[NTG-pdftex] Creating identical PDF files with different pdfTeX runs

[Frank Küster]

Hans Hagen <pragma at wxs.nl> wrote:

> - pdf itself is moving which may demand additional of different
> resources being added - the pdftex stream depends on for instance cm
> directives and font references and there has been changes in this area
> over time (improvements like collapsing, removing redundant code) -
> macro packages may change their implementations of annotations, color,
> graphics and such, which results in different object ordering,
> numbering and content
> - macro packages may add/support new features which in turn may result
> in differences between pdf files; - macro packages may
> improve/change/patch special things (hz metrics and such)
> - font resources may change (metrics are normally stable, but the rest
> may change)

I don't think that these arguments make such tests unuseful.  If such
changes occur, the tests will fail, and the known-good documents need to
be regenerated and manually checked.  However, most of the time this
will *not* happen, and then the tests would be very helpful.

> the best you can do is not to look at the pdf file, but to parse the
> log for errors, like overfull boxes which can be signals of old/new
> code doing weird things, missing fonts, map files, encodings and
> characters.

I don't think the log helps.

The log files contain absolute paths, so they would need lots of
replacements before you can even start comparing.  They contain version
information for the packages - but checking whether a new version gives
identical results is one of our goals.  And renamed files, or splitting
a package into different input files loaded by the "master" file, would
completely break when we would try to automatically parse the log file.

Regards, Frank
-- 
Frank Küster
Single Molecule Spectroscopy, Protein Folding @ Inst. f. Biochemie, Univ. Zürich
Debian Developer (teTeX)