🚀 go-pugleaf

In article <1992Nov14.222532.8727@cs.brown.edu> jgm@cs.brown.edu (Jonathan  
Monsarrat) writes:

    *  Why do text formatters/converters like dvips (for TeX) and
    *  grops (for Troff) define everything upside down in PostScript?
    *  Just to be mean?
Speaking only from my knowledge of troff here.  First of all,
remember that both troff and TeX (even TeX 82) predate PostScript,
but that's probably irrelevant to the issue anyway.

The main reason stems from the nature of printed pages.  Pages of
text, whether Western or Asian, read from top to bottom.  Therefore
there's some sense in defining a coordinate system with (0, 0) at
the top left (for Western style text).  In troff, the first line
of the page is at the top of the page, loosely speaking, and the
y coordinate increases as you move down the page towards the bottom.
The  \v  escape sequence moves down for positive arguments and up
for negative arguments.  The  .sp  request moves down for positive
arguments and up for negative arguments, and so on.

This is opposite from PostScript's coordinate system which places
(0, 0) at the lower left corner of the page, like the regular first
quadrant of a Cartesian coordinate system we all learned about in
school.

To switch between the troff (and I assume TeX) coordinate system
and the PostScript coordinate system is simple -- translate up by
the height of the page and do a 1 -1 scale operation so the CTM is
``upside down'' from the standard PostScript coordinate system.
If you just stop there, of course, all your text will come out
upside down as well, so every time you make a font, you have to
use a [ S 0 0 -S 0 0 ] makefont to get the text coming out the
right way up.

	........  Henry

	Do not meddle in the affairs of troff,
	for she is subtle and quick to anger.
				-----  Bill Joy, circa 1980.