Thermal printer does not know when to stop feeding paper (Length) - delphi

Question

I've made a program for my brother's restaurant, that sends a .txt file to the Thermal printer. The problem that I am having (or at least, what I am thinking of) is in the file's length.
This is the code that I used for the printing procedure (It's from Help needed about printing text file with delphi)
procedure TForm1.PrintTextFile(const FileName: string; const Numbering: boolean = true);
const
FONT_NAME = 'Times New Roman';
FONT_SIZE = 14;
var
MARGIN: integer;
sl1: TStringList;
i, h: Integer;
r, rFooter: TRect;
s: string;
DocEnd: integer;
begin
with TPrintDialog.Create(nil) do
try
if not Execute then
Exit;
finally
Free;
end;
sl1 := TStringList.Create;
try
sl1.LoadFromFile(FileName);
Printer.BeginDoc;
Printer.Title := FileName; // or application name or sth else
Printer.Canvas.Font.Name := FONT_NAME;
Printer.Canvas.Font.Size := FONT_SIZE;
MARGIN := 1*Printer.Canvas.TextWidth('M');
DocEnd := Printer.PageHeight - MARGIN;
if Numbering then
begin
dec(DocEnd, 2*Printer.Canvas.TextHeight('8'));
rFooter := Rect(0, DocEnd, Printer.PageWidth, Printer.PageHeight - MARGIN);
DrawText(Printer.Canvas.Handle,
PChar(IntToStr(Printer.PageNumber)),
length(IntToStr(Printer.PageNumber)),
rFooter,
DT_SINGLELINE or DT_CENTER or DT_BOTTOM);
end;
r.Left := MARGIN;
r.Top := MARGIN;
for i := 0 to sl1.Count - 1 do
begin
r.Right := Printer.PageWidth - MARGIN;
r.Bottom := DocEnd;
s := sl1.Strings[i];
if s = '' then s := ' ';
h := DrawText(Printer.Canvas.Handle, // Height of paragraph on paper
PChar(s),
length(s),
r,
DT_LEFT or DT_TOP or DT_WORDBREAK or DT_CALCRECT);
if r.Top + h >= DocEnd then
begin
Printer.NewPage;
if Numbering then
DrawText(Printer.Canvas.Handle,
PChar(IntToStr(Printer.PageNumber)),
length(IntToStr(Printer.PageNumber)),
rFooter,
DT_SINGLELINE or DT_CENTER or DT_BOTTOM);
r.Top := MARGIN;
r.Bottom := DocEnd;
end;
if h > Printer.PageHeight - 2*MARGIN then
raise Exception.Create('Line too long to fit on single page.');
DrawText(Printer.Canvas.Handle,
PChar(s),
length(s),
r,
DT_LEFT or DT_TOP or DT_WORDBREAK);
inc(r.Top, h);
end;
Printer.EndDoc;
finally
sl1.Free;
end;
end;
This is the .txt file that is sent to the thermal printer:
And this is how it is being printed out:

Answer 1

I think you need to review your printer's driver settings before doing anything. In driver settings you can set the maximum paper height. You can also use Notepad to print the file to printer and compare the results with your program results.
I have some notes about your code as you are printing to thermal printer:
It is not a good idea to use paper height in your calculation.
You don't add new page because this will make the printer to cut the
paper.
If you are using Windows and want to know the printer
margins you can use something like the following function GetActualMargins.
//This function works on the current printer
//Dpi : Dot per inch
procedure GetActualMargins(var DpiX, DpiY : Integer; var LeftMargin, TopMargin: Single);
begin
try
DpiX := GetDeviceCaps(Printer.Handle, LOGPIXELSX);
DpiY := GetDeviceCaps(Printer.Handle, LOGPIXELSY);
LeftMargin := Round((25.4 * GetDeviceCaps(Printer.Handle, PHYSICALOFFSETX)) / DpiX );
TopMargin := Round((25.4 * GetDeviceCaps(Printer.Handle, PHYSICALOFFSETY)) / DpiY );
except
//you can raise Exception here
end;
end;

Answer 2

I have been using thermal printers for some years but I prefer to use EPOS Commands.
I would suggest you test this;-
procedure TForm1.btnprint(Sender: TObject);
Var F:TextFile;
begin
try
AssignFile(F,<printer port>);// e.g LPT1,LPT2,COM1,COM2...
Except
Begin
ShowMessage('Error in assigning printer.');
End;
End;
Rewrite(F);
Writeln(F,'Test printer');
Writeln(F, chr(29)+chr(86)+chr(65));//Cut and feed paper
CloseFile(F);
End;