Re: [Dev-luatex] How to insert at start of hlist/vlist?

7 Dec 2007


      Heiko Oberdiek wrote:
...
Hello,
I have some trouble to insert something at the start
of a list.
weird message indeed; this works

   do
     local hlist = tex.box[0]
     local pdf_literal = node.new(8,8)% \pdfliteral
     pdf_literal.mode = 2 % direct
     pdf_literal.data = "1 0 0 rg 1 0 0 RG"
     pdf_literal.next = hlist.list
     hlist.list = pdf_literal
   end

current assigning to a box (or operating on box related lists are 
somewhat tricky, internal invisible pointers and such; this interface 
will probably change a bit; it helps to copy the list, work on the copy 
and hpack the result
...
Example (complete example file after PS):
\setbox0=\hbox{XY}
\directlua0{
  do
    local hlist = tex.box[0]
    local pdf_literal = node.new(8,8)% \pdfliteral
    pdf_literal.mode = 2 % direct
    pdf_literal.data = "1 0 0 rg 1 0 0 RG"
    local head = hlist.list
    % local current = hlist.list.next % works
    local current = hlist.list % fails  
    hlist.list = node.insert_before(head, current, pdf_literal)  
  end
}
! LuaTeX error Attempt to node.insert_before() a non-existing node.
Have I misunderstood node.insert_before()?
Yours sincerely
  Heiko 
PS: Complete example file that can be used with
    iniTeX, plain-TeX and LaTeX:
\ifnum\catcode`\{=1
\else
  \catcode`\{=1
  \catcode`\}=2
  \hsize=6.5in
  \vsize=8.9in
  \parfillskip=0pt plus 1fil
\fi
\font\f=cmr10
\f
\pdfoutput=1
\setbox0=\hbox{XY}
\directlua0{
  do
    local hlist = tex.box[0]
    local pdf_literal = node.new(8,8)% \pdfliteral
    pdf_literal.mode = 2 % direct
    pdf_literal.data = "1 0 0 rg 1 0 0 RG"
    local head = hlist.list
    % local current = hlist.list.next % works
    local current = hlist.list % fails  
    hlist.list = node.insert_before(head, current, pdf_literal)  
  end
}
\shipout\hbox{[\box0]}
\csname @@end\endcsname
\end
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