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 <limits>
#include <map>

#include "base/i18n/bidi_line_iterator.h"
#include "base/i18n/break_iterator.h"
#include "base/i18n/char_iterator.h"
#include "base/lazy_instance.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/font_fallback.h"
#include "ui/gfx/font_render_params.h"
#include "ui/gfx/utf16_indexing.h"

#if defined(OS_WIN)
#include "ui/gfx/font_fallback_win.h"
#endif

namespace gfx {

namespace {

// Text length limit. Longer strings are slow and not fully tested.
const size_t kMaxTextLength = 10000;

// The maximum number of scripts a Unicode character can belong to. This value
// is arbitrarily chosen to be a good limit because it is unlikely for a single
// character to belong to more scripts.
const size_t kMaxScripts = 5;

// Maps from code points to glyph indices in a font.
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);
}

// Deletes the object at the given pointer after casting it to the given type.
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;
}

// Outputs the |width| and |extents| of the glyph with index |codepoint| in
// |paint|'s font.
void GetGlyphWidthAndExtents(SkPaint* paint,
                             hb_codepoint_t codepoint,
                             hb_position_t* width,
                             hb_glyph_extents_t* extents) {
  DCHECK_LE(codepoint, 0xFFFFU);
  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());
  }
}

// Writes the |glyph| index for the given |unicode| code point. Returns whether
// the glyph exists, i.e. it is not a missing glyph.
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;
}

// Returns the horizontal advance value of the |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_position_t GetGlyphKerning(FontData* font_data,
                              hb_codepoint_t first_glyph,
                              hb_codepoint_t second_glyph) {
  SkTypeface* typeface = font_data->paint_.getTypeface();
  const uint16_t glyphs[2] = { static_cast<uint16_t>(first_glyph),
                               static_cast<uint16_t>(second_glyph) };
  int32_t kerning_adjustments[1] = { 0 };

  if (!typeface->getKerningPairAdjustments(glyphs, 2, kerning_adjustments))
    return 0;

  SkScalar upm = SkIntToScalar(typeface->getUnitsPerEm());
  SkScalar size = font_data->paint_.getTextSize();
  return SkiaScalarToHarfBuzzPosition(
      SkScalarMulDiv(SkIntToScalar(kerning_adjustments[0]), size, upm));
}

hb_position_t GetGlyphHorizontalKerning(hb_font_t* font,
                                        void* data,
                                        hb_codepoint_t left_glyph,
                                        hb_codepoint_t right_glyph,
                                        void* user_data) {
  FontData* font_data = reinterpret_cast<FontData*>(data);
  if (font_data->paint_.isVerticalText()) {
    // We don't support cross-stream kerning.
    return 0;
  }

  return GetGlyphKerning(font_data, left_glyph, right_glyph);
}

hb_position_t GetGlyphVerticalKerning(hb_font_t* font,
                                      void* data,
                                      hb_codepoint_t top_glyph,
                                      hb_codepoint_t bottom_glyph,
                                      void* user_data) {
  FontData* font_data = reinterpret_cast<FontData*>(data);
  if (!font_data->paint_.isVerticalText()) {
    // We don't support cross-stream kerning.
    return 0;
  }

  return GetGlyphKerning(font_data, top_glyph, bottom_glyph);
}

// Writes the |extents| of |glyph|.
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;
}

class FontFuncs {
 public:
  FontFuncs() : font_funcs_(hb_font_funcs_create()) {
    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_kerning_func(
        font_funcs_, GetGlyphHorizontalKerning, 0, 0);
    hb_font_funcs_set_glyph_h_origin_func(
        font_funcs_, GetGlyphHorizontalOrigin, 0, 0);
    hb_font_funcs_set_glyph_v_kerning_func(
        font_funcs_, GetGlyphVerticalKerning, 0, 0);
    hb_font_funcs_set_glyph_extents_func(
        font_funcs_, GetGlyphExtents, 0, 0);
    hb_font_funcs_make_immutable(font_funcs_);
  }

  ~FontFuncs() {
    hb_font_funcs_destroy(font_funcs_);
  }

  hb_font_funcs_t* get() { return font_funcs_; }

 private:
  hb_font_funcs_t* font_funcs_;

  DISALLOW_COPY_AND_ASSIGN(FontFuncs);
};

base::LazyInstance<FontFuncs>::Leaky g_font_funcs = LAZY_INSTANCE_INITIALIZER;

// Returns the raw data of the font table |tag|.
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;

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

  char* buffer_raw = buffer.release();
  return hb_blob_create(buffer_raw, table_size, HB_MEMORY_MODE_WRITABLE,
                        buffer_raw, DeleteArrayByType<char>);
}

void UnrefSkTypeface(void* data) {
  SkTypeface* skia_face = reinterpret_cast<SkTypeface*>(data);
  SkSafeUnref(skia_face);
}

// Wrapper class for a HarfBuzz face created from a given Skia face.
class HarfBuzzFace {
 public:
  HarfBuzzFace() : face_(NULL) {}

  ~HarfBuzzFace() {
    if (face_)
      hb_face_destroy(face_);
  }

  void Init(SkTypeface* skia_face) {
    SkSafeRef(skia_face);
    face_ = hb_face_create_for_tables(GetFontTable, skia_face, UnrefSkTypeface);
    DCHECK(face_);
  }

  hb_face_t* get() {
    return face_;
  }

 private:
  hb_face_t* face_;
};

// Creates a HarfBuzz font from the given Skia face and text size.
hb_font_t* CreateHarfBuzzFont(SkTypeface* skia_face,
                              int text_size,
                              const FontRenderParams& params,
                              bool background_is_transparent) {
  typedef std::pair<HarfBuzzFace, 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.get() == NULL)
    face_cache->first.Init(skia_face);

  hb_font_t* harfbuzz_font = hb_font_create(face_cache->first.get());
  const int scale = SkScalarToFixed(text_size);
  hb_font_set_scale(harfbuzz_font, scale, scale);
  FontData* hb_font_data = new FontData(&face_cache->second);
  hb_font_data->paint_.setTypeface(skia_face);
  hb_font_data->paint_.setTextSize(text_size);
  // TODO(ckocagil): Do we need to update these params later?
  internal::ApplyRenderParams(params, background_is_transparent,
                              &hb_font_data->paint_);
  hb_font_set_funcs(harfbuzz_font, g_font_funcs.Get().get(), hb_font_data,
                    DeleteByType<FontData>);
  hb_font_make_immutable(harfbuzz_font);
  return harfbuzz_font;
}

// Returns true if characters of |block_code| may trigger font fallback.
bool IsUnusualBlockCode(UBlockCode block_code) {
  return block_code == UBLOCK_GEOMETRIC_SHAPES ||
         block_code == UBLOCK_MISCELLANEOUS_SYMBOLS;
}

bool IsBracket(UChar32 character) {
  static const char kBrackets[] = { '(', ')', '{', '}', '<', '>', };
  static const char* kBracketsEnd = kBrackets + arraysize(kBrackets);
  return std::find(kBrackets, kBracketsEnd, character) != kBracketsEnd;
}

// Returns the boundary between a special and a regular character. Special
// characters are brackets or characters that satisfy |IsUnusualBlockCode|.
size_t FindRunBreakingCharacter(const base::string16& text,
                                size_t run_start,
                                size_t run_break) {
  const int32 run_length = static_cast<int32>(run_break - run_start);
  base::i18n::UTF16CharIterator iter(text.c_str() + run_start, run_length);
  const UChar32 first_char = iter.get();
  const UBlockCode first_block = ublock_getCode(first_char);
  const bool first_block_unusual = IsUnusualBlockCode(first_block);
  const bool first_bracket = IsBracket(first_char);

  while (iter.Advance() && iter.array_pos() < run_length) {
    const UChar32 current_char = iter.get();
    const UBlockCode current_block = ublock_getCode(current_char);
    const bool block_break = current_block != first_block &&
        (first_block_unusual || IsUnusualBlockCode(current_block));
    if (block_break || first_bracket != IsBracket(current_char))
      return run_start + iter.array_pos();
  }
  return run_break;
}

// If the given scripts match, returns the one that isn't USCRIPT_COMMON or
// USCRIPT_INHERITED, i.e. the more specific one. Otherwise returns
// USCRIPT_INVALID_CODE.
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;
}

// Writes the script and the script extensions of the character with the
// Unicode |codepoint|. Returns the number of written scripts.
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.
  // Write the character's script property to the first element.
  scripts[0] = uscript_getScript(codepoint, &icu_error);
  if (U_FAILURE(icu_error))
    return 0;
  // Fill the rest of |scripts| with the extensions.
  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);

  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) {
        result[out_size++] = intersection;
        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
//
// Consider 3 characters with the script values {Kana}, {Hira, Kana}, {Kana}.
// Without script extensions only the first script in each set would be taken
// into account, resulting in 3 runs where 1 would be enough.
// TODO(ckocagil): Write a unit test for the case above.
int ScriptInterval(const base::string16& text,
                   size_t start,
                   size_t length,
                   UScriptCode* script) {
  DCHECK_GT(length, 0U);

  UScriptCode scripts[kMaxScripts] = { USCRIPT_INVALID_CODE };

  base::i18n::UTF16CharIterator char_iterator(text.c_str() + start, 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)
      return char_iterator.array_pos();
    *script = scripts[0];
  }

  return length;
}

// A port of hb_icu_script_to_script because harfbuzz on CrOS is built without
// hb-icu. See http://crbug.com/356929
inline hb_script_t ICUScriptToHBScript(UScriptCode script) {
  if (script == USCRIPT_INVALID_CODE)
    return HB_SCRIPT_INVALID;
  return hb_script_from_string(uscript_getShortName(script), -1);
}

// Helper template function for |TextRunHarfBuzz::GetClusterAt()|. |Iterator|
// can be a forward or reverse iterator type depending on the text direction.
template <class Iterator>
void GetClusterAtImpl(size_t pos,
                      Range range,
                      Iterator elements_begin,
                      Iterator elements_end,
                      bool reversed,
                      Range* chars,
                      Range* glyphs) {
  Iterator element = std::upper_bound(elements_begin, elements_end, pos);
  chars->set_end(element == elements_end ? range.end() : *element);
  glyphs->set_end(reversed ? elements_end - element : element - elements_begin);

  DCHECK(element != elements_begin);
  while (--element != elements_begin && *element == *(element - 1));
  chars->set_start(*element);
  glyphs->set_start(
      reversed ? elements_end - element : element - elements_begin);
  if (reversed)
    *glyphs = Range(glyphs->end(), glyphs->start());

  DCHECK(!chars->is_reversed());
  DCHECK(!chars->is_empty());
  DCHECK(!glyphs->is_reversed());
  DCHECK(!glyphs->is_empty());
}

}  // namespace

namespace internal {

TextRunHarfBuzz::TextRunHarfBuzz()
    : width(0.0f),
      preceding_run_widths(0.0f),
      is_rtl(false),
      level(0),
      script(USCRIPT_INVALID_CODE),
      glyph_count(static_cast<size_t>(-1)),
      font_size(0),
      font_style(0),
      strike(false),
      diagonal_strike(false),
      underline(false) {}

TextRunHarfBuzz::~TextRunHarfBuzz() {}

void TextRunHarfBuzz::GetClusterAt(size_t pos,
                                   Range* chars,
                                   Range* glyphs) const {
  DCHECK(range.Contains(Range(pos, pos + 1)));
  DCHECK(chars);
  DCHECK(glyphs);

  if (glyph_count == 0) {
    *chars = range;
    *glyphs = Range();
    return;
  }

  if (is_rtl) {
    GetClusterAtImpl(pos, range, glyph_to_char.rbegin(), glyph_to_char.rend(),
        true, chars, glyphs);
    return;
  }

  GetClusterAtImpl(pos, range, glyph_to_char.begin(), glyph_to_char.end(),
      false, chars, glyphs);
}

Range TextRunHarfBuzz::CharRangeToGlyphRange(const Range& char_range) const {
  DCHECK(range.Contains(char_range));
  DCHECK(!char_range.is_reversed());
  DCHECK(!char_range.is_empty());

  Range start_glyphs;
  Range end_glyphs;
  Range temp_range;
  GetClusterAt(char_range.start(), &temp_range, &start_glyphs);
  GetClusterAt(char_range.end() - 1, &temp_range, &end_glyphs);

  return is_rtl ? Range(end_glyphs.start(), start_glyphs.end()) :
      Range(start_glyphs.start(), end_glyphs.end());
}

size_t TextRunHarfBuzz::CountMissingGlyphs() const {
  static const int kMissingGlyphId = 0;
  size_t missing = 0;
  for (size_t i = 0; i < glyph_count; ++i)
    missing += (glyphs[i] == kMissingGlyphId) ? 1 : 0;
  return missing;
}

Range TextRunHarfBuzz::GetGraphemeBounds(
    base::i18n::BreakIterator* grapheme_iterator,
    size_t text_index) {
  DCHECK_LT(text_index, range.end());
  // TODO(msw): Support floating point grapheme bounds.
  const int preceding_run_widths_int = SkScalarRoundToInt(preceding_run_widths);
  if (glyph_count == 0)
    return Range(preceding_run_widths_int, preceding_run_widths_int + width);

  Range chars;
  Range glyphs;
  GetClusterAt(text_index, &chars, &glyphs);
  const int cluster_begin_x = SkScalarRoundToInt(positions[glyphs.start()].x());
  const int cluster_end_x = glyphs.end() < glyph_count ?
      SkScalarRoundToInt(positions[glyphs.end()].x()) : width;

  // A cluster consists of a number of code points and corresponds to a number
  // of glyphs that should be drawn together. A cluster can contain multiple
  // graphemes. In order to place the cursor at a grapheme boundary inside the
  // cluster, we simply divide the cluster width by the number of graphemes.
  if (chars.length() > 1 && grapheme_iterator) {
    int before = 0;
    int total = 0;
    for (size_t i = chars.start(); i < chars.end(); ++i) {
      if (grapheme_iterator->IsGraphemeBoundary(i)) {
        if (i < text_index)
          ++before;
        ++total;
      }
    }
    DCHECK_GT(total, 0);
    if (total > 1) {
      if (is_rtl)
        before = total - before - 1;
      DCHECK_GE(before, 0);
      DCHECK_LT(before, total);
      const int cluster_width = cluster_end_x - cluster_begin_x;
      const int grapheme_begin_x = cluster_begin_x + static_cast<int>(0.5f +
          cluster_width * before / static_cast<float>(total));
      const int grapheme_end_x = cluster_begin_x + static_cast<int>(0.5f +
          cluster_width * (before + 1) / static_cast<float>(total));
      return Range(preceding_run_widths_int + grapheme_begin_x,
                   preceding_run_widths_int + grapheme_end_x);
    }
  }

  return Range(preceding_run_widths_int + cluster_begin_x,
               preceding_run_widths_int + cluster_end_x);
}

}  // namespace internal

RenderTextHarfBuzz::RenderTextHarfBuzz()
    : RenderText(),
      needs_layout_(false) {
  set_truncate_length(kMaxTextLength);
}

RenderTextHarfBuzz::~RenderTextHarfBuzz() {}

Size RenderTextHarfBuzz::GetStringSize() {
  const SizeF size_f = GetStringSizeF();
  return Size(std::ceil(size_f.width()), size_f.height());
}

SizeF RenderTextHarfBuzz::GetStringSizeF() {
  EnsureLayout();
  return lines()[0].size;
}

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;

    if (offset < middle) {
      return SelectionModel(LayoutIndexToTextIndex(
          run.glyph_to_char[i] + (run.is_rtl ? 1 : 0)),
          (run.is_rtl ? CURSOR_BACKWARD : CURSOR_FORWARD));
    }
    if (offset < end) {
      return SelectionModel(LayoutIndexToTextIndex(
          run.glyph_to_char[i] + (run.is_rtl ? 0 : 1)),
          (run.is_rtl ? CURSOR_FORWARD : CURSOR_BACKWARD));
    }
  }
  return EdgeSelectionModel(CURSOR_RIGHT);
}

std::vector<RenderText::FontSpan> RenderTextHarfBuzz::GetFontSpansForTesting() {
  EnsureLayout();

  std::vector<RenderText::FontSpan> spans;
  for (size_t i = 0; i < runs_.size(); ++i) {
    SkString family_name;
    runs_[i]->skia_face->getFamilyName(&family_name);
    Font font(family_name.c_str(), runs_[i]->font_size);
    spans.push_back(RenderText::FontSpan(font,
        Range(LayoutIndexToTextIndex(runs_[i]->range.start()),
              LayoutIndexToTextIndex(runs_[i]->range.end()))));
  }

  return spans;
}

Range RenderTextHarfBuzz::GetGlyphBounds(size_t index) {
  EnsureLayout();
  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);
  internal::TextRunHarfBuzz* run = runs_[run_index];
  Range bounds = run->GetGraphemeBounds(grapheme_iterator_.get(), layout_index);
  return run->is_rtl ? Range(bounds.end(), bounds.start()) : bounds;
}

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->is_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->is_rtl == (direction == CURSOR_LEFT);
  return forward_motion ? FirstSelectionModelInsideRun(run) :
                          LastSelectionModelInsideRun(run);
}

SelectionModel RenderTextHarfBuzz::AdjacentWordSelectionModel(
    const SelectionModel& selection,
    VisualCursorDirection direction) {
  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;

  // Match OS specific word break behavior.
#if defined(OS_WIN)
  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);
#else
  SelectionModel cur(selection);
  for (;;) {
    cur = AdjacentCharSelectionModel(cur, direction);
    size_t run = GetRunContainingCaret(cur);
    if (run == runs_.size())
      break;
    const bool is_forward = runs_[run]->is_rtl == (direction == CURSOR_LEFT);
    size_t cursor = cur.caret_pos();
    if (is_forward ? iter.IsEndOfWord(cursor) : iter.IsStartOfWord(cursor))
      break;
  }
  return cur;
#endif
}

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.
  for (size_t i = 0; i < runs_.size(); ++i) {
    internal::TextRunHarfBuzz* run = runs_[visual_to_logical_[i]];
    Range intersection = run->range.Intersect(layout_range);
    if (!intersection.IsValid())
      continue;
    DCHECK(!intersection.is_reversed());
    const Range leftmost_character_x = run->GetGraphemeBounds(
        grapheme_iterator_.get(),
        run->is_rtl ? intersection.end() - 1 : intersection.start());
    const Range rightmost_character_x = run->GetGraphemeBounds(
        grapheme_iterator_.get(),
        run->is_rtl ? intersection.start() : intersection.end() - 1);
    Range range_x(leftmost_character_x.start(), rightmost_character_x.end());
    DCHECK(!range_x.is_reversed());
    if (range_x.is_empty())
      continue;

    // 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();
  return !grapheme_iterator_ || grapheme_iterator_->IsGraphemeBoundary(index);
}

void RenderTextHarfBuzz::ResetLayout() {
  needs_layout_ = true;
}

void RenderTextHarfBuzz::EnsureLayout() {
  if (needs_layout_) {
    runs_.clear();
    grapheme_iterator_.reset();

    if (!GetLayoutText().empty()) {
      grapheme_iterator_.reset(new base::i18n::BreakIterator(GetLayoutText(),
          base::i18n::BreakIterator::BREAK_CHARACTER));
      if (!grapheme_iterator_->Init())
        grapheme_iterator_.reset();

      ItemizeText();

      for (size_t i = 0; i < runs_.size(); ++i)
        ShapeRun(runs_[i]);

      // Precalculate run width information.
      float preceding_run_widths = 0.0f;
      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());
    lines[0].baseline = font_list().GetBaseline();
    lines[0].size.set_height(font_list().GetHeight());

    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(),
                                        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_);
  internal::SkiaTextRenderer renderer(canvas);
  ApplyFadeEffects(&renderer);
  ApplyTextShadows(&renderer);
  ApplyCompositionAndSelectionStyles();

  int current_x = 0;
  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);
    renderer.SetFontRenderParams(run.render_params,
                                 background_is_transparent());

    Vector2d origin = line_offset + Vector2d(current_x, lines()[0].baseline);
    scoped_ptr<SkPoint[]> positions(new SkPoint[run.glyph_count]);
    for (size_t j = 0; j < run.glyph_count; ++j) {
      positions[j] = run.positions[j];
      positions[j].offset(SkIntToScalar(origin.x()), SkIntToScalar(origin.y()));
    }

    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 = run.CharRangeToGlyphRange(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(&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(origin.x(), origin.y(), width, run.underline,
                               run.strike, run.diagonal_strike);
    }

    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();
}

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_text_rtl = GetTextDirection() == base::i18n::RIGHT_TO_LEFT;
  DCHECK_NE(0U, text.length());

  // If ICU fails to itemize the text, we create a run that spans the entire
  // text. This is needed because leaving the runs set empty causes some clients
  // to misbehave since they expect non-zero text metrics from a non-empty text.
  base::i18n::BiDiLineIterator bidi_iterator;
  if (!bidi_iterator.Open(text, is_text_rtl, false)) {
    internal::TextRunHarfBuzz* run = new internal::TextRunHarfBuzz;
    run->range = Range(0, text.length());
    runs_.push_back(run);
    visual_to_logical_ = logical_to_visual_ = std::vector<int32_t>(1, 0);
    return;
  }

  // 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);

    int32 script_item_break = 0;
    bidi_iterator.GetLogicalRun(run_break, &script_item_break, &run->level);
    // Odd BiDi embedding levels correspond to RTL runs.
    run->is_rtl = (run->level % 2) == 1;
    // Find the length and script of this script run.
    script_item_break = ScriptInterval(text, 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 at certain characters that need to be rendered separately to
    // prevent either an unusual character from forcing a fallback font on the
    // entire run, or brackets from being affected by a fallback font.
    // http://crbug.com/278913, http://crbug.com/396776
    if (run_break > run->range.start())
      run_break = FindRunBreakingCharacter(text, run->range.start(), run_break);

    DCHECK(IsValidCodePointIndex(text, run_break));
    style.UpdatePosition(LayoutIndexToTextIndex(run_break));
    run->range.set_end(run_break);

    runs_.push_back(run);
  }

  // Undo the temporarily applied composition underlines and selection colors.
  UndoCompositionAndSelectionStyles();

  const size_t num_runs = runs_.size();
  std::vector<UBiDiLevel> levels(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[0], num_runs, &visual_to_logical_[0]);
  logical_to_visual_.resize(num_runs);
  ubidi_reorderLogical(&levels[0], num_runs, &logical_to_visual_[0]);
}

void RenderTextHarfBuzz::ShapeRun(internal::TextRunHarfBuzz* run) {
  const Font& primary_font = font_list().GetPrimaryFont();
  const std::string primary_font_name = primary_font.GetFontName();
  run->font_size = primary_font.GetFontSize();

  size_t best_font_missing = std::numeric_limits<size_t>::max();
  std::string best_font;
  std::string current_font;

  // Try shaping with |primary_font|.
  if (ShapeRunWithFont(run, primary_font_name)) {
    current_font = primary_font_name;
    size_t current_missing = run->CountMissingGlyphs();
    if (current_missing == 0)
      return;
    if (current_missing < best_font_missing) {
      best_font_missing = current_missing;
      best_font = current_font;
    }
  }

#if defined(OS_WIN)
  Font uniscribe_font;
  const base::char16* run_text = &(GetLayoutText()[run->range.start()]);
  if (GetUniscribeFallbackFont(primary_font, run_text, run->range.length(),
                               &uniscribe_font) &&
      ShapeRunWithFont(run, uniscribe_font.GetFontName())) {
    current_font = uniscribe_font.GetFontName();
    size_t current_missing = run->CountMissingGlyphs();
    if (current_missing == 0)
      return;
    if (current_missing < best_font_missing) {
      best_font_missing = current_missing;
      best_font = current_font;
    }
  }
#endif

  // Try shaping with the fonts in the fallback list except the first, which is
  // |primary_font|.
  std::vector<std::string> fonts = GetFallbackFontFamilies(primary_font_name);
  for (size_t i = 1; i < fonts.size(); ++i) {
    if (!ShapeRunWithFont(run, fonts[i]))
      continue;
    current_font = fonts[i];
    size_t current_missing = run->CountMissingGlyphs();
    if (current_missing == 0)
      return;
    if (current_missing < best_font_missing) {
      best_font_missing = current_missing;
      best_font = current_font;
    }
  }

  if (!best_font.empty() &&
      (best_font == current_font || ShapeRunWithFont(run, best_font))) {
    return;
  }

  run->glyph_count = 0;
  run->width = 0.0f;
}

bool RenderTextHarfBuzz::ShapeRunWithFont(internal::TextRunHarfBuzz* run,
                                          const std::string& font_family) {
  const base::string16& text = GetLayoutText();
  skia::RefPtr<SkTypeface> skia_face =
      internal::CreateSkiaTypeface(font_family, run->font_style);
  if (skia_face == NULL)
    return false;
  run->skia_face = skia_face;
  FontRenderParamsQuery query(false);
  query.families.push_back(font_family);
  query.pixel_size = run->font_size;
  query.style = run->font_style;
  run->render_params = GetFontRenderParams(query, NULL);
  hb_font_t* harfbuzz_font = CreateHarfBuzzFont(run->skia_face.get(),
      run->font_size, run->render_params, background_is_transparent());

  // 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, ICUScriptToHBScript(run->script));
  hb_buffer_set_direction(buffer,
      run->is_rtl ? HB_DIRECTION_RTL : HB_DIRECTION_LTR);
  // 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.
  unsigned int glyph_count = 0;
  hb_glyph_info_t* infos = hb_buffer_get_glyph_infos(buffer, &glyph_count);
  run->glyph_count = 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.resize(run->glyph_count);
  run->positions.reset(new SkPoint[run->glyph_count]);
  run->width = 0.0f;
  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 = SkFixedToScalar(hb_positions[i].x_offset);
    const int y_offset = SkFixedToScalar(hb_positions[i].y_offset);
    run->positions[i].set(run->width + x_offset, -y_offset);
    run->width += SkFixedToScalar(hb_positions[i].x_advance);
#if defined(OS_LINUX)
    // Match Pango's glyph rounding logic on Linux.
    if (!run->render_params.subpixel_positioning)
      run->width = std::floor(run->width + 0.5f);
#endif
  }

  hb_buffer_destroy(buffer);
  hb_font_destroy(harfbuzz_font);
  return true;
}

}  // namespace gfx