Layout.cpp

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define LOG_TAG "Minikin"

#include <math.h>
#include <unicode/ubidi.h>
#include <unicode/utf16.h>
#include <algorithm>
#include <fstream>
#include <iostream>  // for debugging
#include <string>
#include <vector>

#include <log/log.h>
#include <utils/JenkinsHash.h>
#include <utils/LruCache.h>
#include <utils/WindowsUtils.h>

#include <hb-icu.h>
#include <hb-ot.h>

#include <minikin/Emoji.h>
#include <minikin/Layout.h>
#include "FontLanguage.h"
#include "FontLanguageListCache.h"
#include "HbFontCache.h"
#include "LayoutUtils.h"
#include "MinikinInternal.h"

namespace minikin {

const int kDirection_Mask = 0x1;

struct LayoutContext {
  MinikinPaint paint;
  FontStyle style;
  std::vector<hb_font_t*> hbFonts;  // parallel to mFaces

  void clearHbFonts() {
    for (size_t i = 0; i < hbFonts.size(); i++) {
      hb_font_set_funcs(hbFonts[i], nullptr, nullptr, nullptr);
      hb_font_destroy(hbFonts[i]);
    }
    hbFonts.clear();
  }
};

// Layout cache datatypes

class LayoutCacheKey {
 public:
  LayoutCacheKey(const std::shared_ptr<FontCollection>& collection,
                 const MinikinPaint& paint,
                 FontStyle style,
                 const uint16_t* chars,
                 size_t start,
                 size_t count,
                 size_t nchars,
                 bool dir)
      : mChars(chars),
        mNchars(nchars),
        mStart(start),
        mCount(count),
        mId(collection->getId()),
        mStyle(style),
        mSize(paint.size),
        mScaleX(paint.scaleX),
        mSkewX(paint.skewX),
        mLetterSpacing(paint.letterSpacing),
        mPaintFlags(paint.paintFlags),
        mHyphenEdit(paint.hyphenEdit),
        mIsRtl(dir),
        mHash(computeHash()) {}
  bool operator==(const LayoutCacheKey& other) const;

  android::hash_t hash() const { return mHash; }

  void copyText() {
    uint16_t* charsCopy = new uint16_t[mNchars];
    memcpy(charsCopy, mChars, mNchars * sizeof(uint16_t));
    mChars = charsCopy;
  }
  void freeText() {
    delete[] mChars;
    mChars = NULL;
  }

  void doLayout(Layout* layout,
                LayoutContext* ctx,
                const std::shared_ptr<FontCollection>& collection) const {
    layout->mAdvances.resize(mCount, 0);
    ctx->clearHbFonts();
    layout->doLayoutRun(mChars, mStart, mCount, mNchars, mIsRtl, ctx,
                        collection);
  }

 private:
  const uint16_t* mChars;
  size_t mNchars;
  size_t mStart;
  size_t mCount;
  uint32_t mId;  // for the font collection
  FontStyle mStyle;
  float mSize;
  float mScaleX;
  float mSkewX;
  float mLetterSpacing;
  int32_t mPaintFlags;
  HyphenEdit mHyphenEdit;
  bool mIsRtl;
  // Note: any fields added to MinikinPaint must also be reflected here.
  // TODO: language matching (possibly integrate into style)
  android::hash_t mHash;

  android::hash_t computeHash() const;
};

class LayoutCache : private android::OnEntryRemoved<LayoutCacheKey, Layout*> {
 public:
  LayoutCache() : mCache(kMaxEntries) {
    mCache.setOnEntryRemovedListener(this);
  }

  void clear() { mCache.clear(); }

  Layout* get(LayoutCacheKey& key,
              LayoutContext* ctx,
              const std::shared_ptr<FontCollection>& collection) {
    Layout* layout = mCache.get(key);
    if (layout == NULL) {
      key.copyText();
      layout = new Layout();
      key.doLayout(layout, ctx, collection);
      mCache.put(key, layout);
    }
    return layout;
  }

 private:
  // callback for OnEntryRemoved
  void operator()(LayoutCacheKey& key, Layout*& value) {
    key.freeText();
    delete value;
  }

  android::LruCache<LayoutCacheKey, Layout*> mCache;

  // static const size_t kMaxEntries = LruCache<LayoutCacheKey,
  // Layout*>::kUnlimitedCapacity;

  // TODO: eviction based on memory footprint; for now, we just use a constant
  // number of strings
  static const size_t kMaxEntries = 5000;
};

class LayoutEngine {
 public:
  LayoutEngine() {
    unicodeFunctions = hb_unicode_funcs_create(hb_icu_get_unicode_funcs());
    hbBuffer = hb_buffer_create();
    hb_buffer_set_unicode_funcs(hbBuffer, unicodeFunctions);
  }

  hb_buffer_t* hbBuffer;
  hb_unicode_funcs_t* unicodeFunctions;
  LayoutCache layoutCache;

  static LayoutEngine& getInstance() {
    static LayoutEngine* instance = new LayoutEngine();
    return *instance;
  }
};

bool LayoutCacheKey::operator==(const LayoutCacheKey& other) const {
  return mId == other.mId && mStart == other.mStart && mCount == other.mCount &&
         mStyle == other.mStyle && mSize == other.mSize &&
         mScaleX == other.mScaleX && mSkewX == other.mSkewX &&
         mLetterSpacing == other.mLetterSpacing &&
         mPaintFlags == other.mPaintFlags && mHyphenEdit == other.mHyphenEdit &&
         mIsRtl == other.mIsRtl && mNchars == other.mNchars &&
         !memcmp(mChars, other.mChars, mNchars * sizeof(uint16_t));
}

android::hash_t LayoutCacheKey::computeHash() const {
  uint32_t hash = android::JenkinsHashMix(0, mId);
  hash = android::JenkinsHashMix(hash, mStart);
  hash = android::JenkinsHashMix(hash, mCount);
  hash = android::JenkinsHashMix(hash, hash_type(mStyle));
  hash = android::JenkinsHashMix(hash, hash_type(mSize));
  hash = android::JenkinsHashMix(hash, hash_type(mScaleX));
  hash = android::JenkinsHashMix(hash, hash_type(mSkewX));
  hash = android::JenkinsHashMix(hash, hash_type(mLetterSpacing));
  hash = android::JenkinsHashMix(hash, hash_type(mPaintFlags));
  hash = android::JenkinsHashMix(hash, hash_type(mHyphenEdit.getHyphen()));
  hash = android::JenkinsHashMix(hash, hash_type(mIsRtl));
  hash = android::JenkinsHashMixShorts(hash, mChars, mNchars);
  return android::JenkinsHashWhiten(hash);
}

android::hash_t hash_type(const LayoutCacheKey& key) {
  return key.hash();
}

void MinikinRect::join(const MinikinRect& r) {
  if (isEmpty()) {
    set(r);
  } else if (!r.isEmpty()) {
    mLeft = std::min(mLeft, r.mLeft);
    mTop = std::min(mTop, r.mTop);
    mRight = std::max(mRight, r.mRight);
    mBottom = std::max(mBottom, r.mBottom);
  }
}

void Layout::reset() {
  mGlyphs.clear();
  mFaces.clear();
  mBounds.setEmpty();
  mAdvances.clear();
  mAdvance = 0;
}

static hb_position_t harfbuzzGetGlyphHorizontalAdvance(hb_font_t* /* hbFont */,
                                                       void* fontData,
                                                       hb_codepoint_t glyph,
                                                       void* /* userData */) {
  MinikinPaint* paint = reinterpret_cast<MinikinPaint*>(fontData);
  float advance = paint->font->GetHorizontalAdvance(glyph, *paint);
  return 256 * advance + 0.5;
}

static hb_bool_t harfbuzzGetGlyphHorizontalOrigin(hb_font_t* /* hbFont */,
                                                  void* /* fontData */,
                                                  hb_codepoint_t /* glyph */,
                                                  hb_position_t* /* x */,
                                                  hb_position_t* /* y */,
                                                  void* /* userData */) {
  // Just return true, following the way that Harfbuzz-FreeType
  // implementation does.
  return true;
}

hb_font_funcs_t* getHbFontFuncs(bool forColorBitmapFont) {
  assertMinikinLocked();

  static hb_font_funcs_t* hbFuncs = nullptr;
  static hb_font_funcs_t* hbFuncsForColorBitmap = nullptr;

  hb_font_funcs_t** funcs =
      forColorBitmapFont ? &hbFuncs : &hbFuncsForColorBitmap;
  if (*funcs == nullptr) {
    *funcs = hb_font_funcs_create();
    if (forColorBitmapFont) {
      // Don't override the h_advance function since we use HarfBuzz's
      // implementation for emoji for performance reasons. Note that it is
      // technically possible for a TrueType font to have outline and embedded
      // bitmap at the same time. We ignore modified advances of hinted outline
      // glyphs in that case.
    } else {
      // Override the h_advance function since we can't use HarfBuzz's
      // implemenation. It may return the wrong value if the font uses hinting
      // aggressively.
      hb_font_funcs_set_glyph_h_advance_func(
          *funcs, harfbuzzGetGlyphHorizontalAdvance, 0, 0);
    }
    hb_font_funcs_set_glyph_h_origin_func(
        *funcs, harfbuzzGetGlyphHorizontalOrigin, 0, 0);
    hb_font_funcs_make_immutable(*funcs);
  }
  return *funcs;
}

static bool isColorBitmapFont(hb_font_t* font) {
  hb_face_t* face = hb_font_get_face(font);
  return hb_ot_color_has_png(face);
}

static float HBFixedToFloat(hb_position_t v) {
  return scalbnf(v, -8);
}

static hb_position_t HBFloatToFixed(float v) {
  return scalbnf(v, +8);
}

void Layout::dump() const {
  for (size_t i = 0; i < mGlyphs.size(); i++) {
    const LayoutGlyph& glyph = mGlyphs[i];
    std::cout << glyph.glyph_id << ": " << glyph.x << ", " << glyph.y
              << std::endl;
  }
}

int Layout::findFace(const FakedFont& face, LayoutContext* ctx) {
  unsigned int ix;
  for (ix = 0; ix < mFaces.size(); ix++) {
    if (mFaces[ix].font == face.font) {
      return ix;
    }
  }
  mFaces.push_back(face);
  // Note: ctx == NULL means we're copying from the cache, no need to create
  // corresponding hb_font object.
  if (ctx != NULL) {
    hb_font_t* font = getHbFontLocked(face.font);
    hb_font_set_funcs(font, getHbFontFuncs(isColorBitmapFont(font)),
                      &ctx->paint, 0);
    ctx->hbFonts.push_back(font);
  }
  return ix;
}

static hb_script_t codePointToScript(hb_codepoint_t codepoint) {
  static hb_unicode_funcs_t* u = 0;
  if (!u) {
    u = LayoutEngine::getInstance().unicodeFunctions;
  }
  return hb_unicode_script(u, codepoint);
}

static hb_codepoint_t decodeUtf16(const uint16_t* chars,
                                  size_t len,
                                  ssize_t* iter) {
  const uint16_t v = chars[(*iter)++];
  // test whether v in (0xd800..0xdfff), lead or trail surrogate
  if ((v & 0xf800) == 0xd800) {
    // test whether v in (0xd800..0xdbff), lead surrogate
    if (size_t(*iter) < len && (v & 0xfc00) == 0xd800) {
      const uint16_t v2 = chars[(*iter)++];
      // test whether v2 in (0xdc00..0xdfff), trail surrogate
      if ((v2 & 0xfc00) == 0xdc00) {
        // (0xd800 0xdc00) in utf-16 maps to 0x10000 in ucs-32
        const hb_codepoint_t delta = (0xd800 << 10) + 0xdc00 - 0x10000;
        return (((hb_codepoint_t)v) << 10) + v2 - delta;
      }
      (*iter) -= 1;
      return 0xFFFDu;
    } else {
      return 0xFFFDu;
    }
  } else {
    return v;
  }
}

static hb_script_t getScriptRun(const uint16_t* chars,
                                size_t len,
                                ssize_t* iter) {
  if (size_t(*iter) == len) {
    return HB_SCRIPT_UNKNOWN;
  }
  uint32_t cp = decodeUtf16(chars, len, iter);
  hb_script_t current_script = codePointToScript(cp);
  for (;;) {
    if (size_t(*iter) == len)
      break;
    const ssize_t prev_iter = *iter;
    cp = decodeUtf16(chars, len, iter);
    const hb_script_t script = codePointToScript(cp);
    if (script != current_script) {
      if (current_script == HB_SCRIPT_INHERITED ||
          current_script == HB_SCRIPT_COMMON) {
        current_script = script;
      } else if (script == HB_SCRIPT_INHERITED || script == HB_SCRIPT_COMMON) {
        continue;
      } else {
        *iter = prev_iter;
        break;
      }
    }
  }
  if (current_script == HB_SCRIPT_INHERITED) {
    current_script = HB_SCRIPT_COMMON;
  }

  return current_script;
}

/**
 * Disable certain scripts (mostly those with cursive connection) from having
 * letterspacing applied. See https://github.com/behdad/harfbuzz/issues/64 for
 * more details.
 */
static bool isScriptOkForLetterspacing(hb_script_t script) {
  return !(script == HB_SCRIPT_ARABIC || script == HB_SCRIPT_NKO ||
           script == HB_SCRIPT_PSALTER_PAHLAVI || script == HB_SCRIPT_MANDAIC ||
           script == HB_SCRIPT_MONGOLIAN || script == HB_SCRIPT_PHAGS_PA ||
           script == HB_SCRIPT_DEVANAGARI || script == HB_SCRIPT_BENGALI ||
           script == HB_SCRIPT_GURMUKHI || script == HB_SCRIPT_MODI ||
           script == HB_SCRIPT_SHARADA || script == HB_SCRIPT_SYLOTI_NAGRI ||
           script == HB_SCRIPT_TIRHUTA || script == HB_SCRIPT_OGHAM);
}

class BidiText {
 public:
  class Iter {
   public:
    struct RunInfo {
      int32_t mRunStart;
      int32_t mRunLength;
      bool mIsRtl;
    };

    Iter(UBiDi* bidi,
         size_t start,
         size_t end,
         size_t runIndex,
         size_t runCount,
         bool isRtl);

    bool operator!=(const Iter& other) const {
      return mIsEnd != other.mIsEnd || mNextRunIndex != other.mNextRunIndex ||
             mBidi != other.mBidi;
    }

    const RunInfo& operator*() const { return mRunInfo; }

    const Iter& operator++() {
      updateRunInfo();
      return *this;
    }

   private:
    UBiDi* const mBidi;
    bool mIsEnd;
    size_t mNextRunIndex;
    const size_t mRunCount;
    const int32_t mStart;
    const int32_t mEnd;
    RunInfo mRunInfo;

    void updateRunInfo();
  };

  BidiText(const uint16_t* buf,
           size_t start,
           size_t count,
           size_t bufSize,
           int bidiFlags);

  ~BidiText() {
    if (mBidi) {
      ubidi_close(mBidi);
    }
  }

  Iter begin() const { return Iter(mBidi, mStart, mEnd, 0, mRunCount, mIsRtl); }

  Iter end() const {
    return Iter(mBidi, mStart, mEnd, mRunCount, mRunCount, mIsRtl);
  }

 private:
  const size_t mStart;
  const size_t mEnd;
  const size_t mBufSize;
  UBiDi* mBidi;
  size_t mRunCount;
  bool mIsRtl;

  BidiText(const BidiText&) = delete;
  void operator=(const BidiText&) = delete;
};

BidiText::Iter::Iter(UBiDi* bidi,
                     size_t start,
                     size_t end,
                     size_t runIndex,
                     size_t runCount,
                     bool isRtl)
    : mBidi(bidi),
      mIsEnd(runIndex == runCount),
      mNextRunIndex(runIndex),
      mRunCount(runCount),
      mStart(start),
      mEnd(end),
      mRunInfo() {
  if (mRunCount == 1) {
    mRunInfo.mRunStart = start;
    mRunInfo.mRunLength = end - start;
    mRunInfo.mIsRtl = isRtl;
    mNextRunIndex = mRunCount;
    return;
  }
  updateRunInfo();
}

void BidiText::Iter::updateRunInfo() {
  if (mNextRunIndex == mRunCount) {
    // All runs have been iterated.
    mIsEnd = true;
    return;
  }
  int32_t startRun = -1;
  int32_t lengthRun = -1;
  const UBiDiDirection runDir =
      ubidi_getVisualRun(mBidi, mNextRunIndex, &startRun, &lengthRun);
  mNextRunIndex++;
  if (startRun == -1 || lengthRun == -1) {
    ALOGE("invalid visual run");
    // skip the invalid run.
    updateRunInfo();
    return;
  }
  const int32_t runEnd = std::min(startRun + lengthRun, mEnd);
  mRunInfo.mRunStart = std::max(startRun, mStart);
  mRunInfo.mRunLength = runEnd - mRunInfo.mRunStart;
  if (mRunInfo.mRunLength <= 0) {
    // skip the empty run.
    updateRunInfo();
    return;
  }
  mRunInfo.mIsRtl = (runDir == UBIDI_RTL);
}

BidiText::BidiText(const uint16_t* buf,
                   size_t start,
                   size_t count,
                   size_t bufSize,
                   int bidiFlags)
    : mStart(start),
      mEnd(start + count),
      mBufSize(bufSize),
      mBidi(NULL),
      mRunCount(1),
      mIsRtl((bidiFlags & kDirection_Mask) != 0) {
  if (bidiFlags == kBidi_Force_LTR || bidiFlags == kBidi_Force_RTL) {
    // force single run.
    return;
  }
  mBidi = ubidi_open();
  if (!mBidi) {
    ALOGE("error creating bidi object");
    return;
  }
  UErrorCode status = U_ZERO_ERROR;
  // Set callbacks to override bidi classes of new emoji
  ubidi_setClassCallback(mBidi, emojiBidiOverride, nullptr, nullptr, nullptr,
                         &status);
  if (!U_SUCCESS(status)) {
    ALOGE("error setting bidi callback function, status = %d", status);
    return;
  }

  UBiDiLevel bidiReq = bidiFlags;
  if (bidiFlags == kBidi_Default_LTR) {
    bidiReq = UBIDI_DEFAULT_LTR;
  } else if (bidiFlags == kBidi_Default_RTL) {
    bidiReq = UBIDI_DEFAULT_RTL;
  }
  ubidi_setPara(mBidi, reinterpret_cast<const UChar*>(buf), mBufSize, bidiReq,
                NULL, &status);
  if (!U_SUCCESS(status)) {
    ALOGE("error calling ubidi_setPara, status = %d", status);
    return;
  }
  const int paraDir = ubidi_getParaLevel(mBidi) & kDirection_Mask;
  const ssize_t rc = ubidi_countRuns(mBidi, &status);
  if (!U_SUCCESS(status) || rc < 0) {
    ALOGW("error counting bidi runs, status = %d", status);
  }
  if (!U_SUCCESS(status) || rc <= 1) {
    mIsRtl = (paraDir == kBidi_RTL);
    return;
  }
  mRunCount = rc;
}

void Layout::doLayout(const uint16_t* buf,
                      size_t start,
                      size_t count,
                      size_t bufSize,
                      bool isRtl,
                      const FontStyle& style,
                      const MinikinPaint& paint,
                      const std::shared_ptr<FontCollection>& collection) {
  std::scoped_lock _l(gMinikinLock);

  LayoutContext ctx;
  ctx.style = style;
  ctx.paint = paint;

  reset();
  mAdvances.resize(count, 0);

  doLayoutRunCached(buf, start, count, bufSize, isRtl, &ctx, start, collection,
                    this, NULL);

  ctx.clearHbFonts();
}

float Layout::measureText(const uint16_t* buf,
                          size_t start,
                          size_t count,
                          size_t bufSize,
                          bool isRtl,
                          const FontStyle& style,
                          const MinikinPaint& paint,
                          const std::shared_ptr<FontCollection>& collection,
                          float* advances) {
  std::scoped_lock _l(gMinikinLock);

  LayoutContext ctx;
  ctx.style = style;
  ctx.paint = paint;

  float advance = doLayoutRunCached(buf, start, count, bufSize, isRtl, &ctx, 0,
                                    collection, NULL, advances);

  ctx.clearHbFonts();
  return advance;
}

float Layout::doLayoutRunCached(
    const uint16_t* buf,
    size_t start,
    size_t count,
    size_t bufSize,
    bool isRtl,
    LayoutContext* ctx,
    size_t dstStart,
    const std::shared_ptr<FontCollection>& collection,
    Layout* layout,
    float* advances) {
  const uint32_t originalHyphen = ctx->paint.hyphenEdit.getHyphen();
  float advance = 0;
  if (!isRtl) {
    // left to right
    size_t wordstart = start == bufSize
                           ? start
                           : getPrevWordBreakForCache(buf, start + 1, bufSize);
    size_t wordend;
    for (size_t iter = start; iter < start + count; iter = wordend) {
      wordend = getNextWordBreakForCache(buf, iter, bufSize);
      // Only apply hyphen to the first or last word in the string.
      uint32_t hyphen = originalHyphen;
      if (iter != start) {  // Not the first word
        hyphen &= ~HyphenEdit::MASK_START_OF_LINE;
      }
      if (wordend < start + count) {  // Not the last word
        hyphen &= ~HyphenEdit::MASK_END_OF_LINE;
      }
      ctx->paint.hyphenEdit = hyphen;
      size_t wordcount = std::min(start + count, wordend) - iter;
      advance += doLayoutWord(buf + wordstart, iter - wordstart, wordcount,
                              wordend - wordstart, isRtl, ctx, iter - dstStart,
                              collection, layout,
                              advances ? advances + (iter - start) : advances);
      wordstart = wordend;
    }
  } else {
    // right to left
    size_t wordstart;
    size_t end = start + count;
    size_t wordend =
        end == 0 ? 0 : getNextWordBreakForCache(buf, end - 1, bufSize);
    for (size_t iter = end; iter > start; iter = wordstart) {
      wordstart = getPrevWordBreakForCache(buf, iter, bufSize);
      // Only apply hyphen to the first (rightmost) or last (leftmost) word in
      // the string.
      uint32_t hyphen = originalHyphen;
      if (wordstart > start) {  // Not the first word
        hyphen &= ~HyphenEdit::MASK_START_OF_LINE;
      }
      if (iter != end) {  // Not the last word
        hyphen &= ~HyphenEdit::MASK_END_OF_LINE;
      }
      ctx->paint.hyphenEdit = hyphen;
      size_t bufStart = std::max(start, wordstart);
      advance += doLayoutWord(
          buf + wordstart, bufStart - wordstart, iter - bufStart,
          wordend - wordstart, isRtl, ctx, bufStart - dstStart, collection,
          layout, advances ? advances + (bufStart - start) : advances);
      wordend = wordstart;
    }
  }
  return advance;
}

float Layout::doLayoutWord(const uint16_t* buf,
                           size_t start,
                           size_t count,
                           size_t bufSize,
                           bool isRtl,
                           LayoutContext* ctx,
                           size_t bufStart,
                           const std::shared_ptr<FontCollection>& collection,
                           Layout* layout,
                           float* advances) {
  LayoutCache& cache = LayoutEngine::getInstance().layoutCache;
  LayoutCacheKey key(collection, ctx->paint, ctx->style, buf, start, count,
                     bufSize, isRtl);

  float wordSpacing =
      count == 1 && isWordSpace(buf[start]) ? ctx->paint.wordSpacing : 0;

  float advance;
  if (ctx->paint.skipCache()) {
    Layout layoutForWord;
    key.doLayout(&layoutForWord, ctx, collection);
    if (layout) {
      layout->appendLayout(&layoutForWord, bufStart, wordSpacing);
    }
    if (advances) {
      layoutForWord.getAdvances(advances);
    }
    advance = layoutForWord.getAdvance();
  } else {
    Layout* layoutForWord = cache.get(key, ctx, collection);
    if (layout) {
      layout->appendLayout(layoutForWord, bufStart, wordSpacing);
    }
    if (advances) {
      layoutForWord->getAdvances(advances);
    }
    advance = layoutForWord->getAdvance();
  }

  if (wordSpacing != 0) {
    advance += wordSpacing;
    if (advances) {
      advances[0] += wordSpacing;
    }
  }
  return advance;
}

static void addFeatures(const std::string& str,
                        std::vector<hb_feature_t>* features) {
  if (!str.size())
    return;

  const char* start = str.c_str();
  const char* end = start + str.size();

  while (start < end) {
    static hb_feature_t feature;
    const char* p = strchr(start, ',');
    if (!p)
      p = end;
    /* We do not allow setting features on ranges.  As such, reject any
     * setting that has non-universal range. */
    if (hb_feature_from_string(start, p - start, &feature) &&
        feature.start == 0 && feature.end == (unsigned int)-1)
      features->push_back(feature);
    start = p + 1;
  }
}

static const hb_codepoint_t CHAR_HYPHEN = 0x2010; /* HYPHEN */

static inline hb_codepoint_t determineHyphenChar(hb_codepoint_t preferredHyphen,
                                                 hb_font_t* font) {
  hb_codepoint_t glyph;
  if (preferredHyphen == 0x058A    /* ARMENIAN_HYPHEN */
      || preferredHyphen == 0x05BE /* HEBREW PUNCTUATION MAQAF */
      || preferredHyphen == 0x1400 /* CANADIAN SYLLABIC HYPHEN */) {
    if (hb_font_get_nominal_glyph(font, preferredHyphen, &glyph)) {
      return preferredHyphen;
    } else {
      // The original hyphen requested was not supported. Let's try and see if
      // the Unicode hyphen is supported.
      preferredHyphen = CHAR_HYPHEN;
    }
  }
  if (preferredHyphen == CHAR_HYPHEN) { /* HYPHEN */
    // Fallback to ASCII HYPHEN-MINUS if the font didn't have a glyph for the
    // preferred hyphen. Note that we intentionally don't do anything special if
    // the font doesn't have a HYPHEN-MINUS either, so a tofu could be shown,
    // hinting towards something missing.
    if (!hb_font_get_nominal_glyph(font, preferredHyphen, &glyph)) {
      return 0x002D;  // HYPHEN-MINUS
    }
  }
  return preferredHyphen;
}

static inline void addHyphenToHbBuffer(hb_buffer_t* buffer,
                                       hb_font_t* font,
                                       uint32_t hyphen,
                                       uint32_t cluster) {
  const uint32_t* hyphenStr = HyphenEdit::getHyphenString(hyphen);
  while (*hyphenStr != 0) {
    hb_codepoint_t hyphenChar = determineHyphenChar(*hyphenStr, font);
    hb_buffer_add(buffer, hyphenChar, cluster);
    hyphenStr++;
  }
}

// Returns the cluster value assigned to the first codepoint added to the
// buffer, which can be used to translate cluster values returned by HarfBuzz to
// input indices.
static inline uint32_t addToHbBuffer(hb_buffer_t* buffer,
                                     const uint16_t* buf,
                                     size_t start,
                                     size_t count,
                                     size_t bufSize,
                                     ssize_t scriptRunStart,
                                     ssize_t scriptRunEnd,
                                     HyphenEdit hyphenEdit,
                                     hb_font_t* hbFont) {
  // Only hyphenate the very first script run for starting hyphens.
  const uint32_t startHyphen =
      (scriptRunStart == 0) ? hyphenEdit.getStart() : HyphenEdit::NO_EDIT;
  // Only hyphenate the very last script run for ending hyphens.
  const uint32_t endHyphen = (static_cast<size_t>(scriptRunEnd) == count)
                                 ? hyphenEdit.getEnd()
                                 : HyphenEdit::NO_EDIT;

  // In the following code, we drop the pre-context and/or post-context if there
  // is a hyphen edit at that end. This is not absolutely necessary, since
  // HarfBuzz uses contexts only for joining scripts at the moment, e.g. to
  // determine if the first or last letter of a text range to shape should take
  // a joining form based on an adjacent letter or joiner (that comes from the
  // context).
  //
  // TODO: Revisit this for:
  // 1. Desperate breaks for joining scripts like Arabic (where it may be better
  // to keep
  //    the context);
  // 2. Special features like start-of-word font features (not implemented in
  // HarfBuzz
  //    yet).

  // We don't have any start-of-line replacement edit yet, so we don't need to
  // check for those.
  if (HyphenEdit::isInsertion(startHyphen)) {
    // A cluster value of zero guarantees that the inserted hyphen will be in
    // the same cluster with the next codepoint, since there is no pre-context.
    addHyphenToHbBuffer(buffer, hbFont, startHyphen, 0 /* cluster value */);
  }

  const uint16_t* hbText;
  int hbTextLength;
  unsigned int hbItemOffset;
  unsigned int hbItemLength = scriptRunEnd - scriptRunStart;  // This is >= 1.

  const bool hasEndInsertion = HyphenEdit::isInsertion(endHyphen);
  const bool hasEndReplacement = HyphenEdit::isReplacement(endHyphen);
  if (hasEndReplacement) {
    // Skip the last code unit while copying the buffer for HarfBuzz if it's a
    // replacement. We don't need to worry about non-BMP characters yet since
    // replacements are only done for code units at the moment.
    hbItemLength -= 1;
  }

  if (startHyphen == HyphenEdit::NO_EDIT) {
    // No edit at the beginning. Use the whole pre-context.
    hbText = buf;
    hbItemOffset = start + scriptRunStart;
  } else {
    // There's an edit at the beginning. Drop the pre-context and start the
    // buffer at where we want to start shaping.
    hbText = buf + start + scriptRunStart;
    hbItemOffset = 0;
  }

  if (endHyphen == HyphenEdit::NO_EDIT) {
    // No edit at the end, use the whole post-context.
    hbTextLength = (buf + bufSize) - hbText;
  } else {
    // There is an edit at the end. Drop the post-context.
    hbTextLength = hbItemOffset + hbItemLength;
  }

  hb_buffer_add_utf16(buffer, hbText, hbTextLength, hbItemOffset, hbItemLength);

  unsigned int numCodepoints;
  hb_glyph_info_t* cpInfo = hb_buffer_get_glyph_infos(buffer, &numCodepoints);

  // Add the hyphen at the end, if there's any.
  if (hasEndInsertion || hasEndReplacement) {
    // When a hyphen is inserted, by assigning the added hyphen and the last
    // codepoint added to the HarfBuzz buffer to the same cluster, we can make
    // sure that they always remain in the same cluster, even if the last
    // codepoint gets merged into another cluster (for example when it's a
    // combining mark).
    //
    // When a replacement happens instead, we want it to get the cluster value
    // of the character it's replacing, which is one "codepoint length" larger
    // than the last cluster. But since the character replaced is always just
    // one code unit, we can just add 1.
    uint32_t hyphenCluster;
    if (numCodepoints == 0) {
      // Nothing was added to the HarfBuzz buffer. This can only happen if
      // we have a replacement that is replacing a one-code unit script run.
      hyphenCluster = 0;
    } else {
      hyphenCluster =
          cpInfo[numCodepoints - 1].cluster + (uint32_t)hasEndReplacement;
    }
    addHyphenToHbBuffer(buffer, hbFont, endHyphen, hyphenCluster);
    // Since we have just added to the buffer, cpInfo no longer necessarily
    // points to the right place. Refresh it.
    cpInfo =
        hb_buffer_get_glyph_infos(buffer, nullptr /* we don't need the size */);
  }
  return cpInfo[0].cluster;
}

void Layout::doLayoutRun(const uint16_t* buf,
                         size_t start,
                         size_t count,
                         size_t bufSize,
                         bool isRtl,
                         LayoutContext* ctx,
                         const std::shared_ptr<FontCollection>& collection) {
  hb_buffer_t* buffer = LayoutEngine::getInstance().hbBuffer;
  std::vector<FontCollection::Run> items;
  collection->itemize(buf + start, count, ctx->style, &items);

  std::vector<hb_feature_t> features;
  // Disable default-on non-required ligature features if letter-spacing
  // See http://dev.w3.org/csswg/css-text-3/#letter-spacing-property
  // "When the effective spacing between two characters is not zero (due to
  // either justification or a non-zero value of letter-spacing), user agents
  // should not apply optional ligatures."
  if (fabs(ctx->paint.letterSpacing) > 0.03) {
    static const hb_feature_t no_liga = {HB_TAG('l', 'i', 'g', 'a'), 0, 0, ~0u};
    static const hb_feature_t no_clig = {HB_TAG('c', 'l', 'i', 'g'), 0, 0, ~0u};
    features.push_back(no_liga);
    features.push_back(no_clig);
  }
  addFeatures(ctx->paint.fontFeatureSettings, &features);

  double size = ctx->paint.size;
  double scaleX = ctx->paint.scaleX;

  float x = mAdvance;
  float y = 0;
  for (int run_ix = isRtl ? items.size() - 1 : 0;
       isRtl ? run_ix >= 0 : run_ix < static_cast<int>(items.size());
       isRtl ? --run_ix : ++run_ix) {
    FontCollection::Run& run = items[run_ix];
    if (run.fakedFont.font == NULL) {
      ALOGE("no font for run starting u+%04x length %d", buf[run.start],
            run.end - run.start);
      continue;
    }
    int font_ix = findFace(run.fakedFont, ctx);
    ctx->paint.font = mFaces[font_ix].font;
    ctx->paint.fakery = mFaces[font_ix].fakery;
    hb_font_t* hbFont = ctx->hbFonts[font_ix];
#ifdef VERBOSE_DEBUG
    ALOGD("Run %zu, font %d [%d:%d]", run_ix, font_ix, run.start, run.end);
#endif

    hb_font_set_ppem(hbFont, size * scaleX, size);
    hb_font_set_scale(hbFont, HBFloatToFixed(size * scaleX),
                      HBFloatToFixed(size));

    const bool is_color_bitmap_font = isColorBitmapFont(hbFont);

    // TODO: if there are multiple scripts within a font in an RTL run,
    // we need to reorder those runs. This is unlikely with our current
    // font stack, but should be done for correctness.

    // Note: scriptRunStart and scriptRunEnd, as well as run.start and run.end,
    // run between 0 and count.
    ssize_t scriptRunEnd;
    for (ssize_t scriptRunStart = run.start; scriptRunStart < run.end;
         scriptRunStart = scriptRunEnd) {
      scriptRunEnd = scriptRunStart;
      hb_script_t script =
          getScriptRun(buf + start, run.end, &scriptRunEnd /* iterator */);
      // After the last line, scriptRunEnd is guaranteed to have increased,
      // since the only time getScriptRun does not increase its iterator is when
      // it has already reached the end of the buffer. But that can't happen,
      // since if we have already reached the end of the buffer, we should have
      // had (scriptRunEnd == run.end), which means (scriptRunStart == run.end)
      // which is impossible due to the exit condition of the for loop. So we
      // can be sure that scriptRunEnd > scriptRunStart.

      double letterSpace = 0.0;
      double letterSpaceHalfLeft = 0.0;
      double letterSpaceHalfRight = 0.0;

      if (ctx->paint.letterSpacing != 0.0 &&
          isScriptOkForLetterspacing(script)) {
        letterSpace = ctx->paint.letterSpacing * size * scaleX;
        if ((ctx->paint.paintFlags & LinearTextFlag) == 0) {
          letterSpace = round(letterSpace);
          letterSpaceHalfLeft = floor(letterSpace * 0.5);
        } else {
          letterSpaceHalfLeft = letterSpace * 0.5;
        }
        letterSpaceHalfRight = letterSpace - letterSpaceHalfLeft;
      }

      hb_buffer_clear_contents(buffer);
      hb_buffer_set_script(buffer, script);
      hb_buffer_set_direction(buffer,
                              isRtl ? HB_DIRECTION_RTL : HB_DIRECTION_LTR);
      const FontLanguages& langList =
          FontLanguageListCache::getById(ctx->style.getLanguageListId());
      if (langList.size() != 0) {
        const FontLanguage* hbLanguage = &langList[0];
        for (size_t i = 0; i < langList.size(); ++i) {
          if (langList[i].supportsHbScript(script)) {
            hbLanguage = &langList[i];
            break;
          }
        }
        hb_buffer_set_language(buffer, hbLanguage->getHbLanguage());
      }

      const uint32_t clusterStart =
          addToHbBuffer(buffer, buf, start, count, bufSize, scriptRunStart,
                        scriptRunEnd, ctx->paint.hyphenEdit, hbFont);

      hb_shape(hbFont, buffer, features.empty() ? NULL : &features[0],
               features.size());
      unsigned int numGlyphs;
      hb_glyph_info_t* info = hb_buffer_get_glyph_infos(buffer, &numGlyphs);
      hb_glyph_position_t* positions =
          hb_buffer_get_glyph_positions(buffer, NULL);

      // At this point in the code, the cluster values in the info buffer
      // correspond to the input characters with some shift. The cluster value
      // clusterStart corresponds to the first character passed to HarfBuzz,
      // which is at buf[start + scriptRunStart] whose advance needs to be saved
      // into mAdvances[scriptRunStart]. So cluster values need to be reduced by
      // (clusterStart - scriptRunStart) to get converted to indices of
      // mAdvances.
      const ssize_t clusterOffset = clusterStart - scriptRunStart;

      if (numGlyphs) {
        mAdvances[info[0].cluster - clusterOffset] += letterSpaceHalfLeft;
        x += letterSpaceHalfLeft;
      }
      for (unsigned int i = 0; i < numGlyphs; i++) {
#ifdef VERBOSE_DEBUG
        ALOGD("%d %d %d %d", positions[i].x_advance, positions[i].y_advance,
              positions[i].x_offset, positions[i].y_offset);
        ALOGD("DoLayout %u: %f; %d, %d", info[i].codepoint,
              HBFixedToFloat(positions[i].x_advance), positions[i].x_offset,
              positions[i].y_offset);
#endif
        if (i > 0 && info[i - 1].cluster != info[i].cluster) {
          mAdvances[info[i - 1].cluster - clusterOffset] +=
              letterSpaceHalfRight;
          mAdvances[info[i].cluster - clusterOffset] += letterSpaceHalfLeft;
          x += letterSpace;
        }

        hb_codepoint_t glyph_ix = info[i].codepoint;
        float xoff = HBFixedToFloat(positions[i].x_offset);
        float yoff = -HBFixedToFloat(positions[i].y_offset);
        xoff += yoff * ctx->paint.skewX;
        LayoutGlyph glyph = {
            font_ix, glyph_ix, x + xoff, y + yoff,
            static_cast<uint32_t>(info[i].cluster - clusterOffset)};
        mGlyphs.push_back(glyph);
        float xAdvance = HBFixedToFloat(positions[i].x_advance);
        if ((ctx->paint.paintFlags & LinearTextFlag) == 0) {
          xAdvance = roundf(xAdvance);
        }
        MinikinRect glyphBounds;
        hb_glyph_extents_t extents = {};
        if (is_color_bitmap_font &&
            hb_font_get_glyph_extents(hbFont, glyph_ix, &extents)) {
          // Note that it is technically possible for a TrueType font to have
          // outline and embedded bitmap at the same time. We ignore modified
          // bbox of hinted outline glyphs in that case.
          glyphBounds.mLeft = roundf(HBFixedToFloat(extents.x_bearing));
          glyphBounds.mTop = roundf(HBFixedToFloat(-extents.y_bearing));
          glyphBounds.mRight =
              roundf(HBFixedToFloat(extents.x_bearing + extents.width));
          glyphBounds.mBottom =
              roundf(HBFixedToFloat(-extents.y_bearing - extents.height));
        } else {
          ctx->paint.font->GetBounds(&glyphBounds, glyph_ix, ctx->paint);
        }
        glyphBounds.offset(x + xoff, y + yoff);
        mBounds.join(glyphBounds);
        if (static_cast<size_t>(info[i].cluster - clusterOffset) < count) {
          mAdvances[info[i].cluster - clusterOffset] += xAdvance;
        } else {
          ALOGE("cluster %zu (start %zu) out of bounds of count %zu",
                info[i].cluster - clusterOffset, start, count);
        }
        x += xAdvance;
      }
      if (numGlyphs) {
        mAdvances[info[numGlyphs - 1].cluster - clusterOffset] +=
            letterSpaceHalfRight;
        x += letterSpaceHalfRight;
      }
    }
  }
  mAdvance = x;
}

void Layout::appendLayout(Layout* src, size_t start, float extraAdvance) {
  int fontMapStack[16];
  int* fontMap;
  if (src->mFaces.size() < sizeof(fontMapStack) / sizeof(fontMapStack[0])) {
    fontMap = fontMapStack;
  } else {
    fontMap = new int[src->mFaces.size()];
  }
  for (size_t i = 0; i < src->mFaces.size(); i++) {
    int font_ix = findFace(src->mFaces[i], NULL);
    fontMap[i] = font_ix;
  }
  // LibTxt: Changed x0 from int to float to prevent rounding that causes text
  // jitter.
  float x0 = mAdvance;
  for (size_t i = 0; i < src->mGlyphs.size(); i++) {
    LayoutGlyph& srcGlyph = src->mGlyphs[i];
    int font_ix = fontMap[srcGlyph.font_ix];
    unsigned int glyph_id = srcGlyph.glyph_id;
    float x = x0 + srcGlyph.x;
    float y = srcGlyph.y;
    LayoutGlyph glyph = {font_ix, glyph_id, x, y,
                         static_cast<uint32_t>(srcGlyph.cluster + start)};
    mGlyphs.push_back(glyph);
  }
  for (size_t i = 0; i < src->mAdvances.size(); i++) {
    mAdvances[i + start] = src->mAdvances[i];
    if (i == 0)
      mAdvances[i + start] += extraAdvance;
  }
  MinikinRect srcBounds(src->mBounds);
  srcBounds.offset(x0, 0);
  mBounds.join(srcBounds);
  mAdvance += src->mAdvance + extraAdvance;

  if (fontMap != fontMapStack) {
    delete[] fontMap;
  }
}

size_t Layout::nGlyphs() const {
  return mGlyphs.size();
}

const MinikinFont* Layout::getFont(int i) const {
  const LayoutGlyph& glyph = mGlyphs[i];
  return mFaces[glyph.font_ix].font;
}

FontFakery Layout::getFakery(int i) const {
  const LayoutGlyph& glyph = mGlyphs[i];
  return mFaces[glyph.font_ix].fakery;
}

unsigned int Layout::getGlyphId(int i) const {
  const LayoutGlyph& glyph = mGlyphs[i];
  return glyph.glyph_id;
}

// libtxt extension
unsigned int Layout::getGlyphCluster(int i) const {
  const LayoutGlyph& glyph = mGlyphs[i];
  return glyph.cluster;
}

float Layout::getX(int i) const {
  const LayoutGlyph& glyph = mGlyphs[i];
  return glyph.x;
}

float Layout::getY(int i) const {
  const LayoutGlyph& glyph = mGlyphs[i];
  return glyph.y;
}

float Layout::getAdvance() const {
  return mAdvance;
}

void Layout::getAdvances(float* advances) {
  memcpy(advances, &mAdvances[0], mAdvances.size() * sizeof(float));
}

void Layout::getBounds(MinikinRect* bounds) const {
  bounds->set(mBounds);
}

void Layout::purgeCaches() {
  std::scoped_lock _l(gMinikinLock);
  LayoutCache& layoutCache = LayoutEngine::getInstance().layoutCache;
  layoutCache.clear();
  purgeHbFontCacheLocked();
}

}  // namespace minikin