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Re: [groff] vertical resolution and page location traps

From: Ralph Corderoy
Subject: Re: [groff] vertical resolution and page location traps
Date: Sat, 16 Jun 2018 11:12:49 +0100

Hi Dave,

> Werner wrote:
> > Reason is that traps are not recursive, IIRC: Traps are not handled
> > while another trap is active (this seems to be missing in the info
> > file).

But they are handled sequentially when a `.sp' passes more than one in a
single bound.

    $ cat
    .de trap1
    'tm trap 1 \\n(nl
    .de trap2
    'tm trap 2 \\n(nl
    .wh 1i trap1
    .wh 2i trap2
    .sp 3i
    $ groff -zTascii
    trap 1 240
    trap 2 480

> > In other words, while your first trap is active, it moves down one
> > line, which passes some traps without triggering them.
> That bit of information is missing from the manual

And from CSTR 54.  Werner, are you sure about that?  I don't recall
hearing it before.

Going back to Dave's supplied test, I get two distinct sets of output.

    $ fgrep .wh
    .wh 2.1i trap1
    .wh 2.2i trap2
    .wh 2.3i trap3
    .wh 2.4i trap4
    .wh 2.5i trap5
    .wh 2.6i trap6
    $ for t in ps pdf lbp lj4 dvi html ascii; do
    >     groff -zT$t 2>tm.$t
    > done
    $ sha1sum tm.* | sort -V
    4c62d9b9c82522b34895da506a4613d91369acb8  tm.dvi
    4c62d9b9c82522b34895da506a4613d91369acb8  tm.lbp
    4c62d9b9c82522b34895da506a4613d91369acb8  tm.lj4
    4c62d9b9c82522b34895da506a4613d91369acb8  tm.pdf
    549f443a863e83c30705b38208f974ccb0a76fb1  tm.ascii
    549f443a863e83c30705b38208f974ccb0a76fb1  tm.html
    $ cat
    trap 1
    trap 2
    trap 4
    trap 6
    $ cat tm.ascii
    trap 2
    trap 4
    trap 5
    trap 6

Appending ` \n(nl' to each `.tm' line and repeated runs, commenting
various `.wh' out, and then marking up what's present in the above
output, and what's a duplicate, gives

    trap 1 156000  present  
    trap 2 168000  present  
    trap 3 168000           same as 2
    trap 4 180000  present  
    trap 5 180000           same as 4
    trap 6 192000  present  

    trap 1 520              same as 2
    trap 2 520     present  
    trap 3 560              same as 4
    trap 4 560     present  
    trap 5 600     present  
    trap 6 640     present  

It's odd that for `ps' it's the first trap to a rounded position that
springs, but for `ascii' it's the second.

Cheers, Ralph.

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