Implement TrueType kerning support for HarfBuzz text path.

Source/core/platform/graphics/harfbuzz/HarfBuzzShaper.cpp

Index: Source/core/platform/graphics/harfbuzz/HarfBuzzShaper.cpp
diff --git a/Source/core/platform/graphics/harfbuzz/HarfBuzzShaper.cpp b/Source/core/platform/graphics/harfbuzz/HarfBuzzShaper.cpp
index e297fe4e220e688875b5bb8cfee54752ed2e37c0..f2e17b803a0a38c1a3961dd21d6be5ff90d851c1 100644
--- a/Source/core/platform/graphics/harfbuzz/HarfBuzzShaper.cpp
+++ b/Source/core/platform/graphics/harfbuzz/HarfBuzzShaper.cpp
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2012 Google Inc. All rights reserved.
+ * Copyright (C) 2013 BlackBerry Limited. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
@@ -49,6 +50,12 @@
 
 namespace WebCore {
 
+const hb_tag_t cligTag = HB_TAG('c', 'l', 'i', 'g');
+const hb_tag_t dligTag = HB_TAG('d', 'l', 'i', 'g');
+const hb_tag_t hligTag = HB_TAG('h', 'l', 'i', 'g');
+const hb_tag_t kernTag = HB_TAG('k', 'e', 'r', 'n');
+const hb_tag_t ligaTag = HB_TAG('l', 'i', 'g', 'a');
+
 template<typename T>
 class HarfBuzzScopedPtr {
 public:
@@ -508,6 +515,71 @@ void HarfBuzzShaper::setFontFeatures()
         m_features.append(vrt2);
     }
 
+    static hb_feature_t kern = { kernTag, 1, 0, static_cast<unsigned>(-1) };
+    static hb_feature_t noKern = { kernTag, 0, 0, static_cast<unsigned>(-1) };
+    if (!(m_font->typesettingFeatures() & Kerning)) {
+        m_features.append(noKern);
+    } else {
+        switch (description.kerning()) {
+        case FontDescription::NormalKerning:
+            m_features.append(kern);
+            break;
+        case FontDescription::NoneKerning:
+            m_features.append(noKern);
+            break;
+        case FontDescription::AutoKerning:
+            break;
+        }
+    }
+
+    static hb_feature_t liga = { ligaTag, 1, 0, static_cast<unsigned>(-1) };
+    static hb_feature_t noLiga = { ligaTag, 0, 0, static_cast<unsigned>(-1) };
+    static hb_feature_t clig = { cligTag, 1, 0, static_cast<unsigned>(-1) };
+    static hb_feature_t noClig = { cligTag, 0, 0, static_cast<unsigned>(-1) };
+    static hb_feature_t dlig = { dligTag, 1, 0, static_cast<unsigned>(-1) };
+    static hb_feature_t noDlig = { dligTag, 0, 0, static_cast<unsigned>(-1) };
+    static hb_feature_t hlig = { hligTag, 1, 0, static_cast<unsigned>(-1) };
+    static hb_feature_t noHlig = { hligTag, 0, 0, static_cast<unsigned>(-1) };
+    if (!(m_font->typesettingFeatures() & Ligatures)) {
+        m_features.append(noLiga);
+        m_features.append(noClig);
+        m_features.append(noDlig);
+        m_features.append(noHlig);
+    } else {
+        switch (description.commonLigaturesState()) {
+        case FontDescription::DisabledLigaturesState:
+            m_features.append(noLiga);
+            m_features.append(noClig);
+            break;
+        case FontDescription::EnabledLigaturesState:
+            m_features.append(liga);

[behdad_google, 2013/11/15 16:26:35]

Don't append features that are enabled by default.  This pollutes harfbuzz's
internal caches unnecessarily.

+            m_features.append(clig);
+            break;
+        case FontDescription::NormalLigaturesState:
+            break;
+        }
+        switch (description.discretionaryLigaturesState()) {
+        case FontDescription::DisabledLigaturesState:
+            m_features.append(noDlig);
+            break;
+        case FontDescription::EnabledLigaturesState:
+            m_features.append(dlig);
+            break;
+        case FontDescription::NormalLigaturesState:
+            break;
+        }
+        switch (description.historicalLigaturesState()) {
+        case FontDescription::DisabledLigaturesState:
+            m_features.append(noHlig);
+            break;
+        case FontDescription::EnabledLigaturesState:
+            m_features.append(hlig);
+            break;
+        case FontDescription::NormalLigaturesState:
+            break;
+        }
+    }
+
     FontFeatureSettings* settings = description.featureSettings();
     if (!settings)
         return;
@@ -687,7 +759,7 @@ bool HarfBuzzShaper::shapeHarfBuzzRuns(bool shouldSetDirection)
         if (m_font->fontDescription().orientation() == Vertical)
             face->setScriptForVerticalGlyphSubstitution(harfBuzzBuffer.get());
 
-        HarfBuzzScopedPtr<hb_font_t> harfBuzzFont(face->createFont(), hb_font_destroy);
+        HarfBuzzScopedPtr<hb_font_t> harfBuzzFont(face->createFont(m_font->typesettingFeatures()), hb_font_destroy);
 
         hb_shape(harfBuzzFont.get(), harfBuzzBuffer.get(), m_features.isEmpty() ? 0 : m_features.data(), m_features.size());
         currentRun->applyShapeResult(harfBuzzBuffer.get());