add font-dependent letterspacing

1 files changed, 254 insertions, 0 deletions

diff --git a/luaotfload-letterspace.lua b/luaotfload-letterspace.lua
new file mode 100644
index 0000000..fabf62b
--- /dev/null
+++ b/luaotfload-letterspace.lua
@@ -0,0 +1,254 @@
+if not modules then modules = { } end modules ['typo-krn'] = {
+    version   = 1.001,
+    comment   = "companion to typo-krn.mkiv",
+    author    = "Hans Hagen, PRAGMA-ADE, Hasselt NL",
+    copyright = "PRAGMA ADE / ConTeXt Development Team",
+    license   = "see context related readme files"
+}
+
+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 free_nodelist      = node.flush_list
+local copy_node          = node.copy
+local copy_nodelist      = node.copy_list
+local insert_node_before = node.insert_before
+local insert_node_after  = node.insert_after
+
+local nodepool           = nodes.pool
+local tasks              = nodes.tasks
+
+local new_kern           = nodepool.kern
+local new_glue           = nodepool.glue
+
+local nodecodes          = nodes.nodecodes
+local kerncodes          = nodes.kerncodes
+local skipcodes          = nodes.skipcodes
+
+local glyph_code         = nodecodes.glyph
+local kern_code          = nodecodes.kern
+local disc_code          = nodecodes.disc
+local glue_code          = nodecodes.glue
+local hlist_code         = nodecodes.hlist
+local vlist_code         = nodecodes.vlist
+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
+
+typesetters              = typesetters or { }
+local typesetters        = typesetters
+
+typesetters.kernfont     = typesetters.kernfont or { }
+local kernfont           = typesetters.kernfont
+
+kernfont.keepligature    = false
+kernfont.keeptogether    = false
+
+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
+
+local kernfactors = { } --- fontid -> factor
+
+local kerncharacters
+kerncharacters = function (head)
+  local start, done   = head, false
+  local lastfont      = nil
+  local keepligature  = kernfont.keepligature --- function
+  local keeptogether  = kernfont.keeptogether --- function
+  local fillup        = false
+
+  local identifiers   = fonthashes.identifiers
+  local kernfactors   = kernfactors
+
+  while start do
+    local attr = start[attribute]
+    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
+          goto nextnode
+        end
+      end
+
+      if krn == "max" then
+        krn = .25
+        fillup = true
+      else
+        fillup = false
+      end
+
+      lastfont = fontid
+      local c = start.components
+
+      if c then
+        if keepligature and keepligature(start) then
+          -- keep 'm
+        else
+          c = kerncharacters (c)
+          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
+
+      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 or prev[a_fontkern] then
+            if keeptogether and prev.prev.id == glyph_code and keeptogether(prev.prev,start) then -- we could also pass start
+              -- keep 'm
+            else
+              -- not yet ok, as injected kerns can be overlays (from node-inj.lua)
+              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
+
+kernfont.handler = kerncharacters
+
+--- vim:sw=2:ts=2:expandtab
+