Re: drawing commands in groff(7) (was: undiagnosed pic error)

[G. Branden Robinson]

Hi Steve,

At 2023-06-08T18:19:39-0400, Steve Izma wrote:
> On Tue, Jun 06, 2023 at 03:07:07PM -0500, G. Branden Robinson wrote:
> > Subject: drawing commands in groff(7) (was: undiagnosed pic error)
> 
> >     \D't n'
> >         Set line thickness of geometric objects to to n basic units.
> >         A zero n selects the minimal supported thickness.  A
> >         negative n selects a thickness proportional to the type
> >         size; this is the default.
> > 
> > Comments?
> 
> Is it worth pointing out here that \D't n' is not zero-width?

Er, well, our Texinfo manual _did_ point this out, but I took it out for
space reasons and because I think it is a bug.  It's apparently a
long-standing one.

> e.g.:
> 
> .sp 1i
> .po 1i
> .ps 12s
> .ll 24P
> \D'l \n[.l]u 0'
> .br
> \D't .5p'\D'l \n[.l]u 0'
> .br
> 
> In fill mode, the second drawing command produces this error:
> 
> troff: thick:7: warning [p 1, 1.2i]: can't break line
> 
> The troff output:
> 
> x T ps
> x res 72000 1 1
> x init
> p1
> V84000
> H72000
> md
> DFd
> s12000
> Dl 288000 0
> n12000 0
> V96000
> H72000
> Dt 500 0
> Dl 288000 0
> n12000 0
> x trailer
> V792000
> x stop
> 
> shows that \D't .5p' has a width of 500 units, which is output as
> a 500-unit space. For as long as I can remember, I've needed to
> use this instead:
> 
> \Z'\D't .5p''\D'l \n[.l]u 0'
> 
> I'm pretty sure this anomaly has been discussed on the groff list
> before, but I don't know of any explanation in the documentation.

It was there until literally days ago.  It seemed like such a subtle
point that I thought I might get a Savannah ticket open against it and
maybe even fixed for groff-next before anyone noticed.  Sorry.  :(

  commit be22fd2cad951093e6d6da02e6c506df30dc856e
  Author:     G. Branden Robinson <g.branden.robinson@gmail.com>
  AuthorDate: Tue Jun 6 21:32:35 2023 -0500
...
  -Nonintuitively, the current point is moved horizontally to the
  -right by@tie{}@var{n}.
...

You can tell that whoever wrote that had PostScript on the brain.

Regards,
Branden

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