{Ebooks and paper size: Output routine hacking made~easy} 
{Boris Veytsman and Michael Ware}
{It might be surprising for a casual \TeX{} user, but the classical
\TeX{} engine does not know anything about the physical dimensions
of the paper the text is printed upon.  One may argue that it
imitates the traditional compositor, who prepared the matrix, but
was not involved in the actual printing.  Another explanation would
be that a printer (a device, not a person) usually has a stock of
pre-cut paper sheets, and there is not much use in trying change the
paper size from the typesetting program.

While both dvips and pdf\TeX{} provide the possibility to set the
paper dimensions using either PostScript or \PDF\ commands embedded in
the text, it is commonly done only once per document.  This practice
assumes uniform paper size for all pages.

The situation with ebooks is different.  ``Paper'' for them is
virtual, and we are not constrained by the constant page size of
traditional books.  On the other hand, typesetting for the screen
\emph{requires} paper size tuning.

Since the page size is determined during \CS{shipout}, we need to
deal with the output routine\Dash the task often considered to be
too arcane for unexperienced \TeX nicians.

In this talk we show that playing with the output routines does not
necessarily involve high wizardry.  We show how to use the output
routine to determine the required paper size and to communicate it
to the driver.

The talk is intended for a beginning to intermediate \TeX{} hacker.  
}