Add support for shaping a substring to HarfBuzzShaper

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

Index: third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzShaper.h
diff --git a/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzShaper.h b/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzShaper.h
index 7db9bcb48b7cbc1dc2b0b971e8baaa44cdd47ecb..aa331429b9ef084d253306975c2fd6c545e4f3cb 100644
--- a/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzShaper.h
+++ b/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzShaper.h
@@ -31,54 +31,77 @@
 #ifndef HarfBuzzShaper_h
 #define HarfBuzzShaper_h
 
+#include <hb.h>
+#include <unicode/uscript.h>
+#include <memory>
+#include "platform/fonts/shaping/RunSegmenter.h"
 #include "platform/fonts/shaping/ShapeResult.h"
 #include "platform/text/TextRun.h"
 #include "wtf/Allocator.h"
 #include "wtf/Deque.h"
 #include "wtf/Vector.h"
-#include <hb.h>
-#include <memory>
-#include <unicode/uscript.h>
 
 namespace blink {
 
 class Font;
 class SimpleFontData;
 class HarfBuzzShaper;
+struct HolesQueueItem;
 
 class PLATFORM_EXPORT HarfBuzzShaper final {
  public:
-  HarfBuzzShaper(const UChar*, unsigned length, TextDirection);
-  PassRefPtr<ShapeResult> shapeResult(const Font*) const;
-  ~HarfBuzzShaper() {}
+  HarfBuzzShaper(const UChar*, unsigned length);
+
+  // Shape a range, defined by the start and end parameters, of the string
+  // supplied to the constructor.
+  // The start and end positions should represent boundaries where a break may
+  // occur, such as at the beginning or end of lines or at element boundaries.
+  // If given arbitrary positions the results are not guaranteed to be correct.
+  // May be called multiple times; font and direction may vary between calls.
+  PassRefPtr<ShapeResult> shape(const Font*,
+                                TextDirection,
+                                unsigned start,
+                                unsigned end) const;
 
-  enum HolesQueueItemAction { HolesQueueNextFont, HolesQueueRange };
+  // Shape the entire string with a single font and direction.
+  // Equivalent to calling the range version with a start offset of zero and an
+  // end offset equal to the length.
+  PassRefPtr<ShapeResult> shape(const Font*, TextDirection) const;
 
-  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){};
-  };
+  ~HarfBuzzShaper() {}
 
  private:
+  using FeaturesVector = Vector<hb_feature_t, 6>;
+
+  // Shapes a single seqment, as identified by the RunSegmenterRange parameter,
+  // one or more times taking font fallback into account. The start and end
+  // parameters are for the entire text run, not the segment, and are used to
+  // determine pre- and post-context for shaping.
+  void shapeSegment(ShapeResult*,
+                    Deque<HolesQueueItem>*,
+                    hb_buffer_t*,
+                    const Font*,
+                    TextDirection,
+                    FeaturesVector*,
+                    RunSegmenter::RunSegmenterRange,
+                    unsigned start,
+                    unsigned end) const;
+
   bool extractShapeResults(hb_buffer_t*,
                            ShapeResult*,
                            bool& fontCycleQueued,
                            Deque<HolesQueueItem>*,
                            const HolesQueueItem&,
                            const Font*,
+                           TextDirection,
                            const SimpleFontData*,
                            UScriptCode,
                            bool isLastResort) const;
-  bool collectFallbackHintChars(const Deque<HolesQueueItem>&,
+  bool collectFallbackHintChars(const Deque<HolesQueueItem>*,
                                 Vector<UChar32>& hint) const;
 
-  const UChar* m_normalizedBuffer;
-  unsigned m_normalizedBufferLength;
-  TextDirection m_textDirection;
+  const UChar* m_text;
+  unsigned m_textLength;
 };
 
 }  // namespace blink