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

local cos, tan, rad, format = math.cos, math.tan, math.rad, string.format
local utfbyte, utfchar = utf.byte, utf.char

local trace_combining     = false  trackers.register("fonts.combining",     function(v) trace_combining     = v end)
local trace_combining_all = false  trackers.register("fonts.combining.all", function(v) trace_combining_all = v end)

local force_combining     = false -- just for demo purposes (see mk)

trackers.register("fonts.composing", "fonts.combining")

local report_combining = logs.reporter("fonts","combining")

local allocate = utilities.storage.allocate

--[[ldx--
<p>This is very experimental code!</p>
--ldx]]--

local fonts              = fonts
local handlers           = fonts.handlers
local constructors       = fonts.constructors
local vf                 = handlers.vf
local commands           = vf.combiner.commands

local otffeatures        = constructors.newfeatures("otf")
local registerotffeature = otffeatures.register

local afmfeatures        = constructors.newfeatures("afm")
local registerafmfeature = afmfeatures.register

local unicodecharacters  = characters.data
local unicodefallbacks   = characters.fallbacks

local push               = vf.predefined.push
local pop                = vf.predefined.pop
local force_composed     = false
local cache              = { }  -- we could make these weak
local fraction           = 0.15 -- 30 units for lucida

local function composecharacters(tfmdata)
    -- this assumes that slot 1 is self, there will be a proper self some day
    local characters   = tfmdata.characters
    local descriptions = tfmdata.descriptions
    local parameters   = tfmdata.parameters
    local properties   = tfmdata.properties
    local Xdesc        = descriptions[utfbyte("X")]
    local xdesc        = descriptions[utfbyte("x")]
    if Xdesc and xdesc then
        local scale        = parameters.factor or 1
        local deltaxheight = scale * (Xdesc.boundingbox[4] - xdesc.boundingbox[4])
        local extraxheight = fraction * deltaxheight -- maybe use compose value
        local italicfactor = parameters.italicfactor or 0
        local vfspecials   = backends.tables.vfspecials --brr
        local red, green, blue, black
        if trace_combining then
            red   = vfspecials.red
            green = vfspecials.green
            blue  = vfspecials.blue
            black = vfspecials.black
        end
        local compose = fonts.goodies.getcompositions(tfmdata)
        if compose and trace_combining then
            report_combining("using compose information from goodies file")
        end
        local done = false
        for i,c in next, unicodecharacters do -- loop over all characters ... not that efficient but a specials hash takes memory
            if force_combining or not characters[i] then
                local s = c.specials
                if s and s[1] == 'char' then
                    local chr = s[2]
                    local charschr = characters[chr]
                    if charschr then
                        local cc = c.category
                        if cc == 'll' or cc == 'lu' or cc == 'lt' then -- characters.is_letter[cc]
                            local acc = s[3]
                            local t = { }
                            for k, v in next, charschr do
                                if k ~= "commands" then
                                    t[k] = v
                                end
                            end
                            local charsacc = characters[acc]
                        --~ local ca = charsacc.category
                        --~ if ca == "mn" then
                        --~     -- mark nonspacing
                        --~ elseif ca == "ms" then
                        --~     -- mark spacing combining
                        --~ elseif ca == "me" then
                        --~     -- mark enclosing
                        --~ else
                            if not charsacc then -- fallback accents
                                acc = unicodefallbacks[acc]
                                charsacc = acc and characters[acc]
                            end
                            local chr_t = cache[chr]
                            if not chr_t then
                                chr_t = {"slot", 1, chr}
                                cache[chr] = chr_t
                            end
                            if charsacc then
                                if trace_combining_all then
                                    report_combining("%s (U+%05X) = %s (U+%05X) + %s (U+%05X)",utfchar(i),i,utfchar(chr),chr,utfchar(acc),acc)
                                end
                                local acc_t = cache[acc]
                                if not acc_t then
                                    acc_t = {"slot", 1, acc}
                                    cache[acc] = acc_t
                                end
                                local cb = descriptions[chr].boundingbox
                                local ab = descriptions[acc].boundingbox
                                -- todo: adapt height
                                if cb and ab then
                                    -- can be sped up for scale == 1
                                    local c_llx, c_lly, c_urx, c_ury = scale*cb[1], scale*cb[2], scale*cb[3], scale*cb[4]
                                    local a_llx, a_lly, a_urx, a_ury = scale*ab[1], scale*ab[2], scale*ab[3], scale*ab[4]
                                    local dx = (c_urx - a_urx - a_llx + c_llx)/2
                                    local dd = (c_urx - c_llx)*italicfactor
                                    if a_ury < 0  then
                                        if trace_combining then
                                            t.commands = { push, {"right", dx-dd}, red, acc_t, black, pop, chr_t }
                                        else
                                            t.commands = { push, {"right", dx-dd},      acc_t,        pop, chr_t }
                                        end
                                    elseif c_ury > a_lly then -- messy test
                                        local dy
                                        if compose then
                                            -- experimental: we could use sx but all that testing
                                            -- takes time and code
                                            dy = compose[i]
                                            if dy then
                                                dy = dy.DY
                                            end
                                            if not dy then
                                                dy = compose[acc]
                                                if dy then
                                                    dy = dy and dy.DY
                                                end
                                            end
                                            if not dy then
                                                dy = compose.DY
                                            end
                                            if not dy then
                                                dy = - deltaxheight + extraxheight
                                            elseif dy > -1.5 and dy < 1.5 then
                                                -- we assume a fraction of (percentage)
                                                dy = - dy * deltaxheight
                                            else
                                                -- we assume fontunits (value smaller than 2 make no sense)
                                                dy = - dy * scale
                                            end
                                        else
                                            dy = - deltaxheight + extraxheight
                                        end
                                        if trace_combining then
                                            t.commands = { push, {"right", dx+dd}, {"down", dy}, green, acc_t, black, pop, chr_t }
                                        else
                                            t.commands = { push, {"right", dx+dd}, {"down", dy},        acc_t,        pop, chr_t }
                                        end
                                    else
                                        if trace_combining then
                                            t.commands = { push, {"right", dx+dd},               blue,  acc_t, black, pop, chr_t }
                                        else
                                            t.commands = { push, {"right", dx+dd},                      acc_t,        pop, chr_t }
                                        end
                                    end
                                else
                                    t.commands = { chr_t } -- else index mess
                                end
                            else
                                if trace_combining_all then
                                    report_combining("%s (U+%05X) = %s (U+%05X) (simplified)",utfchar(i),i,utfchar(chr),chr)
                                end
                                t.commands = { chr_t } -- else index mess
                            end
                            done = true
                            characters[i] = t
                            local d = { }
                            for k, v in next, descriptions[chr] do
                                d[k] = v
                            end
                            descriptions[i] = d
                        end
                    end
                end
            end
        end
        if done then
            properties.virtualized = true
        end
    end
end

registerotffeature {
    name        = "compose",
    description = "additional composed characters",
    manipulators = {
        base = composecharacters,
        node = composecharacters,
    }
}

registerafmfeature {
    name        = "compose",
    description = "additional composed characters",
    manipulators = {
        base = composecharacters,
        node = composecharacters,
    }
}

vf.helpers.composecharacters = composecharacters

-- This installs the builder into the regular virtual font builder,
-- which only makes sense as demo.

commands["compose.trace.enable"] = function()
    trace_combining = true
end

commands["compose.trace.disable"] = function()
    trace_combining = false
end

commands["compose.force.enable"] = function()
    force_combining = true
end

commands["compose.force.disable"] = function()
    force_combining = false
end

commands["compose.trace.set"] = function(g,v)
    if v[2] == nil then
        trace_combining = true
    else
        trace_combining = v[2]
    end
end

commands["compose.apply"] = function(g,v)
    composecharacters(g)
end

-- vf builder

-- {'special', 'pdf: q ' .. s .. ' 0 0 '.. s .. ' 0 0 cm'},
-- {'special', 'pdf: q 1 0 0 1 ' .. -w .. ' ' .. -h .. ' cm'},
-- {'special', 'pdf: /Fm\XX\space Do'},
-- {'special', 'pdf: Q'},
-- {'special', 'pdf: Q'},