[pdftex] define pdf variable and then reference it?

[ivo welch]

thank you, ross (and martin).

I know even less about FDF than I know about PDF.  Do you have a short
example template  you could post?

Sticking to the same number of bytes would not be a problem NOW THAT I
KNOW IT.  I could simply make the defined unusual string pretty long
(80 characters), and replace it with my string plus spaces.  In my
application, typesetting would not be a problem---I would probably
want my pdf document to display the string somewhere on a left side,
not followed by anything.  (This brings me back to my original
definition: does pdf have an easy variable mechanism that can be
resolved at run time?  this would seem a lot easier than the FDF
multiple request route.)

regards,

/iaw


On 6/1/06, Ross Moore <ross at ics.mq.edu.au> wrote:
> Hello Ivo,
>
> On 01/06/2006, at 12:41 PM, ivo welch wrote:
>
> > I have a strange question.  I would like to customize a large pdftex
> > generated document for everyone who downloads it.  For example, I
> > would like to write in the headings of each page "hello, george".
> > alas, I do not want to have to re-latex for every downloader.
>
> This is hardly strange.
> There are several sites where this kind of thing is implemented.
>
> >
> > One solution would be to turn off all pdftex compression, and then
> > look for a very unusual string that I would put into the heading, and
> > which would be replaced.  (I know that the typesetting of this string
> > may be off.)  Is this the best solution?
>
> Well, it just isn't a solution at all, unless you also ensure
> that all of your replacement strings have the same lengths;
> that is, exactly the same number of bytes.
>
> On the other hand, the PDF spec allows for incremental changes
> to be made at the end of a PDF document, with a mechanism to
> store the complete history of changes.
> I've only seen Acrobat Pro do this, but doubtless there is other
> software around that does it also.
>
> However, this might cost a significant amount of $s.
>
>
> >
> > I do not know much about pdf, but if it were to allow me to set a
> > variable and pdftex were to allow me to use this variable later, it
> > would solve this very elegantly.  something like
> >    \pdfdefinevariable{\someheading}{VERYUNUSUALSTRING}
> >    \pagestyle{myheadings}
> >    \markboth{\someheading \hfill}
> > the resolution would occur at display time, not at
> > latex-typesetting-compile time.  a simple sed program could replace
> > VERYUNUSUALSTRING with "hello, george", and every page heading would
> > have "hello, george" on it.
>
> Another approach, which *can* be implemented using pdf-TeX and
> a sripting language (such as Perl), is to make use of JavaScript
> form fields, and the FDF (Forms Data Format) specification.
>
> This works as follows.
>
>    When a user clicks a hyperlink to download your document,
> your web-server sends the request to a script that will be
> interpreted by the scripting engine (e.g. Perl).
>
> This script constructs a short text-file in FDF format,
> specifying
>    a.  a URL for the real PDF document
>    b.  the values of (variable) fields within that PDF.
>
> The web-server sends out this FDF file.
> When the user's browser receives this FDF it will (if
> configured correctly)
>    (i)  launch an instance of  Adobe Reader ;
>   (ii)  emit a request for the real PDF file;
> (iii)  merge the values contained in the FDF file
>         with the fields inside the PDF doc
>
> Actually it is the Adobe Reader that does steps (ii)
> and (iii), but it needs to cooperate with the browser
> to achieve these tasks.
>
>
> The result is similar to what you are asking for.
> However, you don't get the same typesetting quality
> that you might like, as the field data must be
> a flat text-string --- in Unicode, would be best.
>
>
> >
> > Is the latter possible?  advice appreciated.
>
> We use this FDF mechanism a lot with student quizzes.
> These are personalised for each student. The Perl scripts
> do a lot more; e.g., keeping track of when requests are
> made, and from where. They also check whether the student
> is indeed enrolled in the course, and contribute lines
> to a personal log of each student's activity concerning
> these downloadable quizzes.
>
> Here's a typical URL for one of our courses:
>
> http://rutherglen.ics.mq.edu.au/~maths/S106/123/quizzes.html
>
> For the "Name" and "Student ID" try  'guest'  or  'staff'.
> These names allow the enrolment checking to be bypassed.
>
>
> >
> > /ivo welch
>
> Going back to your original statement of intent ...
>
> >   For example, I
> > would like to write in the headings of each page "hello, george".
> > alas, I do not want to have to re-latex for every downloader.
>
>   ... the re-latex route need not be inappropriate.
>
> This is what we do for student assignments, to personalise a cover-sheet
> for each student.  For example, at:
>
>     http://rutherglen.ics.mq.edu.au/~maths/S106/123/assign.html
>
> This time the assignment sheets are typeset afresh, using the
> name and student ID provided from the web-site.
>
>
> For larger documents, there is an interesting strategy that can be
> used. You pre-load  pdflatex  processes, which run until encoutering
> a \write18 statement which waits for a specific signal.
> Such a signal might be the existence of a file containing the name
> to be used in your running headers.
> Now your web-server's script gets the information provided by the user
> and writes it into a file with the prescribed name. This releases
> the waiting pdflatex job, allowing it to finish. Once done, the
> web-server serves up the newly created PDF to the user.
>
> Provided your document isn't too complicated, this can be quite fast.
> If you expect a lot of usage, preload hundreds of processes, each
> with a different trigger.
>
> Use of the  pdfpages  package may be appropriate with larger documents,
> to reduce the amount of time pdfTeX spends in digesting macro
> expansions.
>
>
>
> Hope this helps,
>
>         Ross
>
> ------------------------------------------------------------------------
> Ross Moore                                         ross at maths.mq.edu.au
> Mathematics Department                             office: E7A-419
> Macquarie University                               tel: +61 +2 9850 8955
> Sydney, Australia  2109                            fax: +61 +2 9850 8114
> ------------------------------------------------------------------------
>
>
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