Hi there,
the way I read the documentation on the buildpage_filter callback it is
supposed to be called whenever LuaTeX is ready to move material to the
main vertical list.
My understanding was that this means the cases that are documented in
the TeX book as "...exercises the pagebuilder"
However, it seems to be that the callback is run far more often and in
cases where it is definitely clear that there is no way whatsoever to
move something to the main vertical list, e.g. it seems to be called
whenever a box is packaged by tex.linebreak regardless of what happens
with the output of the linebreaking
Of course in such a case the recent contributions are empty so nothing
much happens but the following simple input
\input{ltluatex}
\directlua{
function buildpage ( context )
print ( "************* buildpage at: " .. context .. " at " ..
tex.inputlineno)
return true
end
luatexbase.add_to_callback("buildpage_filter", buildpage, "new buildpage
callback")
}
\input tufte
\bye
