[bug #64285] [troff] \D't' (set line thickness) drawing command alters drawing position

[G. Branden Robinson]

URL:
  <https://savannah.gnu.org/bugs/?64285>

                 Summary: [troff] \D't' (set line thickness) drawing command
alters drawing position
                   Group: GNU roff
               Submitter: gbranden
               Submitted: Thu 08 Jun 2023 10:43:26 PM UTC
                Category: Core
                Severity: 3 - Normal
              Item Group: Incorrect behaviour
                  Status: Confirmed
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None


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Follow-up Comments:


-------------------------------------------------------
Date: Thu 08 Jun 2023 10:43:26 PM UTC By: G. Branden Robinson <gbranden>
Steve Izma [reported
https://lists.gnu.org/archive/html/groff/2023-06/msg00055.html]:


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.


As noted in the follow-up, I regressed notice of this in the documentation
(which didn't really treat it as a bug), and within 2 days Steve stumbled
across this issue.

But like "STUPID_DRAWING_POSITIONING" in the source code, it is a bug and we
should fix it.







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