A macro I wrote exhibited rare misaligned formatting. While debugging
it, I discovered some inconsistencies with page dimensions and offsets
that I didn't expect from nroff output to a pager.
The alleged (maybe I don't understand something) inconsistencies pertain
to values of various registers. The register for page offset (\n[.o])
always reports a 0 value, as one would expect for an unpaged document.
I eventually figured out that I was near the bottom of a page by using
the .mk action, which does report a vertical offset from a given page
(though not the same value as \n[.o] in a document formatted with
troff). Comparing the .mk value with the page height register (\n[.p]),
I could see that my formatting problem occurred when I attempted to .sp
up to a line that was printed before a phantom page break.
Using .mk to isolate the problem also suggests a work-around. Use the
value reported by .mk in place of the page offset register. Easier
still would be to detect nroff mode and if in nroff, just issue a .bp
before every multi-line object since .bp seems to have no effect on the
output beyond resetting the position reported by the .mk action.
I sent this bug report to make a record of the issue in case it helps
someone diagnose and work-around a similar problem. I'm not sure if
this is something you would work on. In reading the 10-year-old mission
statement, this issue doesn't apply to either of the two areas of
development. If you want more information, I would be happy to provide
more information and a simplified roff-script to manifest the problem.
I'm not sure how you'd fix it, and maybe you can't. Having a page
offset from the top of the document risks integer overflow, especially
with troff output where the my pdf line height is 12,000 basic units, so
I can see an argument for having virtual pages to limit the internal
page offset value as reported by .mk.
- nroff mode paging inconsistencies Chuck Jungmann
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