Add Unicode Variation Selector support to harfBuzzGetGlyph

Source/platform/fonts/shaping/HarfBuzzFace.cpp

 /*
  * Copyright (c) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 125 matching lines @@
 }
 
 void HarfBuzzFace::setScriptForVerticalGlyphSubstitution(hb_buffer_t* buffer)
 {
     if (m_scriptForVerticalText == HB_SCRIPT_INVALID)
         m_scriptForVerticalText = findScriptForVerticalGlyphSubstitution(m_face);
     hb_buffer_set_script(buffer, m_scriptForVerticalText);
 }
 
 struct HarfBuzzFontData {
-    HarfBuzzFontData(WTF::HashMap<uint32_t, uint16_t>* glyphCacheForFaceCacheEntry)
+    HarfBuzzFontData(WTF::HashMap<uint32_t, uint16_t>* glyphCacheForFaceCacheEntry, hb_face_t* face)
         : m_glyphCacheForFaceCacheEntry(glyphCacheForFaceCacheEntry)
+        , m_face(face)
+        , m_hbOpenTypeFont(nullptr)
     { }
+
+    ~HarfBuzzFontData()
+    {
+        if (m_hbOpenTypeFont)
+            hb_font_destroy(m_hbOpenTypeFont);
+    }
+
     SkPaint m_paint;
     RefPtr<SimpleFontData> m_simpleFontData;
     WTF::HashMap<uint32_t, uint16_t>* m_glyphCacheForFaceCacheEntry;
+    hb_face_t* m_face;
+    hb_font_t* m_hbOpenTypeFont;
 };
 
 static hb_position_t SkiaScalarToHarfBuzzPosition(SkScalar value)
 {
     return SkScalarToFixed(value);
 }
 
 static void SkiaGetGlyphWidthAndExtents(SkPaint* paint, hb_codepoint_t codepoint, hb_position_t* width, hb_glyph_extents_t* extents)
 {
     ASSERT(codepoint <= 0xFFFF);
@@ skipping 10 matching lines @@
         // Invert y-axis because Skia is y-grows-down but we set up HarfBuzz to be y-grows-up.
         extents->x_bearing = SkiaScalarToHarfBuzzPosition(skBounds.fLeft);
         extents->y_bearing = SkiaScalarToHarfBuzzPosition(-skBounds.fTop);
         extents->width = SkiaScalarToHarfBuzzPosition(skBounds.width());
         extents->height = SkiaScalarToHarfBuzzPosition(-skBounds.height());
     }
 }
 
 static hb_bool_t harfBuzzGetGlyph(hb_font_t* hbFont, void* fontData, hb_codepoint_t unicode, hb_codepoint_t variationSelector, hb_codepoint_t* glyph, void* userData)
 {
-    // Variation selectors not supported.
-    if (variationSelector)
+    HarfBuzzFontData* hbFontData = reinterpret_cast<HarfBuzzFontData*>(fontData);
+
+    if (variationSelector) {
+#if OS(LINUX)
+        // TODO(kojii): Linux non-official builds cannot use new HB APIs
+        // until crbug.com/462689 resolved or pangoft2 updates its HB.
         return false;
-
-    HarfBuzzFontData* hbFontData = reinterpret_cast<HarfBuzzFontData*>(fontData);
+#else
+        // Skia does not support variation selectors, but hb does.
+        // We're not fully ready to switch to hb-ot-font yet,
+        // but are good enough to get glyph IDs for OpenType fonts.
+        if (!hbFontData->m_hbOpenTypeFont) {
+            hbFontData->m_hbOpenTypeFont = hb_font_create(hbFontData->m_face);
+            hb_ot_font_set_funcs(hbFontData->m_hbOpenTypeFont);
+        }
+        return hb_font_get_glyph(hbFontData->m_hbOpenTypeFont, unicode, variationSelector, glyph);
+        // When not found, glyph_func should return false rather than fallback to the base.
+        // http://lists.freedesktop.org/archives/harfbuzz/2015-May/004888.html
+#endif
+    }
 
     WTF::HashMap<uint32_t, uint16_t>::AddResult result = hbFontData->m_glyphCacheForFaceCacheEntry->add(unicode, 0);
     if (result.isNewEntry) {
         SkPaint* paint = &hbFontData->m_paint;
         paint->setTextEncoding(SkPaint::kUTF32_TextEncoding);
         uint16_t glyph16;
         paint->textToGlyphs(&unicode, sizeof(hb_codepoint_t), &glyph16);
         result.storedValue->value = glyph16;
         *glyph = glyph16;
     }
@@ skipping 129 matching lines @@
     hb_face_t* face = hb_coretext_face_create(m_platformData->cgFont());
 #else
     hb_face_t* face = hb_face_create_for_tables(harfBuzzSkiaGetTable, m_platformData->typeface(), 0);
 #endif
     ASSERT(face);
     return face;
 }
 
 hb_font_t* HarfBuzzFace::createFont()
 {
-    HarfBuzzFontData* hbFontData = new HarfBuzzFontData(m_glyphCacheForFaceCacheEntry);
+    HarfBuzzFontData* hbFontData = new HarfBuzzFontData(m_glyphCacheForFaceCacheEntry, m_face);
     m_platformData->setupPaint(&hbFontData->m_paint);
     hbFontData->m_simpleFontData = FontCache::fontCache()->fontDataFromFontPlatformData(m_platformData);
     ASSERT(hbFontData->m_simpleFontData);
     hb_font_t* font = hb_font_create(m_face);
     hb_font_set_funcs(font, harfBuzzSkiaGetFontFuncs(), hbFontData, destroyHarfBuzzFontData);
     float size = m_platformData->size();
     int scale = SkiaScalarToHarfBuzzPosition(size);
     hb_font_set_scale(font, scale, scale);
     hb_font_make_immutable(font);
     return font;
 }
 
 } // namespace blink