draw box around glyphs

drawcharbox.lua

luatexbase.provides_module(
{
  name        = 'drawcharbox',
  date        = '2011/05/20',
  version     = 0.2,
  description = 'draw char box for each char',
  author      = 'Dohyun Kim',
  license     = 'Public Domain',
})

local rule	= node.id("rule")
local kern	= node.id("kern")
local hlist	= node.id("hlist")
local vlist	= node.id("vlist")
local glyph	= node.id("glyph")
local nodenew	= node.new
local traverse	= node.traverse
local has_attribute	= node.has_attribute
local drawcharboxattr	= luatexbase.attributes.drawcharboxattr
local insert_after	= node.insert_after
local add_to_callback	= luatexbase.add_to_callback

local function newrule (w,h,d)
  local r = nodenew(rule)
  r.width = w or 0
  r.height = h or 0
  r.depth = d or 0
  return r
end

local function newkern (w)
  local k = nodenew(kern, 1)
  k.kern = w or 0
  return k
end

local function push_color (data)
  local p = nodenew("whatsit", "pdf_colorstack")
  p.stack   = 0
  p.command = 1
  p.data    = data or "0 G"
  return p
end

local function pop_color ()
  local p = nodenew("whatsit", "pdf_colorstack")
  p.stack   = 0
  p.command = 2
  return p
end

local lw = 0.1*65536
local hlw = lw/2
local tlw = lw*2/3

local function insertcharbox (head)
  for curr in traverse(head) do
    if curr.id == hlist or curr.id == vlist then
      insertcharbox(curr.head)
    elseif curr.id == glyph and has_attribute(curr, drawcharboxattr) then
      local wd, ht, dp = curr.width, curr.height, curr.depth
      insert_after(head, curr, pop_color())
      insert_after(head, curr, newrule(wd, tlw, tlw))	  -- baseline
      insert_after(head, curr, push_color("0 0 1 RG"))
      insert_after(head, curr, pop_color())
      insert_after(head, curr, newkern(-wd+hlw))
      insert_after(head, curr, newrule(wd-lw, hlw+ht, hlw-ht)) -- top
      insert_after(head, curr, newkern(-wd))
      insert_after(head, curr, newrule(lw, ht+hlw, dp+hlw))	  -- right
      insert_after(head, curr, newrule(wd-lw, hlw-dp, hlw+dp)) -- bottom
      insert_after(head, curr, newrule(lw, ht+hlw, dp+hlw))	  -- left
      insert_after(head, curr, newkern(-wd-hlw))
      insert_after(head, curr, push_color("1 0 0 RG"))
    end
  end
  return true
end

add_to_callback("pre_output_filter", insertcharbox, "char_box_pre_output")

drawcharbox.sty

% written by Dohyun Kim
% Public Domain

\ProvidesPackage{drawcharbox}[2011/05/19 v0.1 Draw Char Box]

\newattribute\drawcharboxattr

\directlua{require "drawcharbox"}

\def\drawcharbox{\drawcharboxattr\@ne}

\endinput

% todo:
%   * color choice by user
%   * line width choice by user