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

15 Mar 2006


      On 2006-03-15 15:06:43 +0100, Frank Küster wrote:
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Martin Schröder  wrote:
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This will only get you so far. If you want to compare PDFs, you
should not test for identical files, but for identical output:
Render the PDF to a bitmap (e.g. with ghostscript) and compare
the generated bitmaps. Otherwise your test will fail whenever the
output of pdfTeX is changed in any way.
That's a point; on the other hand, all I get then is glyphs on a page,
but the information about the internal structure is lost: hyperlinks,
character information (will a search for "fl" find the fl ligature, or
will "ü" be pasted correctly?), etc.
How far will you get with the logfile with a suitable combination
of \tracingoutput etc.?
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Even then your tests will
fail when we improve the typesetting of pdfTeX. :-}
I don't expect those tests, or rather the known-good documents, to be
carved in stone.  There will be chances on occasion which require manual
checking of the new document.
Agreed.
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I guess it's best to have both kinds of test:  Comparing the bitmaps
gives information about the actual typesetting (and about the
differences you wouldn't spot when checking by eye), comparing the pdf
files gives additional information about the document structure.
Agreed.
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A start would be setting the system date -- this would seed /ID
and /CreationDate. Note that /ID also includes the filename.
The system date?  You need to be root to do that, or is there a way to
fake the system date in the local environment?
I don't know. What you would probably need is a way to dump und
set all run-specific settings of pdfTeX (seeds for various random
numbers, date etc).
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Is it possible to achieve identical pdf files directly, by adding the
proper commands, or would it be possible to add this feature?
Currently it's impossible (and that's a feature :). Adding the
feature can't be that hard, though.
I would very much appreciate this.
File a feature request, please. :-)

Best
    Martin
-- 
                    http://www.tm.oneiros.de