Re: pdftex core dump when including certain pdf files

Hi all,

I was writing this before Karl’s message arrived.
But I’ll send it anyway.

On Jul 16, 2016, at 8:57 PM, Norbert Preining <[email protected]<mailto:[email protected]>> wrote:

Hi all


    fd = epdf_create_fontdescriptor(fontmap, round(stemV->getNum()));

Sounds excellent.

What about the other values? As far I understood Ross's email, many of the other values can be real, too.

Norbert


With all due respect, why do anything that changes the number
that has been read from a font file?

Surely all (modulo a case discussed below) pdfTeX does with  stemV  is to build
the font-descriptor dictionary, which is written into the PDF file as a string.

So by all means read the  stemV  value from a font file as a number (integer or float)
but then immediately convert it into its string representation, which is how it should
be written out again, preserving the accuracy that was originally supplied.


The problem case is surely when there is no  stemV  supplied in the font,
as with  TTF fonts, but it must be included in the font-descriptor to get valid PDF.
See the following conversation:

 https://stackoverflow.com/questions/35485179/stemv-value-of-the-truetype-font

If no  stemV  value is supplied, then one must be created;
e.g. estimate it using the width of a non-serifed `I’ in the font family.
If the font is italiced, multiply by cosine of the italic-angle.
Or produce some other approximate heuristic, as a truly exact value is rarely required.

Something of this kind is going on here, isn’t it?

writefont.c-    fd->font_dim[DESCENT_CODE].val = i < 0 ? i : 0;
writefont.c:    fd->font_dim[STEMV_CODE].val =
writefont.c-        dividescaled(getcharwidth(f, '.') / 3, pdffontsize[f], 3);
writefont.c-    fd->font_dim[XHEIGHT_CODE].val =
writefont.c-        dividescaled(getxheight(f), pdffontsize[f], 3);

but the result is an integer.

If such a calculation were to produce a float, then approximate/truncate it in some fashion
and convert to a string for inclusion in the font-descriptor.


It is clear from the following link that other software treats  stemV  as non-integer:

https://documentation.devexpress.com/#CoreLibraries/DevExpressPdfPdfFontDescriptor_StemVtopic

Indeed here it is declared as a  double !!



Hope this help,

Ross


Dr Ross Moore

Mathematics Dept | Level 2, S2.638 AHH
Macquarie University, NSW 2109, Australia

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