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

Tomas Rokicki rokicki at gmail.com
Sat Jan 26 18:49:26 CET 2019

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.


On Sat, Jan 26, 2019 at 9:46 AM Doug McKenna <doug at mathemaesthetics.com>

> Thanks, Tom.
> But now I'm confused, because you're talking about an "epsf" *macro*,
> which sounds like something written in TeX that by virtue of being a macro
> must be relying on some even lower primitive command (a PDF extension
> command in pdftex?) to get the bounding box numbers from the graphics file
> living in the outside world.
> Does any TeX code, running on the TeX engine, actually parse the PDF (or
> EPSF) data to determine its bounding box?
> Or does the implementation (in WEB, or C, or whatever) of some primitive
> command parse the graphic data to get the bounding box?
> I'm trying to determine on which side of the TeX virtual machine/engine
> barrier the bounding box info in a PDF file gets converted to a fixed-point
> Dimension value stored inside the TeX engine.
> In other words, who is responsible for scaling the big point numbers by
> 72.27/72.0 to bring them into TeX's internal world, where all dimensions
> are stored as [16:16] fixed point numbers and where the integer part always
> measures points at 72.27/inch?
> - Doug McKenna
> ------------------------------
> *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 9:47:58 AM
> *Subject: *Re: [tex-k] Where does conversion of PostScript pts to TeX pts
> occur?
> I'm sorry; I mean bp (big point) units.
> On Sat, Jan 26, 2019 at 8:46 AM Tomas Rokicki <rokicki at gmail.com> wrote:
>> The epsf macro reads the bounding box and interprets it using
>> TeX truept units.

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