");
                        }

                        reader.Dispose();

                        reader[0].ToString();

                        con.Close();
                    }
                    catch (Exception ex)
                    {
                        await context.Response.WriteAsync(ex.Message);
                    }
                }
            }

我可以用它来对齐中心

(function(API){
API.centerText = function(txt, options, x, y) {
    options = options ||{};
    /* Use the options align property to specify desired text alignment
     * Param x will be ignored if desired text alignment is 'center'.
     * Usage of options can easily extend the function to apply different text 
     * styles and sizes 
    */
    if( options.align == "center" ){
        // Get current font size
        var fontSize = this.internal.getFontSize();

        // Get page width
        var pageWidth = this.internal.pageSize.width;

        // Get the actual text's width
        /* You multiply the unit width of your string by your font size and divide
         * by the internal scale factor. The division is necessary
         * for the case where you use units other than 'pt' in the constructor
         * of jsPDF.
        */
        txtWidth = this.getStringUnitWidth(txt)*fontSize/this.internal.scaleFactor;

        // Calculate text's x coordinate
        x = ( pageWidth - txtWidth ) / 2;
    }

    // Draw text at x,y
    this.text(txt,x,y);
}
})(jsPDF.API);

但是它仅适用于一行，如果文本为多行，则无效

doc.centerText('this is first line',{align: "center"},0,40);

如何对齐多条线的中心？