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I'm trying to start using plain tex (in fact, the pdftex that comes with texlive2010) to write a document but I'm having some trouble with the page layout. My question is at which point is it decided what the dimensions of the page and the margins will be?

As far as I investigated the \plainoutput routine in plain.tex only sets the height and width of the \box255 plus headers, footers, etc, but page dimensions (like A4, letter, portrait, landscape, etc) and margins are never defined. Moreover the TEXBOOK says that by default the page layout has 1in of margin at each side (page 251) but I don't know when are these margins defined nor why in my final pdf output the document appears with A4 size, 1in of left margin and approximatley 0.7in of right margin. So the question again is when are these dimensions decided?

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  • The default \hsize in plain TeX is 6.5in and it centers content on page only when paper width is 8.5in, leaving 1in margin on both sides. US Letter paper has this page width. The default \hsize gives slightly shorter right margin (~0.77in) with default page size (A4 with width 8.27in). Setting \hsize=6.27in corrects the margins for A4 paper. I figured this out while trying to make \centerline actually center the line on page. – pii_ke Jan 6 '17 at 7:29
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The 1 inch offsets come actually from TeX itself, and are kind of a pain because you need to take them into account as late as possible in any calculations.

The paper size is defined in a configuration file (I forget its name), but with PDFTeX, you should be able to use commands \pdfpagewidth (default 210 true mm for A4), and \pdfpageheight (default 297 true mm for A4).

Most relevant settings regarding page layout are:

  • \hsize for h orizontal size (typeblock width)
  • \vsize for v ertical size (typeblock height)
  • \hoffset for h orizontal offset (offset from 1 inch from left edge of paper)
  • \voffset for v ertical offset (offset from 1 inch from top edge of paper)

For spread layout, you can just toggle the \hoffset in the output routine.

Because you define the \hsize and \hoffset, there's no need to define margins, but I guess you could write a macro for counting \hsize and \hoffset based on given margins.

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  • Certainly in LaTeX margins are something that is calculated 'for convenience', since as you say the underlying mechanism doesn't need them. Depending on the use case, though, they may make a more sensible interface (with the calculation hidden away). – Joseph Wright♦ Aug 7 '13 at 13:08
  • @morbusg So you are saying that the 1in margins come directly from the TEX82 program and cannot be changed by any parameter? – eciii Aug 7 '13 at 14:03
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    @Felipe: TEX82, yes, I think, but pdfTeX, I'm not so sure; there's a file, $TEXLIVE/texmf-config/tex/generic/config/pdftexconfig.tex which has commands: \pdfhorigin and \pdfvorigin which seem like they could control those. – morbusg Aug 7 '13 at 16:08

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