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Re: [Groff] pic and nroff

From: Tadziu Hoffmann
Subject: Re: [Groff] pic and nroff
Date: Mon, 19 Mar 2007 17:00:00 +0100
User-agent: Mutt/1.5.13 (2006-08-11)

> Strictly speaking, <ESC>[40m means "set background to the
> colour specified in slot zero of the colour palette"; on
> most terminals that happens to be black.

Yes, that's why I said "normally".  However, viewing the
numbers as indices into a palette that can be remapped may be
a feature of the more modern terminals.  There are a number
of standards (e.g., ISO 6429 or ECMA-48) where the colors are
understood to be fixed.  (By the way, it's easy to remember
which number corresponds to which color by viewing it as a
three-bit "true color" representation -- bit 0 = 1 = red,
bit 1 = 2 = green, and bit 2 = 4 = blue; then simply add up
the desired components.)

Coming back to the original problem, I think this is due to
a "misunderstanding" between pic and grotty.  Groff knows a
"glyph color" and a "fill color"; in grotty, these are
equated to "foreground color" and "background color".
(On non-character-cell devices, the concept of a "background
color" may not be meaningful, since there is no obvious way
to define the "background area" of a glyph -- e.g., does
it correspond to the bounding box or does it extend from
baseline to baseline?)

Anyhow, pic sets the fill color to black for filling the
arrowheads, and from that point on grotty writes all text
with a black background.  The fix appears to be rather easy:
let pic set the fill color not to black (\D'Fg 0.000'), but
to "default" (\D'Fd'); this seems to work correctly with
grops and also lets grotty write the text normally.

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