Re: pdftex core dump when including certain pdf files

Hi Thanh,

On Jul 17, 2016, at 7:41 PM, The Thanh Han <[email protected]<mailto:[email protected]>> 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.





​Thanh​


Hope this helps.

Ross


Dr Ross Moore

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

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