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

[Bjarni Ingi Gislason]

On Thu, Jun 08, 2023 at 06:19:39PM -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?
> 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.
> 

  How does \D't ...' influence the height of the text baseline as it is
just changing the "graphic pen" and moving it horizontally (in the air)
to its next position?

  The general interpretation of \D'c x' is to do 'c' and end at
position x from the starting point.

  How does "tbl" handle its lines' thickness?

> [...]