From 7b271baae19db1528fbe6621bdf50af89a5a336b Mon Sep 17 00:00:00 2001
From: Hans Hagen <pragma@wxs.nl>
Date: Fri, 22 Feb 2019 20:29:46 +0100
Subject: 2019-02-22 19:43:00

---
 tex/context/base/mkiv/font-imp-ligatures.lua | 136 +++++++++++++++++++++++++++
 1 file changed, 136 insertions(+)
 create mode 100644 tex/context/base/mkiv/font-imp-ligatures.lua

(limited to 'tex/context/base/mkiv/font-imp-ligatures.lua')

diff --git a/tex/context/base/mkiv/font-imp-ligatures.lua b/tex/context/base/mkiv/font-imp-ligatures.lua
new file mode 100644
index 000000000..091eb5d4b
--- /dev/null
+++ b/tex/context/base/mkiv/font-imp-ligatures.lua
@@ -0,0 +1,136 @@
+if not modules then modules = { } end modules ['font-imp-ligatures'] = {
+    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 lpegmatch = lpeg.match
+local utfsplit = utf.split
+local settings_to_array = utilities.parsers.settings_to_array
+
+local fonts              = fonts
+local otf                = fonts.handlers.otf
+local registerotffeature = otf.features.register
+local addotffeature      = otf.addfeature
+
+-- This is a quick and dirty hack.
+
+local lookups = { }
+local protect = { }
+local revert  = { }
+local zwjchar = 0x200C
+local zwj     = { zwjchar }
+
+addotffeature {
+    name    = "blockligatures",
+    type    = "chainsubstitution",
+    nocheck = true, -- because there is no 0x200C in the font
+    prepend = true, -- make sure we do it early
+    future  = true, -- avoid nilling due to no steps yet
+    lookups = {
+        {
+            type = "multiple",
+            data = lookups,
+        },
+    },
+    data = {
+        rules = protect,
+    }
+}
+
+addotffeature {
+    name     = "blockligatures",
+    type     = "chainsubstitution",
+    nocheck  = true,  -- because there is no 0x200C in the font
+    append   = true,  -- this is done late
+    overload = false, -- we don't want to overload the previous definition
+    lookups  = {
+        {
+            type = "ligature",
+            data = lookups,
+        },
+    },
+    data = {
+        rules = revert,
+    }
+}
+
+registerotffeature {
+    name        = 'blockligatures',
+    description = 'block certain ligatures',
+}
+
+local splitter = lpeg.splitat(":")
+
+local function blockligatures(str)
+
+    local t = settings_to_array(str)
+
+    for i=1,#t do
+        local ti = t[i]
+        local before, current, after = lpegmatch(splitter,ti)
+        if current and after then -- before is returned when no match
+            -- experimental joke
+            if before then
+                before = utfsplit(before)
+                for i=1,#before do
+                    before[i] = { before[i] }
+                end
+            end
+            if current then
+                current = utfsplit(current)
+            end
+            if after then
+                after = utfsplit(after)
+                for i=1,#after do
+                    after[i] = { after[i] }
+                end
+            end
+        else
+            before  = nil
+            current = utfsplit(ti)
+            after   = nil
+        end
+        if #current > 1 then
+            local one = current[1]
+            local two = current[2]
+            lookups[one] = { one, zwjchar }
+            local one = { one }
+            local two = { two }
+            local new = #protect + 1
+            protect[new] = {
+                before  = before,
+                current = { one, two },
+                after   = after,
+                lookups = { 1 }, -- not shared !
+            }
+            revert[new] = {
+             -- before = before,
+                current = { one, zwj },
+             -- after   = { two, unpack(after) },
+                after   = { two },
+                lookups = { 1 }, -- not shared !
+            }
+        end
+    end
+end
+
+-- blockligatures("\0\0")
+
+otf.helpers.blockligatures = blockligatures
+
+-- blockligatures("fi,ff")
+-- blockligatures("fl")
+-- blockligatures("u:fl:age")
+
+if context then
+
+    interfaces.implement {
+        name      = "blockligatures",
+        arguments = "string",
+        actions   = blockligatures,
+    }
+
+end
-- 
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