Re: [NTG-pdftex] images in formats

27 Jun 2007

      "Martin Schröder"  writes:
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2007/6/27, David Kastrup :
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"Martin Schröder"  writes:
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2007/6/27, David Kastrup :
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For example, preview-latex uses mylatex.ltx to dump the state of the
TeX at \begin{document} time.  Not allowing any image references (like
in \savebox commands) before that point of time is a rather brutal
restriction.
Why do you need it
What?  preview-latex?  mylatex.ltx?
\savebox
It is the mechanism LaTeX _offers_ to users (it will commonly get used
in connection with fancyhdr.sty, for example).  And it uses a similar
mechanism itself in \AtBeginDVI.

Saying that it shouldn't is a bit late in the game.
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and what do you gain by using \savebox?
Uh, it is _there_.  For a reason.  Saying that it (and similar
functionality) should not get used anymore is creating a rather sordid
restriction and backward incompatibility.
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The speed increase is most likely minimal
The speed increase of what is most likely minimal?
The speed increase of using \savebox.
It is there and gets used.
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and the document needs to read the image anyway -- unless you want
to dump fragments of pdf code into the format.
In DVI mode, a pointer to the image gets dumped in the form of a
special.  A similarly sufficient amount of information would have to
get there in PDF mode.
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If we expanded the dvi model we would dump the meta information
about pdf things and then undump them later. This needs code for
dumping and undumping this meta information. And
\immediate\pdfximage would still fail.
[...]
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Don't forget: pdfTeX is one-pass, while TeX->dvips is two-pass.
Where is the relevance?
It was not designed with making two-pass-like solutions (which we
are discussing here) working, instead the two passes are
intermingled.
I don't see that.  PDFTeX has to deal with boxes and hlists/vlists
being boxed, reboxed, unboxed, thrown away and duplicated.  So this is
basically a two-pass process between creation of an object and a
list-capable reference to it, and shipout.  An object might appear in
arbitrary duplication (including zero times) in multiple shipouts, so
the multipass abstraction that makes it possible to copy boxes already
needs to be present in PDFTeX.
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The "sufficient amount of information" aka "meta information" is
most likely not in the code in one piece and there is currently no
way to dump and undump that. And a proper solution would not only
handle \pdfximage, but also \pdfobj, \pdfxform, ...
Sure.  But as I said, PDFTeX already _needs_ to organize its meta
information in order to deal with box manipulations.

-- 
David Kastrup