On 5/29/2024 10:08 PM, Linas Stonys wrote:

I know I'm asking impossible but who knows... Maybe in the "near" future luatex could adapt user_defined whatsit to have some more fields where it could store lastskip, lastpenalty, ... So that \last... checkers could point to this corresponding field to check the value  if it sees that last node is user_defined whatsit

that would then also involve some guesswork and be somewhat alien to how these state variables are handled you could set a property (or attribute) on x that stores the skip, and then redefine lastskip to look at the list and if found fetch that value or otherwise report the normal one or you can be adventurous and intercept the builder in a callback

:) because injecting whatsits this way will likely mess up your page building unless you take precautions you can as well do something

aa \vskip10pt \skip0\lastskip \vskip-\lastskip \directlua{% local x = node.new('whatsit', 'user_defined') x.type = 115 x.value = "TEXT" node.write(x) }% \vskip\skip0 bb with a bit testing and maybe some penalties .. it all depends on how / what / where you inject, after all you probably want to keep the whatsit bound to what comes before anyway (as you check the skip) Hans ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl -----------------------------------------------------------------

Thanks Max, I'm thinking the same to add attribute and property with corresponding tags and then add whatsits on the 255 box shipout. I just need to think about discardable items. If one wants to mark up tex sources for xml or tagged pdf a common issue how to safely mark start and end of semantic text without effecting output. For example  if there would be few primitives which could add an attribute or/and properties to next (yet to be created) non discardable item like \luaAddFeaturesNodeNext {{attr=1, properties={"<section>}}} \section{foo} \luaAddFeaturesNodePrev{{attr=1, properties={"</section>}}} It could save a lot of headache. Of course this is not an easy task because of page breaks.

You can set an attribute on the previous node, then add the node itself in pre_output_filter:

\directlua{% user_nodes = {} % Better to use luatexbase.new_attribute and luatexbase.add_to_callback attribute_number = 1234 % "pre_shipout_filter" is better if you're using LaTeX or OpTeX callback.register("pre_output_filter", function(head) % Better if this recurses through any nested lists local n = head while n do local attr attr, n = node.find_attribute(n.next, attribute_number) if not n then break end head, n = node.insert_after(head, n, user_nodes[attr]) end return head end) }

aa \vskip11.1pt \showthe\lastskip \directlua{% % I'm using a rule to make the effect obvious local x = node.new("rule") x.width = 655360 x.height = 655360 x.depth = 0 table.insert(user_nodes, x) node.set_attribute( tex.nest[tex.nest.ptr].tail, attribute_number, \luaescapestring{#}user_nodes ) }% \showthe\lastskip bb \bye

It's a little risky to mess with tex.nest.tail, but just setting an attribute should be mostly safe.

Thanks, -- Max

Hi Linas, On Thu, 2024-05-30 at 10:39 +0300, Linas Stonys wrote:

For example  if there would be few primitives which could add an attribute or/and properties to next (yet to be created) non discardable item like \luaAddFeaturesNodeNext {{attr=1, properties={"<section>}}} \section{foo} \luaAddFeaturesNodePrev{{attr=1, properties={"</section>}}}

The primitive \attribute is pretty close. You just need a little bit of Lua to make it behave exactly like you want: \attributedef\myattribute=1234 % or use \newattribute \newcount\mycount \def\addattribute#1{% \advance\mycount by 1 \global\myattribute=\mycount \global\expandafter\def\csname myattribute\the\mycount\endcsname{#1}% } \catcode`\~=12 \directlua{% attribute_number = token.create("myattribute").index local function recurse(head) for n in node.traverse(head) do if n.list then recurse(n.list) end local attr = node.get_attribute(n, attribute_number) local value if attr and n.id ~= node.id("glue") and n.id ~= node.id("local_par") then value = token.get_macro("myattribute" .. attr) token.set_macro("myattribute" .. attr, nil, "global") end if value and value ~= "" then local colour = node.new("whatsit", "pdf_literal") node.unset_attribute(colour, attribute_number) colour.mode = 2 colour.data = value node.insert_before(head, n, colour) end end return head end callback.register("pre_output_filter", recurse) } \addattribute{1 0 0 rg} abc \addattribute{0 1 0 rg} def \addattribute{0 0 1 rg} ghi \bye -- Max