[tex-live] [Fwd: [OS X TeX] Bug in latest pdfTeX (and/or teTeX) with respect to \magnification?]

Bruno Voisin bvoisin at mac.com
Tue Dec 21 06:48:53 EST 2004

Le 21 déc. 04, à 01:23, Gerben Wierda a écrit :

> I played post office with this question from Bruno:

Thanks for this, and to Hartmut for the clarification that followed.

So if I understood correctly, here is what happens:

- With previous versions of pdfTeX, up to TL2003, there were two ways 
to set parameters: via TeX primitives in the TeX input file, and via 
parameters in the configuration file pdftex.cfg. From the documentation 
of TL2003:

> A typical pdftex.cfg file looks like this, setting up output for A4 
> paper size and the standard TEX offset of 1 inch, and loading two map 
> files for fonts:
> 	[...]
> 	page_width	210 true mm	% A4 paper width
> 	page_height	297 true mm	% A4 paper height
> 	horigin		1 true in		% horizontal origin offset
> 	vorigin		1 true in		% vertical origin offset
> 	[...]
> The configuration file sets default values for these parameters, and 
> apart from the map entry, they all can be over--ridden in the TEX 
> source file. Dimensions can be specified as true, which makes them 
> immune for magnification (when set).

The corresponding TeX primitives were:

> Most parameters in the configuration file have a corresponding 
> internal register. When not set during the TEX run, pdfTEX uses the 
> values as specified in the configuration file.
> internal name	parameters	type
> [...]
> \pdfhorigin		horigin		dimension
> \pdfvorigin		vorigin		dimension
> \pdfpageheight	page_height	dimension
> \pdfpagewidth 	page_width	dimension
> [...]

- With TL2004 the parameters have been suppressed, as well as the file 
pdftex.cfg which is ignored, and all is set via the TeX primitives 
which are initialized in the file pdftexconfig.tex read during the 
creation of format files:

> % Set pdfTeX parameters for pdf mode (replacing pdftex.cfg file).
> % Thomas Esser, 2004. public domain.
> [...]
> \pdfpagewidth=594.99 true bp
> \pdfpageheight=841.99 true bp
> \pdfhorigin=1 true in
> \pdfvorigin=1 true in
> [...]

- Now comes the question of \magnification. With TL2003, putting in a 
plain TeX input file, processed by pdfTeX, the line


magnified the text by 1.2 and reinitialized the size of the output box 
(= the width and height of text) to their plain TeX default (= US 
Letter paper). The parameters page_width, page_height, horigin and 
vorigin, which had been set in pdftex.cfg in true units, were not 
affected by the magnification and remained unchanged (= A4 paper for 

- With TL2004, the line


has the same effect on the size of text and output box as with TL2003. 
It should also not affect the TeX primitives \pdfpagewidth, 
\pdfpageheight, \pdfhorigin, \pdfvorigin, set in true units in the file 
pdftexconfig.tex, but apparently it does: the page dimensions are also 
multiplied by \magstep1 (= 1.2).

I verified in pdftex.log that the file pdftexconfig.tex has indeed been 
read when creating pdftex.fmt. So what can be happening? Is this 
normal, or a bug?

This behaviour might be a problem with respect to backwards 
compatibility and compatibility with other TeX engines: take story.tex 
and add at its beginning the single line


That is a perfectly legitimate plain TeX file, not using any 
dvips-specific or eTeX-specific or anything-specific extension, and 
yielding a given output with TeX + dvips + GhostScript. Then process 
the same file with pdfTeX, you'll get a different output. At least 
that's what it does on my setup.

Or am I making a lot of fuss for nothing, and is the page size, as 
displayed by Acrobat Reader, for example, irrelevant, given that when 
you send the file to a printer only the size of the text and the 
position of the origin will be taken into account, so that the printed 
output will be the same for dvips and pdfTeX? (Assuming that you 
disabled Acrobat's automatic rescaling to fit the page size specified 
in the GUI printer driver.)

I had not noticed before the fact that \magnification reinitialized the 
page size to US Letter, since I had always followed it by specification 
of \hsize, \vsize, \hoffset and \voffset to fit with A4 paper. At least 
now I understand why, in the letter example at the beginning of 
Appendix E of the TeXbook, Knuth says

	\input letterformat

(letterformat.tex setting \hsize, \vsize and \voffset), and not

	\input letterformat

Thus the moral of the story seems to be: after setting \mag or 
\magnification, always redefine TeX page size parameters (\hsize, 
\vsize, \hoffset and \voffset) and pdfTeX page size parameters 
(\pdfpagewidth, \pdfpageheight, \pdfhorigin and \pdfvorigin), in true 
units. It's a pity these two sets of parameters are not made 
transparently dependent on each other, as they are in LaTeX, so that 
you don't have to set one and the other.

Bruno Voisin
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