Skip redundant fonts returned by FontFallbackIterator

third_party/WebKit/Source/platform/fonts/FontFallbackIterator.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef FontFallbackIterator_h
 #define FontFallbackIterator_h
 
 #include "platform/fonts/FontDataForRangeSet.h"
 #include "platform/fonts/FontFallbackPriority.h"
 #include "wtf/HashMap.h"
@@ skipping 12 matching lines @@
 class SimpleFontData;
 class FontFamily;
 
 class FontFallbackIterator : public RefCounted<FontFallbackIterator> {
     WTF_MAKE_NONCOPYABLE(FontFallbackIterator);
 
 public:
     static PassRefPtr<FontFallbackIterator> create(const FontDescription&, PassRefPtr<FontFallbackList>,
         FontFallbackPriority);
 
-    // Returns whether a list of all remaining characters to be shaped is
-    // needed.  Needed by the FontfallbackIterator in order to check whether a
-    // font from a segmented range should be loaded.
-    bool needsHintList() const;
-
     bool hasNext() const { return m_fallbackStage != OutOfLuck; };
 
     // Some system fallback APIs (Windows, Android) require a character, or a
     // portion of the string to be passed.  On Mac and Linux, we get a list of
     // fonts without passing in characters.
     const PassRefPtr<FontDataForRangeSet> next(const Vector<UChar32>& hintList);
 
 private:
     FontFallbackIterator(const FontDescription&, PassRefPtr<FontFallbackList>,
         FontFallbackPriority);
     bool rangeSetContributesForHint(const Vector<UChar32> hintList, const FontDataForRangeSet*);
     bool alreadyLoadingRangeForHintChar(UChar32 hintChar);
     void willUseRange(const AtomicString& family, const FontDataForRangeSet&);
 
+    const PassRefPtr<FontDataForRangeSet> uniqueOrNext(PassRefPtr<FontDataForRangeSet> candidate, const Vector<UChar32>& hintList);
+
     const PassRefPtr<SimpleFontData> fallbackPriorityFont(UChar32 hint);
     const PassRefPtr<SimpleFontData> uniqueSystemFontForHint(UChar32 hint);
 
     const FontDescription& m_fontDescription;
     RefPtr<FontFallbackList> m_fontFallbackList;
     int m_currentFontDataIndex;
     unsigned m_segmentedFaceIndex;
 
     enum FallbackStage {
         FallbackPriorityFonts,
         FontGroupFonts,
         SegmentedFace,
         PreferencesFonts,
         SystemFonts,
         OutOfLuck
     };
 
     FallbackStage m_fallbackStage;
     HashSet<UChar32> m_previouslyAskedForHint;
+    // FontFallbackIterator is meant for single use by HarfBuzzShaper,
+    // traversing through the fonts for shaping only once. We must not return
+    // duplicate FontDataForRangeSet objects from the next() iteration functions
+    // as returning a duplicate value causes a shaping run that won't return any
+    // results.
+    HashSet<uint32_t> m_uniqueFontDataForRangeSetsReturned;
     Vector<RefPtr<FontDataForRangeSet>> m_trackedLoadingRangeSets;
     FontFallbackPriority m_fontFallbackPriority;
 };
 
 } // namespace blink
 
 #endif