[pdftex] pdftex core dump when including certain pdf files

[The Thanh Han]

Hi Ross,


On 18 July 2016 at 03:01, Ross Moore <ross.moore at mq.edu.au> wrote:

> Hi Thanh,
>
> On Jul 17, 2016, at 7:41 PM, The Thanh Han <hanthethanh at gmail.com> wrote:
>
>
> ​the real question one should ask is why StemV is required, since it's
> already included in the font itself.​
>
>
> I think I can explain that.
>
> For a Type 1 font,  StemV  is the  Hinting parameter  StdVW .
> pdfTeX already knows this:
>    ptexlib.h:363:    , {"StemV", "StdVW”}
>
> http://partners.adobe.com/public/developer/en/font/T1_SPEC.PDF
>
>
> PDF uses the Font Descriptor dictionary in several ways.
>
>  #1.  Firstly, if the font program itself is *not* present, then it can
> substitute
>       something that looks similar, having similar widths in vertical
> strokes.
>
>  #2.  When the font *is* available, there are still issues; especially at
>       low resolution. Then the “hinting” is used in choosing which pixels
> to
>       include when following the outline description.
>
>  #3.  Even at high resolution, there is a possible use, related to #1.
>       The time required to produce the full hi-res image of a portion of
>       a page may be quite large (a few seconds, say).
>       Instead of presenting a blank page until it’s ready, a quick mock-up
>       is first shown, perhaps using a substitute font with cached letter
> forms.
>       This is later replaced with the full image, when ready.
>
> I cannot find any documentation to justify that #3 is used in any specific
> renderer,
> but I've certainly seen rough images appear prior to the full hi-res.
> version.
> Note that the  /Flags  parameter conveys information about characteristics
> of the script that the font implements, so is used in the selection of
> substitute fonts.
>
>
> Here’s an extract from the PDF Spec. which certainly refers to usage #1;
>
>
> 9.8  Font Descriptors
>
> 9.8.1General
>
> A font descriptor specifies metrics and other attributes of a simple font
> or a CIDFont as a whole, as distinct from the metrics of individual glyphs.
> These font metrics provide information that enables a conforming reader to
> synthesize a substitute font or select a similar font when the font program
> is unavailable. The font descriptor may also be used to embed the font
> program in the PDF file.
>
>
>
>
​thanks for the excellent explanation.​

​I was aware about #1, i.e. pdf browsers might make use of info in font
descriptor to mimic the font. pdftex supports creating pdfs without
embedding the fonts, too. However I think those pdfs without embedded fonts
are rather useless.

Back to the original issue: I agree it makes more sense to copy StemV as
real number, not integer.

Regards,
Thanh
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