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

[Henri Menke]

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

I only see

"vbox"
"vbox"
"vbox"

in the log.


> 
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