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-rw-r--r--luaotfload-letterspace.lua276
1 files changed, 270 insertions, 6 deletions
diff --git a/luaotfload-letterspace.lua b/luaotfload-letterspace.lua
index 978029f..aa89651 100644
--- a/luaotfload-letterspace.lua
+++ b/luaotfload-letterspace.lua
@@ -6,12 +6,18 @@ if not modules then modules = { } end modules ['letterspace'] = {
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
@@ -20,30 +26,167 @@ local new_kern = nodepool.kern
local new_glue = nodepool.glue
local nodecodes = nodes.nodecodes
-local kerncodes = nodes.kerncodes
local glyph_code = nodecodes.glyph
local kern_code = nodecodes.kern
local disc_code = nodecodes.disc
local math_code = nodecodes.math
-local kerning_code = kerncodes.kerning
-local userkern_code = kerncodes.userkern
-
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 “typesetters” inside the
+ “luaotfload” table.
+
+--doc]]--
luaotfload.typesetters = luaotfload.typesetters or { }
local typesetters = luaotfload.typesetters
-
typesetters.kernfont = typesetters.kernfont or { }
local kernfont = typesetters.kernfont
kernfont.keepligature = false
kernfont.keeptogether = false
-local kern_injector = function (fillup,kern)
+---=================================================================---
+--- preliminary definitions
+---=================================================================---
+-- We set up a layer emulating some Context internals that are needed
+-- for the letterspacing callback.
+-----------------------------------------------------------------------
+--- node-ini
+-----------------------------------------------------------------------
+
+nodes = nodes or { } --- should be present with luaotfload
+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
@@ -267,5 +410,126 @@ end
kernfont.handler = kerncharacters
+---=================================================================---
+--- integration
+---=================================================================---
+
+--- kernfont_callback : fontwise
+--- · callback: kernfont.handler
+--- · 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( kernfont.handler
+ , "typesetters.kernfont"
+ , "pre_linebreak_filter"
+ , "hpack_filter")
+end
+
+--- unit -> bool
+local disablefontkerning = function ( )
+ return remove_processor "typesetters.kernfont"
+end
+
+--- fontwise kerning uses a font property for passing along the
+--- letterspacing factor
+
+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