Are you sure you can’t achieve whatever you want with
pre_linebreak_filter (whose return value is passed to
linebreak_filter) or post_linebreak_filter (which receives the return
value of linebreak_filter)?
Pretty much yes, let me explain: it's in gregorio (gregorian chant
scores), where clef changes (quite a big glyph, with spacings and
another glyph associated to it) should not appear at the beginning of
lines: if they are the first glyph of a line, they should not be printed
(as they will be already printed in the localleftbox). For example:
ok:
some notes ... some notes clef change some notes ... some notes
new clef (localleftbox) some notes ... some notes
not ok:
some notes ... some notes
old clef (localleftbox) new clef some notes ... some notes
If a line breaks before new clef, I'll arrive in the not ok scheme. I
could replace old clef by new clef in the localleftbox by hacking
gregorio a bit; but if I remove the second new clef (the one not in
localleftbox) in postlinebreak_filter, the line will have way too much
spacing...
Do you see any solution? You've hacked LuaTeX quite a lot, I'm sure you
will have more ideas than I do!
Otherwise, you can use the tex.linebreak() function, which does what
linebreak_filter does by default:
local function myfunc (head, ...)
-- Do something.
local newhead = tex.linebreak(head)
-- Do something else.
return newhead
end
callback.register("linebreak_filter", myfunc)
Well, If I understand correctly, I cannot: I need to modify the
algorithm a bit (so that it removes the glyph when it evaluates the
length of lines, before taking a linebreak decision), which I cannot do
with the tex.linebreak function...
There is, or at least there was, a Lua version of the TeX algorithm,
but as far as I’m concerned it lasted a few seconds only in my editor
before I killed the buffer thinking “Ok, later.” Later never came,
though. (Note however that I’ve never tried to read the TeX
implementation to begin with, and I guess it’s mandatory if you want
to understand anything.)
Hmmm... do you still have it?
Thank you,
--
Elie
