[XeTeX] c.t.t. post re: \mag

[Bruno Voisin]

Le 19 févr. 08 à 23:28, Will Robertson a écrit :

> There was some discussion on c.t.t. a while back about this:
> <http://groups.google.com/group/comp.text.tex/browse_frm/thread/db780edfaae6950e/ 
> >
>
> Non-zero offset makes \mag very unintuitive, from what I can  
> understand. The pdftex developers were trying to make sense of how  
> to reconcile the coordinate system of the pdf page vs the coordinate  
> system of the TeX page.
>
> But since I don't play with \mag or \offset very often, I didn't pay  
> much attention :)

Thanks for pointing attention to that thread. I must admit I stand  
with the advocates of backwards compatibility, and against Heiko  
Oberdiek on that matter.

All this talk about the pecularities of the PDF format, about / 
MediaBox and such, feels like rhetorical nonsense for me: the only  
thing that matters is that, with exactly the same input, the PDF page  
displayed on screen when typesetting with pdfTeX should be absolutely  
identical to the paper page output by a printer when typesetting with  
TeX + dvips. This used to be the case before teTeX 2, but is no longer  
true since teTeX 3, provided \mag or \magnification is involved.

Unfortunately, I used \magnification in practically all the plain TeX  
documents that I wrote. Which means that I cannot typeset them with  
pdfTeX: owing to the way pdfTeX deals with \mag, if pdfTeX is used  
then the documents will no longer appear as they were meant to be.

To put it differently: when you typeset your plain TeX document and  
send the output to the printer, the size of the media on which this  
output is printed isn't affected by \mag or \magnification, it is the  
size of the sheet of paper used by the printer. \mag or \magnification  
are used simply as tricks to affect the character size, similar to the  
[10pt], [11pt] and [12pt] options of LaTeX.

Accordingly, for somebody who used (plain) TeX for years before  
getting introduced to pdfTeX, it is expected that \mag and  
\magnification won't affect the media size. Which they do if I'm not  
mistaken. Which prevents typesetting of old documents, and hence  
breaks backwards compatibility.

XeTeX is much more respectful of TeX as designed by Knuth in this  
respect: whatever the \mag, the page origin is always 1 true in from  
the top and left borders of the page (or sheet of paper).

Bruno