[luatex] inserting

[Arno Trautmann]

Hi all,

I'm becoming desparate and I guess it's only a small error I'm making. I
try to (please don't ask why …) to colorize all letters in a document. I
do so by registering the following function in the post_linebreak_filter:

local color_push = node.new(WHAT,COL)
local color_pop = node.new(WHAT,COL)
color_push.cmd = 1
color_pop.cmd = 2

uppercasecolor = function (head)
  for line in node.traverse_id(HLIST,head) do
    for letter in node.traverse_id(GLYPH,line.head) do
        color_push.data = math.random().." .5 .5 rg"
        node.insert_before(line.head,letter,node.copy(color_push))
        node.insert_after(line.head,letter,node.copy(color_pop))
    end
  end
  return head
end

This works fine /except/ for the first letter of every line except the
first line. So the first line is fine, but for every following line in a
paragraph, the first letter is not colored. I also get warnings

LuaTeX warning: pop empty color page stack 0

so it seems that the color_push does not work in that cases? But I don't
see what I'm doing wrong …
To understand what mistake I'm making, I tried to use

letter = node.first_glyph(line) [or line.head?]

instead of the for loop, but then letter doesn't seem to be a node at all.

I work with LuaLaTeX, luacode and luatexbase, and
This is LuaTeX, Version beta-0.70.1-2011061410 (rev 4277)

cheers
Arno

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