Add support for shaping a substring to HarfBuzzShaper

third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzShaper.cpp

Index: third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzShaper.cpp
diff --git a/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzShaper.cpp b/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzShaper.cpp
index 82d77dd14ac74d3b5cd34c0105860e824b5455ec..6acc661df81dd129ec977b3a4859bc046b362e32 100644
--- a/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzShaper.cpp
+++ b/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzShaper.cpp
@@ -40,7 +40,6 @@
 #include "platform/fonts/opentype/OpenTypeCapsSupport.h"
 #include "platform/fonts/shaping/CaseMappingHarfBuzzBufferFiller.h"
 #include "platform/fonts/shaping/HarfBuzzFace.h"
-#include "platform/fonts/shaping/RunSegmenter.h"
 #include "platform/fonts/shaping/ShapeResultInlineHeaders.h"
 #include "platform/text/TextBreakIterator.h"
 #include "wtf/Compiler.h"
@@ -56,6 +55,17 @@
 namespace blink {
 using FeaturesVector = Vector<hb_feature_t, 6>;
 
+enum HolesQueueItemAction { HolesQueueNextFont, HolesQueueRange };
+
+struct HolesQueueItem {
+  DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
+  HolesQueueItemAction m_action;
+  unsigned m_startIndex;
+  unsigned m_numCharacters;
+  HolesQueueItem(HolesQueueItemAction action, unsigned start, unsigned num)
+      : m_action(action), m_startIndex(start), m_numCharacters(num){};
+};
+
 template <typename T>
 class HarfBuzzScopedPtr {
   STACK_ALLOCATED();
@@ -81,12 +91,8 @@ class HarfBuzzScopedPtr {
   DestroyFunction m_destroy;
 };
 
-HarfBuzzShaper::HarfBuzzShaper(const UChar* text,
-                               unsigned length,
-                               TextDirection direction)
-    : m_normalizedBuffer(text),
-      m_normalizedBufferLength(length),
-      m_textDirection(direction) {}
+HarfBuzzShaper::HarfBuzzShaper(const UChar* text, unsigned length)
+    : m_text(text), m_textLength(length) {}
 
 namespace {
 
@@ -112,7 +118,7 @@ static inline hb_direction_t TextDirectionToHBDirection(
                                     : harfBuzzDirection;
 }
 
-inline bool shapeRange(hb_buffer_t* harfBuzzBuffer,
+inline bool shapeRange(hb_buffer_t* buffer,
                        hb_feature_t* fontFeatures,
                        unsigned fontFeaturesSize,
                        const SimpleFontData* currentFont,
@@ -127,24 +133,25 @@ inline bool shapeRange(hb_buffer_t* harfBuzzBuffer,
     return false;
   }
 
-  hb_buffer_set_language(harfBuzzBuffer, language);
-  hb_buffer_set_script(harfBuzzBuffer, ICUScriptToHBScript(currentRunScript));
-  hb_buffer_set_direction(harfBuzzBuffer, direction);
+  hb_buffer_set_language(buffer, language);
+  hb_buffer_set_script(buffer, ICUScriptToHBScript(currentRunScript));
+  hb_buffer_set_direction(buffer, direction);
 
   hb_font_t* hbFont = face->getScaledFont(std::move(currentFontRangeSet));
-  hb_shape(hbFont, harfBuzzBuffer, fontFeatures, fontFeaturesSize);
+  hb_shape(hbFont, buffer, fontFeatures, fontFeaturesSize);
 
   return true;
 }
 
 }  // namespace
 
-bool HarfBuzzShaper::extractShapeResults(hb_buffer_t* harfBuzzBuffer,
+bool HarfBuzzShaper::extractShapeResults(hb_buffer_t* buffer,
                                          ShapeResult* shapeResult,
                                          bool& fontCycleQueued,
                                          Deque<HolesQueueItem>* holesQueue,
                                          const HolesQueueItem& currentQueueItem,
                                          const Font* font,
+                                         TextDirection textDirection,
                                          const SimpleFontData* currentFont,
                                          UScriptCode currentRunScript,
                                          bool isLastResort) const {
@@ -154,9 +161,9 @@ bool HarfBuzzShaper::extractShapeResults(hb_buffer_t* harfBuzzBuffer,
   unsigned previousCluster = 0;
   unsigned currentCluster = 0;
 
-  // Find first notdef glyph in harfBuzzBuffer.
-  unsigned numGlyphs = hb_buffer_get_length(harfBuzzBuffer);
-  hb_glyph_info_t* glyphInfo = hb_buffer_get_glyph_infos(harfBuzzBuffer, 0);
+  // Find first notdef glyph in buffer.
+  unsigned numGlyphs = hb_buffer_get_length(buffer);
+  hb_glyph_info_t* glyphInfo = hb_buffer_get_glyph_infos(buffer, 0);
 
   unsigned lastChangePosition = 0;
 
@@ -212,7 +219,7 @@ bool HarfBuzzShaper::extractShapeResults(hb_buffer_t* harfBuzzBuffer,
     unsigned numCharacters = 0;
     unsigned numGlyphsToInsert = 0;
     unsigned startIndex = 0;
-    if (HB_DIRECTION_IS_FORWARD(hb_buffer_get_direction(harfBuzzBuffer))) {
+    if (HB_DIRECTION_IS_FORWARD(hb_buffer_get_direction(buffer))) {
       startIndex = glyphInfo[lastChangePosition].cluster;
       if (glyphIndex == numGlyphs) {
         numCharacters = currentQueueItem.m_startIndex +
@@ -260,14 +267,13 @@ bool HarfBuzzShaper::extractShapeResults(hb_buffer_t* harfBuzzBuffer,
     // choice than adding boxes to the ShapeResult.
     if ((currentClusterResult == NotDef && numCharacters) || isLastResort) {
       hb_direction_t direction = TextDirectionToHBDirection(
-          m_textDirection, font->getFontDescription().orientation(),
-          currentFont);
+          textDirection, font->getFontDescription().orientation(), currentFont);
       // Here we need to specify glyph positions.
       ShapeResult::RunInfo* run = new ShapeResult::RunInfo(
           currentFont, direction, ICUScriptToHBScript(currentRunScript),
           startIndex, numGlyphsToInsert, numCharacters);
       shapeResult->insertRun(WTF::wrapUnique(run), lastChangePosition,
-                             numGlyphsToInsert, harfBuzzBuffer);
+                             numGlyphsToInsert, buffer);
     }
     lastChangePosition = glyphIndex;
   }
@@ -290,23 +296,22 @@ static inline const SimpleFontData* fontDataAdjustedForOrientation(
 }
 
 bool HarfBuzzShaper::collectFallbackHintChars(
-    const Deque<HolesQueueItem>& holesQueue,
+    const Deque<HolesQueueItem>* holesQueue,
     Vector<UChar32>& hint) const {
-  if (!holesQueue.size())
+  DCHECK(holesQueue);
+  if (!holesQueue->size())
     return false;
 
   hint.clear();
 
   size_t numCharsAdded = 0;
-  for (auto it = holesQueue.begin(); it != holesQueue.end(); ++it) {
+  for (auto it = holesQueue->begin(); it != holesQueue->end(); ++it) {
     if (it->m_action == HolesQueueNextFont)
       break;
 
     UChar32 hintChar;
-    RELEASE_ASSERT(it->m_startIndex + it->m_numCharacters <=
-                   m_normalizedBufferLength);
-    UTF16TextIterator iterator(m_normalizedBuffer + it->m_startIndex,
-                               it->m_numCharacters);
+    RELEASE_ASSERT(it->m_startIndex + it->m_numCharacters <= m_textLength);
+    UTF16TextIterator iterator(m_text + it->m_startIndex, it->m_numCharacters);
     while (iterator.consume(hintChar)) {
       hint.push_back(hintChar);
       numCharsAdded++;
@@ -317,13 +322,11 @@ bool HarfBuzzShaper::collectFallbackHintChars(
 }
 
 namespace {
-using HolesQueueItem = HarfBuzzShaper::HolesQueueItem;
-using HolesQueueItemAction = HarfBuzzShaper::HolesQueueItemAction;
 
 void splitUntilNextCaseChange(
     const UChar* normalizedBuffer,
-    Deque<HolesQueueItem>* queue,
-    HolesQueueItem& currentQueueItem,
+    Deque<blink::HolesQueueItem>* queue,
+    blink::HolesQueueItem& currentQueueItem,
     SmallCapsIterator::SmallCapsBehavior& smallCapsBehavior) {
   unsigned numCharactersUntilCaseChange = 0;
   SmallCapsIterator smallCapsIterator(
@@ -332,8 +335,8 @@ void splitUntilNextCaseChange(
   smallCapsIterator.consume(&numCharactersUntilCaseChange, &smallCapsBehavior);
   if (numCharactersUntilCaseChange > 0 &&
       numCharactersUntilCaseChange < currentQueueItem.m_numCharacters) {
-    queue->prepend(HolesQueueItem(
-        HolesQueueItemAction::HolesQueueRange,
+    queue->prepend(blink::HolesQueueItem(
+        blink::HolesQueueItemAction::HolesQueueRange,
         currentQueueItem.m_startIndex + numCharactersUntilCaseChange,
         currentQueueItem.m_numCharacters - numCharactersUntilCaseChange));
     currentQueueItem.m_numCharacters = numCharactersUntilCaseChange;
@@ -546,132 +549,154 @@ CapsFeatureSettingsScopedOverlay::~CapsFeatureSettingsScopedOverlay() {
 
 }  // namespace
 
-PassRefPtr<ShapeResult> HarfBuzzShaper::shapeResult(const Font* font) const {
-  RefPtr<ShapeResult> result =
-      ShapeResult::create(font, m_normalizedBufferLength, m_textDirection);
-  HarfBuzzScopedPtr<hb_buffer_t> harfBuzzBuffer(hb_buffer_create(),
-                                                hb_buffer_destroy);
-  FeaturesVector fontFeatures;
-  setFontFeatures(font, &fontFeatures);
+void HarfBuzzShaper::shapeSegment(ShapeResult* result,
+                                  Deque<HolesQueueItem>* holesQueue,
+                                  hb_buffer_t* buffer,
+                                  const Font* font,
+                                  FeaturesVector* fontFeatures,
+                                  RunSegmenter::RunSegmenterRange segment,
+                                  unsigned start,
+                                  unsigned end,
+                                  TextDirection textDirection) const {
+  DCHECK(result);
+  DCHECK(holesQueue);
+  DCHECK(buffer);
+
+  holesQueue->append(HolesQueueItem(HolesQueueNextFont, 0, 0));
+  holesQueue->append(HolesQueueItem(HolesQueueRange, segment.start,
+                                    segment.end - segment.start));
+
+  RefPtr<FontFallbackIterator> fallbackIterator =
+      font->createFontFallbackIterator(segment.fontFallbackPriority);
+
+  RefPtr<FontDataForRangeSet> currentFontDataForRangeSet;
+
   const FontDescription& fontDescription = font->getFontDescription();
+  bool fontCycleQueued = false;
+  bool needsCapsHandling =
+      fontDescription.variantCaps() != FontDescription::CapsNormal;
+  FontOrientation orientation = fontDescription.orientation();
   const hb_language_t language =
       fontDescription.localeOrDefault().harfbuzzLanguage();
 
-  bool needsCapsHandling =
-      fontDescription.variantCaps() != FontDescription::CapsNormal;
   OpenTypeCapsSupport capsSupport;
-  FontOrientation orientation = font->getFontDescription().orientation();
-
-  RunSegmenter::RunSegmenterRange segmentRange = {
-      0, 0, USCRIPT_INVALID_CODE, OrientationIterator::OrientationInvalid,
-      FontFallbackPriority::Invalid};
-  RunSegmenter runSegmenter(m_normalizedBuffer, m_normalizedBufferLength,
-                            orientation);
-
   Vector<UChar32> fallbackCharsHint;
-
-  // TODO: Check whether this treatAsZerowidthspace from the previous script
-  // segmentation plays a role here, does the new scriptRuniterator handle that
-  // correctly?
-  Deque<HolesQueueItem> holesQueue;
-  while (runSegmenter.consume(&segmentRange)) {
-    RefPtr<FontFallbackIterator> fallbackIterator =
-        font->createFontFallbackIterator(segmentRange.fontFallbackPriority);
-
-    holesQueue.append(HolesQueueItem(HolesQueueNextFont, 0, 0));
-    holesQueue.append(HolesQueueItem(HolesQueueRange, segmentRange.start,
-                                     segmentRange.end - segmentRange.start));
-
-    RefPtr<FontDataForRangeSet> currentFontDataForRangeSet;
-
-    bool fontCycleQueued = false;
-    while (holesQueue.size()) {
-      HolesQueueItem currentQueueItem = holesQueue.takeFirst();
-
-      if (currentQueueItem.m_action == HolesQueueNextFont) {
-        // For now, we're building a character list with which we probe
-        // for needed fonts depending on the declared unicode-range of a
-        // segmented CSS font. Alternatively, we can build a fake font
-        // for the shaper and check whether any glyphs were found, or
-        // define a new API on the shaper which will give us coverage
-        // information?
-        if (!collectFallbackHintChars(holesQueue, fallbackCharsHint)) {
-          // Give up shaping since we cannot retrieve a font fallback
-          // font without a hintlist.
-          holesQueue.clear();
-          break;
-        }
-
-        currentFontDataForRangeSet = fallbackIterator->next(fallbackCharsHint);
-        if (!currentFontDataForRangeSet->fontData()) {
-          DCHECK(!holesQueue.size());
-          break;
-        }
-        fontCycleQueued = false;
-        continue;
+  while (holesQueue->size()) {
+    HolesQueueItem currentQueueItem = holesQueue->takeFirst();
+    DCHECK(currentQueueItem.m_numCharacters);
+
+    if (currentQueueItem.m_action == HolesQueueNextFont) {
+      // For now, we're building a character list with which we probe
+      // for needed fonts depending on the declared unicode-range of a
+      // segmented CSS font. Alternatively, we can build a fake font
+      // for the shaper and check whether any glyphs were found, or
+      // define a new API on the shaper which will give us coverage
+      // information?
+      if (!collectFallbackHintChars(holesQueue, fallbackCharsHint)) {
+        // Give up shaping since we cannot retrieve a font fallback
+        // font without a hintlist.
+        holesQueue->clear();
+        break;
       }
 
-      const SimpleFontData* fontData = currentFontDataForRangeSet->fontData();
-      SmallCapsIterator::SmallCapsBehavior smallCapsBehavior =
-          SmallCapsIterator::SmallCapsSameCase;
-      if (needsCapsHandling) {
-        capsSupport =
-            OpenTypeCapsSupport(fontData->platformData().harfBuzzFace(),
-                                fontDescription.variantCaps(),
-                                ICUScriptToHBScript(segmentRange.script));
-        if (capsSupport.needsRunCaseSplitting()) {
-          splitUntilNextCaseChange(m_normalizedBuffer, &holesQueue,
-                                   currentQueueItem, smallCapsBehavior);
-        }
+      currentFontDataForRangeSet = fallbackIterator->next(fallbackCharsHint);
+      if (!currentFontDataForRangeSet->fontData()) {
+        DCHECK(!holesQueue->size());
+        break;
       }
+      fontCycleQueued = false;
+      continue;
+    }
 
-      ASSERT(currentQueueItem.m_numCharacters);
+    const SimpleFontData* fontData = currentFontDataForRangeSet->fontData();
+    SmallCapsIterator::SmallCapsBehavior smallCapsBehavior =
+        SmallCapsIterator::SmallCapsSameCase;
+    if (needsCapsHandling) {
+      capsSupport = OpenTypeCapsSupport(fontData->platformData().harfBuzzFace(),
+                                        fontDescription.variantCaps(),
+                                        ICUScriptToHBScript(segment.script));
+      if (capsSupport.needsRunCaseSplitting()) {
+        splitUntilNextCaseChange(m_text, holesQueue, currentQueueItem,
+                                 smallCapsBehavior);
+      }
+    }
 
-      const SimpleFontData* smallcapsAdjustedFont =
-          needsCapsHandling && capsSupport.needsSyntheticFont(smallCapsBehavior)
-              ? fontData->smallCapsFontData(fontDescription).get()
-              : fontData;
+    const SimpleFontData* smallcapsAdjustedFont =
+        needsCapsHandling && capsSupport.needsSyntheticFont(smallCapsBehavior)
+            ? fontData->smallCapsFontData(fontDescription).get()
+            : fontData;
+
+    // Compatibility with SimpleFontData approach of keeping a flag for
+    // overriding drawing direction.
+    // TODO: crbug.com/506224 This should go away in favor of storing that
+    // information elsewhere, for example in ShapeResult.
+    const SimpleFontData* directionAndSmallCapsAdjustedFont =
+        fontDataAdjustedForOrientation(smallcapsAdjustedFont, orientation,
+                                       segment.renderOrientation);
+
+    CaseMapIntend caseMapIntend = CaseMapIntend::KeepSameCase;
+    if (needsCapsHandling)
+      caseMapIntend = capsSupport.needsCaseChange(smallCapsBehavior);
+
+    CaseMappingHarfBuzzBufferFiller(
+        caseMapIntend, fontDescription.localeOrDefault(), buffer,
+        m_text + start, m_textLength, currentQueueItem.m_startIndex,
+        currentQueueItem.m_numCharacters);
+
+    CapsFeatureSettingsScopedOverlay capsOverlay(
+        fontFeatures, capsSupport.fontFeatureToUse(smallCapsBehavior));
+    hb_direction_t direction = TextDirectionToHBDirection(
+        textDirection, orientation, directionAndSmallCapsAdjustedFont);
+
+    if (!shapeRange(buffer, fontFeatures->isEmpty() ? 0 : fontFeatures->data(),
+                    fontFeatures->size(), directionAndSmallCapsAdjustedFont,
+                    currentFontDataForRangeSet->ranges(), segment.script,
+                    direction, language))
+      DLOG(ERROR) << "Shaping range failed.";
+
+    if (!extractShapeResults(buffer, result, fontCycleQueued, holesQueue,
+                             currentQueueItem, font, textDirection,
+                             directionAndSmallCapsAdjustedFont, segment.script,
+                             !fallbackIterator->hasNext()))
+      DLOG(ERROR) << "Shape result extraction failed.";
+
+    hb_buffer_reset(buffer);
+  }
+}
 
-      // Compatibility with SimpleFontData approach of keeping a flag for
-      // overriding drawing direction.
-      // TODO: crbug.com/506224 This should go away in favor of storing that
-      // information elsewhere, for example in ShapeResult.
-      const SimpleFontData* directionAndSmallCapsAdjustedFont =
-          fontDataAdjustedForOrientation(smallcapsAdjustedFont, orientation,
-                                         segmentRange.renderOrientation);
+PassRefPtr<ShapeResult> HarfBuzzShaper::shape(const Font* font,
+                                              TextDirection textDirection,
+                                              unsigned start,
+                                              unsigned end) const {
+  DCHECK(end >= start);
+  DCHECK(end <= m_textLength);
 
-      CaseMapIntend caseMapIntend = CaseMapIntend::KeepSameCase;
-      if (needsCapsHandling)
-        caseMapIntend = capsSupport.needsCaseChange(smallCapsBehavior);
+  unsigned length = end - start;
+  RefPtr<ShapeResult> result = ShapeResult::create(font, length, textDirection);
+  HarfBuzzScopedPtr<hb_buffer_t> buffer(hb_buffer_create(), hb_buffer_destroy);
 
-      CaseMappingHarfBuzzBufferFiller(
-          caseMapIntend, fontDescription.localeOrDefault(),
-          harfBuzzBuffer.get(), m_normalizedBuffer, m_normalizedBufferLength,
-          currentQueueItem.m_startIndex, currentQueueItem.m_numCharacters);
+  FeaturesVector fontFeatures;
+  setFontFeatures(font, &fontFeatures);
+  FontOrientation orientation = font->getFontDescription().orientation();
 
-      CapsFeatureSettingsScopedOverlay capsOverlay(
-          &fontFeatures, capsSupport.fontFeatureToUse(smallCapsBehavior));
+  Deque<HolesQueueItem> holesQueue;
+  RunSegmenter::RunSegmenterRange segmentRange = RunSegmenter::nullRange();
+  RunSegmenter runSegmenter(m_text + start, length, orientation);

[drott, 2017/02/07 23:12:41]

Offsetting the RunSegmenter to a start at an offset or restricting it to a
certain length has side effects on script and emoji segmentation, so the result
of shaping a sub-run is only ensured to be identical to its shaping result as
part of the whole run without offsets if the offsets are not splitting emoji
sequences, or if the offsets do not cut a string between for example brackets
that would otherwise resolve to the same script or before/after SCRIPT_COMMON 
sequences that can no longer be resolved due to missing context.

It might be tricky to ensure this stability above this interface. So one
possible way to adress this would be to segment everything, e.g. fast forward
the consume and only start start shaping at the first useful RunSegmenterRange
that covers "start", and discard the further consume() results after "start +
length".

 
-      hb_direction_t direction = TextDirectionToHBDirection(
-          m_textDirection, orientation, directionAndSmallCapsAdjustedFont);
-
-      if (!shapeRange(harfBuzzBuffer.get(),
-                      fontFeatures.isEmpty() ? 0 : fontFeatures.data(),
-                      fontFeatures.size(), directionAndSmallCapsAdjustedFont,
-                      currentFontDataForRangeSet->ranges(), segmentRange.script,
-                      direction, language))
-        DLOG(ERROR) << "Shaping range failed.";
-
-      if (!extractShapeResults(
-              harfBuzzBuffer.get(), result.get(), fontCycleQueued, &holesQueue,
-              currentQueueItem, font, directionAndSmallCapsAdjustedFont,
-              segmentRange.script, !fallbackIterator->hasNext()))
-        DLOG(ERROR) << "Shape result extraction failed.";
-
-      hb_buffer_reset(harfBuzzBuffer.get());
-    }
+  // TODO: Check whether this treatAsZerowidthspace from the previous script
+  // segmentation plays a role here, does the new scriptRuniterator handle
+  // that correctly?
+  while (runSegmenter.consume(&segmentRange)) {
+    shapeSegment(result.get(), &holesQueue, buffer.get(), font, &fontFeatures,
+                 segmentRange, start, end, textDirection);
   }
+
   return result.release();
 }
 
+PassRefPtr<ShapeResult> HarfBuzzShaper::shape(
+    const Font* font,
+    TextDirection textDirection) const {
+  return shape(font, textDirection, 0, m_textLength);
+}
 }  // namespace blink