Implement TrueType kerning support for HarfBuzz text path.

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

Index: Source/core/platform/graphics/harfbuzz/HarfBuzzFaceSkia.cpp
diff --git a/Source/core/platform/graphics/harfbuzz/HarfBuzzFaceSkia.cpp b/Source/core/platform/graphics/harfbuzz/HarfBuzzFaceSkia.cpp
index 961707a3f82e6c73013a4bd0ebfb46de52ff2aee..2619edb83d0aa8cee2de930b3004bed6bf06b7f4 100644
--- a/Source/core/platform/graphics/harfbuzz/HarfBuzzFaceSkia.cpp
+++ b/Source/core/platform/graphics/harfbuzz/HarfBuzzFaceSkia.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
@@ -117,6 +118,50 @@ static hb_bool_t harfBuzzGetGlyphHorizontalOrigin(hb_font_t* hbFont, void* fontD
     return true;
 }
 
+static hb_position_t harfBuzzGetGlyphHorizontalKerning(hb_font_t*, void* fontData, hb_codepoint_t leftGlyph, hb_codepoint_t rightGlyph, void*)
+{
+    HarfBuzzFontData* hbFontData = reinterpret_cast<HarfBuzzFontData*>(fontData);
+    if (hbFontData->m_paint.isVerticalText()) {
+        // We don't support cross-stream kerning
+        return 0;
+    }
+
+    SkTypeface* typeface = hbFontData->m_paint.getTypeface();
+
+    const uint16_t glyphs[2] = { leftGlyph, rightGlyph };
+    int32_t kerningAdjustments[1] = { 0 };
+
+    if (typeface->getKerningPairAdjustments(glyphs, 2, kerningAdjustments)) {
+        SkScalar upm = SkIntToScalar(typeface->getUnitsPerEm());
+        SkScalar size = hbFontData->m_paint.getTextSize();
+        return SkiaScalarToHarfBuzzPosition(SkScalarMulDiv(SkIntToScalar(kerningAdjustments[0]), size, upm));
+    }
+
+    return 0;
+}
+
+static hb_position_t harfBuzzGetGlyphVerticalKerning(hb_font_t*, void* fontData, hb_codepoint_t topGlyph, hb_codepoint_t bottomGlyph, void*)
+{
+    HarfBuzzFontData* hbFontData = reinterpret_cast<HarfBuzzFontData*>(fontData);
+    if (!hbFontData->m_paint.isVerticalText()) {
+        // We don't support cross-stream kerning
+        return 0;
+    }
+
+    SkTypeface* typeface = hbFontData->m_paint.getTypeface();
+
+    const uint16_t glyphs[2] = { topGlyph, bottomGlyph };
+    int32_t kerningAdjustments[1] = { 0 };
+
+    if (typeface->getKerningPairAdjustments(glyphs, 2, kerningAdjustments)) {
+        SkScalar upm = SkIntToScalar(typeface->getUnitsPerEm());
+        SkScalar size = hbFontData->m_paint.getTextSize();
+        return SkiaScalarToHarfBuzzPosition(SkScalarMulDiv(SkIntToScalar(kerningAdjustments[0]), size, upm));
+    }
+
+    return 0;
+}
+
 static hb_bool_t harfBuzzGetGlyphExtents(hb_font_t* hbFont, void* fontData, hb_codepoint_t glyph, hb_glyph_extents_t* extents, void* userData)
 {
     HarfBuzzFontData* hbFontData = reinterpret_cast<HarfBuzzFontData*>(fontData);
@@ -125,9 +170,24 @@ static hb_bool_t harfBuzzGetGlyphExtents(hb_font_t* hbFont, void* fontData, hb_c
     return true;
 }
 
-static hb_font_funcs_t* harfBuzzSkiaGetFontFuncs()
+static hb_font_funcs_t* harfBuzzSkiaGetFontFuncs(const TypesettingFeatures& features)
 {
     static hb_font_funcs_t* harfBuzzSkiaFontFuncs = 0;
+    static hb_font_funcs_t* harfBuzzSkiaFontFuncsWithKerning = 0; // includes TrueType ("kern" table) kerning
+
+    if (features & Kerning) {
+        if (!harfBuzzSkiaFontFuncsWithKerning) {
+            harfBuzzSkiaFontFuncsWithKerning = hb_font_funcs_create();
+            hb_font_funcs_set_glyph_func(harfBuzzSkiaFontFuncsWithKerning, harfBuzzGetGlyph, 0, 0);
+            hb_font_funcs_set_glyph_h_advance_func(harfBuzzSkiaFontFuncsWithKerning, harfBuzzGetGlyphHorizontalAdvance, 0, 0);
+            hb_font_funcs_set_glyph_h_kerning_func(harfBuzzSkiaFontFuncsWithKerning, harfBuzzGetGlyphHorizontalKerning, 0, 0);
+            hb_font_funcs_set_glyph_h_origin_func(harfBuzzSkiaFontFuncsWithKerning, harfBuzzGetGlyphHorizontalOrigin, 0, 0);
+            hb_font_funcs_set_glyph_v_kerning_func(harfBuzzSkiaFontFuncsWithKerning, harfBuzzGetGlyphVerticalKerning, 0, 0);
+            hb_font_funcs_set_glyph_extents_func(harfBuzzSkiaFontFuncsWithKerning, harfBuzzGetGlyphExtents, 0, 0);
+            hb_font_funcs_make_immutable(harfBuzzSkiaFontFuncsWithKerning);
+        }
+        return harfBuzzSkiaFontFuncsWithKerning;

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

This is the wrong approach to control kerning.

+    }
 
     // We don't set callback functions which we can't support.
     // HarfBuzz will use the fallback implementation if they aren't set.
@@ -175,12 +235,12 @@ hb_face_t* HarfBuzzFace::createFace()
     return face;
 }
 
-hb_font_t* HarfBuzzFace::createFont()
+hb_font_t* HarfBuzzFace::createFont(const TypesettingFeatures& features)
 {
     HarfBuzzFontData* hbFontData = new HarfBuzzFontData(m_glyphCacheForFaceCacheEntry);
     m_platformData->setupPaint(&hbFontData->m_paint);
     hb_font_t* font = hb_font_create(m_face);
-    hb_font_set_funcs(font, harfBuzzSkiaGetFontFuncs(), hbFontData, destroyHarfBuzzFontData);
+    hb_font_set_funcs(font, harfBuzzSkiaGetFontFuncs(features), hbFontData, destroyHarfBuzzFontData);
     float size = m_platformData->size();
     int scale = SkiaScalarToHarfBuzzPosition(size);
     hb_font_set_scale(font, scale, scale);