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 node, nodes, attributes, fonts, tex = node, nodes, attributes, fonts, tex
local type, tonumber, next = type, tonumber, next
local gmatch = string.gmatch
local formatters = string.formatters
local compactfloat = number.compactfloat

-- 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.

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

----- 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 getdepth            = nuts.getdepth
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 setmetatableindex   = table.setmetatableindex

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_layer             = attributes.private("viewerlayer")

local band  = bit32.band
local bor   = bit32.bor

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 trace_expansion
-- local trace_line
-- local trace_space

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,
    expansion     =  65536,
    line          = 131072,
    space         = 262144,
    depth         = 524288,
}

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, l_expansion, l_line, l_space, l_depth

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 userrule -- bah, not yet defined: todo, delayed(nuts.rules,"userrule")

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
    l_expansion     = layers.expansion
    l_line          = layers.line
    l_space         = layers.space
    l_depth         = layers.depth
    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
    --
    if not userrule then
       userrule = nuts.rules.userrule
    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 = bor(a,preset_makeup)
        end
    elseif n == "boxes" then
        if not a or a == 0 or a == unsetvalue then
            a = preset_boxes
        else
            a = bor(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 = bor(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 = bor(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) -- currently the same
    setattr(n,a_visual,setvisual(mode,getattr(n,a_visual),true,true))
end

-- fast setters

do

    local cached = setmetatableindex(function(t,k)
        if k == true then
            return texgetattribute(a_visual)
        elseif not k then
            t[k] = unsetvalue
            return unsetvalue
        else
            local v = setvisual(k)
            t[k] = v
            return v
        end
    end)

 -- local function applyvisuals(n,mode)
 --     local a = cached[mode]
 --     apply_to_nodes(n,function(n) setattr(n,a_visual,a) end)
 -- end

    local a = unsetvalue

    local f = function(n) setattr(n,a_visual,a) end

    local function applyvisuals(n,mode)
        a = cached[mode]
        apply_to_nodes(n,f)
    end

    nuts.applyvisuals = applyvisuals

    function nodes.applyvisuals(n,mode)
        applyvisuals(tonut(n),mode)
    end

    function visualizers.attribute(mode)
        return cached[mode]
    end

    visualizers.attributes = cached

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_space_x         = "trace:m"
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:d"
local c_expansion       = "trace:o"
local c_depth           = "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_space_x_d       = "trace:dm"
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:dd"
local c_expansion_d     = "trace:do"
local c_depth_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) -- a bit overkill: double wrapped
    end
    if layer then
        setattr(info,a_layer,layer)
    end
    return info, width
end

local function someblob(str,layer,color,textcolor,width)
    local text = hpack_string(str,usedfont)
    local size = getwidth(text)
    local rule = new_rule(width,2*exheight,exheight/2)
    local kern = new_kern(-width + (width-size)/2)
    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)
    info = new_hlist(info)
    if layer then
        setattr(info,a_layer,layer)
    end
    return info, width
end

local caches = setmetatableindex("table")

local fontkern, italickern do

    local f_cache = caches["fontkern"]
    local i_cache = caches["italickern"]

    local function somekern(head,current,cache,color,layer)
        local width = getkern(current)
        local extra = getfield(current,"expansion_factor")
        local kern  = width + extra
        local info  = cache[kern]
        if not info then
            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,color)
            setcolor(rule,color)
            settransparency(rule,color)
            setshift(text,-5 * exheight)
            info = new_hlist(setlink(rule,text))
            setattr(info,a_layer,layer)
            f_cache[kern] = info
        end
        head = insert_node_before(head,current,copy_list(info))
        return head, current
    end

    fontkern = function(head,current)
        return somekern(head,current,f_cache,c_text_d,l_fontkern)
    end

    italickern = function(head,current)
        return somekern(head,current,i_cache,c_glyph_d,l_italic)
    end

end

local glyphexpansion do

    local f_cache = caches["glyphexpansion"]

    glyphexpansion = function(head,current)
        local extra = getfield(current,"expansion_factor")
        if extra ~= 0 then
            extra = extra / 1000
            local info = f_cache[extra]
            if not info then
                local text = hpack_string(compactfloat(extra,"%.1f"),usedfont)
                local rule = new_rule(emwidth/fraction,exheight,2*exheight)
                local list = getlist(text)
                if extra > 0 then
                    setlistcolor(list,c_positive_d)
                elseif extra < 0 then
                    setlistcolor(list,c_negative_d)
                end
                setlisttransparency(list,c_text_d)
                setcolor(rule,c_text_d)
                settransparency(rule,c_text_d)
                setshift(text,1.5 * exheight)
                info = new_hlist(setlink(rule,text))
                setattr(info,a_layer,l_expansion)
                f_cache[extra] = info
            end
            head = insert_node_before(head,current,copy_list(info))
            return head, current
        end
        return head, current
    end

end

local kernexpansion do

    local f_cache = caches["kernexpansion"]

    kernexpansion = function(head,current)
        local extra = getfield(current,"expansion_factor")
        if extra ~= 0 then
            extra = extra / 1000
            local info = f_cache[extra]
            if not info then
                local text = hpack_string(compactfloat(extra,"%.1f"),usedfont)
                local rule = new_rule(emwidth/fraction,exheight,4*exheight)
                local list = getlist(text)
                if extra > 0 then
                    setlistcolor(list,c_positive_d)
                elseif extra < 0 then
                    setlistcolor(list,c_negative_d)
                end
                setlisttransparency(list,c_text_d)
                setcolor(rule,c_text_d)
                settransparency(rule,c_text_d)
                setshift(text,3.5 * exheight)
                info = new_hlist(setlink(rule,text))
                setattr(info,a_layer,l_expansion)
                f_cache[extra] = info
            end
            head = insert_node_before(head,current,copy_list(info))
            return head, current
        end
        return head, current
    end

end

local whatsit do

    local whatsitcodes = nodes.whatsitcodes
    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 mathcodes = nodes.mathcodes
    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 ruleddepth do

    ruleddepth = function(current,wd,ht,dp)
        local wd, ht, dp = getwhd(current)
        if dp ~= 0 then
            local rule = new_rule(wd,0,dp)
            setcolor(rule,c_depth)
            settransparency(rule,c_zero)
            setattr(rule,a_layer,l_depth)
            setlist(current,setlink(rule,new_kern(-wd),getlist(current)))
        end
    end

end

local ruledbox do

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

    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
         -- )
            --
            -- userrules:
            --
            local info = setlink(
                this and copy_list(this) or nil,
                userrule {
                    width  = wd,
                    height = ht,
                    depth  = dp,
                    line   = linewidth,
                    type   = "box",
                    dashed = 3*size,
                }
            )
            --
            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 and prev > 0 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

    -- see boundingbox feature .. maybe a pdf stream is more efficient, after all we
    -- have a frozen color anyway or i need a more detailed cache .. below is a more
    -- texie approach

    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 info
            --
            -- original
            --
         -- local baseline
         -- 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)
         -- 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
         -- )
            --
            -- experiment with subtype outline
            --
         -- if (dp >= 0 and ht >= 0) or (dp <= 0 and ht <= 0) then
         --     baseline = new_rule(wd,linewidth/2,0)
         -- end
         -- local r = new_rule(wd-linewidth,ht-linewidth/4,dp-linewidth/4)
         -- setsubtype(r,nodes.rulecodes.outline)
         -- setfield(r,"transform",linewidth)
         -- info = setlink(
         --     new_kern(linewidth/4),
         --     r,
         --     new_kern(-wd+linewidth/2),
         --     baseline
         -- )
            --
            -- userrules:
            --
            info = setlink(
                userrule {
                    width  = wd,
                    height = ht,
                    depth  = dp,
                    line   = linewidth,
                    type   = "box",
                },
                new_kern(-wd)
            )
            --
            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

    function visualizers.setruledglyph(f)
        ruledglyph = f or ruledglyph
    end

end

local ruledglue do

    local gluecodes      = nodes.gluecodes
    local cleaders_code  = gluecodes.cleaders
    local userskip_code  = gluecodes.userskip
    local space_code     = gluecodes.spaceskip
    local xspace_code    = gluecodes.xspaceskip
    local leftskip_code  = gluecodes.leftskip
    local rightskip_code = gluecodes.rightskip

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

    local tags = {
     -- userskip              = "US",
        [gluecodes.lineskip]              = "LS",
        [gluecodes.baselineskip]          = "BS",
        [gluecodes.parskip]               = "PS",
        [gluecodes.abovedisplayskip]      = "DA",
        [gluecodes.belowdisplayskip]      = "DB",
        [gluecodes.abovedisplayshortskip] = "SA",
        [gluecodes.belowdisplayshortskip] = "SB",
        [gluecodes.leftskip]              = "LS",
        [gluecodes.rightskip]             = "RS",
        [gluecodes.topskip]               = "TS",
        [gluecodes.splittopskip]          = "ST",
        [gluecodes.tabskip]               = "AS",
        [gluecodes.spaceskip]             = "SP",
        [gluecodes.xspaceskip]            = "XS",
        [gluecodes.parfillskip]           = "PF",
        [gluecodes.thinmuskip]            = "MS",
        [gluecodes.medmuskip]             = "MM",
        [gluecodes.thickmuskip]           = "ML",
        [gluecodes.leaders]               = "NL",
        [gluecodes.cleaders]              = "CL",
        [gluecodes.xleaders]              = "XL",
        [gluecodes.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
                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

 -- ruledspace = function(head,current,parent)
 --     local subtype = getsubtype(current)
 --     if subtype == space_code or subtype == xspace_code then
 --         local width  = effectiveglue(current,parent)
 --         local amount = formatters["%s:%0.3f"](tags[subtype] or "HS",width*pt_factor)
 --         local info   = g_cache_h[amount]
 --         if info then
 --             -- print("space hit")
 --         else
 --             info = sometext(amount,l_glue,c_space)
 --             g_cache_h[amount] = info
 --         end
 --         info = copy_list(info)
 --         head, current = insert_node_before(head,current,info)
 --         return head, getnext(current)
 --     else
 --         return head, current
 --     end
 -- end

    local g_cache_s = caches["space"]
    local g_cache_x = caches["xspace"]

    ruledspace = function(head,current,parent)
        local subtype = getsubtype(current)
        if subtype == space_code or subtype == xspace_code then -- not yet all space
            local width = effectiveglue(current,parent)
            local info
            if subtype == space_code then
                info = g_cache_s[width]
                if not info then
                    info = someblob("SP",l_glue,c_space,nil,width)
                    g_cache_s[width] = info
                end
            else
                info = g_cache_x[width]
                if not info then
                    info = someblob("XS",l_glue,c_space_x,nil,width)
                    g_cache_x[width] = info
                end
            end
            info = copy_list(info)
            head, current = insert_node_before(head,current,info)
            return head, getnext(current)
        else
            return head, current
        end
    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 cache = vertical and k_cache_v or k_cache_h
        local info  = cache[kern]
        if not info then
            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
            cache[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["italic"]

    ruleditalic = function(head,current)
        local kern = getkern(current)
        local info = i_cache[kern]
        if not info then
            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

do

    local disc_code           = nodecodes.disc
    local kern_code           = nodecodes.kern
    local glyph_code          = nodecodes.glyph
    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 hlist_code          = nodecodes.hlist
    local vlist_code          = nodecodes.vlist

    local kerncodes           = nodes.kerncodes
    local font_kern_code      = kerncodes.fontkern
    local italic_kern_code    = kerncodes.italiccorrection
    ----- user_kern_code      = kerncodes.userkern

    local listcodes           = nodes.listcodes
    local line_code           = listcodes.line

    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 trace_discretionary  = false
        local trace_expansion      = false
        local trace_line           = false
        local trace_space          = false
        local trace_depth          = false
        local current              = head
        local previous             = nil
        local attr                 = unsetvalue
        local prev_trace_fontkern  = nil
        local prev_trace_italic    = nil
        local prev_trace_expansion = 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
                prev_trace_italic    = trace_italic
                prev_trace_expansion = trace_expansion
                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
                    trace_expansion     = false
                    trace_line          = false
                    trace_space         = false
                    trace_depth         = false
                else -- dead slow:
                    trace_hbox          = band(a,     1) ~= 0
                    trace_vbox          = band(a,     2) ~= 0
                    trace_vtop          = band(a,     4) ~= 0
                    trace_kern          = band(a,     8) ~= 0
                    trace_glue          = band(a,    16) ~= 0
                    trace_penalty       = band(a,    32) ~= 0
                    trace_fontkern      = band(a,    64) ~= 0
                    trace_strut         = band(a,   128) ~= 0
                    trace_whatsit       = band(a,   256) ~= 0
                    trace_glyph         = band(a,   512) ~= 0
                    trace_simple        = band(a,  1024) ~= 0
                    trace_user          = band(a,  2048) ~= 0
                    trace_math          = band(a,  4096) ~= 0
                    trace_italic        = band(a,  8192) ~= 0
                    trace_origin        = band(a, 16384) ~= 0
                    trace_discretionary = band(a, 32768) ~= 0
                    trace_expansion     = band(a, 65536) ~= 0
                    trace_line          = band(a,131072) ~= 0
                    trace_space         = band(a,262144) ~= 0
                    trace_depth         = band(a,524288) ~= 0
                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
                if trace_expansion then
                    head, current = glyphexpansion(head,current)
                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)
                if subtype == font_kern_code then
                    if trace_fontkern or prev_trace_fontkern then
                        head, current = fontkern(head,current)
                    end
                    if trace_expansion or prev_trace_expansion then
                        head, current = kernexpansion(head,current)
                    end
                elseif subtype == italic_kern_code then
                    if trace_italic or prev_trace_italic then
                        head, current = italickern(head,current)
                    elseif trace_kern then
                        head, current = ruleditalic(head,current)
                    end
                else
                    if 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)
                elseif trace_space then
                    head, current = ruledspace(head,current,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_depth then
                    ruleddepth(current)
                end
                if trace_line and getsubtype(current) == line_code then
                    head, current = ruledbox(head,current,false,l_line,"L__",trace_simple,previous,trace_origin,parent)
                elseif 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

    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)

    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

end

do

    local hlist_code = nodecodes.hlist
    local vlist_code = nodecodes.vlist

    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

do

    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
    }

end
