On 7/8/2022 9:40 AM, Max Chernoff via ntg-context wrote:
This is because you need to pass a list that conforms to what the
builder expects and the callback that you use doesn't do that for you
(after all, it also gets hbox content).
Isn't "processors/after" the same as "pre_linebreak_filter"? I thought
that only "hpack_filter" gets \hbox content? Anyways, my actual function
has this guard at the very start:
if (head.id ~= par_id and context) or -- Ensure that we were
actually given a par
status.output_active or -- Don't run during the output routine
tex.nest.ptr > 1 -- Don't run inside boxes
then
return head
end
so I think that I'm only processing actual top-level paragraphs here.
There is no 'callback sequence handler' for the par builder (currently
i see no need for it, also given the extra overhead involved) but this
what what you can do:
\startluacode
function builders.paragraphs.constructors.methods.preroll_a(head)
local result, info = tex.linebreak(head)
tex.prevdepth = info.prevdepth
tex.prevgraf = info.prevgraf
return result
end
function builders.paragraphs.constructors.methods.preroll_b(head)
local result, info = tex.linebreak(nodes.nuts.copylist(head))
inspect(info)
return true
end
\stopluacode
\defineparbuilder[preroll_a]
\defineparbuilder[preroll_b]
\starttext
\setmainparbuilder[default] \input tufte \par \input tufte \page
\setmainparbuilder[preroll_a] \input tufte \par \input tufte \page
\setmainparbuilder[preroll_b] \input tufte \par \input tufte \page
\stoptext
I think that that code is for replacing the linebreaker entirely, like
with using "linebreak_filter"? My goal isn't to replace the linebreaker;
I just want to be able to inspect the paragraph before it is broken,
without modifying anything.
as long as you return true the built in will do the work but you can
still do the preroll so basically nothing gets replaced .. it's just a
more natural hook;l keep in mind that if someone replaces the linebreak
your code woudl fail to do its work anyway
What I'm trying to do *very* roughly looks like the following:
paragraphs = {}
attribute = 1234
function pre_linebreak_filter(head)
if head.id ~= node.id"par" then
return head
end
local nat_node, nat_info = tex.linebreak(node.copylist(head))
node.freelist(nat_node)
local long_node, long_info = tex.linebreak(
node.copylist(head), {looseness = 1}
)
if long_info.prevgraf == nat_info.prevgraf + 1 then
table.insert(paragraphs, long_node)
end
return head
end
function post_linebreak_filter(head)
node.setattribute(head, attribute, #paragraphs)
node.setattribute(node.slide(head), attribute, #paragraphs)
return head
end
function pre_output_filter(head)
if tex.outputpenalty ~= tex.widowpenalty then
return head
end
-- Pick a paragraph from `paragraphs` somehow
-- Replace that paragraph on the page with the one
-- from `paragraphs`
-- Move the last line of the page onto the top of
-- tex.lists.contributehead
return head
end
(The full implementation is in the module "lua-widow-control" on CTAN,
TeX Live, and modules.contextgarden.net, or directly at
"https://github.com/gucci-on-fleek/lua-widow-control/blob/master/source/lua-widow-control.lua";.
It's pretty long though, so I'm just trying to summarize here.)
This works pretty well with Plain LuaTeX, LuaLaTeX, OpTeX, MkIV, and
MkXL before the latest upload, but something broke with the latest
upload in MkXL. I understand that I'm mucking around with volatile
interfaces, and I have no problem making a bunch of changes whenever the
engine/format changes; the problem is that I'm not too sure what changed
in the engine, so I don't know what I need to change in my code.
the tricky part is probably to make sure that it doesn't interfere with
what other functions hooked into the callbacks are doing because who
knows what gets injected in those lists
On the to do is a to add a 'prepare' helper that adds the mandate
nodes (par fillers etc)
Maybe that's all that I need? If that's the case, I have no problem
coding my own "prepare helper" if you think that it'll be awhile before
you get around to it; the problem is that I'm not entirely sure what
nodes I would need to add. These new nodes aren't added until after
"pre_linebreak_filter", and they're gone after the linebreaker runs, so
I can't inspect a "regular" paragraph to see where these nodes belong.
there will be (untested on what you do)
tex.preparelinebreak(par)
that will add the additional stuff needed (and bark if something is
there already).
btw, a par builder - even in luatex - needs a parfillskip to properly do
its work, some penalty and in the case of context lmtx also a
leftparfill skip and optionally initleft and right skip
Hans
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