Skip redundant fonts returned by FontFallbackIterator

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

 // 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.
 
 #include "platform/fonts/FontFallbackIterator.h"
 
 #include "platform/Logging.h"
 #include "platform/fonts/FontCache.h"
 #include "platform/fonts/FontDescription.h"
 #include "platform/fonts/FontFallbackList.h"
@@ skipping 16 matching lines @@
     FontFallbackPriority fontFallbackPriority)
     : m_fontDescription(description)
     , m_fontFallbackList(fallbackList)
     , m_currentFontDataIndex(0)
     , m_segmentedFaceIndex(0)
     , m_fallbackStage(FontGroupFonts)
     , m_fontFallbackPriority(fontFallbackPriority)
 {
 }
 
-bool FontFallbackIterator::needsHintList() const
-{
-    if (m_fallbackStage != FontGroupFonts && m_fallbackStage != SegmentedFace) {
-        return false;
-    }
-
-    const FontData* fontData = m_fontFallbackList->fontDataAt(m_fontDescription, m_currentFontDataIndex);
-    return fontData && fontData->isSegmented();
-}
-
 bool FontFallbackIterator::alreadyLoadingRangeForHintChar(UChar32 hintChar)
 {
     for (auto it = m_trackedLoadingRangeSets.begin(); it != m_trackedLoadingRangeSets.end(); ++it) {
         if ((*it)->contains(hintChar))
             return true;
     }
     return false;
 }
 
 bool FontFallbackIterator::rangeSetContributesForHint(const Vector<UChar32> hintList, const FontDataForRangeSet* segmentedFace)
 {
     for (auto it = hintList.begin(); it != hintList.end(); ++it) {
         if (segmentedFace->contains(*it)) {
             if (!alreadyLoadingRangeForHintChar(*it))
                 return true;
         }
     }
     return false;
 }
 
 void FontFallbackIterator::willUseRange(const AtomicString& family, const FontDataForRangeSet& rangeSet)
 {
     FontSelector* selector = m_fontFallbackList->getFontSelector();
     if (!selector)
         return;
 
     selector->willUseRange(m_fontDescription, family, rangeSet);
 }
 
+const PassRefPtr<FontDataForRangeSet> FontFallbackIterator::uniqueOrNext(
+    PassRefPtr<FontDataForRangeSet> candidate,
+    const Vector<UChar32>& hintList) {
+    SkTypeface* candidateTypeface = candidate->fontData()->platformData().typeface();
+    if (!candidateTypeface)
+        return next(hintList);
+
+    uint32_t candidateId = candidateTypeface->uniqueID();
+    if (m_uniqueFontDataForRangeSetsReturned.contains(candidateId)) {

[behdad, 2016/08/15 21:09:19]

Shouldn't this be a while loop, skipping until something unseen is seen?

[drott, 2016/08/23 18:20:31]

Can you explain a bit more what you were expecting instead? I am using the
uniqueOrNext() as a wrapper for the return of the next() iterator call. If the
next() iterator has found a font, but filtering it in uniqueOrNext() finds that
this font has already been returned, we continue the recursion and call next()
to continue searching for a new font.

+        return next(hintList);
+    }
+
+    // We don't want to skip subsetted ranges because HarfBuzzShaper's behavior
+    // depends on the subsetting.
+    if (candidate->isEntireRange())
+        m_uniqueFontDataForRangeSetsReturned.add(candidateId);
+    return candidate;
+}
+
+
 const PassRefPtr<FontDataForRangeSet> FontFallbackIterator::next(const Vector<UChar32>& hintList)
 {
     if (m_fallbackStage == OutOfLuck)
         return adoptRef(new FontDataForRangeSet());
 
     if (m_fallbackStage == FallbackPriorityFonts) {
         // Only try one fallback priority font,
         // then proceed to regular system fallback.
         m_fallbackStage = SystemFonts;
         RefPtr<FontDataForRangeSet> fallbackPriorityFontRange = adoptRef(new FontDataForRangeSet(fallbackPriorityFont(hintList[0])));
         if (fallbackPriorityFontRange->hasFontData())
-            return fallbackPriorityFontRange.release();
+            return uniqueOrNext(fallbackPriorityFontRange.release(), hintList);
         return next(hintList);
     }
 
     if (m_fallbackStage == SystemFonts) {
         // We've reached pref + system fallback.
         ASSERT(hintList.size());
         RefPtr<SimpleFontData> systemFont = uniqueSystemFontForHint(hintList[0]);
         if (systemFont) {
             // Fallback fonts are not retained in the FontDataCache.
-            return adoptRef(new FontDataForRangeSet(systemFont));
+            return uniqueOrNext(adoptRef(new FontDataForRangeSet(systemFont)), hintList);
         }
 
         // If we don't have options from the system fallback anymore or had
         // previously returned them, we only have the last resort font left.
         // TODO: crbug.com/42217 Improve this by doing the last run with a last
         // resort font that has glyphs for everything, for example the Unicode
         // LastResort font, not just Times or Arial.
         FontCache* fontCache = FontCache::fontCache();
         m_fallbackStage = OutOfLuck;
         RefPtr<SimpleFontData> lastResort = fontCache->getLastResortFallbackFont(m_fontDescription).get();
         RELEASE_ASSERT(lastResort);
+        // Don't skip the LastResort font in uniqueOrNext() since HarfBuzzShaper
+        // needs to use this one to place missing glyph boxes.
         return adoptRef(new FontDataForRangeSetFromCache(lastResort));
     }
 
     ASSERT(m_fallbackStage == FontGroupFonts
         || m_fallbackStage == SegmentedFace);
     const FontData* fontData = m_fontFallbackList->fontDataAt(
         m_fontDescription, m_currentFontDataIndex);
 
     if (!fontData) {
         // If there is no fontData coming from the fallback list, it means
         // we are now looking at system fonts, either for prioritized symbol
         // or emoji fonts or by calling system fallback API.
         m_fallbackStage = isNonTextFallbackPriority(m_fontFallbackPriority)
             ? FallbackPriorityFonts
             : SystemFonts;
         return next(hintList);
     }
 
     // Otherwise we've received a fontData from the font-family: set of fonts,
     // and a non-segmented one in this case.
     if (!fontData->isSegmented()) {
         // Skip forward to the next font family for the next call to next().
         m_currentFontDataIndex++;
         if (!fontData->isLoading()) {
             RefPtr<SimpleFontData> nonSegmented = const_cast<SimpleFontData*>(toSimpleFontData(fontData));
             // The fontData object that we have here is tracked in m_fontList of
             // FontFallbackList and gets released in the font cache when the
             // FontFallbackList is destroyed.
-            return adoptRef(new FontDataForRangeSet(nonSegmented));
+            return uniqueOrNext(adoptRef(new FontDataForRangeSet(nonSegmented)), hintList);
         }
         return next(hintList);
     }
 
     // Iterate over ranges of a segmented font below.
 
     const SegmentedFontData* segmented = toSegmentedFontData(fontData);
     if (m_fallbackStage != SegmentedFace) {
         m_segmentedFaceIndex = 0;
         m_fallbackStage = SegmentedFace;
     }
 
     ASSERT(m_segmentedFaceIndex < segmented->numFaces());
     RefPtr<FontDataForRangeSet> currentSegmentedFace = segmented->faceAt(m_segmentedFaceIndex);
     m_segmentedFaceIndex++;
 
     if (m_segmentedFaceIndex == segmented->numFaces()) {
         // Switch from iterating over a segmented face to the next family from
         // the font-family: group of fonts.
         m_fallbackStage = FontGroupFonts;
         m_currentFontDataIndex++;
     }
 
     if (rangeSetContributesForHint(hintList, currentSegmentedFace.get())) {
         const SimpleFontData* fontData = currentSegmentedFace->fontData();
         if (const CustomFontData* customFontData = fontData->customFontData())
             customFontData->beginLoadIfNeeded();
         if (!fontData->isLoading())
-            return currentSegmentedFace;
+            return uniqueOrNext(currentSegmentedFace, hintList);
         m_trackedLoadingRangeSets.append(currentSegmentedFace);
     }
 
     return next(hintList);
 }
 
 const PassRefPtr<SimpleFontData> FontFallbackIterator::fallbackPriorityFont(
     UChar32 hint)
 {
     return FontCache::fontCache()->fallbackFontForCharacter(
@@ skipping 10 matching lines @@
     // already.
     if (!hint || m_previouslyAskedForHint.contains(hint))
         return nullptr;
 
     FontCache* fontCache = FontCache::fontCache();
     m_previouslyAskedForHint.add(hint);
     return fontCache->fallbackFontForCharacter(m_fontDescription, hint, m_fontFallbackList->primarySimpleFontData(m_fontDescription));
 }
 
 } // namespace blink