[pdftex] pdftex deterministic?
matteo at metatype.it
Wed Apr 4 10:54:27 CEST 2007
On Tue, 2007-04-03 at 22:19 +0200, Reinhard Kotucha wrote:
> >>>>> "Matteo" == Matteo Centonza <matteo at metatype.it> writes:
> > Using checksums is the cheapest way of comparing two files (even
> > cheaper than a byte comparison) and give you absolute confidence
> > on the result.
> Yes, but a PDF file contains a time stamp. Hence you cannot produce
> two PDF files which have the same checksum.
> Even if you could force pdftex to create two files with the same
> timestamp, you'll get different checksums if you compare the output of
> pdftex 1.30 and pdftex 1.40, while what you see on screen is absolutely
> the same.
probably you missed some bits:
In my case i'm comparing PDFs generated by the same binary application,
and maybe what you see on screen is not "absolutely" the same, it is
indeed, under your requirements.
> I assume that the only way to compare PDF files is to compare bitmaps.
> Of course, you can compare files with a resolution of one scaled point
> unless you are running MS-DOS or something derived from it. Even with
> a finite amount of memory. You don't have to to create bitmaps of the
> whole page. You can run two processes at the same time which convert
> the PDF files to bitmaps and compare them line-by-line where the
> height of each line is one scaled point.
well, that's just one way of doing the comparison. Under different
conditions, you can find different algorithms.
> I don't see any problems here though I fear that such a program will
> not provide a result within a few seconds. You have to be very patient.
i'm generally a patient guy ;)
But not when i'd like to provide a networked production system
with timings in the magnitude of a latex compile.
Thanks for your response,
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