[luatex] pre_output_filter: How to get the vertical list of the full page?

[Hans Hagen]

On 5/1/2018 11:50 PM, Henri Menke wrote:
> On 02/05/18 03:17, Hans Hagen wrote:
>> On 5/1/2018 12:16 PM, Henri Menke wrote:
>>> Dear list,
>>>
>>> It seems as if the pre_output_filter only gives you the nodes in the
>>> body block but without the \headline and \footline.  I would have
>>> expected that those are included because \plainoutput performs
>>>
>>>     \shipout\vbox{\makeheadline\pagebody\makefootline}
>>>
>>> and I would have expected to get the vlist defined by the above \vbox
>>> inside the callback.  Am I doing it wrong or am I using the wrong 
>>> callback?
>> you can for instance use vpack_filter
> 
> But how do I detect whether what is being packed is the main vertical 
> list?  According the manual `groupcode` should be <empty> for the main 
> vertical list but that just never happens.  With the following MWE
> 
>      \directlua{
>      callback.register("vpack_filter",
>                        function(head,groupcode)
>                            print('"' .. groupcode .. '"')
>                            return head
>                        end)
>      }
> 
>      Hello World!
> 
>      \bye

build_page_filter

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