[NTG-pdftex] Incomplete CharSet causes failure with PDF/A validation

Ross Moore ross.moore at mq.edu.au
Thu Jun 14 23:49:15 CEST 2018


Hi Karl,

On Jun 15, 2018, at 7:27 AM, Karl Berry <karl at freefriends.org<mailto:karl at freefriends.org>> wrote:

Ross and all - back on your mail about /CharSet from two years ago.

Glad you have had a look at this.




Date: Sat, 11 Jun 2016 00:15:05 +0000
From: Ross Moore <ross.moore at mq.edu.au<mailto:ross.moore at mq.edu.au>>

[ https://mailman.ntg.nl/pipermail/ntg-pdftex/2016-June/004087.html<https://protect-au.mimecast.com/s/cWKXCjZ12RfxNX4h5FA-T?domain=mailman.ntg.nl> ]

As far as I can tell, the problem as reported relates to the seac
operator. Heiko, Thanh, Ross, anyone, up for looking into the code to
get the seac referents into the output /CharSet list? Not something I am
familiar with, so it would take me a while. (More below.)

Getting the  /CharSet  correct automatically would be nice, but not actually necessary.
For validation purposes, the  /CharSet  could be left out entirely.
The characters used from a font can be found by other means.
That is, having  /CharSet  is a convenience, not a necessity.

But, if the /CharSet  is specified, it must be complete; Adobe’s Preflight checks this.

Perhaps we could just have a command-line switch that allows writing the /CharSet to be omitted?


The other way to get a valid PDF is,…

 ... once having checked validation, with Preflight say, and found that there
are missing characters in the /CharSet , they can be added using

  \pdfglyphtounicode{a}{0061}         % Latin small letter a
  \pdfglyphtounicode{acute}{0301}   % Combining acute accent

then rerun the job.

Note that with this specification for ‘acute’, it will copy/paste as a combining character.
This means that one has to also hack at either the  \accent  primitive, or LaTeX’s \set at accent   command,
to get the characters placed in the correct order when using  \'{a}  with  OT1 encoding.

TeX places the (above) accent first, then the base character,
but Unicode requires the base first with the combining accent character coming next.



For example, this pdftex -ini file shows the problem, unrelated to the
pdf/x or latex:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\pdfoutput=1 \catcode`\{=1 \catcode`\}=2
\pdfcompresslevel=0 \pdfobjcompresslevel=0
\pdfglyphtounicode{aacute}{00E1}\pdfgentounicode=1
\font\b = fver8t \b % ecrm1000
\hsize=5pt
\hfil\char225 % aacute
\end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
$ pdftex -ini foo.tex
..
$ fgrep -a /CharSet try.pdf
/CharSet (/aacute)

Whereas the correct output should also include /a and /acute (as it does
with gs, which has code to handle the seac pieces):
/CharSet(/a/aacute/acute)

Looking at the definition for /aacute (t1disasm <fver8a.pfb):
/aacute {
50 596 hsbw
192 170 0 97 194 seac
} ND
where 97 is "a" and 194 is "acute". Just have to insert those into the
output list, presumably.

The code to output /CharSet from the glyph tree is in pdftexdir/writefont.c:
pdf_puts("/CharSet (");
for (glyph = (char *) avl_t_first(&t, fd->gl_tree); glyph != NULL;
glyph = (char *) avl_t_next(&t))
pdf_printf("/%s", glyph);

And the code to handle seac is in writet1.c:
case CS_SEAC:
a1 = cc_get(3);
a2 = cc_get(4);
cc_clear();
mark_cs(standard_glyph_names[a1]);
mark_cs(standard_glyph_names[a2]);
break;

"Just" have to get these pieces together, which doesn't seem like it
should be too hard ... ?


By the way, I checked a few other fonts. For EC (ecrm1000), Latin Modern
(ec-lmr10), and txfonts (t1xr) (mentioned in
tex.stackexchange.com/questions/81927)<https://protect-au.mimecast.com/s/yN1BCk815RCJGjyF9G1DQ?domain=tex.stackexchange.com>, seac is not used. This is a
reasonable choice for font implementors, as seac is deprecated all over
the place, as it assumes AdobeStandardEncoding etc.

I’ve not looked at the details of how the font is encoded.
Instead I work at the top-most level, and patch (LaTeX) macros, wherever possible.


dvips|ps2pdf does not output the /a and /acute for those fonts either;
presumably Adobe programs don't either. This seems correct, since the /a
and /acute character definitions are not in fact used in those cases.
Hopefully that is ok with the new standards. I can't imagine a decent
way to change it. --best, karl.

P.S. Unrelated to the problem, but I noticed while looking into it ...
although at one time writet1.c in pdftex and dvips were close, Pali's
changes last year to support encodings for bitmap fonts made the two
versions very different. I doubt they can reasonably be merged again. :(.


Cheers

Ross


Dr Ross Moore

Mathematics Dept | 12 Wally’s Walk, 734
Macquarie University, NSW 2109, Australia

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