计算字符串在画布内的高度和宽度

          len:=Round(254*Printer.Canvas.TextWidth(RowList[i])/dpi);
          len1:=Printer.Canvas.TextHeight(RowList[i]);  //Round(254*Printer.Canvas.TextHeight(RowList[i])/dpi);
          Memo1.Lines.Add(RowList[i]+#9+floattostr(Len/10)+"mm"+#9+floattostr(Len1/10)+"mm");