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

[Steve Izma]

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?
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.

        -- Steve

-- 
Steve Izma
-
Home: 35 Locust St., Kitchener, Ontario, Canada  N2H 1W6
E-mail: sizma@golden.net  phone: 519-745-1313
cell (text only; not frequently checked): 519-998-2684

==
The most erroneous stories are those we think we know best – and
therefore never scrutinize or question.
    -- Stephen Jay Gould, *Full House: The Spread of Excellence
       from Plato to Darwin*, 1996