Re: Dubious "checksum mismatch" message on log file

[Vladimir Lomov <lomov.vl@gmail.com>]

Hello,
** Hans Hagen [2012-02-01 15:22:58 +0100]:

> On 1-2-2012 15:15, Ulrike Fischer wrote:
> >Am Wed, 1 Feb 2012 10:54:04 +0100 schrieb luigi scarso:

>>>It's not related to MKIV but to luatex.

>>I think it is related to MKIV (or more precisely to the fontloader).

>>It is a bit difficult to demonstrate it with context (how to you use
>>luatex without mkiv there?) but latex (or plain) it is quite easy:

>>The followings examples load pplr7t.vf.  Both give the checksum
>>mismatch message in the log if and only if the lua-fontloader
>>luaotfload it also loaded:

>>%LaTeX
>>\documentclass{article}
>>\usepackage{luaotfload}
>>\begin{document}
>>\font\test=pplr7t \test abc
>>\end{document}

>>%plain
>>\input luaotfload.sty
>>\font\test=pplr7t \test abc
>>\bye

>>So the code from luaotfload (which is based on the context
>>fontloader code) changes a checksum (either in the vf or in the
>>tfm-information) and so the check in the luatex engines fails.

>>(Imho it is only a minor problem, vf-fonts are not much used with
>>luatex).

> Afaik nothing is done with a checksum. There is a checksum field in
> the loaded tfm but I don't think one has to be passed to luatex.
> Maybe one should be passed when a regular tfm file is used but even
> then, loading a vf file is independent.

> So, it's best to just ignore that message.

Correct me if I'm wrong, but this how I understand TFM font and currect
state of tex engines (actually pdftex, xetex and luatex):
1. to use any font in tex one need a TFM file (file name = fontname.TFM),
that file actually contain informationabout font, not how exatly glyphs
are constructed;
2. when [original] tex read a document file it searches for TFM and VF
files, read them and write DVI file with information about that files;
3. after that user can send file to printer or publisher to print it on
printer. As I understand the purpose of checksum was to be sure that
publisher or printer would use exatly the same fonts as user. If user
converts DVI file to PS/PDF one on his/she computer using dvips or
dvipdfm* the checksum mostly useless, assuming files are not corrupted.

Nowadays pdftex, xetex and luatex are widely used and most time users
generate PDF files on the same computer they write documents, send PDF
files which have they own mechanism to check font consistency.

But still there are [plenty] DVI files around, as well as luatex engine
might generate DVI file. The convertion to PS/PDF is performed by
dvips/dvipdfm* programs, that's ok. But what about luatex with DVI
output?

My conclusion:
1. if PDF output is only interesting then it is Ok, ignore that message,
because font information is already in PDF and PDF programs should deal
with it;
2. if DVI output is concerned then luatex _must_ be consistent with
pdftex (also can write DVI files), which, imho (don't check), takes care
about both TFM and VF checksums.

---
WBR, Vladimir Lomov

-- 
The happiest time of a person's life is after his first divorce.
		-- J.K. Galbraith 
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