if not modules then modules = { } end modules ['letterspace'] = {
version = "2.5",
comment = "companion to luaotfload-main.lua",
author = "Hans Hagen, PRAGMA-ADE, Hasselt NL; adapted by Philipp Gesang",
copyright = "PRAGMA ADE / ConTeXt Development Team",
license = "see context related readme files"
}
local getmetatable = getmetatable
local require = require
local setmetatable = setmetatable
local tonumber = tonumber
local next = next
local nodes, node, fonts = nodes, node, fonts
local find_node_tail = node.tail or node.slide
local free_node = node.free
local copy_node = node.copy
local new_node = node.new
local insert_node_before = node.insert_before
local nodepool = nodes.pool
local new_kern = nodepool.kern
local new_glue = nodepool.glue
local nodecodes = nodes.nodecodes
local glyph_code = nodecodes.glyph
local kern_code = nodecodes.kern
local disc_code = nodecodes.disc
local math_code = nodecodes.math
local fonthashes = fonts.hashes
local chardata = fonthashes.characters
local quaddata = fonthashes.quads
local otffeatures = fonts.constructors.newfeatures "otf"
--[[doc--
Since the letterspacing method was derived initially from Context’s
typo-krn.lua we keep the sub-namespace “letterspace” inside the
“luaotfload” table.
--doc]]--
luaotfload.letterspace = luaotfload.letterspace or { }
local letterspace = luaotfload.letterspace
letterspace.keepligature = false
letterspace.keeptogether = false
---=================================================================---
--- preliminary definitions
---=================================================================---
-- We set up a layer emulating some Context internals that are needed
-- for the letterspacing callback.
-----------------------------------------------------------------------
--- node-ini
-----------------------------------------------------------------------
local bothways = function (t) return table.swapped (t, t) end
local kerncodes = bothways { [0] = "fontkern"
, [1] = "userkern"
, [2] = "accentkern"
}
kerncodes.kerning = kerncodes.fontkern --- idiosyncrasy
local kerning_code = kerncodes.kerning
local userkern_code = kerncodes.userkern
-----------------------------------------------------------------------
--- node-res
-----------------------------------------------------------------------
nodes.pool = nodes.pool or { }
local pool = nodes.pool
local kern = new_node ("kern", kerncodes.userkern)
local glue_spec = new_node "glue_spec"
pool.kern = function (k)
local n = copy_node (kern)
n.kern = k
return n
end
pool.glue = function (width, stretch, shrink,
stretch_order, shrink_order)
local n = new_node"glue"
if not width then
-- no spec
elseif width == false or tonumber(width) then
local s = copy_node(glue_spec)
if width then s.width = width end
if stretch then s.stretch = stretch end
if shrink then s.shrink = shrink end
if stretch_order then s.stretch_order = stretch_order end
if shrink_order then s.shrink_order = shrink_order end
n.spec = s
else
-- shared
n.spec = copy_node(width)
end
return n
end
-----------------------------------------------------------------------
--- font-hsh
-----------------------------------------------------------------------
--- some initialization resembling font-hsh
local fonthashes = fonts.hashes
local identifiers = fonthashes.identifiers --- was: fontdata
local chardata = fonthashes.characters
local quaddata = fonthashes.quads
local parameters = fonthashes.parameters
--- ('a, 'a) hash -> (('a, 'a) hash -> 'a -> 'a) -> ('a, 'a) hash
local setmetatableindex = function (t, f)
local mt = getmetatable(t)
if mt then
mt.__index = f
else
setmetatable(t, { __index = f })
end
return t
end
if not parameters then
parameters = { }
setmetatableindex(parameters, function(t, k)
if k == true then
return parameters[currentfont()]
else
local parameters = identifiers[k].parameters
t[k] = parameters
return parameters
end
end)
--fonthashes.parameters = parameters
end
if not chardata then
chardata = { }
setmetatableindex(chardata, function(t, k)
if k == true then
return chardata[currentfont()]
else
local tfmdata = identifiers[k]
if not tfmdata then --- unsafe
tfmdata = font.fonts[k]
end
if tfmdata then
local characters = tfmdata.characters
t[k] = characters
return characters
end
end
end)
fonthashes.characters = chardata
end
if not quaddata then
quaddata = { }
setmetatableindex(quaddata, function(t, k)
if k == true then
return quads[currentfont()]
else
local parameters = parameters[k]
local quad = parameters and parameters.quad or 0
t[k] = quad
return quad
end
end)
--fonthashes.quads = quaddata
end
---=================================================================---
--- character kerning functionality
---=================================================================---
local kern_injector = function (fillup, kern)
if fillup then
local g = new_glue(kern)
local s = g.spec
s.stretch = kern
s.stretch_order = 1
return g
else
return new_kern(kern)
end
end
--[[doc--
Caveat lector.
This is an adaptation of the Context character kerning mechanism
that emulates XeTeX-style fontwise letterspacing. Note that in its
present state it is far inferior to the original, which is
attribute-based and ignores font-boundaries. Nevertheless, due to
popular demand the following callback has been added.
--doc]]--
local kernfactors = { } --- fontid -> factor
local kerncharacters
kerncharacters = function (head)
local start, done = head, false
local lastfont = nil
local keepligature = letterspace.keepligature --- function
local keeptogether = letterspace.keeptogether --- function
local fillup = false
local identifiers = fonthashes.identifiers
local kernfactors = kernfactors
local firstkern = true
while start do
local id = start.id
if id == glyph_code then
--- 1) look up kern factor (slow, but cached rudimentarily)
local krn
local fontid = start.font
do
krn = kernfactors[fontid]
if not krn then
local tfmdata = identifiers[fontid]
if not tfmdata then -- unsafe
tfmdata = font.fonts[fontid]
end
if tfmdata then
fontproperties = tfmdata.properties
if fontproperties then
krn = fontproperties.kerncharacters
end
end
kernfactors[fontid] = krn
end
if not krn or krn == 0 then
firstkern = true
goto nextnode
elseif firstkern then
firstkern = false
if (id ~= disc_code) and (not start.components) then
--- not a ligature, skip node
goto nextnode
end
end
end
if krn == "max" then
krn = .25
fillup = true
else
fillup = false
end
lastfont = fontid
--- 2) resolve ligatures
local c = start.components
if c then
if keepligature and keepligature(start) then
-- keep 'm
else
--- c = kerncharacters (c) --> taken care of after replacing
local s = start
local p, n = s.prev, s.next
local tail = find_node_tail(c)
if p then
p.next = c
c.prev = p
else
head = c
end
if n then
n.prev = tail
end
tail.next = n
start = c
s.components = nil
-- we now leak nodes !
-- free_node(s)
done = true
end
end -- kern ligature
--- 3) apply the extra kerning
local prev = start.prev
if prev then
local pid = prev.id
if not pid then
-- nothing
elseif pid == kern_code then
if prev.subtype == kerning_code --- context does this by means of an
or prev.subtype == userkern_code --- attribute; we may need a test
then
if keeptogether and prev.prev.id == glyph_code and keeptogether(prev.prev,start) then
-- keep
else
prev.subtype = userkern_code
prev.kern = prev.kern + quaddata[lastfont]*krn -- here
done = true
end
end
elseif pid == glyph_code then
if prev.font == lastfont then
local prevchar, lastchar = prev.char, start.char
if keeptogether and keeptogether(prev,start) then
-- keep 'm
elseif identifiers[lastfont] then
local kerns = chardata[lastfont][prevchar].kerns
local kern = kerns and kerns[lastchar] or 0
krn = kern + quaddata[lastfont]*krn -- here
insert_node_before(head,start,kern_injector(fillup,krn))
done = true
end
else
krn = quaddata[lastfont]*krn -- here
insert_node_before(head,start,kern_injector(fillup,krn))
done = true
end
elseif pid == disc_code then
-- a bit too complicated, we can best not copy and just calculate
-- but we could have multiple glyphs involved so ...
local disc = prev -- disc
local pre, post, replace = disc.pre, disc.post, disc.replace
local prv, nxt = disc.prev, disc.next
if pre and prv then -- must pair with start.prev
-- this one happens in most cases
local before = copy_node(prv)
pre.prev = before
before.next = pre
before.prev = nil
pre = kerncharacters (before)
pre = pre.next
pre.prev = nil
disc.pre = pre
free_node(before)
end
if post and nxt then -- must pair with start
local after = copy_node(nxt)
local tail = find_node_tail(post)
tail.next = after
after.prev = tail
after.next = nil
post = kerncharacters (post)
tail.next = nil
disc.post = post
free_node(after)
end
if replace and prv and nxt then -- must pair with start and start.prev
local before = copy_node(prv)
local after = copy_node(nxt)
local tail = find_node_tail(replace)
replace.prev = before
before.next = replace
before.prev = nil
tail.next = after
after.prev = tail
after.next = nil
replace = kerncharacters (before)
replace = replace.next
replace.prev = nil
after.prev.next = nil
disc.replace = replace
free_node(after)
free_node(before)
elseif identifiers[lastfont] then
if prv and prv.id == glyph_code and prv.font == lastfont then
local prevchar, lastchar = prv.char, start.char
local kerns = chardata[lastfont][prevchar].kerns
local kern = kerns and kerns[lastchar] or 0
krn = kern + quaddata[lastfont]*krn -- here
else
krn = quaddata[lastfont]*krn -- here
end
disc.replace = kern_injector(false,krn) -- only kerns permitted, no glue
end
end
end
end
::nextnode::
if start then
start = start.next
end
end
return head, done
end
---=================================================================---
--- integration
---=================================================================---
--- · callback: kerncharacters
--- · enabler: enablefontkerning
--- · disabler: disablefontkerning
--- callback wrappers
--- (node_t -> node_t) -> string -> string list -> bool
local registered_as = { } --- procname -> callbacks
local add_processor = function (processor, name, ...)
local callbacks = { ... }
for i=1, #callbacks do
luatexbase.add_to_callback(callbacks[i], processor, name)
end
registered_as[name] = callbacks --- for removal
return true
end
--- string -> bool
local remove_processor = function (name)
local callbacks = registered_as[name]
if callbacks then
for i=1, #callbacks do
luatexbase.remove_from_callback(callbacks[i], name)
end
return true
end
return false --> unregistered
end
--- now for the simplistic variant
--- unit -> bool
local enablefontkerning = function ( )
return add_processor( kerncharacters
, "luaotfload.letterspace"
, "pre_linebreak_filter"
, "hpack_filter")
end
--- unit -> bool
local disablefontkerning = function ( )
return remove_processor "luaotfload.letterspace"
end
--[[doc--
Fontwise kerning is enabled via the “kernfactor” option at font
definition time. Unlike the Context implementation which relies on
Luatex attributes, it uses a font property for passing along the
letterspacing factor of a node.
The callback is activated the first time a letterspaced font is
requested and stays active until the end of the run. Since the font
is a property of individual glyphs, every glyph in the entire
document must be checked for the kern property. This is quite
inefficient compared to Context’s attribute based approach, but Xetex
compatibility reduces our options significantly.
--doc]]--
local fontkerning_enabled = false --- callback state
--- fontobj -> float -> unit
local initializefontkerning = function (tfmdata, factor)
if factor ~= "max" then
factor = tonumber (factor) or 0
end
if factor == "max" or factor ~= 0 then
local fontproperties = tfmdata.properties
if fontproperties then
--- hopefully this field stays unused otherwise
fontproperties.kerncharacters = factor
end
if not fontkerning_enabled then
fontkerning_enabled = enablefontkerning ()
end
end
end
--- like the font colorization, fontwise kerning is hooked into the
--- feature mechanism
otffeatures.register {
name = "kernfactor",
description = "kernfactor",
initializers = {
base = initializefontkerning,
node = initializefontkerning,
}
}
--[[doc--
The “letterspace” feature is essentially identical with the above
“kernfactor” method, but scales the factor to percentages to match
Xetex’s behavior. (See the Xetex reference, page 5, section 1.2.2.)
Since Xetex doesn’t appear to have a (documented) “max” keyword, we
assume all input values are numeric.
--doc]]--
local initializecompatfontkerning = function (tfmdata, percentage)
local factor = tonumber (percentage)
if not factor then
logs.names_report ("both", 0, "letterspace",
"Invalid argument to letterspace: %s (type %q), " ..
"was expecting percentage as Lua number instead.",
percentage, type (percentage))
return
end
return initializefontkerning (tfmdata, factor * 0.01)
end
otffeatures.register {
name = "letterspace",
description = "letterspace",
initializers = {
base = initializecompatfontkerning,
node = initializecompatfontkerning,
}
}
--[[example--
See https://bitbucket.org/phg/lua-la-tex-tests/src/tip/pln-letterspace-8-compare.tex
for an example.
--example]]--
--- vim:sw=2:ts=2:expandtab:tw=71