Re: units used in `ss` request (was: device-dependent warnings)

[G. Branden Robinson]

At 2023-05-13T12:52:06-0500, Dave Kemper wrote:
> On 5/13/23, G. Branden Robinson <g.branden.robinson@gmail.com> wrote:
> >> At 2023-05-10T12:28:02-0500, Dave Kemper wrote:
> >> > And I just learned (or maybe relearned) this is a deviation from
> >> > AT&T troff's .ss units, which are a fixed 1/36 em.
> >
> > I am beginning to think that it was only Ossanna troff for which
> > that was true, and CSTR #54 was simply never updated in this
> > respect.
> 
> True, I was going by CSTR #54 rather than observed behavior.  However,
> the Heirloom documentation (derived from CSTR #54) echoes the 1/36-em
> claim, and its behavior appears to be consistent with that.
> 
> .nf
> .ss 36
> foo bar
> .ss 48
> foo bar
> foo\h'1m'bar
> 
> In Heirloom troff, the space on the first and third lines match.  In
> groff (both 1.22.4 and 1.23 rc4), the second and third lines do.

On DWB 3.3 troff, a direct descendant of Kernighan troff, and the basis
for Heirloom Doctools troff, the second and third lines match:

x T post
x res 720 1 1
x init
V0
p1
x font 1 R
# unnecessary font loading snipped
s10
f1
H720
V120
cf
33o50owh125cb
50a44rn120 0
H720
V240
cf
33o50owh150cb
50a44rn120 0
H720
V360
cf
33o50oh150cb
50a44rn120 0
x trailer
V7920
x stop

> Both of these are consistent with their respective documentation.

I don't think I trust Heirloom here.  First, I suspect what they did was
treat the CSTR #54 as more authoritative than empirically measured
formatter behavior.  As can be seen in my numerous arguments with Ralph
Corderoy, I find the Galilean episteme superior to the pontifical one.

Secondly, Heirloom's arithmetic seems to be slightly off.

x T ps
x res 72000 1 1
x init
V0
p1
x font 1 R /home/branden/heirloom/lib/doctools/font/devps/R.afm 4
# unnecessary font loading snipped
s10
f1
x X LC_CTYPE en_US.UTF-8
H72000
V12000
cf
h3330co
h5000co
wh14990cb
h5000ca
h4440cr
n12000 0
H72000
V24000
cf
h3330co
h5000co
wh18320cb
h5000ca
h4440cr
n12000 0
H72000
V36000
cf
h3330co
h5000co
h15000cb
h5000ca
h4440cr
n12000 0
x trailer
V792000
x stop

In case the difference is hard to make out:

h3330co     h3330co
h5000co     h5000co
wh14990cb   h15000cb
h5000ca     h5000ca
h4440cr     h4440cr

...but I'll grant that 1/7,200 inch difference is unlikely to be
noticed, even if it accumulated several times across an output line.

Maybe if one's printer does better than 600dpi...

I won't hold my breath waiting for anyone to point at Heirloom and
shriek "deviation!" like Donald Sutherland at the end of the 1978
_Invasion of the Body Snatchers_.  Partisans know one thing, and that's
to stay partisan.

Regards,
Branden

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