ComplexTextController.cpp   [plain text]

/*
 * Copyright (C) 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "config.h"
#include "ComplexTextController.h"

#include "CharacterProperties.h"
#include "FloatSize.h"
#include "FontCascade.h"
#include "RenderBlock.h"
#include "RenderText.h"
#include "TextRun.h"
#include <unicode/ubrk.h>
#include <wtf/Optional.h>
#include <wtf/StdLibExtras.h>
#include <wtf/text/TextBreakIterator.h>
#include <wtf/unicode/CharacterNames.h>

#if PLATFORM(IOS)
#include <CoreText/CoreText.h>
#endif

namespace WebCore {

class TextLayout {
    WTF_MAKE_FAST_ALLOCATED;
public:
    static bool isNeeded(RenderText& text, const FontCascade& font)
    {
        TextRun run = RenderBlock::constructTextRun(text, text.style());
        return font.codePath(run) == FontCascade::Complex;
    }

    TextLayout(RenderText& text, const FontCascade& font, float xPos)
        : m_font(font)
        , m_run(constructTextRun(text, xPos))
        , m_controller(std::make_unique<ComplexTextController>(m_font, m_run, true))
    {
    }

    float width(unsigned from, unsigned len, HashSet<const Font*>* fallbackFonts)
    {
        m_controller->advance(from, 0, ByWholeGlyphs, fallbackFonts);
        float beforeWidth = m_controller->runWidthSoFar();
        if (m_font.wordSpacing() && from && FontCascade::treatAsSpace(m_run[from]))
            beforeWidth += m_font.wordSpacing();
        m_controller->advance(from + len, 0, ByWholeGlyphs, fallbackFonts);
        float afterWidth = m_controller->runWidthSoFar();
        return afterWidth - beforeWidth;
    }

private:
    static TextRun constructTextRun(RenderText& text, float xPos)
    {
        TextRun run = RenderBlock::constructTextRun(text, text.style());
        run.setXPos(xPos);
        return run;
    }

    // ComplexTextController has only references to its FontCascade and TextRun so they must be kept alive here.
    FontCascade m_font;
    TextRun m_run;
    std::unique_ptr<ComplexTextController> m_controller;
};

void TextLayoutDeleter::operator()(TextLayout* layout) const
{
#if !PLATFORM(WIN)
    delete layout;
#else
    ASSERT_UNUSED(layout, !layout);
#endif
}

std::unique_ptr<TextLayout, TextLayoutDeleter> FontCascade::createLayout(RenderText& text, float xPos, bool collapseWhiteSpace) const
{
#if !PLATFORM(WIN)
    if (!collapseWhiteSpace || !TextLayout::isNeeded(text, *this))
        return nullptr;
    return std::unique_ptr<TextLayout, TextLayoutDeleter>(new TextLayout(text, *this, xPos));
#else
    UNUSED_PARAM(text);
    UNUSED_PARAM(xPos);
    UNUSED_PARAM(collapseWhiteSpace);
    return nullptr;
#endif
}

float FontCascade::width(TextLayout& layout, unsigned from, unsigned len, HashSet<const Font*>* fallbackFonts)
{
#if !PLATFORM(WIN)
    return layout.width(from, len, fallbackFonts);
#else
    UNUSED_PARAM(layout);
    UNUSED_PARAM(from);
    UNUSED_PARAM(len);
    UNUSED_PARAM(fallbackFonts);
    ASSERT_NOT_REACHED();
    return 0;
#endif
}

void ComplexTextController::computeExpansionOpportunity()
{
    if (!m_expansion)
        m_expansionPerOpportunity = 0;
    else {
        unsigned expansionOpportunityCount = FontCascade::expansionOpportunityCount(m_run.text(), m_run.ltr() ? LTR : RTL, m_run.expansionBehavior()).first;

        if (!expansionOpportunityCount)
            m_expansionPerOpportunity = 0;
        else
            m_expansionPerOpportunity = m_expansion / expansionOpportunityCount;
    }
}

ComplexTextController::ComplexTextController(const FontCascade& font, const TextRun& run, bool mayUseNaturalWritingDirection, HashSet<const Font*>* fallbackFonts, bool forTextEmphasis)
    : m_fallbackFonts(fallbackFonts)
    , m_font(font)
    , m_run(run)
    , m_end(run.length())
    , m_expansion(run.expansion())
    , m_mayUseNaturalWritingDirection(mayUseNaturalWritingDirection)
    , m_forTextEmphasis(forTextEmphasis)
{
#if PLATFORM(WIN)
    ASSERT_NOT_REACHED();
#endif

    computeExpansionOpportunity();

    collectComplexTextRuns();

    finishConstruction();
}

ComplexTextController::ComplexTextController(const FontCascade& font, const TextRun& run, Vector<Ref<ComplexTextRun>>& runs)
    : m_font(font)
    , m_run(run)
    , m_end(run.length())
    , m_expansion(run.expansion())
{
    computeExpansionOpportunity();

    for (auto& run : runs)
        m_complexTextRuns.append(run.ptr());

    finishConstruction();
}

void ComplexTextController::finishConstruction()
{
    adjustGlyphsAndAdvances();

    if (!m_isLTROnly) {
        m_runIndices.reserveInitialCapacity(m_complexTextRuns.size());

        m_glyphCountFromStartToIndex.reserveInitialCapacity(m_complexTextRuns.size());
        unsigned glyphCountSoFar = 0;
        for (unsigned i = 0; i < m_complexTextRuns.size(); ++i) {
            m_glyphCountFromStartToIndex.uncheckedAppend(glyphCountSoFar);
            glyphCountSoFar += m_complexTextRuns[i]->glyphCount();
        }
    }
}

unsigned ComplexTextController::offsetForPosition(float h, bool includePartialGlyphs)
{
    if (h >= m_totalWidth)
        return m_run.ltr() ? m_end : 0;

    if (h < 0)
        return m_run.ltr() ? 0 : m_end;

    float x = h;

    size_t runCount = m_complexTextRuns.size();
    unsigned offsetIntoAdjustedGlyphs = 0;

    for (size_t r = 0; r < runCount; ++r) {
        const ComplexTextRun& complexTextRun = *m_complexTextRuns[r];
        for (unsigned j = 0; j < complexTextRun.glyphCount(); ++j) {
            unsigned index = offsetIntoAdjustedGlyphs + j;
            float adjustedAdvance = m_adjustedBaseAdvances[index].width();
            if (x < adjustedAdvance) {
                unsigned hitGlyphStart = complexTextRun.indexAt(j);
                unsigned hitGlyphEnd;
                if (m_run.ltr())
                    hitGlyphEnd = std::max(hitGlyphStart, j + 1 < complexTextRun.glyphCount() ? complexTextRun.indexAt(j + 1) : complexTextRun.indexEnd());
                else
                    hitGlyphEnd = std::max(hitGlyphStart, j > 0 ? complexTextRun.indexAt(j - 1) : complexTextRun.indexEnd());

                // FIXME: Instead of dividing the glyph's advance equally between the characters, this
                // could use the glyph's "ligature carets". This is available in CoreText via CTFontGetLigatureCaretPositions().
                unsigned hitIndex = hitGlyphStart + (hitGlyphEnd - hitGlyphStart) * (m_run.ltr() ? x / adjustedAdvance : 1 - x / adjustedAdvance);
                unsigned stringLength = complexTextRun.stringLength();
                CachedTextBreakIterator cursorPositionIterator(StringView(complexTextRun.characters(), stringLength), TextBreakIterator::Mode::Caret, nullAtom());
                unsigned clusterStart;
                if (cursorPositionIterator.isBoundary(hitIndex))
                    clusterStart = hitIndex;
                else
                    clusterStart = cursorPositionIterator.preceding(hitIndex).value_or(0);

                if (!includePartialGlyphs)
                    return complexTextRun.stringLocation() + clusterStart;

                unsigned clusterEnd = cursorPositionIterator.following(hitIndex).value_or(stringLength);

                float clusterWidth;
                // FIXME: The search stops at the boundaries of complexTextRun. In theory, it should go on into neighboring ComplexTextRuns
                // derived from the same CTLine. In practice, we do not expect there to be more than one CTRun in a CTLine, as no
                // reordering and no font fallback should occur within a CTLine.
                if (clusterEnd - clusterStart > 1) {
                    clusterWidth = adjustedAdvance;
                    if (j) {
                        unsigned firstGlyphBeforeCluster = j - 1;
                        while (complexTextRun.indexAt(firstGlyphBeforeCluster) >= clusterStart && complexTextRun.indexAt(firstGlyphBeforeCluster) < clusterEnd) {
                            float width = m_adjustedBaseAdvances[offsetIntoAdjustedGlyphs + firstGlyphBeforeCluster].width();
                            clusterWidth += width;
                            x += width;
                            if (!firstGlyphBeforeCluster)
                                break;
                            firstGlyphBeforeCluster--;
                        }
                    }
                    unsigned firstGlyphAfterCluster = j + 1;
                    while (firstGlyphAfterCluster < complexTextRun.glyphCount() && complexTextRun.indexAt(firstGlyphAfterCluster) >= clusterStart && complexTextRun.indexAt(firstGlyphAfterCluster) < clusterEnd) {
                        clusterWidth += m_adjustedBaseAdvances[offsetIntoAdjustedGlyphs + firstGlyphAfterCluster].width();
                        firstGlyphAfterCluster++;
                    }
                } else {
                    clusterWidth = adjustedAdvance / (hitGlyphEnd - hitGlyphStart);
                    x -=  clusterWidth * (m_run.ltr() ? hitIndex - hitGlyphStart : hitGlyphEnd - hitIndex - 1);
                }
                if (x <= clusterWidth / 2)
                    return complexTextRun.stringLocation() + (m_run.ltr() ? clusterStart : clusterEnd);
                return complexTextRun.stringLocation() + (m_run.ltr() ? clusterEnd : clusterStart);
            }
            x -= adjustedAdvance;
        }
        offsetIntoAdjustedGlyphs += complexTextRun.glyphCount();
    }

    ASSERT_NOT_REACHED();
    return 0;
}

// FIXME: We should consider reimplementing this function using ICU to advance by grapheme.
// The current implementation only considers explicitly emoji sequences and emoji variations.
static bool advanceByCombiningCharacterSequence(const UChar*& iterator, const UChar* end, UChar32& baseCharacter, unsigned& markCount)
{
    ASSERT(iterator < end);

    markCount = 0;

    unsigned i = 0;
    unsigned remainingCharacters = end - iterator;
    U16_NEXT(iterator, i, remainingCharacters, baseCharacter);
    iterator = iterator + i;
    if (U_IS_SURROGATE(baseCharacter))
        return false;

    // Consume marks.
    bool sawEmojiGroupCandidate = isEmojiGroupCandidate(baseCharacter);
    bool sawJoiner = false;
    while (iterator < end) {
        UChar32 nextCharacter;
        unsigned markLength = 0;
        bool shouldContinue = false;
        ASSERT(end >= iterator);
        U16_NEXT(iterator, markLength, static_cast<unsigned>(end - iterator), nextCharacter);

        if (isVariationSelector(nextCharacter) || isEmojiFitzpatrickModifier(nextCharacter))
            shouldContinue = true;

        if (sawJoiner && isEmojiGroupCandidate(nextCharacter))
            shouldContinue = true;

        sawJoiner = false;
        if (sawEmojiGroupCandidate && nextCharacter == zeroWidthJoiner) {
            sawJoiner = true;
            shouldContinue = true;
        }
        
        if (!shouldContinue && !(U_GET_GC_MASK(nextCharacter) & U_GC_M_MASK))
            break;

        markCount += markLength;
        iterator += markLength;
    }

    return true;
}

// FIXME: Capitalization is language-dependent and context-dependent and should operate on grapheme clusters instead of codepoints.
static inline std::optional<UChar32> capitalized(UChar32 baseCharacter)
{
    if (U_GET_GC_MASK(baseCharacter) & U_GC_M_MASK)
        return std::nullopt;

    UChar32 uppercaseCharacter = u_toupper(baseCharacter);
    ASSERT(uppercaseCharacter == baseCharacter || (U_IS_BMP(baseCharacter) == U_IS_BMP(uppercaseCharacter)));
    if (uppercaseCharacter != baseCharacter)
        return uppercaseCharacter;
    return std::nullopt;
}

static bool shouldSynthesize(bool dontSynthesizeSmallCaps, const Font* nextFont, UChar32 baseCharacter, std::optional<UChar32> capitalizedBase, FontVariantCaps fontVariantCaps, bool engageAllSmallCapsProcessing)
{
    if (dontSynthesizeSmallCaps)
        return false;
    if (!nextFont || nextFont == Font::systemFallback())
        return false;
    if (engageAllSmallCapsProcessing && isASCIISpace(baseCharacter))
        return false;
    if (!engageAllSmallCapsProcessing && !capitalizedBase)
        return false;
    return !nextFont->variantCapsSupportsCharacterForSynthesis(fontVariantCaps, baseCharacter);
}

void ComplexTextController::collectComplexTextRuns()
{
    if (!m_end)
        return;

    // We break up glyph run generation for the string by Font.
    const UChar* cp;

    if (m_run.is8Bit()) {
        String stringFor8BitRun = String::make16BitFrom8BitSource(m_run.characters8(), m_run.length());
        m_stringsFor8BitRuns.append(WTFMove(stringFor8BitRun));
        cp = m_stringsFor8BitRuns.last().characters16();
    } else
        cp = m_run.characters16();

    auto fontVariantCaps = m_font.fontDescription().variantCaps();
    bool dontSynthesizeSmallCaps = !static_cast<bool>(m_font.fontDescription().fontSynthesis() & FontSynthesisSmallCaps);
    bool engageAllSmallCapsProcessing = fontVariantCaps == FontVariantCaps::AllSmall || fontVariantCaps == FontVariantCaps::AllPetite;
    bool engageSmallCapsProcessing = engageAllSmallCapsProcessing || fontVariantCaps == FontVariantCaps::Small || fontVariantCaps == FontVariantCaps::Petite;

    if (engageAllSmallCapsProcessing || engageSmallCapsProcessing)
        m_smallCapsBuffer.resize(m_end);

    unsigned indexOfFontTransition = 0;
    const UChar* curr = cp;
    const UChar* end = cp + m_end;

    const Font* font;
    const Font* nextFont;
    const Font* synthesizedFont = nullptr;
    const Font* smallSynthesizedFont = nullptr;

    unsigned markCount;
    UChar32 baseCharacter;
    if (!advanceByCombiningCharacterSequence(curr, end, baseCharacter, markCount))
        return;

    nextFont = m_font.fontForCombiningCharacterSequence(cp, curr - cp);

    bool isSmallCaps = false;
    bool nextIsSmallCaps = false;

    auto capitalizedBase = capitalized(baseCharacter);
    if (shouldSynthesize(dontSynthesizeSmallCaps, nextFont, baseCharacter, capitalizedBase, fontVariantCaps, engageAllSmallCapsProcessing)) {
        synthesizedFont = &nextFont->noSynthesizableFeaturesFont();
        smallSynthesizedFont = synthesizedFont->smallCapsFont(m_font.fontDescription());
        UChar32 characterToWrite = capitalizedBase ? capitalizedBase.value() : cp[0];
        unsigned characterIndex = 0;
        U16_APPEND_UNSAFE(m_smallCapsBuffer, characterIndex, characterToWrite);
        for (unsigned i = characterIndex; cp + i < curr; ++i)
            m_smallCapsBuffer[i] = cp[i];
        nextIsSmallCaps = true;
    }

    while (curr < end) {
        font = nextFont;
        isSmallCaps = nextIsSmallCaps;
        unsigned index = curr - cp;

        if (!advanceByCombiningCharacterSequence(curr, end, baseCharacter, markCount))
            return;

        if (synthesizedFont) {
            if (auto capitalizedBase = capitalized(baseCharacter)) {
                unsigned characterIndex = index;
                U16_APPEND_UNSAFE(m_smallCapsBuffer, characterIndex, capitalizedBase.value());
                for (unsigned i = 0; i < markCount; ++i)
                    m_smallCapsBuffer[i + characterIndex] = cp[i + characterIndex];
                nextIsSmallCaps = true;
            } else {
                if (engageAllSmallCapsProcessing) {
                    for (unsigned i = 0; i < curr - cp - index; ++i)
                        m_smallCapsBuffer[index + i] = cp[index + i];
                }
                nextIsSmallCaps = engageAllSmallCapsProcessing;
            }
        }

        if (baseCharacter == zeroWidthJoiner)
            nextFont = font;
        else
            nextFont = m_font.fontForCombiningCharacterSequence(cp + index, curr - cp - index);

        capitalizedBase = capitalized(baseCharacter);
        if (!synthesizedFont && shouldSynthesize(dontSynthesizeSmallCaps, nextFont, baseCharacter, capitalizedBase, fontVariantCaps, engageAllSmallCapsProcessing)) {
            // Rather than synthesize each character individually, we should synthesize the entire "run" if any character requires synthesis.
            synthesizedFont = &nextFont->noSynthesizableFeaturesFont();
            smallSynthesizedFont = synthesizedFont->smallCapsFont(m_font.fontDescription());
            nextIsSmallCaps = true;
            curr = cp + indexOfFontTransition;
            continue;
        }

        if (nextFont != font || nextIsSmallCaps != isSmallCaps) {
            unsigned itemLength = index - indexOfFontTransition;
            if (itemLength) {
                unsigned itemStart = indexOfFontTransition;
                if (synthesizedFont) {
                    if (isSmallCaps)
                        collectComplexTextRunsForCharacters(m_smallCapsBuffer.data() + itemStart, itemLength, itemStart, smallSynthesizedFont);
                    else
                        collectComplexTextRunsForCharacters(cp + itemStart, itemLength, itemStart, synthesizedFont);
                } else
                    collectComplexTextRunsForCharacters(cp + itemStart, itemLength, itemStart, font);
                if (nextFont != font) {
                    synthesizedFont = nullptr;
                    smallSynthesizedFont = nullptr;
                    nextIsSmallCaps = false;
                }
            }
            indexOfFontTransition = index;
        }
    }

    ASSERT(m_end >= indexOfFontTransition);
    unsigned itemLength = m_end - indexOfFontTransition;
    if (itemLength) {
        unsigned itemStart = indexOfFontTransition;
        if (synthesizedFont) {
            if (nextIsSmallCaps)
                collectComplexTextRunsForCharacters(m_smallCapsBuffer.data() + itemStart, itemLength, itemStart, smallSynthesizedFont);
            else
                collectComplexTextRunsForCharacters(cp + itemStart, itemLength, itemStart, synthesizedFont);
        } else
            collectComplexTextRunsForCharacters(cp + itemStart, itemLength, itemStart, nextFont);
    }

    if (!m_run.ltr())
        m_complexTextRuns.reverse();
}

unsigned ComplexTextController::ComplexTextRun::indexAt(unsigned i) const
{
    ASSERT(i < m_glyphCount);

    return m_coreTextIndices[i];
}

void ComplexTextController::ComplexTextRun::setIsNonMonotonic()
{
    ASSERT(m_isMonotonic);
    m_isMonotonic = false;

    Vector<bool, 64> mappedIndices(m_stringLength, false);
    for (unsigned i = 0; i < m_glyphCount; ++i) {
        ASSERT(indexAt(i) < m_stringLength);
        mappedIndices[indexAt(i)] = true;
    }

    m_glyphEndOffsets.grow(m_glyphCount);
    for (unsigned i = 0; i < m_glyphCount; ++i) {
        unsigned nextMappedIndex = m_indexEnd;
        for (unsigned j = indexAt(i) + 1; j < m_stringLength; ++j) {
            if (mappedIndices[j]) {
                nextMappedIndex = j;
                break;
            }
        }
        m_glyphEndOffsets[i] = nextMappedIndex;
    }
}

unsigned ComplexTextController::indexOfCurrentRun(unsigned& leftmostGlyph)
{
    leftmostGlyph = 0;
    
    size_t runCount = m_complexTextRuns.size();
    if (m_currentRun >= runCount)
        return runCount;

    if (m_isLTROnly) {
        for (unsigned i = 0; i < m_currentRun; ++i)
            leftmostGlyph += m_complexTextRuns[i]->glyphCount();
        return m_currentRun;
    }

    if (m_runIndices.isEmpty()) {
        unsigned firstRun = 0;
        unsigned firstRunOffset = stringBegin(*m_complexTextRuns[0]);
        for (unsigned i = 1; i < runCount; ++i) {
            unsigned offset = stringBegin(*m_complexTextRuns[i]);
            if (offset < firstRunOffset) {
                firstRun = i;
                firstRunOffset = offset;
            }
        }
        m_runIndices.uncheckedAppend(firstRun);
    }

    while (m_runIndices.size() <= m_currentRun) {
        unsigned offset = stringEnd(*m_complexTextRuns[m_runIndices.last()]);

        for (unsigned i = 0; i < runCount; ++i) {
            if (offset == stringBegin(*m_complexTextRuns[i])) {
                m_runIndices.uncheckedAppend(i);
                break;
            }
        }
    }

    unsigned currentRunIndex = m_runIndices[m_currentRun];
    leftmostGlyph = m_glyphCountFromStartToIndex[currentRunIndex];
    return currentRunIndex;
}

unsigned ComplexTextController::incrementCurrentRun(unsigned& leftmostGlyph)
{
    if (m_isLTROnly) {
        leftmostGlyph += m_complexTextRuns[m_currentRun++]->glyphCount();
        return m_currentRun;
    }

    m_currentRun++;
    leftmostGlyph = 0;
    return indexOfCurrentRun(leftmostGlyph);
}

float ComplexTextController::runWidthSoFarFraction(unsigned glyphStartOffset, unsigned glyphEndOffset, unsigned oldCharacterInCurrentGlyph, GlyphIterationStyle iterationStyle) const
{
    // FIXME: Instead of dividing the glyph's advance equally between the characters, this
    // could use the glyph's "ligature carets". This is available in CoreText via CTFontGetLigatureCaretPositions().
    if (glyphStartOffset == glyphEndOffset) {
        // When there are multiple glyphs per character we need to advance by the full width of the glyph.
        ASSERT(m_characterInCurrentGlyph == oldCharacterInCurrentGlyph);
        return 1;
    }

    if (iterationStyle == ByWholeGlyphs) {
        if (!oldCharacterInCurrentGlyph)
            return 1;
        return 0;
    }

    return static_cast<float>(m_characterInCurrentGlyph - oldCharacterInCurrentGlyph) / (glyphEndOffset - glyphStartOffset);
}

void ComplexTextController::advance(unsigned offset, GlyphBuffer* glyphBuffer, GlyphIterationStyle iterationStyle, HashSet<const Font*>* fallbackFonts)
{
    if (offset > m_end)
        offset = m_end;

    if (offset <= m_currentCharacter) {
        m_runWidthSoFar = 0;
        m_numGlyphsSoFar = 0;
        m_currentRun = 0;
        m_glyphInCurrentRun = 0;
        m_characterInCurrentGlyph = 0;
    }

    m_currentCharacter = offset;

    size_t runCount = m_complexTextRuns.size();

    unsigned indexOfLeftmostGlyphInCurrentRun = 0; // Relative to the beginning of ComplexTextController.
    unsigned currentRunIndex = indexOfCurrentRun(indexOfLeftmostGlyphInCurrentRun);
    while (m_currentRun < runCount) {
        const ComplexTextRun& complexTextRun = *m_complexTextRuns[currentRunIndex];
        bool ltr = complexTextRun.isLTR();
        unsigned glyphCount = complexTextRun.glyphCount();
        unsigned glyphIndexIntoCurrentRun = ltr ? m_glyphInCurrentRun : glyphCount - 1 - m_glyphInCurrentRun;
        unsigned glyphIndexIntoComplexTextController = indexOfLeftmostGlyphInCurrentRun + glyphIndexIntoCurrentRun;
        if (fallbackFonts && &complexTextRun.font() != &m_font.primaryFont())
            fallbackFonts->add(&complexTextRun.font());

        // We must store the initial advance for the first glyph we are going to draw.
        // When leftmostGlyph is 0, it represents the first glyph to draw, taking into
        // account the text direction.
        if (!indexOfLeftmostGlyphInCurrentRun && glyphBuffer)
            glyphBuffer->setInitialAdvance(GlyphBufferAdvance(complexTextRun.initialAdvance().width(), complexTextRun.initialAdvance().height()));

        while (m_glyphInCurrentRun < glyphCount) {
            unsigned glyphStartOffset = complexTextRun.indexAt(glyphIndexIntoCurrentRun);
            unsigned glyphEndOffset;
            if (complexTextRun.isMonotonic()) {
                if (ltr)
                    glyphEndOffset = std::max(glyphStartOffset, glyphIndexIntoCurrentRun + 1 < glyphCount ? complexTextRun.indexAt(glyphIndexIntoCurrentRun + 1) : complexTextRun.indexEnd());
                else
                    glyphEndOffset = std::max(glyphStartOffset, glyphIndexIntoCurrentRun > 0 ? complexTextRun.indexAt(glyphIndexIntoCurrentRun - 1) : complexTextRun.indexEnd());
            } else
                glyphEndOffset = complexTextRun.endOffsetAt(glyphIndexIntoCurrentRun);

            FloatSize adjustedBaseAdvance = m_adjustedBaseAdvances[glyphIndexIntoComplexTextController];

            if (glyphStartOffset + complexTextRun.stringLocation() >= m_currentCharacter)
                return;

            if (glyphBuffer && !m_characterInCurrentGlyph) {
                auto currentGlyphOrigin = glyphOrigin(glyphIndexIntoComplexTextController);
                GlyphBufferAdvance paintAdvance(adjustedBaseAdvance);
                if (!glyphIndexIntoCurrentRun) {
                    // The first layout advance of every run includes the "initial layout advance." However, here, we need
                    // paint advances, so subtract it out before transforming the layout advance into a paint advance.
                    paintAdvance.setWidth(paintAdvance.width() - (complexTextRun.initialAdvance().width() - currentGlyphOrigin.x()));
                    paintAdvance.setHeight(paintAdvance.height() - (complexTextRun.initialAdvance().height() - currentGlyphOrigin.y()));
                }
                paintAdvance.setWidth(paintAdvance.width() + glyphOrigin(glyphIndexIntoComplexTextController + 1).x() - currentGlyphOrigin.x());
                paintAdvance.setHeight(paintAdvance.height() + glyphOrigin(glyphIndexIntoComplexTextController + 1).y() - currentGlyphOrigin.y());
                if (glyphIndexIntoCurrentRun == glyphCount - 1 && currentRunIndex + 1 < runCount) {
                    // Our paint advance points to the end of the run. However, the next run may have an
                    // initial advance, and our paint advance needs to point to the location of the next
                    // glyph. So, we need to add in the next run's initial advance.
                    paintAdvance.setWidth(paintAdvance.width() - glyphOrigin(glyphIndexIntoComplexTextController + 1).x() + m_complexTextRuns[currentRunIndex + 1]->initialAdvance().width());
                    paintAdvance.setHeight(paintAdvance.height() - glyphOrigin(glyphIndexIntoComplexTextController + 1).y() + m_complexTextRuns[currentRunIndex + 1]->initialAdvance().height());
                }
                paintAdvance.setHeight(-paintAdvance.height()); // Increasing y points down
                glyphBuffer->add(m_adjustedGlyphs[glyphIndexIntoComplexTextController], &complexTextRun.font(), paintAdvance, complexTextRun.indexAt(m_glyphInCurrentRun));
            }

            unsigned oldCharacterInCurrentGlyph = m_characterInCurrentGlyph;
            m_characterInCurrentGlyph = std::min(m_currentCharacter - complexTextRun.stringLocation(), glyphEndOffset) - glyphStartOffset;
            m_runWidthSoFar += adjustedBaseAdvance.width() * runWidthSoFarFraction(glyphStartOffset, glyphEndOffset, oldCharacterInCurrentGlyph, iterationStyle);

            if (glyphEndOffset + complexTextRun.stringLocation() > m_currentCharacter)
                return;

            m_numGlyphsSoFar++;
            m_glyphInCurrentRun++;
            m_characterInCurrentGlyph = 0;
            if (ltr) {
                glyphIndexIntoCurrentRun++;
                glyphIndexIntoComplexTextController++;
            } else {
                glyphIndexIntoCurrentRun--;
                glyphIndexIntoComplexTextController--;
            }
        }
        currentRunIndex = incrementCurrentRun(indexOfLeftmostGlyphInCurrentRun);
        m_glyphInCurrentRun = 0;
    }
}

static inline std::pair<bool, bool> expansionLocation(bool ideograph, bool treatAsSpace, bool ltr, bool isAfterExpansion, bool forbidLeadingExpansion, bool forbidTrailingExpansion, bool forceLeadingExpansion, bool forceTrailingExpansion)
{
    bool expandLeft = ideograph;
    bool expandRight = ideograph;
    if (treatAsSpace) {
        if (ltr)
            expandRight = true;
        else
            expandLeft = true;
    }
    if (isAfterExpansion)
        expandLeft = false;
    ASSERT(!forbidLeadingExpansion || !forceLeadingExpansion);
    ASSERT(!forbidTrailingExpansion || !forceTrailingExpansion);
    if (forbidLeadingExpansion)
        expandLeft = false;
    if (forbidTrailingExpansion)
        expandRight = false;
    if (forceLeadingExpansion)
        expandLeft = true;
    if (forceTrailingExpansion)
        expandRight = true;
    return std::make_pair(expandLeft, expandRight);
}

void ComplexTextController::adjustGlyphsAndAdvances()
{
    bool afterExpansion = (m_run.expansionBehavior() & LeadingExpansionMask) == ForbidLeadingExpansion;
    size_t runCount = m_complexTextRuns.size();
    bool hasExtraSpacing = (m_font.letterSpacing() || m_font.wordSpacing() || m_expansion) && !m_run.spacingDisabled();
    bool runForcesLeadingExpansion = (m_run.expansionBehavior() & LeadingExpansionMask) == ForceLeadingExpansion;
    bool runForcesTrailingExpansion = (m_run.expansionBehavior() & TrailingExpansionMask) == ForceTrailingExpansion;
    bool runForbidsLeadingExpansion = (m_run.expansionBehavior() & LeadingExpansionMask) == ForbidLeadingExpansion;
    bool runForbidsTrailingExpansion = (m_run.expansionBehavior() & TrailingExpansionMask) == ForbidTrailingExpansion;

    // We are iterating in glyph order, not string order. Compare this to WidthIterator::advanceInternal()
    for (size_t runIndex = 0; runIndex < runCount; ++runIndex) {
        ComplexTextRun& complexTextRun = *m_complexTextRuns[runIndex];
        unsigned glyphCount = complexTextRun.glyphCount();
        const Font& font = complexTextRun.font();

        if (!complexTextRun.isLTR())
            m_isLTROnly = false;

        const CGGlyph* glyphs = complexTextRun.glyphs();
        const FloatSize* advances = complexTextRun.baseAdvances();

        float spaceWidth = font.spaceWidth() - font.syntheticBoldOffset();
        const UChar* cp = complexTextRun.characters();
        FloatPoint glyphOrigin;
        unsigned lastCharacterIndex = m_run.ltr() ? std::numeric_limits<unsigned>::min() : std::numeric_limits<unsigned>::max();
        bool isMonotonic = true;

        for (unsigned i = 0; i < glyphCount; i++) {
            unsigned characterIndex = complexTextRun.indexAt(i);
            if (m_run.ltr()) {
                if (characterIndex < lastCharacterIndex)
                    isMonotonic = false;
            } else {
                if (characterIndex > lastCharacterIndex)
                    isMonotonic = false;
            }
            UChar ch = *(cp + characterIndex);

            bool treatAsSpace = FontCascade::treatAsSpace(ch);
            CGGlyph glyph = treatAsSpace ? font.spaceGlyph() : glyphs[i];
            FloatSize advance = treatAsSpace ? FloatSize(spaceWidth, advances[i].height()) : advances[i];

            if (ch == '\t' && m_run.allowTabs())
                advance.setWidth(m_font.tabWidth(font, m_run.tabSize(), m_run.xPos() + m_totalWidth));
            else if (FontCascade::treatAsZeroWidthSpace(ch) && !treatAsSpace) {
                advance.setWidth(0);
                glyph = font.spaceGlyph();
            }

            if (!i) {
                advance.expand(complexTextRun.initialAdvance().width(), complexTextRun.initialAdvance().height());
                if (auto* origins = complexTextRun.glyphOrigins())
                    advance.expand(-origins[0].x(), -origins[0].y());
            }

            advance.expand(font.syntheticBoldOffset(), 0);

            if (hasExtraSpacing) {
                // If we're a glyph with an advance, add in letter-spacing.
                // That way we weed out zero width lurkers. This behavior matches the fast text code path.
                if (advance.width())
                    advance.expand(m_font.letterSpacing(), 0);

                unsigned characterIndexInRun = characterIndex + complexTextRun.stringLocation();
                bool isFirstCharacter = !(characterIndex + complexTextRun.stringLocation());
                bool isLastCharacter = characterIndexInRun + 1 == m_run.length() || (U16_IS_LEAD(ch) && characterIndexInRun + 2 == m_run.length() && U16_IS_TRAIL(*(cp + characterIndex + 1)));

                bool forceLeadingExpansion = false; // On the left, regardless of m_run.ltr()
                bool forceTrailingExpansion = false; // On the right, regardless of m_run.ltr()
                bool forbidLeadingExpansion = false;
                bool forbidTrailingExpansion = false;
                if (runForcesLeadingExpansion)
                    forceLeadingExpansion = m_run.ltr() ? isFirstCharacter : isLastCharacter;
                if (runForcesTrailingExpansion)
                    forceTrailingExpansion = m_run.ltr() ? isLastCharacter : isFirstCharacter;
                if (runForbidsLeadingExpansion)
                    forbidLeadingExpansion = m_run.ltr() ? isFirstCharacter : isLastCharacter;
                if (runForbidsTrailingExpansion)
                    forbidTrailingExpansion = m_run.ltr() ? isLastCharacter : isFirstCharacter;
                // Handle justification and word-spacing.
                bool ideograph = FontCascade::isCJKIdeographOrSymbol(ch);
                if (treatAsSpace || ideograph || forceLeadingExpansion || forceTrailingExpansion) {
                    // Distribute the run's total expansion evenly over all expansion opportunities in the run.
                    if (m_expansion) {
                        bool expandLeft, expandRight;
                        std::tie(expandLeft, expandRight) = expansionLocation(ideograph, treatAsSpace, m_run.ltr(), afterExpansion, forbidLeadingExpansion, forbidTrailingExpansion, forceLeadingExpansion, forceTrailingExpansion);
                        if (expandLeft) {
                            m_expansion -= m_expansionPerOpportunity;
                            // Increase previous width
                            if (m_adjustedBaseAdvances.isEmpty()) {
                                advance.expand(m_expansionPerOpportunity, 0);
                                complexTextRun.growInitialAdvanceHorizontally(m_expansionPerOpportunity);
                            } else {
                                m_adjustedBaseAdvances.last().expand(m_expansionPerOpportunity, 0);
                                m_totalWidth += m_expansionPerOpportunity;
                            }
                        }
                        if (expandRight) {
                            m_expansion -= m_expansionPerOpportunity;
                            advance.expand(m_expansionPerOpportunity, 0);
                            afterExpansion = true;
                        }
                    } else
                        afterExpansion = false;

                    // Account for word-spacing.
                    if (treatAsSpace && (ch != '\t' || !m_run.allowTabs()) && (characterIndex > 0 || runIndex > 0) && m_font.wordSpacing())
                        advance.expand(m_font.wordSpacing(), 0);
                } else
                    afterExpansion = false;
            }

            m_totalWidth += advance.width();

            // FIXME: Combining marks should receive a text emphasis mark if they are combine with a space.
            if (m_forTextEmphasis && (!FontCascade::canReceiveTextEmphasis(ch) || (U_GET_GC_MASK(ch) & U_GC_M_MASK)))
                glyph = 0;

            m_adjustedBaseAdvances.append(advance);
            if (auto* origins = complexTextRun.glyphOrigins()) {
                ASSERT(m_glyphOrigins.size() < m_adjustedBaseAdvances.size());
                m_glyphOrigins.grow(m_adjustedBaseAdvances.size());
                m_glyphOrigins[m_glyphOrigins.size() - 1] = origins[i];
                ASSERT(m_glyphOrigins.size() == m_adjustedBaseAdvances.size());
            }
            m_adjustedGlyphs.append(glyph);
            
            FloatRect glyphBounds = font.boundsForGlyph(glyph);
            glyphBounds.move(glyphOrigin.x(), glyphOrigin.y());
            m_minGlyphBoundingBoxX = std::min(m_minGlyphBoundingBoxX, glyphBounds.x());
            m_maxGlyphBoundingBoxX = std::max(m_maxGlyphBoundingBoxX, glyphBounds.maxX());
            m_minGlyphBoundingBoxY = std::min(m_minGlyphBoundingBoxY, glyphBounds.y());
            m_maxGlyphBoundingBoxY = std::max(m_maxGlyphBoundingBoxY, glyphBounds.maxY());
            glyphOrigin.move(advance);
            
            lastCharacterIndex = characterIndex;
        }
        if (!isMonotonic)
            complexTextRun.setIsNonMonotonic();
    }
}

// Missing glyphs run constructor. Core Text will not generate a run of missing glyphs, instead falling back on
// glyphs from LastResort. We want to use the primary font's missing glyph in order to match the fast text code path.
ComplexTextController::ComplexTextRun::ComplexTextRun(const Font& font, const UChar* characters, unsigned stringLocation, unsigned stringLength, unsigned indexBegin, unsigned indexEnd, bool ltr)
    : m_font(font)
    , m_characters(characters)
    , m_stringLength(stringLength)
    , m_indexBegin(indexBegin)
    , m_indexEnd(indexEnd)
    , m_stringLocation(stringLocation)
    , m_isLTR(ltr)
{
    auto runLengthInCodeUnits = m_indexEnd - m_indexBegin;
    m_coreTextIndices.reserveInitialCapacity(runLengthInCodeUnits);
    unsigned r = m_indexBegin;
    while (r < m_indexEnd) {
        m_coreTextIndices.uncheckedAppend(r);
        UChar32 character;
        U16_NEXT(m_characters, r, m_stringLength, character);
    }
    m_glyphCount = m_coreTextIndices.size();
    if (!ltr) {
        for (unsigned r = 0, end = m_glyphCount - 1; r < m_glyphCount / 2; ++r, --end)
            std::swap(m_coreTextIndices[r], m_coreTextIndices[end]);
    }

    // Synthesize a run of missing glyphs.
    m_glyphs.fill(0, m_glyphCount);
    m_baseAdvances.fill(FloatSize(m_font.widthForGlyph(0), 0), m_glyphCount);
}

ComplexTextController::ComplexTextRun::ComplexTextRun(const Vector<FloatSize>& advances, const Vector<FloatPoint>& origins, const Vector<Glyph>& glyphs, const Vector<unsigned>& stringIndices, FloatSize initialAdvance, const Font& font, const UChar* characters, unsigned stringLocation, unsigned stringLength, unsigned indexBegin, unsigned indexEnd, bool ltr)
    : m_baseAdvances(advances)
    , m_glyphOrigins(origins)
    , m_glyphs(glyphs)
    , m_coreTextIndices(stringIndices)
    , m_initialAdvance(initialAdvance)
    , m_font(font)
    , m_characters(characters)
    , m_stringLength(stringLength)
    , m_indexBegin(indexBegin)
    , m_indexEnd(indexEnd)
    , m_glyphCount(glyphs.size())
    , m_stringLocation(stringLocation)
    , m_isLTR(ltr)
{
}

} // namespace WebCore