# [NTG-pdftex] images in formats

David Kastrup dak at gnu.org
Wed Jun 27 14:40:07 CEST 2007

"Martin Schröder" <martin at oneiros.de> writes:

> 2007/6/27, David Kastrup <dak at gnu.org>:
>> 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?

> 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.

> The speed increase is most likely minimal

The speed increase of what is most likely minimal?  Of dumping a
format with the preamble?  Absolutely not.  It is very relevant in
preview-latex, for common editing work on single formulas easily a
factor of 5.  And we are talking about an interactive editing task and
its response time here.

> 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.

> 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.
>
>> Again: the \AtBeginDvi command was added to LaTeX precisely in order
>> to conserve pretypeset stuff that would otherwise get lost at a format
>> dump.
>
> So store the commands there. Do you really need their expansion?

Not the expansion, the typeset result.  This is what LaTeX uses and
preserves.  Since it is not untypical to put something in there which
would rely on \@onlypreamble stuff, I don't see that anything except
preserving the actual h/vlists could be depended on to work.

> Don't forget: pdfTeX is one-pass, while TeX->dvips is two-pass.

Where is the relevance?

--
David Kastrup