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Re: [Groff] The \D request in nroff and troff modes


From: Anton Shepelev
Subject: Re: [Groff] The \D request in nroff and troff modes
Date: Thu, 15 Jul 2010 18:52:13 +0400

Hello, Werner.

Many  thanks  for  the  info. I see that the problem
lies deeper than I had thought.

> It's obvious that the  values  0..23  are  somehow
> 'assigned'  to  character cell 0, and for orthogo-
> nality we have to assign  position 24  already  to
> character cell 1.

This is indeed only meet and logical. The 24th  unit
is not a boundary between cells, but the first 'bit'
of the next cell. The boundary has no  size  and  is
between the 23rd and 24th units.

> Another  complication  is  that  everything  which
> specifies a length is  rounded  internally  to  be
> multiples  of  either  \n[.H] or \n[.V].  In nroff
> mode this means that a horizontal length of 12u is
> still one character cell, but 13u is rounded up to
> be two character cells.

Hmmmm.  But  shouldn't  12u round to zero and 13u to
one (this would make lines one symbol shorter). Does
grotty 'see' the rounded values?

> Does  this explain why a single horizontal line is
> one character cell too long?
> <...>
> BTW, if you always shorten horizontal lines  by  a
> small correction value, the above tables look like
> this:

So  this  is  done generally to help tbl draw tables
properly? If it is so, then it keep tbl device-inde-
pendent but makes the \D request tbl-dependent...

Anton



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