More or less implement RenderTextHarfBuzz

ui/gfx/render_text_harfbuzz.cc

+// Copyright 2014 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 "ui/gfx/render_text_harfbuzz.h"
+
+#include <map>
+
+#include "base/i18n/break_iterator.h"
+#include "base/i18n/char_iterator.h"
+#include "third_party/harfbuzz-ng/src/hb-icu.h"
+#include "third_party/harfbuzz-ng/src/hb.h"
+#include "third_party/icu/source/common/unicode/ubidi.h"
+#include "third_party/skia/include/core/SkColor.h"
+#include "third_party/skia/include/core/SkTypeface.h"
+#include "ui/gfx/canvas.h"
+#include "ui/gfx/utf16_indexing.h"
+
+#if defined(OS_WIN)
+#include "ui/gfx/font_smoothing_win.h"
+#endif
+
+namespace gfx {
+
+namespace {
+
+// The maximum number of scripts a unicode character can belong to.
+const size_t kMaxScripts = 5;
+
+typedef std::map<uint32_t, uint16_t> GlyphCache;
+
+// Font data provider for HarfBuzz using Skia. Copied from Blink.
+// TODO(ckocagil): Eliminate the duplication. http://crbug.com/368375
+struct FontData {
+  FontData(GlyphCache* glyph_cache) : glyph_cache_(glyph_cache) {}
+
+  SkPaint paint_;
+  GlyphCache* glyph_cache_;
+};
+
+hb_position_t SkiaScalarToHarfBuzzPosition(SkScalar value) {
+  return SkScalarToFixed(value);
+}
+
+template<typename Type>
+void DeleteByType(void* data) {
+  Type* typed_data = reinterpret_cast<Type*>(data);
+  delete typed_data;
+}
+
+template<typename Type>
+void DeleteArrayByType(void* data) {
+  Type* typed_data = reinterpret_cast<Type*>(data);
+  delete[] typed_data;
+}
+
+void GetGlyphWidthAndExtents(SkPaint* paint,
+                             hb_codepoint_t codepoint,
+                             hb_position_t* width,
+                             hb_glyph_extents_t* extents) {
+  CHECK_LE(codepoint, 0xFFFFU);

[Alexei Svitkine (slow), 2014/05/13 15:23:27]

Does this need to be a CHECK rather than a DCHECK? (i.e. what happens if this
fails?)

[ckocagil, 2014/05/16 13:47:25]

This is actually supposed to be a DCHECK, I mistranslated the webkit assertion
macro. Fixed. I also changed another CHECK to DCHECK below.

+  paint->setTextEncoding(SkPaint::kGlyphID_TextEncoding);
+
+  SkScalar sk_width;
+  SkRect sk_bounds;
+  uint16_t glyph = codepoint;
+
+  paint->getTextWidths(&glyph, sizeof(glyph), &sk_width, &sk_bounds);
+  if (width)
+    *width = SkiaScalarToHarfBuzzPosition(sk_width);
+  if (extents) {
+    // Invert y-axis because Skia is y-grows-down but we set up HarfBuzz to be
+    // y-grows-up.
+    extents->x_bearing = SkiaScalarToHarfBuzzPosition(sk_bounds.fLeft);
+    extents->y_bearing = SkiaScalarToHarfBuzzPosition(-sk_bounds.fTop);
+    extents->width = SkiaScalarToHarfBuzzPosition(sk_bounds.width());
+    extents->height = SkiaScalarToHarfBuzzPosition(-sk_bounds.height());
+  }
+}
+
+hb_bool_t GetGlyph(hb_font_t* font,
+                   void* data,
+                   hb_codepoint_t unicode,
+                   hb_codepoint_t variation_selector,
+                   hb_codepoint_t* glyph,
+                   void* user_data) {
+  FontData* font_data = reinterpret_cast<FontData*>(data);
+  GlyphCache* cache = font_data->glyph_cache_;
+
+  bool exists = cache->count(unicode) != 0;
+  if (!exists) {
+    SkPaint* paint = &font_data->paint_;
+    paint->setTextEncoding(SkPaint::kUTF32_TextEncoding);
+    paint->textToGlyphs(&unicode, sizeof(hb_codepoint_t), &(*cache)[unicode]);
+  }
+  *glyph = (*cache)[unicode];
+  return !!*glyph;
+}
+
+hb_position_t GetGlyphHorizontalAdvance(hb_font_t* font,
+                                        void* data,
+                                        hb_codepoint_t glyph,
+                                        void* user_data) {
+  FontData* font_data = reinterpret_cast<FontData*>(data);
+  hb_position_t advance = 0;
+
+  GetGlyphWidthAndExtents(&font_data->paint_, glyph, &advance, 0);
+  return advance;
+}
+
+hb_bool_t GetGlyphHorizontalOrigin(hb_font_t* font,
+                                   void* data,
+                                   hb_codepoint_t glyph,
+                                   hb_position_t* x,
+                                   hb_position_t* y,
+                                   void* user_data) {
+  // Just return true, like the HarfBuzz-FreeType implementation.
+  return true;
+}
+
+hb_bool_t GetGlyphExtents(hb_font_t* font,
+                          void* data,
+                          hb_codepoint_t glyph,
+                          hb_glyph_extents_t* extents,
+                          void* user_data) {
+  FontData* font_data = reinterpret_cast<FontData*>(data);
+
+  GetGlyphWidthAndExtents(&font_data->paint_, glyph, 0, extents);
+  return true;
+}
+
+hb_font_funcs_t* GetFontFuncs() {
+  static hb_font_funcs_t* font_funcs = 0;
+
+  // We don't set callback functions which we can't support.
+  // HarfBuzz will use the fallback implementation if they aren't set.
+  // TODO(ckocagil): Merge Blink's kerning funcs.
+  if (!font_funcs) {
+    font_funcs = hb_font_funcs_create();

[Alexei Svitkine (slow), 2014/05/13 15:23:27]

Is this intentionally leaked? If so, please add a comment mentioning this is
intentional.

[ckocagil, 2014/05/16 13:47:25]

Done.

+    hb_font_funcs_set_glyph_func(font_funcs, GetGlyph, 0, 0);
+    hb_font_funcs_set_glyph_h_advance_func(
+        font_funcs, GetGlyphHorizontalAdvance, 0, 0);
+    hb_font_funcs_set_glyph_h_origin_func(
+        font_funcs, GetGlyphHorizontalOrigin, 0, 0);
+    hb_font_funcs_set_glyph_extents_func(
+        font_funcs, GetGlyphExtents, 0, 0);
+    hb_font_funcs_make_immutable(font_funcs);
+  }
+  return font_funcs;
+}
+
+hb_blob_t* GetFontTable(hb_face_t* face, hb_tag_t tag, void* user_data) {
+  SkTypeface* typeface = reinterpret_cast<SkTypeface*>(user_data);
+
+  const size_t table_size = typeface->getTableSize(tag);
+  if (!table_size)
+    return 0;
+
+  char* buffer = new char[table_size];

[Alexei Svitkine (slow), 2014/05/13 15:23:27]

How about:

scoped_ptr<char[]> buffer(new char[table_size]);
size_t actual_size = typeface->getTableData(tag, 0, table_size, buffer);
if (table_size != actual_size)
  return 0;

// Harbuzz takes ownership of |buffer|.
return hb_blob_create(buffer.release(), ...);

[ckocagil, 2014/05/16 13:47:25]

Oh, good idea. Done! Sadly I had to assign the released ptr to another variable
since the function needs it twice.

+  if (!buffer)
+    return 0;
+  size_t actual_size = typeface->getTableData(tag, 0, table_size, buffer);
+  if (table_size != actual_size) {
+    delete[] buffer;
+    return 0;
+  }
+
+  return hb_blob_create(buffer, table_size, HB_MEMORY_MODE_WRITABLE, buffer,
+                        DeleteArrayByType<char>);
+}
+
+void UnrefSkTypeface(void* data) {
+  SkTypeface* skia_face = reinterpret_cast<SkTypeface*>(data);
+  SkSafeUnref(skia_face);
+}
+
+hb_face_t* CreateHarfBuzzFace(SkTypeface* skia_face) {
+  SkSafeRef(skia_face);
+  hb_face_t* face = hb_face_create_for_tables(GetFontTable, skia_face,
+                                              UnrefSkTypeface);
+  CHECK(face);
+  return face;
+}
+
+hb_font_t* CreateHarfBuzzFont(SkTypeface* skia_face, int text_size) {
+  typedef std::pair<hb_face_t*, GlyphCache> FaceCache;
+
+  // TODO(ckocagil): This shouldn't grow indefinitely. Maybe use base::MRUCache?
+  static std::map<SkFontID, FaceCache> face_caches;
+
+  FaceCache* face_cache = &face_caches[skia_face->uniqueID()];
+  if (face_cache->first == 0) {
+    hb_face_t* harfbuzz_face = CreateHarfBuzzFace(skia_face);
+    *face_cache = FaceCache(harfbuzz_face, GlyphCache());
+  }
+
+  hb_font_t* harfbuzz_font = hb_font_create(face_cache->first);
+  // TODO(ckocagil): Investigate whether disabling hinting here has any effect
+  // on text quality.
+  int upem = hb_face_get_upem(face_cache->first);
+  hb_font_set_scale(harfbuzz_font, upem, upem);
+  FontData* hb_font_data = new FontData(&face_cache->second);
+  hb_font_data->paint_.setTypeface(skia_face);
+  hb_font_data->paint_.setTextSize(text_size);
+  hb_font_set_funcs(harfbuzz_font, GetFontFuncs(), hb_font_data,
+                    DeleteByType<FontData>);
+  hb_font_make_immutable(harfbuzz_font);
+  return harfbuzz_font;
+}
+
+size_t CharToGlyph(const internal::TextRunHarfBuzz& run, size_t pos) {

[Alexei Svitkine (slow), 2014/05/13 15:23:27]

Can you add short 1-line comments for all these functions in the anon namespace?

[ckocagil, 2014/05/16 13:47:25]

Done.

+  DCHECK(run.range.start() <= pos && pos < run.range.end());
+
+  if (run.direction == UBIDI_LTR) {
+    for (size_t i = 0; i < run.glyph_count - 1; ++i) {
+      if (pos < run.glyph_to_char[i + 1])
+        return i;
+    }
+    return run.glyph_count - 1;
+  }
+
+  for (size_t i = 0; i < run.glyph_count; ++i) {
+    if (pos >= run.glyph_to_char[i])
+      return i;
+  }
+  NOTREACHED();
+  return 0;
+}
+
+// Returns the corresponding glyph range of the given character range.
+// |range| is in text-space (0 corresponds to |GetLayoutText()[0]|).
+// Returned value is in run-space (0 corresponds to the first glyph in the run).
+Range CharRangeToGlyphRange(const internal::TextRunHarfBuzz& run,
+                            const Range& range) {
+  DCHECK(run.range.Contains(range));
+  DCHECK(!range.is_reversed());
+  DCHECK(!range.is_empty());
+
+  const size_t first = CharToGlyph(run, range.start());
+  const size_t last = CharToGlyph(run, range.end() - 1);
+  return Range(std::min(first, last), std::max(first, last) + 1);
+}
+
+// Returns true if characters of |block_code| may trigger font fallback.
+bool IsUnusualBlockCode(const UBlockCode block_code) {
+  return block_code == UBLOCK_GEOMETRIC_SHAPES ||
+         block_code == UBLOCK_MISCELLANEOUS_SYMBOLS;
+}
+
+bool HasMissingGlyphs(const internal::TextRunHarfBuzz& run) {

[Alexei Svitkine (slow), 2014/05/13 15:23:27]

Can this be a method on TextRunHarfbuzz rather than a free-standing function?

Same for all the other free-standing functions you currently have that take
|run| as the first param.

[ckocagil, 2014/05/16 13:47:25]

Good idea, but should we make it a proper class with accessors? Google C++ style
guide seems to require that. (it says anything more than a collection of data
should be a class, and classes should always expose data via accessors)

[Alexei Svitkine (slow), 2014/05/16 18:22:52]

I think it's OK to have a struct with a few methods.

Though, if making it a full-fledged class with accessors, etc isn't super
intrusive, then that SGTM to me too.

[ckocagil, 2014/05/20 18:35:10]

Done, moved these to the struct.

+  static const int kMissingGlyphId = 0;
+  for (size_t i = 0; i < run.glyph_count; ++i) {
+    if (run.glyphs[i] == kMissingGlyphId)
+      return true;
+  }
+  return false;
+}
+
+UScriptCode ScriptIntersect(UScriptCode first, UScriptCode second) {
+  if (first == second ||
+      (second > USCRIPT_INVALID_CODE && second <= USCRIPT_INHERITED)) {
+    return first;
+  }
+  if (first > USCRIPT_INVALID_CODE && first <= USCRIPT_INHERITED)
+    return second;
+  return USCRIPT_INVALID_CODE;
+}
+
+int GetScriptExtensions(UChar32 codepoint, UScriptCode* scripts) {
+  UErrorCode icu_error = U_ZERO_ERROR;
+  // ICU documentation incorrectly states that the result of
+  // |uscript_getScriptExtensions| will contain the regular script property.
+  // Call |uscript_getScript| to get the script property.
+  scripts[0] = uscript_getScript(codepoint, &icu_error);
+  if (U_FAILURE(icu_error))
+    return 0;
+  int count = uscript_getScriptExtensions(codepoint, scripts + 1,
+                                          kMaxScripts - 1, &icu_error);
+  if (U_FAILURE(icu_error))
+    count = 0;
+  return count + 1;
+}
+
+// Intersects the script extensions set of |codepoint| with |result| and writes
+// to |result|, reading and updating |result_size|.
+void ScriptSetIntersect(UChar32 codepoint,
+                        UScriptCode* result,
+                        size_t* result_size) {
+  UScriptCode scripts[kMaxScripts] = { USCRIPT_INVALID_CODE };
+  int count = GetScriptExtensions(codepoint, scripts);
+
+  UScriptCode* out = result;
+  size_t out_size = 0;
+
+  for (size_t i = 0; i < *result_size; ++i) {
+    for (int j = 0; j < count; ++j) {
+      UScriptCode intersection = ScriptIntersect(result[i], scripts[j]);
+      if (intersection != USCRIPT_INVALID_CODE) {
+        *out++ = intersection;
+        ++out_size;
+        break;
+      }
+    }
+  }
+
+  *result_size = out_size;
+}
+
+// Find the longest sequence of characters from 0 and up to |length| that
+// have at least one common UScriptCode value. Writes the common script value to
+// |script| and returns the length of the sequence. Takes the characters' script
+// extensions into account. http://www.unicode.org/reports/tr24/#ScriptX
+int ScriptInterval(const base::char16* text,

[Alexei Svitkine (slow), 2014/05/13 15:23:27]

Can |text| be passed by const ref?

[ckocagil, 2014/05/16 13:47:25]

Done.

+                    size_t length,

[Alexei Svitkine (slow), 2014/05/13 15:23:27]

Nit: Align params.

[ckocagil, 2014/05/16 13:47:25]

Done.

+                    UScriptCode* script) {
+  DCHECK_GE(length, 0U);
+
+  UScriptCode scripts[kMaxScripts] = { USCRIPT_INVALID_CODE };
+
+  base::i18n::UTF16CharIterator char_iterator(text, length);
+  size_t scripts_size = GetScriptExtensions(char_iterator.get(), scripts);
+  *script = scripts[0];
+
+  while (char_iterator.Advance()) {
+    ScriptSetIntersect(char_iterator.get(), scripts, &scripts_size);
+    if (scripts_size > 0U)
+      *script = scripts[0];
+    else
+      return char_iterator.array_pos();
+  }
+
+  return length;
+}
+
+}  // namespace
+
+namespace internal {
+
+TextRunHarfBuzz::TextRunHarfBuzz()
+    : width(0),
+      preceding_run_widths(0),
+      direction(UBIDI_LTR),
+      level(0),
+      script(USCRIPT_INVALID_CODE),
+      glyph_count(-1),
+      font_size(0),
+      font_style(0),
+      strike(false),
+      diagonal_strike(false),
+      underline(false) {}
+
+TextRunHarfBuzz::~TextRunHarfBuzz() {}
+
+}  // namespace internal
+
+RenderTextHarfBuzz::RenderTextHarfBuzz()
+    : RenderText(),
+      needs_layout_(false) {}
+
+RenderTextHarfBuzz::~RenderTextHarfBuzz() {}
+
+Size RenderTextHarfBuzz::GetStringSize() {
+  EnsureLayout();
+  return Size(lines()[0].size.width(), font_list().GetHeight());
+}
+
+SelectionModel RenderTextHarfBuzz::FindCursorPosition(const Point& point) {
+  EnsureLayout();
+
+  int x = ToTextPoint(point).x();
+  int offset = 0;
+  size_t run_index = GetRunContainingXCoord(x, &offset);
+  if (run_index >= runs_.size())
+    return EdgeSelectionModel((x < 0) ? CURSOR_LEFT : CURSOR_RIGHT);
+  const internal::TextRunHarfBuzz& run = *runs_[run_index];
+
+  for (size_t i = 0; i < run.glyph_count; ++i) {
+    const SkScalar end =
+        i + 1 == run.glyph_count ? run.width : run.positions[i + 1].x();
+    const SkScalar middle = (end + run.positions[i].x()) / 2;
+    const bool is_rtl = run.direction == UBIDI_RTL;
+    if (offset < middle) {
+      return SelectionModel(LayoutIndexToTextIndex(
+          run.glyph_to_char[i] + (is_rtl ? 1 : 0)),
+          (is_rtl ? CURSOR_BACKWARD : CURSOR_FORWARD));
+    }
+    if (offset < end) {
+      return SelectionModel(LayoutIndexToTextIndex(
+          run.glyph_to_char[i] + (is_rtl ? 0 : 1)),
+          (is_rtl ? CURSOR_FORWARD : CURSOR_BACKWARD));
+    }
+  }
+  return EdgeSelectionModel(CURSOR_RIGHT);
+}
+
+std::vector<RenderText::FontSpan> RenderTextHarfBuzz::GetFontSpansForTesting() {
+  NOTIMPLEMENTED();
+  return std::vector<RenderText::FontSpan>();
+}
+
+int RenderTextHarfBuzz::GetLayoutTextBaseline() {
+  EnsureLayout();
+  return lines()[0].baseline;
+}
+
+SelectionModel RenderTextHarfBuzz::AdjacentCharSelectionModel(
+    const SelectionModel& selection,
+    VisualCursorDirection direction) {
+  DCHECK(!needs_layout_);
+  internal::TextRunHarfBuzz* run;
+  size_t run_index = GetRunContainingCaret(selection);
+  if (run_index >= runs_.size()) {
+    // The cursor is not in any run: we're at the visual and logical edge.
+    SelectionModel edge = EdgeSelectionModel(direction);
+    if (edge.caret_pos() == selection.caret_pos())
+      return edge;
+    int visual_index = (direction == CURSOR_RIGHT) ? 0 : runs_.size() - 1;
+    run = runs_[visual_to_logical_[visual_index]];
+  } else {
+    // If the cursor is moving within the current run, just move it by one
+    // grapheme in the appropriate direction.
+    run = runs_[run_index];
+    size_t caret = selection.caret_pos();
+    bool forward_motion =
+        (run->direction == UBIDI_RTL) == (direction == CURSOR_LEFT);
+    if (forward_motion) {
+      if (caret < LayoutIndexToTextIndex(run->range.end())) {
+        caret = IndexOfAdjacentGrapheme(caret, CURSOR_FORWARD);
+        return SelectionModel(caret, CURSOR_BACKWARD);
+      }
+    } else {
+      if (caret > LayoutIndexToTextIndex(run->range.start())) {
+        caret = IndexOfAdjacentGrapheme(caret, CURSOR_BACKWARD);
+        return SelectionModel(caret, CURSOR_FORWARD);
+      }
+    }
+    // The cursor is at the edge of a run; move to the visually adjacent run.
+    int visual_index = logical_to_visual_[run_index];
+    visual_index += (direction == CURSOR_LEFT) ? -1 : 1;
+    if (visual_index < 0 || visual_index >= static_cast<int>(runs_.size()))
+      return EdgeSelectionModel(direction);
+    run = runs_[visual_to_logical_[visual_index]];
+  }
+  bool forward_motion =
+      (run->direction == UBIDI_RTL) == (direction == CURSOR_LEFT);
+  return forward_motion ? FirstSelectionModelInsideRun(run) :
+                          LastSelectionModelInsideRun(run);
+}
+
+SelectionModel RenderTextHarfBuzz::AdjacentWordSelectionModel(
+    const SelectionModel& selection,
+    VisualCursorDirection direction) {
+  // TODO(ckocagil): This implementation currently matches RenderTextWin, but it
+  // should match the native behavior on other platforms.
+  if (obscured())
+    return EdgeSelectionModel(direction);
+
+  base::i18n::BreakIterator iter(text(), base::i18n::BreakIterator::BREAK_WORD);
+  bool success = iter.Init();
+  DCHECK(success);
+  if (!success)
+    return selection;
+
+  size_t pos;
+  if (direction == CURSOR_RIGHT) {
+    pos = std::min(selection.caret_pos() + 1, text().length());
+    while (iter.Advance()) {
+      pos = iter.pos();
+      if (iter.IsWord() && pos > selection.caret_pos())
+        break;
+    }
+  } else {  // direction == CURSOR_LEFT
+    // Notes: We always iterate words from the beginning.
+    // This is probably fast enough for our usage, but we may
+    // want to modify WordIterator so that it can start from the
+    // middle of string and advance backwards.
+    pos = std::max<int>(selection.caret_pos() - 1, 0);
+    while (iter.Advance()) {
+      if (iter.IsWord()) {
+        size_t begin = iter.pos() - iter.GetString().length();
+        if (begin == selection.caret_pos()) {
+          // The cursor is at the beginning of a word.
+          // Move to previous word.
+          break;
+        } else if (iter.pos() >= selection.caret_pos()) {
+          // The cursor is in the middle or at the end of a word.
+          // Move to the top of current word.
+          pos = begin;
+          break;
+        }
+        pos = iter.pos() - iter.GetString().length();
+      }
+    }
+  }
+  return SelectionModel(pos, CURSOR_FORWARD);
+}
+
+Range RenderTextHarfBuzz::GetGlyphBounds(size_t index) {
+  const size_t run_index =
+      GetRunContainingCaret(SelectionModel(index, CURSOR_FORWARD));
+  // Return edge bounds if the index is invalid or beyond the layout text size.
+  if (run_index >= runs_.size())
+    return Range(GetStringSize().width());
+  const size_t layout_index = TextIndexToLayoutIndex(index);
+  return Range(GetGlyphXBoundary(run_index, layout_index, false),
+               GetGlyphXBoundary(run_index, layout_index, true));
+}
+
+std::vector<Rect> RenderTextHarfBuzz::GetSubstringBounds(const Range& range) {
+  DCHECK(!needs_layout_);
+  DCHECK(Range(0, text().length()).Contains(range));
+  Range layout_range(TextIndexToLayoutIndex(range.start()),
+                     TextIndexToLayoutIndex(range.end()));
+  DCHECK(Range(0, GetLayoutText().length()).Contains(layout_range));
+
+  std::vector<Rect> rects;
+  if (layout_range.is_empty())
+    return rects;
+  std::vector<Range> bounds;
+
+  // Add a Range for each run/selection intersection.
+  // TODO(msw): The bounds should probably not always be leading the range ends.
+  for (size_t i = 0; i < runs_.size(); ++i) {
+    const internal::TextRunHarfBuzz* run = runs_[visual_to_logical_[i]];
+    Range intersection = run->range.Intersect(layout_range);
+    if (intersection.IsValid()) {
+      DCHECK(!intersection.is_reversed());
+      Range range_x(GetGlyphXBoundary(i, intersection.start(), false),
+                    GetGlyphXBoundary(i, intersection.end(), false));
+      if (range_x.is_empty())
+        continue;
+      range_x = Range(range_x.GetMin(), range_x.GetMax());
+      // Union this with the last range if they're adjacent.
+      DCHECK(bounds.empty() || bounds.back().GetMax() <= range_x.GetMin());
+      if (!bounds.empty() && bounds.back().GetMax() == range_x.GetMin()) {
+        range_x = Range(bounds.back().GetMin(), range_x.GetMax());
+        bounds.pop_back();
+      }
+      bounds.push_back(range_x);
+    }
+  }
+  for (size_t i = 0; i < bounds.size(); ++i) {
+    std::vector<Rect> current_rects = TextBoundsToViewBounds(bounds[i]);
+    rects.insert(rects.end(), current_rects.begin(), current_rects.end());
+  }
+  return rects;
+}
+
+size_t RenderTextHarfBuzz::TextIndexToLayoutIndex(size_t index) const {
+  DCHECK_LE(index, text().length());
+  ptrdiff_t i = obscured() ? UTF16IndexToOffset(text(), 0, index) : index;
+  CHECK_GE(i, 0);
+  // Clamp layout indices to the length of the text actually used for layout.
+  return std::min<size_t>(GetLayoutText().length(), i);
+}
+
+size_t RenderTextHarfBuzz::LayoutIndexToTextIndex(size_t index) const {
+  if (!obscured())
+    return index;
+
+  DCHECK_LE(index, GetLayoutText().length());
+  const size_t text_index = UTF16OffsetToIndex(text(), 0, index);
+  DCHECK_LE(text_index, text().length());
+  return text_index;
+}
+
+bool RenderTextHarfBuzz::IsValidCursorIndex(size_t index) {
+  if (index == 0 || index == text().length())
+    return true;
+  if (!IsValidLogicalIndex(index))
+    return false;
+  EnsureLayout();
+  // Disallow indices amid multi-character graphemes by checking glyph bounds.
+  // These characters are not surrogate-pairs, but may yield a single glyph:
+  //   \x0915\x093f - (ki) - one of many Devanagari biconsonantal conjuncts.
+  //   \x0e08\x0e33 - (cho chan + sara am) - a Thai consonant and vowel pair.
+  return GetGlyphBounds(index) != GetGlyphBounds(index - 1);
+}
+
+void RenderTextHarfBuzz::ResetLayout() {
+  needs_layout_ = true;
+}
+
+void RenderTextHarfBuzz::EnsureLayout() {
+  if (needs_layout_) {
+    runs_.clear();
+
+    if (!GetLayoutText().empty()) {
+      ItemizeText();
+
+      for (size_t i = 0; i < runs_.size(); ++i)
+        ShapeRun(runs_[i]);
+
+      // Precalculate run width information.
+      size_t preceding_run_widths = 0;
+      for (size_t i = 0; i < runs_.size(); ++i) {
+        internal::TextRunHarfBuzz* run = runs_[visual_to_logical_[i]];
+        run->preceding_run_widths = preceding_run_widths;
+        preceding_run_widths += run->width;
+      }
+    }
+
+    needs_layout_ = false;
+    std::vector<internal::Line> empty_lines;
+    set_lines(&empty_lines);
+  }
+
+  if (lines().empty()) {
+    std::vector<internal::Line> lines;
+    lines.push_back(internal::Line());
+
+    int current_x = 0;
+    SkPaint paint;
+
+    for (size_t i = 0; i < runs_.size(); ++i) {
+      const internal::TextRunHarfBuzz& run = *runs_[visual_to_logical_[i]];
+      internal::LineSegment segment;
+      segment.x_range = Range(current_x, current_x + run.width);
+      segment.char_range = run.range;
+      segment.run = i;
+      lines[0].segments.push_back(segment);
+
+      paint.setTypeface(run.skia_face.get());
+      paint.setTextSize(run.font_size);
+      SkPaint::FontMetrics metrics;
+      paint.getFontMetrics(&metrics);
+
+      lines[0].size.set_width(lines[0].size.width() + run.width);
+      lines[0].size.set_height(std::max(lines[0].size.height(),
+          SkScalarRoundToInt(metrics.fDescent - metrics.fAscent)));
+      lines[0].baseline = std::max(lines[0].baseline,
+                                   SkScalarRoundToInt(-metrics.fAscent));
+    }
+
+    set_lines(&lines);
+  }
+}
+
+void RenderTextHarfBuzz::DrawVisualText(Canvas* canvas) {
+  DCHECK(!needs_layout_);
+
+  int current_x = 0;
+
+  internal::SkiaTextRenderer renderer(canvas);
+  ApplyFadeEffects(&renderer);
+  ApplyTextShadows(&renderer);
+
+#if defined(OS_WIN)
+  bool smoothing_enabled;
+  bool cleartype_enabled;
+  GetCachedFontSmoothingSettings(&smoothing_enabled, &cleartype_enabled);
+  // Note that |cleartype_enabled| corresponds to Skia's |enable_lcd_text|.
+  renderer.SetFontSmoothingSettings(
+      smoothing_enabled, cleartype_enabled && !background_is_transparent(),
+      smoothing_enabled /* subpixel_positioning */);
+#endif
+
+  ApplyCompositionAndSelectionStyles();
+
+  const Vector2d line_offset = GetLineOffset(0);
+
+  for (size_t i = 0; i < runs_.size(); ++i) {
+    const internal::TextRunHarfBuzz& run = *runs_[visual_to_logical_[i]];
+    renderer.SetTypeface(run.skia_face.get());
+    renderer.SetTextSize(run.font_size);
+
+    canvas->Save();
+    Vector2d origin = line_offset + Vector2d(current_x, lines()[0].baseline);
+    canvas->Translate(origin);
+
+    for (BreakList<SkColor>::const_iterator it =
+             colors().GetBreak(run.range.start());
+         it != colors().breaks().end() && it->first < run.range.end();
+         ++it) {
+      const Range intersection = colors().GetRange(it).Intersect(run.range);
+      const Range colored_glyphs = CharRangeToGlyphRange(run, intersection);
+      // The range may be empty if a portion of a multi-character grapheme is
+      // selected, yielding two colors for a single glyph. For now, this just
+      // paints the glyph with a single style, but it should paint it twice,
+      // clipped according to selection bounds. See http://crbug.com/366786
+      if (colored_glyphs.is_empty())
+        continue;
+
+      renderer.SetForegroundColor(it->second);
+      renderer.DrawPosText(&run.positions[colored_glyphs.start()],
+                           &run.glyphs[colored_glyphs.start()],
+                           colored_glyphs.length());
+      int width = (colored_glyphs.end() == run.glyph_count ? run.width :
+              run.positions[colored_glyphs.end()].x()) -
+          run.positions[colored_glyphs.start()].x();
+      renderer.DrawDecorations(0, 0, width, run.underline, run.strike,
+                               run.diagonal_strike);
+    }
+
+    canvas->Restore();
+    current_x += run.width;
+  }
+
+  renderer.EndDiagonalStrike();
+
+  UndoCompositionAndSelectionStyles();
+}
+
+size_t RenderTextHarfBuzz::GetRunContainingCaret(
+    const SelectionModel& caret) const {
+  DCHECK(!needs_layout_);
+  size_t layout_position = TextIndexToLayoutIndex(caret.caret_pos());
+  LogicalCursorDirection affinity = caret.caret_affinity();
+  for (size_t run = 0; run < runs_.size(); ++run) {
+    if (RangeContainsCaret(runs_[run]->range, layout_position, affinity))
+      return run;
+  }
+  return runs_.size();
+}
+
+size_t RenderTextHarfBuzz::GetRunContainingXCoord(int x, int* offset) const {
+  DCHECK(!needs_layout_);
+  if (x < 0)
+    return runs_.size();
+  // Find the text run containing the argument point (assumed already offset).
+  int current_x = 0;
+  for (size_t i = 0; i < runs_.size(); ++i) {
+    size_t run = visual_to_logical_[i];
+    current_x += runs_[run]->width;
+    if (x < current_x) {
+      *offset = x - (current_x - runs_[run]->width);
+      return run;
+    }
+  }
+  return runs_.size();
+}
+
+int RenderTextHarfBuzz::GetGlyphXBoundary(size_t run_index,
+                                          size_t text_index,
+                                          bool trailing) {
+  const internal::TextRunHarfBuzz& run = *runs_[run_index];
+  int x = run.preceding_run_widths;
+
+  Range glyph_range;
+  if (text_index == run.range.end()) {
+    trailing = true;
+    glyph_range = run.direction == UBIDI_LTR ?
+        Range(run.glyph_count - 1, run.glyph_count) : Range(0, 1);
+  } else {
+    glyph_range = CharRangeToGlyphRange(run, Range(text_index, text_index + 1));
+  }
+  const int trailing_step = trailing ? 1 : 0;
+  const size_t glyph_pos = glyph_range.start() +
+      (run.direction == UBIDI_LTR ? trailing_step : (1 - trailing_step));
+  x += glyph_pos < run.glyph_count ?
+      SkScalarRoundToInt(run.positions[glyph_pos].x()) : run.width;
+  return x;
+}
+
+SelectionModel RenderTextHarfBuzz::FirstSelectionModelInsideRun(
+    const internal::TextRunHarfBuzz* run) {
+  size_t position = LayoutIndexToTextIndex(run->range.start());
+  position = IndexOfAdjacentGrapheme(position, CURSOR_FORWARD);
+  return SelectionModel(position, CURSOR_BACKWARD);
+}
+
+SelectionModel RenderTextHarfBuzz::LastSelectionModelInsideRun(
+    const internal::TextRunHarfBuzz* run) {
+  size_t position = LayoutIndexToTextIndex(run->range.end());
+  position = IndexOfAdjacentGrapheme(position, CURSOR_BACKWARD);
+  return SelectionModel(position, CURSOR_FORWARD);
+}
+
+void RenderTextHarfBuzz::ItemizeText() {
+  const base::string16& text = GetLayoutText();
+  const bool is_rtl = GetTextDirection() == base::i18n::RIGHT_TO_LEFT;
+  DCHECK_NE(0U, text.length());
+
+  bool fake_runs = false;
+  UErrorCode result = U_ZERO_ERROR;
+
+  UBiDi* line = ubidi_openSized(text.length(), 0, &result);
+  if (U_FAILURE(result)) {
+    NOTREACHED();
+    fake_runs = true;
+  } else {
+    ubidi_setPara(line, text.c_str(), text.length(),
+                  is_rtl ? UBIDI_DEFAULT_RTL : UBIDI_DEFAULT_LTR, NULL,
+                  &result);
+    if (U_FAILURE(result)) {
+      NOTREACHED();
+      fake_runs = true;
+    }
+  }
+
+  // Temporarily apply composition underlines and selection colors.
+  ApplyCompositionAndSelectionStyles();
+
+  // Build the list of runs from the script items and ranged styles. Use an
+  // empty color BreakList to avoid breaking runs at color boundaries.
+  BreakList<SkColor> empty_colors;
+  empty_colors.SetMax(text.length());
+  internal::StyleIterator style(empty_colors, styles());
+
+  for (size_t run_break = 0; run_break < text.length();) {
+    internal::TextRunHarfBuzz* run = new internal::TextRunHarfBuzz;
+    run->range.set_start(run_break);
+    run->font_style = (style.style(BOLD) ? Font::BOLD : 0) |
+                      (style.style(ITALIC) ? Font::ITALIC : 0);
+    run->strike = style.style(STRIKE);
+    run->diagonal_strike = style.style(DIAGONAL_STRIKE);
+    run->underline = style.style(UNDERLINE);
+
+    if (fake_runs) {
+      run_break = text.length();
+    } else {
+      int32 script_item_break = 0;
+      ubidi_getLogicalRun(line, run_break, &script_item_break, &run->level);
+      // Find the length and script of this script run.
+      script_item_break = ScriptInterval(text.c_str() + run_break,
+          script_item_break - run_break, &run->script) + run_break;
+
+      // Find the next break and advance the iterators as needed.
+      run_break = std::min(static_cast<size_t>(script_item_break),
+                           TextIndexToLayoutIndex(style.GetRange().end()));
+
+      // Break runs adjacent to character substrings in certain code blocks.
+      // This avoids using their fallback fonts for more characters than needed,
+      // in cases like "\x25B6 Media Title", etc. http://crbug.com/278913
+      if (run_break > run->range.start()) {
+        const size_t run_start = run->range.start();
+        const int32 run_length = static_cast<int32>(run_break - run_start);
+        base::i18n::UTF16CharIterator iter(text.c_str() + run_start,
+                                           run_length);
+        const UBlockCode first_block_code = ublock_getCode(iter.get());
+        const bool first_block_unusual = IsUnusualBlockCode(first_block_code);
+        while (iter.Advance() && iter.array_pos() < run_length) {
+          const UBlockCode current_block_code = ublock_getCode(iter.get());
+          if (current_block_code != first_block_code &&
+              (first_block_unusual || IsUnusualBlockCode(current_block_code))) {
+            run_break = run_start + iter.array_pos();
+            break;
+          }
+        }
+      }
+    }
+
+    DCHECK(IsValidCodePointIndex(text, run_break));
+    style.UpdatePosition(LayoutIndexToTextIndex(run_break));
+    run->range.set_end(run_break);
+    const UChar* uchar_start = ubidi_getText(line);
+    // TODO(ckocagil): Add |ubidi_getBaseDirection| to i18n::BiDiLineIterator
+    // and remove the bare ICU use here.
+    run->direction = ubidi_getBaseDirection(uchar_start + run->range.start(),
+                                            run->range.length());
+    if (run->direction == UBIDI_NEUTRAL)
+      run->direction = is_rtl ? UBIDI_RTL : UBIDI_LTR;
+    runs_.push_back(run);
+  }
+
+  ubidi_close(line);
+
+  // Undo the temporarily applied composition underlines and selection colors.
+  UndoCompositionAndSelectionStyles();
+
+  const size_t num_runs = runs_.size();
+  scoped_ptr<UBiDiLevel[]> levels(new UBiDiLevel[num_runs]);
+  for (size_t i = 0; i < num_runs; ++i)
+    levels[i] = runs_[i]->level;
+  visual_to_logical_.resize(num_runs);
+  ubidi_reorderVisual(levels.get(), num_runs, &visual_to_logical_[0]);
+  logical_to_visual_.resize(num_runs);
+  ubidi_reorderLogical(levels.get(), num_runs, &logical_to_visual_[0]);
+}
+
+void RenderTextHarfBuzz::ShapeRun(internal::TextRunHarfBuzz* run) {
+  const base::string16& text = GetLayoutText();
+  // TODO(ckocagil|yukishiino): Implement font fallback.
+  const Font& primary_font = font_list().GetPrimaryFont();
+  run->skia_face = internal::CreateSkiaTypeface(primary_font.GetFontName(),
+                                                run->font_style);
+  run->font_size = primary_font.GetFontSize();
+
+  hb_font_t* harfbuzz_font = CreateHarfBuzzFont(run->skia_face.get(),
+                                                run->font_size);
+
+  // Create a HarfBuzz buffer and add the string to be shaped. The HarfBuzz
+  // buffer holds our text, run information to be used by the shaping engine,
+  // and the resulting glyph data.
+  hb_buffer_t* buffer = hb_buffer_create();
+  hb_buffer_add_utf16(buffer, reinterpret_cast<const uint16*>(text.c_str()),
+                      text.length(), run->range.start(), run->range.length());
+  hb_buffer_set_script(buffer, hb_icu_script_to_script(run->script));
+  hb_buffer_set_direction(buffer,
+      run->direction == UBIDI_LTR ? HB_DIRECTION_LTR : HB_DIRECTION_RTL);
+  // TODO(ckocagil): Should we determine the actual language?
+  hb_buffer_set_language(buffer, hb_language_get_default());
+
+  // Shape the text.
+  hb_shape(harfbuzz_font, buffer, NULL, 0);
+
+  // Populate the run fields with the resulting glyph data in the buffer.
+  hb_glyph_info_t* infos = hb_buffer_get_glyph_infos(buffer, &run->glyph_count);
+  hb_glyph_position_t* hb_positions = hb_buffer_get_glyph_positions(buffer,
+                                                                    NULL);
+  run->glyphs.reset(new uint16[run->glyph_count]);
+  run->glyph_to_char.reset(new uint32[run->glyph_count]);
+  run->positions.reset(new SkPoint[run->glyph_count]);
+  for (size_t i = 0; i < run->glyph_count; ++i) {
+    run->glyphs[i] = infos[i].codepoint;
+    run->glyph_to_char[i] = infos[i].cluster;
+    const int x_offset =
+        SkScalarRoundToInt(SkFixedToScalar(hb_positions[i].x_offset));
+    const int y_offset =
+        SkScalarRoundToInt(SkFixedToScalar(hb_positions[i].y_offset));
+    run->positions[i].set(run->width + x_offset, y_offset);
+    run->width +=
+        SkScalarRoundToInt(SkFixedToScalar(hb_positions[i].x_advance));
+  }
+
+  hb_buffer_destroy(buffer);
+  hb_font_destroy(harfbuzz_font);
+}
+
+}  // namespace gfx