Font problem with TL'20

[Paulo Ney de Souza]

Thanks, I'll check it out. I don't know if I mention it publicly, but we
almost printed a 5K run of this book that was caught only at the last
minute, so I am deeply interested in the subject.

Our system does a gazillion checks for conformity on the sources and PDF,
but it is not able to recognize this type of problems. Interestingly enough
NONE of the pre-flight tools I have access to have been able to detect
this, in the PDF file, even though the two characters occupying the same
space in the PDF source is very clear.

I have been thinking about writing something that could detect it, but it
will have to deal with a fair amount of false-positives like "\not\in" and
with slow algorithms to detect when they intersect.

Does anyone know of work in that direction?

Paulo Ney

On Tue, Dec 15, 2020 at 7:15 AM Jonathan Fine <jfine2358 at gmail.com> wrote:

> Hi Paulo
>
> You wrote
>
> Do you know a way one can automatically check a PDF file for this kind of
>> overprinting?
>>
>
>  I know something that helps. The overprinting was caused by change in the
> TeX-Live software (which then affected the font selection).
>
> Here's my automatic check. It is a regression test. Suppose A.tex produced
> 2019-A.pdf when run with TeX Live 2019, and similarly for 2020-A.pdf. Now
> convert the pdf files to bitmaps, and perform a diff on the bitmaps.
>
> I've already written a utility for doing this, when we want to check some
> PDF manipulation software that was used to improve accessibility of the
> PDFs. But it introduced visual errors. This diff on bitmaps, made visual,
> allowed errors to be easily spotted.
>
> Related is using the output produced by the --recorder option. As part of
> a final production run, use --recorder, and augment it with the git hash of
> the files read.
>
> jfine at lemon:~$ tex --recorder story
> This is TeX, Version 3.14159265 (TeX Live 2019) (preloaded format=tex)
> (/usr/local/texlive/2019/texmf-dist/tex/plain/knuth-lib/story.tex [1])
> *\end
> Output written on story.dvi (1 page, 680 bytes).
> Transcript written on story.log.
>
> $ cat story.fls
> PWD /home/jfine
> INPUT /usr/local/texlive/2019/texmf.cnf
> INPUT /usr/local/texlive/2019/texmf-dist/web2c/texmf.cnf
> INPUT /usr/local/texlive/2019/texmf-var/web2c/tex/tex.fmt
> INPUT /usr/local/texlive/2019/texmf-dist/tex/plain/knuth-lib/story.tex
> OUTPUT story.log
> OUTPUT story.dvi
>
> This example shows that to avoid binary noise, you'll want to similarly
> fingerprint the creation of tex.fmt.
>
> I hope this helps.
> --
> Jonathan
>
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