[bug #58581] doc/groff.texi, man/groff_font.5.man: spacewidth value has incorrect units

[G. Branden Robinson]

Follow-up Comment #10, bug #58581 (project groff):

Hi Bjarni,

[comment #4 comment #4:]
>   I read the definition of "unitwidth", so then I understood, that the
> numbers in the font files are _relative_(!) to the "unitwidth" value.
> 
>   So the actual size of a space is "spacewidth / unitwidth" part of the
> point size of the font.

This reasoning does not work for, e.g., the utf8 device.


$ grep unitwidth font/devutf8/DESC.proto
unitwidth 10
$ grep spacewidth font/devutf8/R.in
spacewidth 24


Your formula would give an actual size of a space on the utf8 device of 2.4
times the point size.

As it turns out the space width on the utf8 device is, as one would guess, 1
em.


$ ./build/test-groff -b -ww -Tutf8
.nr m \w'm'
.nr s \w' '
.tm m:\nm space:\ns
m:24 space:24


However, the horizontal resolution of this device is also 24, which exactly
matches the space width.


$ grep hor font/devutf8/DESC.proto
hor 24


I think I'm going to go study CSTR #54 and #97; our own documentation really
does not do a good job here IMO.

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