[tex-k] Where does conversion of PostScript pts to TeX pts occur?

[Tomas Rokicki]

TexLive, which will include pdftex, is moving to github.

   https://github.com/TeX-Live/texlive-source

The file you are looking for is


https://github.com/TeX-Live/texlive-source/blob/trunk/texk/web2c/pdftexdir/pdftex.web

Note that github is still not the "single truth" for TeXLive but it may be
getting there.

-tom

On Sat, Jan 26, 2019 at 1:12 PM Doug McKenna <doug at mathemaesthetics.com>
wrote:

> Tom -
>
> Thanks for the info what happens with EPSF text files.  That makes sense.
>
> For PDF, I've now read up on the two pdftex primitives, \pdfximage and
> \pdfimageresolution in the pdftex manual, Section 7.5 of, e.g.,
>
> <http://vlado.fmf.uni-lj.si/texceh/kako/tex2pdf/ex/pdftex-s.pdf>
>
> \pdfimageresolution is a settable parameter relied upon by \pdfximage, and
> this parameter defaults to 72 (big points) if never set to something else
> (i.e., if it's 0).
>
> So I think that answers my question, which is that the TeX source code
> invoking the primitive \pdfximage is in charge of knowing and declaring any
> resolution other than 72/inch, and that the primitive \pdfximage doesn't
> care what the bounding box numbers are associated with the image file.  It
> appears that \pdfximage just scales them by \pdfimageresolution before
> doing other stuff to manage or record the image into the node tree, and its
> default is to treat the numbers it finds as measuring big points
> (PostScript points).  So setting \pdfimageresolution to 72.27 converts the
> sizes of a PDF image into the same exact size on the TeX page.
>
> All of this is presumption from reading the documentation.  I'm not sure
> where the source code (change file?) for \pdfximage can be perused to know
> for sure.
>
> Onward, into the fog ...
>
> - Doug McK.
>
>
> From: "Tom Rokicki" <rokicki at gmail.com>
> To: "Doug McKenna" <doug at mathemaesthetics.com>
> Cc: tex-k at tug.org
> Sent: Saturday, January 26, 2019 10:49:26 AM
> Subject: Re: [tex-k] Where does conversion of PostScript pts to TeX pts
> occur?
>
> The EPSF macros literally read the EPSF file line by line looking
> for the bounding box.
>
> The scaling by 72.27/72.00 is done when the bounding box numbers
> are interpreted in Don's bp dimensions directly in the EPSF macros.
>
> The EPSF macros are pretty simple; you can look at them directly.
>
> I don't know what happens for PDF.
>
> -tom
>


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