if not modules then modules = { } end modules ['trac-vis'] = {
    version   = 1.001,
    comment   = "companion to trac-vis.mkiv",
    author    = "Hans Hagen, PRAGMA-ADE, Hasselt NL",
    copyright = "PRAGMA ADE / ConTeXt Development Team",
    license   = "see context related readme files"
}

local string, number, table = string, number, table
local node, nodes, attributes, fonts, tex = node, nodes, attributes, fonts, tex
local type = type
local gmatch = string.gmatch
local formatters = string.formatters

-- This module started out in the early days of mkiv and luatex with
-- visualizing kerns related to fonts. In the process of cleaning up the
-- visual debugger code it made sense to integrate some other code that
-- I had laying around and replace the old supp-vis debugging code. As
-- only a subset of the old visual debugger makes sense it has become a
-- different implementation. Soms of the m-visual functionality will also
-- be ported. The code is rather trivial. The caching is not really needed
-- but saves upto 50% of the time needed to add visualization. Of course
-- the overall runtime is larger because of color and layer processing in
-- the backend (can be times as much) so the runtime is somewhat larger
-- with full visualization enabled. In practice this will never happen
-- unless one is demoing.

-- We could use pdf literals and re stream codes but it's not worth the
-- trouble because we would end up in color etc mess. Maybe one day I'll
-- make a nodeinjection variant.

-- todo: global switch (so no attributes)
-- todo: maybe also xoffset, yoffset of glyph
-- todo: inline concat (more efficient)
-- todo: tags can also be numbers (just add to hash)

-- todo: dir and localpar nodes

local nodecodes           = nodes.nodecodes
local disc_code           = nodecodes.disc
local kern_code           = nodecodes.kern
local glyph_code          = nodecodes.glyph
local hlist_code          = nodecodes.hlist
local vlist_code          = nodecodes.vlist
local glue_code           = nodecodes.glue
local penalty_code        = nodecodes.penalty
local whatsit_code        = nodecodes.whatsit
local user_code           = nodecodes.user
local math_code           = nodecodes.math
local gluespec_code       = nodecodes.gluespec

local kerncodes           = nodes.kerncodes
local font_kern_code      = kerncodes.fontkern
local user_kern_code      = kerncodes.userkern

local gluecodes           = nodes.gluecodes
local cleaders_code       = gluecodes.cleaders
local userskip_code       = gluecodes.userskip
local space_code          = gluecodes.space
local xspace_code         = gluecodes.xspace
local leftskip_code       = gluecodes.leftskip
local rightskip_code      = gluecodes.rightskip

local whatsitcodes        = nodes.whatsitcodes
local mathcodes           = nodes.mathcodes

local nuts                = nodes.nuts
local tonut               = nuts.tonut
local tonode              = nuts.tonode

local setfield            = nuts.setfield
local setboth             = nuts.setboth
local setlink             = nuts.setlink
local setdisc             = nuts.setdisc
local setlist             = nuts.setlist
local setleader           = nuts.setleader
local setsubtype          = nuts.setsubtype
local setattr             = nuts.setattr
local setwidth            = nuts.setwidth
local setshift            = nuts.setshift

local getfield            = nuts.getfield
local getid               = nuts.getid
local getfont             = nuts.getfont
local getattr             = nuts.getattr
local getsubtype          = nuts.getsubtype
local getchar             = nuts.getchar
local getbox              = nuts.getbox
local getlist             = nuts.getlist
local getleader           = nuts.getleader
local getnext             = nuts.getnext
local getprev             = nuts.getprev
local getboth             = nuts.getboth
local getdisc             = nuts.getdisc
local getwhd              = nuts.getwhd
local getkern             = nuts.getkern
local getpenalty          = nuts.getpenalty
local getdir              = nuts.getdir
local getwidth            = nuts.getwidth
local getshift            = nuts.getshift

local hpack_nodes         = nuts.hpack
local vpack_nodes         = nuts.vpack
local copy_list           = nuts.copy_list
local flush_node_list     = nuts.flush_list
local insert_node_before  = nuts.insert_before
local insert_node_after   = nuts.insert_after
local traverse_nodes      = nuts.traverse
local apply_to_nodes      = nuts.apply
local find_tail           = nuts.tail
local effectiveglue       = nuts.effective_glue

local hpack_string        = nuts.typesetters.tohpack

local texgetattribute     = tex.getattribute
local texsetattribute     = tex.setattribute

local unsetvalue          = attributes.unsetvalue

local current_font        = font.current

local fonthashes          = fonts.hashes
local chardata            = fonthashes.characters
local exheights           = fonthashes.exheights
local emwidths            = fonthashes.emwidths
local pt_factor           = number.dimenfactors.pt

local nodepool            = nuts.pool
local new_rule            = nodepool.rule
local new_kern            = nodepool.kern
local new_glue            = nodepool.glue
local new_hlist           = nodepool.hlist
local new_vlist           = nodepool.vlist

local tracers             = nodes.tracers
local visualizers         = nodes.visualizers

local setcolor            = tracers.colors.set
local setlistcolor        = tracers.colors.setlist
local settransparency     = tracers.transparencies.set
local setlisttransparency = tracers.transparencies.setlist

local starttiming         = statistics.starttiming
local stoptiming          = statistics.stoptiming

local a_visual            = attributes.private("visual")
local a_fontkern          = attributes.private("fontkern")
local a_layer             = attributes.private("viewerlayer")

local hasbit              = number.hasbit
local bit                 = number.bit
local setbit              = number.setbit
local clearbit            = number.clearbit

local enableaction        = nodes.tasks.enableaction

local trace_hbox
local trace_vbox
local trace_vtop
local trace_kern
local trace_glue
local trace_penalty
local trace_fontkern
local trace_strut
local trace_whatsit
local trace_user
local trace_math
local trace_italic
local trace_discretionary

local report_visualize = logs.reporter("visualize")

local modes = {
    hbox          =     1,
    vbox          =     2,
    vtop          =     4,
    kern          =     8,
    glue          =    16,
 -- skip          =    16,
    penalty       =    32,
    fontkern      =    64,
    strut         =   128,
    whatsit       =   256,
    glyph         =   512,
    simple        =  1024,
    simplehbox    =  1024 + 1,
    simplevbox    =  1024 + 2,
    simplevtop    =  1024 + 4,
    user          =  2048,
    math          =  4096,
    italic        =  8192,
    origin        = 16384,
    discretionary = 32768,
}

local usedfont, exheight, emwidth
local l_penalty, l_glue, l_kern, l_fontkern, l_hbox, l_vbox, l_vtop, l_strut, l_whatsit, l_glyph, l_user, l_math, l_italic, l_origin, l_discretionary

local enabled = false
local layers  = { }

local preset_boxes  = modes.hbox + modes.vbox + modes.origin
local preset_makeup = preset_boxes
                    + modes.kern + modes.glue + modes.penalty
local preset_all    = preset_makeup
                    + modes.fontkern + modes.whatsit + modes.glyph + modes.user + modes.math

function visualizers.setfont(id)
    usedfont = id or current_font()
    exheight = exheights[usedfont]
    emwidth  = emwidths[usedfont]
end

-- we can preset a bunch of bits

local function enable()
    if not usedfont then
        -- we use a narrow monospaced font -- infofont ?
        visualizers.setfont(fonts.definers.define { name = "lmmonoltcond10regular", size = tex.sp("4pt") })
    end
    for mode, value in next, modes do
        local tag = formatters["v_%s"](mode)
        attributes.viewerlayers.define {
            tag       = tag,
            title     = formatters["visualizer %s"](mode),
            visible   = "start",
            editable  = "yes",
            printable = "yes"
        }
        layers[mode] = attributes.viewerlayers.register(tag,true)
    end
    l_hbox          = layers.hbox
    l_vbox          = layers.vbox
    l_vtop          = layers.vtop
    l_glue          = layers.glue
    l_kern          = layers.kern
    l_penalty       = layers.penalty
    l_fontkern      = layers.fontkern
    l_strut         = layers.strut
    l_whatsit       = layers.whatsit
    l_glyph         = layers.glyph
    l_user          = layers.user
    l_math          = layers.math
    l_italic        = layers.italic
    l_origin        = layers.origin
    l_discretionary = layers.discretionary
    enableaction("shipouts","nodes.visualizers.handler")
    report_visualize("enabled")
    enabled = true
    tex.setcount("global","c_syst_visualizers_state",1) -- so that we can optimize at the tex end
end

local function setvisual(n,a,what,list) -- this will become more efficient when we have the bit lib linked in
    if not n or n == "reset" then
        return unsetvalue
    elseif n == true or n == "makeup" then
        if not a or a == 0 or a == unsetvalue then
            a = preset_makeup
        else
            a = setbit(a,preset_makeup)
        end
    elseif n == "boxes" then
        if not a or a == 0 or a == unsetvalue then
            a = preset_boxes
        else
            a = setbit(a,preset_boxes)
        end
    elseif n == "all" then
        if what == false then
            return unsetvalue
        elseif not a or a == 0 or a == unsetvalue then
            a = preset_all
        else
            a = setbit(a,preset_all)
        end
    else
        for s in gmatch(n,"[a-z]+") do
            local m = modes[s]
            if not m then
                -- go on
            elseif not a or a == 0 or a == unsetvalue then
                a = m
            else
                a = setbit(a,m)
            end
        end
    end
    if not a or a == 0 or a == unsetvalue then
        return unsetvalue
    elseif not enabled then -- must happen at runtime (as we don't store layers yet)
        enable()
    end
    return a
end

function nuts.setvisual(n,mode)
    setattr(n,a_visual,setvisual(mode,getattr(n,a_visual),true))
end

function nuts.setvisuals(n,mode)
    setattr(n,a_visual,setvisual(mode,getattr(n,a_visual),true,true))
end

function nuts.applyvisuals(n,mode)
    local a = unsetvalue
    if mode == true then
        a = texgetattribute (a_visual)
    elseif mode then
        a = setvisual(mode)
    end
    apply_to_nodes(n,function(n) setattr(n,a_visual,a) end)
end

function nuts.copyvisual(n,m)
    setattr(n,a_visual,getattr(m,a_visual))
end

function visualizers.setvisual(n)
    texsetattribute(a_visual,setvisual(n,texgetattribute(a_visual)))
end

function visualizers.setlayer(n)
    texsetattribute(a_layer,layers[n] or unsetvalue)
end

local function set(mode,v)
    texsetattribute(a_visual,setvisual(mode,texgetattribute(a_visual),v))
end

for mode, value in next, modes do
    trackers.register(formatters["visualizers.%s"](mode), function(v) set(mode,v) end)
end

local raisepenalties = false

directives.register("visualizers.raisepenalties",function(v) raisepenalties = v end)

local fraction = 10

trackers  .register("visualizers.reset",    function(v) set("reset", v) end)
trackers  .register("visualizers.all",      function(v) set("all",   v) end)
trackers  .register("visualizers.makeup",   function(v) set("makeup",v) end)
trackers  .register("visualizers.boxes",    function(v) set("boxes", v) end)
directives.register("visualizers.fraction", function(v) fraction = (v and tonumber(v)) or (v == "more" and 5) or 10 end)

local c_positive        = "trace:b"
local c_negative        = "trace:r"
local c_zero            = "trace:g"
local c_text            = "trace:s"
local c_space           = "trace:y"
local c_skip_a          = "trace:c"
local c_skip_b          = "trace:m"
local c_glyph           = "trace:o"
local c_ligature        = "trace:s"
local c_white           = "trace:w"
local c_math            = "trace:r"
local c_origin          = "trace:o"
local c_discretionary   = "trace:o"

local c_positive_d      = "trace:db"
local c_negative_d      = "trace:dr"
local c_zero_d          = "trace:dg"
local c_text_d          = "trace:ds"
local c_space_d         = "trace:dy"
local c_skip_a_d        = "trace:dc"
local c_skip_b_d        = "trace:dm"
local c_glyph_d         = "trace:do"
local c_ligature_d      = "trace:ds"
local c_white_d         = "trace:dw"
local c_math_d          = "trace:dr"
local c_origin_d        = "trace:do"
local c_discretionary_d = "trace:do"

local function sometext(str,layer,color,textcolor,lap) -- we can just paste verbatim together .. no typesteting needed
    local text = hpack_string(str,usedfont)
    local size = getwidth(text)
    local rule = new_rule(size,2*exheight,exheight/2)
    local kern = new_kern(-size)
    if color then
        setcolor(rule,color)
    end
    if textcolor then
        setlistcolor(getlist(text),textcolor)
    end
    local info = setlink(rule,kern,text)
    setlisttransparency(info,c_zero)
    info = hpack_nodes(info)
    local width = getwidth(info)
    if lap then
        info = new_hlist(setlink(new_kern(-width),info))
    else
        info = new_hlist(info)
    end
    if layer then
        setattr(info,a_layer,layer)
    end
    return info, width
end

local caches = table.setmetatableindex("table")

local fontkern do

    local f_cache = caches["fontkern"]

    fontkern = function(head,current)
        local width = getkern(current)
        local extra = getfield(current,"expansion_factor")
        local kern  = width + extra
        local info  = f_cache[kern]
     -- report_visualize("fontkern: %p ex %p",width,extra)
        if info then
            -- print("hit fontkern")
        else
            local text = hpack_string(formatters[" %0.3f"](kern*pt_factor),usedfont)
            local rule = new_rule(emwidth/fraction,6*exheight,2*exheight)
            local list = getlist(text)
            if kern > 0 then
                setlistcolor(list,c_positive_d)
            elseif kern < 0 then
                setlistcolor(list,c_negative_d)
            else
                setlistcolor(list,c_zero_d)
            end
            setlisttransparency(list,c_text_d)
            setcolor(rule,c_text_d)
            settransparency(rule,c_text_d)
            setshift(text,-5 * exheight)
            info = new_hlist(setlink(rule,text))
            setattr(info,a_layer,l_fontkern)
            f_cache[kern] = info
        end
        head = insert_node_before(head,current,copy_list(info))
        return head, current
    end

end

local whatsit do

    local w_cache = caches["whatsit"]

    local tags    = {
        open             = "FIC",
        write            = "FIW",
        close            = "FIC",
        special          = "SPE",
        latelua          = "LUA",
        savepos          = "POS",
        userdefined      = "USR",
     -- backend stuff
        pdfliteral       = "PDF",
        pdfrefobj        = "PDF",
        pdfannot         = "PDF",
        pdfstartlink     = "PDF",
        pdfendlink       = "PDF",
        pdfdest          = "PDF",
        pdfthread        = "PDF",
        pdfstartthread   = "PDF",
        pdfendthread     = "PDF",
        pdfthreaddata    = "PDF",
        pdflinkdata      = "PDF",
        pdfcolorstack    = "PDF",
        pdfsetmatrix     = "PDF",
        pdfsave          = "PDF",
        pdfrestore       = "PDF",
    }

    whatsit = function(head,current)
        local what = getsubtype(current)
        local info = w_cache[what]
        if info then
            -- print("hit whatsit")
        else
            local tag = whatsitcodes[what]
            -- maybe different text colors per tag
            info = sometext(formatters["W:%s"](tag and tags[tag] or what),usedfont,nil,c_white)
            setattr(info,a_layer,l_whatsit)
            w_cache[what] = info
        end
        head, current = insert_node_after(head,current,copy_list(info))
        return head, current
    end

end

local user do

    local u_cache = caches["user"]

    user = function(head,current)
        local what = getsubtype(current)
        local info = u_cache[what]
        if info then
            -- print("hit user")
        else
            info = sometext(formatters["U:%s"](what),usedfont)
            setattr(info,a_layer,l_user)
            u_cache[what] = info
        end
        head, current = insert_node_after(head,current,copy_list(info))
        return head, current
    end

end

local math do

    local m_cache = {
        beginmath = caches["bmath"],
        endmath   = caches["emath"],
    }

    local tags    = {
        beginmath = "B",
        endmath   = "E",
    }

    math = function(head,current)
        local what = getsubtype(current)
        local tag  = mathcodes[what]
        local skip = getkern(current) + getwidth(current) -- surround
        local info = m_cache[tag][skip]
        if info then
            -- print("hit math")
        else
            local text, width = sometext(formatters["M:%s"](tag and tags[tag] or what),usedfont,nil,c_math_d)
            local rule = new_rule(skip,-655360/fraction,2*655360/fraction)
            setcolor(rule,c_math_d)
            settransparency(rule,c_math_d)
            setattr(rule,a_layer,l_math)
            if tag == "beginmath" then
                info = new_hlist(setlink(new_glue(-skip),rule,new_glue(-width),text))
            else
                info = new_hlist(setlink(new_glue(-skip),rule,new_glue(-skip),text))
            end
            setattr(info,a_layer,l_math)
            m_cache[tag][skip] = info
        end
        head, current = insert_node_after(head,current,copy_list(info))
        return head, current
    end

end

local ruledbox do

    local b_cache = caches["box"]
    local o_cache = caches["origin"]

    table.setmetatableindex(o_cache,function(t,size)
        local rule   = new_rule(2*size,size,size)
        local origin = hpack_nodes(rule)
        setcolor(rule,c_origin_d)
        settransparency(rule,c_origin_d)
        setattr(rule,a_layer,l_origin)
        t[size] = origin
        return origin
    end)

    ruledbox = function(head,current,vertical,layer,what,simple,previous,trace_origin,parent)
        local wd, ht, dp = getwhd(current)
        if wd ~= 0 then
            local shift = getshift(current)
            local dir   = getdir(current)
         -- if dir == "LTL" or dir == "RRT" then
         --     wd, ht, dp = ht + dp, wd, 0
         -- end
            local next = getnext(current)
            local prev = previous
         -- local prev = getprev(current) -- prev can be wrong in math mode < 0.78.3
            setboth(current)
            local linewidth = emwidth/fraction
            local size      = 2*linewidth
            local baseline, baseskip
            if dp ~= 0 and ht ~= 0 then
                if wd > 20*linewidth then
                    local targetsize = wd - size
                    baseline = b_cache[targetsize]
                    if not baseline then
                        -- due to an optimized leader color/transparency we need to set the glue node in order
                        -- to trigger this mechanism
                        local leader = setlink(new_glue(size),new_rule(3*size,linewidth,0),new_glue(size))
                        leader = hpack_nodes(leader)
                        baseline = new_glue(0,65536,0,2,0)
                        setleader(baseline,leader)
                        setsubtype(baseline,cleaders_code)
                        setlisttransparency(baseline,c_text)
                        baseline = hpack_nodes(baseline,targetsize)
                        b_cache[targetsize] = baseline
                    end
                    baseline = copy_list(baseline)
                    baseskip = new_kern(-wd+linewidth)
                else
                    baseline = new_rule(wd-size,linewidth,0)
                    baseskip = new_kern(-wd+size)
                end
            end
            local this
            if not simple then
                this = b_cache[what]
                if not this then
                    local text = hpack_string(what,usedfont)
                    this = setlink(new_kern(-getwidth(text)),text)
                    setlisttransparency(this,c_text)
                    this = new_hlist(this)
                    b_cache[what] = this
                end
            end
            -- we need to trigger the right mode (else sometimes no whatits)
            local info = setlink(
                this and copy_list(this) or nil,
                new_rule(linewidth,ht,dp),
                new_rule(wd-size,-dp+linewidth,dp),
                new_rule(linewidth,ht,dp),
                new_kern(-wd+linewidth),
                new_rule(wd-size,ht,-ht+linewidth),
                baseskip,
                baseskip and baseline or nil
            )
            setlisttransparency(info,c_text)
            info = new_hlist(info)
            --
            setattr(info,a_layer,layer)
            if vertical then
                if shift == 0 then
                    info = setlink(current,dp ~= 0 and new_kern(-dp) or nil,info)
                elseif trace_origin then
                    local size   = 2*size
                    local origin = o_cache[size]
                    origin = copy_list(origin)
                    if getid(parent) == vlist_code then
                        setshift(origin,-shift)
                        info = setlink(current,new_kern(-size),origin,new_kern(-size-dp),info)
                    else
                        -- todo .. i need an example
                        info = setlink(current,dp ~= 0 and new_kern(-dp) or nil,info)
                    end
                    setshift(current,0)
                else
                    info = setlink(current,new_dp ~= 0 and new_kern(-dp) or nil,info)
                    setshift(current,0)
                end
                info = new_vlist(info,wd,ht,dp,shift)
            else
                if shift == 0 then
                    info = setlink(current,new_kern(-wd),info)
                elseif trace_origin then
                    local size   = 2*size
                    local origin = o_cache[size]
                    origin = copy_list(origin)
                    if getid(parent) == vlist_code then
                        info = setlink(current,new_kern(-wd-size-shift),origin,new_kern(-size+shift),info)
                    else
                        setshift(origin,-shift)
                        info = setlink(current,new_kern(-wd-size),origin,new_kern(-size),info)
                    end
                    setshift(current,0)
                else
                    info = setlink(current,new_kern(-wd),info)
                    setshift(current,0)
                end
                info = new_hlist(info,wd,ht,dp,shift)
            end
            if next then
                setlink(info,next)
            end
            if prev then
                if getid(prev) == gluespec_code then
                    report_visualize("ignoring invalid prev")
                    -- weird, how can this happen, an inline glue-spec, probably math
                else
                    setlink(prev,info)
                end
            end
            if head == current then
                return info, info
            else
                return head, info
            end
        else
            return head, current
        end
    end

end

local ruledglyph do

    ruledglyph = function(head,current,previous) -- wrong for vertical glyphs
        local wd = getwidth(current)
     -- local wd = chardata[getfont(current)][getchar(current)].width
        if wd ~= 0 then
            local wd, ht, dp = getwhd(current)
    --         local dir = getdir(current)
    -- if dir == "LTL" or dir = "RTT" then
    --     wd, ht, dp = ht + dp, wd, 0
    -- end
            local next = getnext(current)
            local prev = previous
            setboth(current)
            local linewidth = emwidth/(2*fraction)
            local baseline
         -- if dp ~= 0 and ht ~= 0 then
            if (dp >= 0 and ht >= 0) or (dp <= 0 and ht <= 0) then
                baseline = new_rule(wd-2*linewidth,linewidth,0)
            end
            local doublelinewidth = 2*linewidth
            -- could be a pdf rule (or a user rule now)
            local info = setlink(
                new_rule(linewidth,ht,dp),
                new_rule(wd-doublelinewidth,-dp+linewidth,dp),
                new_rule(linewidth,ht,dp),
                new_kern(-wd+linewidth),
                new_rule(wd-doublelinewidth,ht,-ht+linewidth),
                new_kern(-wd+doublelinewidth),
                baseline
            )
            local char = chardata[getfont(current)][getchar(current)]
            if char and type(char.unicode) == "table" then -- hackery test
                setlistcolor(info,c_ligature)
                setlisttransparency(info,c_ligature_d)
            else
                setlistcolor(info,c_glyph)
                setlisttransparency(info,c_glyph_d)
            end
            info = new_hlist(info)
            setattr(info,a_layer,l_glyph)
            local info = setlink(current,new_kern(-wd),info)
            info = hpack_nodes(info)
            setwidth(info,wd)
            if next then
                setlink(info,next)
            end
            if prev then
                setlink(prev,info)
            end
            if head == current then
                return info, info
            else
                return head, info
            end
        else
            return head, current
        end
    end

end

local ruledglue do

    local g_cache_v = caches["vglue"]
    local g_cache_h = caches["hglue"]

    local tags = {
     -- userskip              = "US",
        lineskip              = "LS",
        baselineskip          = "BS",
        parskip               = "PS",
        abovedisplayskip      = "DA",
        belowdisplayskip      = "DB",
        abovedisplayshortskip = "SA",
        belowdisplayshortskip = "SB",
        leftskip              = "LS",
        rightskip             = "RS",
        topskip               = "TS",
        splittopskip          = "ST",
        tabskip               = "AS",
        spaceskip             = "SS",
        xspaceskip            = "XS",
        parfillskip           = "PF",
        thinmuskip            = "MS",
        medmuskip             = "MM",
        thickmuskip           = "ML",
        leaders               = "NL",
        cleaders              = "CL",
        xleaders              = "XL",
        gleaders              = "GL",
     -- true                  = "VS",
     -- false                 = "HS",
    }

    -- we sometimes pass previous as we can have issues in math (not watertight for all)

    ruledglue = function(head,current,vertical,parent)
        local subtype = getsubtype(current)
        local width   = effectiveglue(current,parent)
        local amount  = formatters["%s:%0.3f"](tags[subtype] or (vertical and "VS") or "HS",width*pt_factor)
        local info    = (vertical and g_cache_v or g_cache_h)[amount]
        if info then
            -- print("glue hit")
        else
            if subtype == space_code or subtype == xspace_code then -- not yet all space
                info = sometext(amount,l_glue,c_space)
            elseif subtype == leftskip_code or subtype == rightskip_code then
                info = sometext(amount,l_glue,c_skip_a)
            elseif subtype == userskip_code then
                if width > 0 then
                    info = sometext(amount,l_glue,c_positive)
                elseif width < 0 then
                    info = sometext(amount,l_glue,c_negative)
                else
                    info = sometext(amount,l_glue,c_zero)
                end
            else
                info = sometext(amount,l_glue,c_skip_b)
            end
            (vertical and g_cache_v or g_cache_h)[amount] = info
        end
        info = copy_list(info)
        if vertical then
            info = vpack_nodes(info)
        end
        head, current = insert_node_before(head,current,info)
        return head, getnext(current)
    end

end

local ruledkern do

    local k_cache_v = caches["vkern"]
    local k_cache_h = caches["hkern"]

    ruledkern = function(head,current,vertical)
        local kern = getkern(current)
        local info = (vertical and k_cache_v or k_cache_h)[kern]
        if info then
            -- print("kern hit")
        else
            local amount = formatters["%s:%0.3f"](vertical and "VK" or "HK",kern*pt_factor)
            if kern > 0 then
                info = sometext(amount,l_kern,c_positive)
            elseif kern < 0 then
                info = sometext(amount,l_kern,c_negative)
            else
                info = sometext(amount,l_kern,c_zero)
            end
            (vertical and k_cache_v or k_cache_h)[kern] = info
        end
        info = copy_list(info)
        if vertical then
            info = vpack_nodes(info)
        end
        head, current = insert_node_before(head,current,info)
        return head, getnext(current)
    end

end

local ruleditalic do

    local i_cache = caches["itatalic"]

    ruleditalic = function(head,current)
        local kern = getkern(current)
        local info = i_cache[kern]
        if info then
            -- print("kern hit")
        else
            local amount = formatters["%s:%0.3f"]("IC",kern*pt_factor)
            if kern > 0 then
                info = sometext(amount,l_kern,c_positive)
            elseif kern < 0 then
                info = sometext(amount,l_kern,c_negative)
            else
                info = sometext(amount,l_kern,c_zero)
            end
            i_cache[kern] = info
        end
        info = copy_list(info)
        head, current = insert_node_before(head,current,info)
        return head, getnext(current)
    end

end

local ruleddiscretionary do

    local d_cache = caches["discretionary"]

    ruleddiscretionary = function(head,current)
        local d = d_cache[true]
        if not the_discretionary then
            local rule = new_rule(4*emwidth/fraction,4*exheight,exheight)
            local kern = new_kern(-2*emwidth/fraction)
            setlink(kern,rule)
            setcolor(rule,c_discretionary_d)
            settransparency(rule,c_discretionary_d)
            setattr(rule,a_layer,l_discretionary)
            d = new_hlist(kern)
            d_cache[true] = d
        end
        insert_node_after(head,current,copy_list(d))
        return head, current
    end

end

local ruledpenalty do

    local p_cache_v = caches["vpenalty"]
    local p_cache_h = caches["hpenalty"]

    ruledpenalty = function(head,current,vertical)
        local penalty = getpenalty(current)
        local info = (vertical and p_cache_v or p_cache_h)[penalty]
        if info then
            -- print("penalty hit")
        else
            local amount = formatters["%s:%s"](vertical and "VP" or "HP",penalty)
            if penalty > 0 then
                info = sometext(amount,l_penalty,c_positive)
            elseif penalty < 0 then
                info = sometext(amount,l_penalty,c_negative)
            else
                info = sometext(amount,l_penalty,c_zero)
            end
            (vertical and p_cache_v or p_cache_h)[penalty] = info
        end
        info = copy_list(info)
        if vertical then
            info = vpack_nodes(info)
        elseif raisepenalties then
            setshift(info,-65536*4)
        end
        head, current = insert_node_before(head,current,info)
        return head, getnext(current)
    end

end

local function visualize(head,vertical,forced,parent)
    local trace_hbox     = false
    local trace_vbox     = false
    local trace_vtop     = false
    local trace_kern     = false
    local trace_glue     = false
    local trace_penalty  = false
    local trace_fontkern = false
    local trace_strut    = false
    local trace_whatsit  = false
    local trace_glyph    = false
    local trace_simple   = false
    local trace_user     = false
    local trace_math     = false
    local trace_italic   = false
    local trace_origin   = false
    local current        = head
    local previous       = nil
    local attr           = unsetvalue
    local prev_trace_fontkern = nil
    while current do
        local id = getid(current)
        local a = forced or getattr(current,a_visual) or unsetvalue
        if a ~= attr then
            prev_trace_fontkern = trace_fontkern
            if a == unsetvalue then
                trace_hbox          = false
                trace_vbox          = false
                trace_vtop          = false
                trace_kern          = false
                trace_glue          = false
                trace_penalty       = false
                trace_fontkern      = false
                trace_strut         = false
                trace_whatsit       = false
                trace_glyph         = false
                trace_simple        = false
                trace_user          = false
                trace_math          = false
                trace_italic        = false
                trace_origin        = false
                trace_discretionary = false
            else -- dead slow:
                trace_hbox          = hasbit(a,    1)
                trace_vbox          = hasbit(a,    2)
                trace_vtop          = hasbit(a,    4)
                trace_kern          = hasbit(a,    8)
                trace_glue          = hasbit(a,   16)
                trace_penalty       = hasbit(a,   32)
                trace_fontkern      = hasbit(a,   64)
                trace_strut         = hasbit(a,  128)
                trace_whatsit       = hasbit(a,  256)
                trace_glyph         = hasbit(a,  512)
                trace_simple        = hasbit(a, 1024)
                trace_user          = hasbit(a, 2048)
                trace_math          = hasbit(a, 4096)
                trace_italic        = hasbit(a, 8192)
                trace_origin        = hasbit(a,16384)
                trace_discretionary = hasbit(a,32768)
            end
            attr = a
        end
        if trace_strut then
            setattr(current,a_layer,l_strut)
        elseif id == glyph_code then
            if trace_glyph then
                head, current = ruledglyph(head,current,previous)
            end
        elseif id == disc_code then
            if trace_discretionary then
                head, current = ruleddiscretionary(head,current)
            end
            local pre, post, replace = getdisc(current)
            if pre then
                pre = visualize(pre,false,a,parent)
            end
            if post then
                post = visualize(post,false,a,parent)
            end
            if replace then
                replace = visualize(replace,false,a,parent)
            end
            setdisc(current,pre,post,replace)
        elseif id == kern_code then
            local subtype = getsubtype(current)
            -- tricky ... we don't copy the trace attribute in node-inj (yet)
            if subtype == font_kern_code or getattr(current,a_fontkern) then
                if trace_fontkern or prev_trace_fontkern then
                    head, current = fontkern(head,current)
                end
            else -- if subtype == user_kern_code then
                if trace_italic then
                    head, current = ruleditalic(head,current)
                elseif trace_kern then
                    head, current = ruledkern(head,current,vertical)
                end
            end
        elseif id == glue_code then
            local content = getleader(current)
            if content then
                setleader(current,visualize(content,false,nil,parent))
            elseif trace_glue then
                head, current = ruledglue(head,current,vertical,parent)
            end
        elseif id == penalty_code then
            if trace_penalty then
                head, current = ruledpenalty(head,current,vertical)
            end
        elseif id == hlist_code then
            local content = getlist(current)
            if content then
                setlist(current,visualize(content,false,nil,current))
            end
            if trace_hbox then
                head, current = ruledbox(head,current,false,l_hbox,"H__",trace_simple,previous,trace_origin,parent)
            end
        elseif id == vlist_code then
            local content = getlist(current)
            if content then
                setlist(current,visualize(content,true,nil,current))
            end
            if trace_vtop then
                head, current = ruledbox(head,current,true,l_vtop,"_T_",trace_simple,previous,trace_origin,parent)
            elseif trace_vbox then
                head, current = ruledbox(head,current,true,l_vbox,"__V",trace_simple,previous,trace_origin,parent)
            end
        elseif id == whatsit_code then
            if trace_whatsit then
                head, current = whatsit(head,current)
            end
        elseif id == user_code then
            if trace_user then
                head, current = user(head,current)
            end
        elseif id == math_code then
            if trace_math then
                head, current = math(head,current)
            end
        end
        previous = current
        current  = getnext(current)
    end
    return head
end

do

    local function cleanup()
        for tag, cache in next, caches do
            for k, v in next, cache do
                flush_node_list(v)
            end
        end
        cleanup = function()
            report_visualize("error, duplicate cleanup")
        end
    end

    local function handler(head)
        if usedfont then
            starttiming(visualizers)
            head = visualize(tonut(head),true)
            stoptiming(visualizers)
            return tonode(head), true
        else
            return head, false
        end
    end

    visualizers.handler = handler

    luatex.registerstopactions(cleanup)

end

function visualizers.box(n)
    if usedfont then
        starttiming(visualizers)
        local box = getbox(n)
        if box then
            setlist(box,visualize(getlist(box),getid(box) == vlist_code))
        end
        stoptiming(visualizers)
        return head, true
    else
        return head, false
    end
end

do

    local last = nil
    local used = nil

    local mark = {
        "trace:1", "trace:2", "trace:3",
        "trace:4", "trace:5", "trace:6",
        "trace:7",
    }

    local function markfonts(list)
        for n in traverse_nodes(list) do
            local id = getid(n)
            if id == glyph_code then
                local font = getfont(n)
                local okay = used[font]
                if not okay then
                    last = last + 1
                    okay = mark[last]
                    used[font] = okay
                end
                setcolor(n,okay)
            elseif id == hlist_code or id == vlist_code then
                markfonts(getlist(n))
            end
        end
    end

    function visualizers.markfonts(list)
        last, used = 0, { }
        markfonts(type(n) == "number" and getlist(getbox(n)) or n)
    end

end

statistics.register("visualization time",function()
    if enabled then
     -- cleanup() -- in case we don't don't do it each time
        return formatters["%s seconds"](statistics.elapsedtime(visualizers))
    end
end)

-- interface

local implement = interfaces.implement

implement {
    name      = "setvisual",
    arguments = "string",
    actions   = visualizers.setvisual
}

implement {
    name      = "setvisuals",
    arguments = "string",
    actions   = visualizers.setvisual
}

implement {
    name      = "getvisual",
    arguments = "string",
    actions   = { setvisual, context }
}

    implement {
    name      = "setvisuallayer",
    arguments = "string",
    actions   = visualizers.setlayer
}

implement {
    name      = "markvisualfonts",
    arguments = "integer",
    actions   = visualizers.markfonts
}

implement {
    name      = "setvisualfont",
    arguments = "integer",
    actions   = visualizers.setfont
}