SimpleLineLayoutTextFragmentIterator.cpp   [plain text]

/*
 * Copyright (C) 2015 Apple Inc. All rights reserved.
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#include "config.h"
#include "SimpleLineLayoutTextFragmentIterator.h"

#include "RenderBlockFlow.h"
#include "RenderChildIterator.h"
#include "SimpleLineLayoutFlowContents.h"

namespace WebCore {
namespace SimpleLineLayout {

TextFragmentIterator::Style::Style(const RenderStyle& style)
    : font(style.fontCascade())
    , textAlign(style.textAlign())
    , collapseWhitespace(style.collapseWhiteSpace())
    , preserveNewline(style.preserveNewline())
    , wrapLines(style.autoWrap())
    , breakWordOnOverflow(style.overflowWrap() == BreakOverflowWrap && (wrapLines || preserveNewline))
    , spaceWidth(font.width(TextRun(StringView(&space, 1))))
    , tabWidth(collapseWhitespace ? 0 : style.tabSize())
    , locale(style.locale())
{
}

TextFragmentIterator::TextFragmentIterator(const RenderBlockFlow& flow)
    : m_flowContents(flow)
    , m_currentSegment(m_flowContents.begin())
    , m_lineBreakIterator(m_currentSegment->text, flow.style().locale())
    , m_style(flow.style())
{
}

TextFragmentIterator::TextFragment TextFragmentIterator::nextTextFragment(float xPosition)
{
    TextFragmentIterator::TextFragment nextFragment = findNextTextFragment(xPosition);
    m_atEndOfSegment = (m_currentSegment == m_flowContents.end()) || (m_position == m_currentSegment->end);
    return nextFragment;
}

TextFragmentIterator::TextFragment TextFragmentIterator::findNextTextFragment(float xPosition)
{
    // A fragment can either be
    // 1. line break when <br> is present or preserveNewline is on (not considered as whitespace) or
    // 2. whitespace (collasped, non-collapsed multi or single) or
    // 3. non-whitespace characters.
    // 4. content end.
    ASSERT(m_currentSegment != m_flowContents.end());
    unsigned startPosition = m_position;
    if (m_atEndOfSegment)
        ++m_currentSegment;

    if (m_currentSegment == m_flowContents.end())
        return TextFragment(startPosition, startPosition, 0, TextFragment::ContentEnd);
    if (isHardLineBreak(m_currentSegment))
        return TextFragment(startPosition, startPosition, 0, TextFragment::HardLineBreak);
    if (isSoftLineBreak(startPosition)) {
        unsigned endPosition = ++m_position;
        return TextFragment(startPosition, endPosition, 0, TextFragment::SoftLineBreak);
    }
    float width = 0;
    bool overlappingFragment = false;
    unsigned endPosition = skipToNextPosition(PositionType::NonWhitespace, startPosition, width, xPosition, overlappingFragment);
    unsigned segmentEndPosition = m_currentSegment->end;
    ASSERT(startPosition <= endPosition);
    if (startPosition < endPosition) {
        bool multipleWhitespace = startPosition + 1 < endPosition;
        bool isCollapsed = multipleWhitespace && m_style.collapseWhitespace;
        bool isBreakable = !isCollapsed && multipleWhitespace;
        m_position = endPosition;
        return TextFragment(startPosition, endPosition, width, TextFragment::Whitespace, endPosition == segmentEndPosition, false, isCollapsed, m_style.collapseWhitespace, isBreakable);
    }
    endPosition = skipToNextPosition(PositionType::Breakable, startPosition, width, xPosition, overlappingFragment);
    m_position = endPosition;
    return TextFragment(startPosition, endPosition, width, TextFragment::NonWhitespace, endPosition == segmentEndPosition, overlappingFragment, false, false, m_style.breakWordOnOverflow);
}

void TextFragmentIterator::revertToEndOfFragment(const TextFragment& fragment)
{
    ASSERT(m_position >= fragment.end());
    while (m_currentSegment->start > fragment.end())
        --m_currentSegment;
    // TODO: It reverts to the last fragment on the same position, but that's ok for now as we don't need to
    // differentiate multiple renderers on the same position.
    m_position = fragment.end();
    m_atEndOfSegment = false;
}

template <typename CharacterType>
unsigned TextFragmentIterator::nextBreakablePosition(const FlowContents::Segment& segment, unsigned startPosition)
{
    ASSERT(startPosition < segment.end);
    if (segment.text.impl() != m_lineBreakIterator.string().impl()) {
        const String& currentText = m_lineBreakIterator.string();
        unsigned textLength = currentText.length();
        UChar lastCharacter = textLength > 0 ? currentText[textLength - 1] : 0;
        UChar secondToLastCharacter = textLength > 1 ? currentText[textLength - 2] : 0;
        m_lineBreakIterator.setPriorContext(lastCharacter, secondToLastCharacter);
        m_lineBreakIterator.resetStringAndReleaseIterator(segment.text, m_style.locale, LineBreakIteratorModeUAX14);
    }
    const auto* characters = segment.text.characters<CharacterType>();
    unsigned segmentLength = segment.end - segment.start;
    unsigned segmentPosition = startPosition - segment.start;
    return segment.start + nextBreakablePositionNonLoosely<CharacterType, NBSPBehavior::IgnoreNBSP>(m_lineBreakIterator, characters, segmentLength, segmentPosition);
}

template <typename CharacterType>
unsigned TextFragmentIterator::nextNonWhitespacePosition(const FlowContents::Segment& segment, unsigned startPosition)
{
    ASSERT(startPosition < segment.end);
    const auto* text = segment.text.characters<CharacterType>();
    unsigned position = startPosition;
    for (; position < segment.end; ++position) {
        auto character = text[position - segment.start];
        bool isWhitespace = character == ' ' || character == '\t' || (!m_style.preserveNewline && character == '\n');
        if (!isWhitespace)
            return position;
    }
    return position;
}

float TextFragmentIterator::textWidth(unsigned from, unsigned to, float xPosition) const
{
    auto& segment = *m_currentSegment;
    ASSERT(segment.start <= from && from <= segment.end && segment.start <= to && to <= segment.end);
    ASSERT(is<RenderText>(segment.renderer));
    if (m_style.font.isFixedPitch() || (from == segment.start && to == segment.end))
        return downcast<RenderText>(segment.renderer).width(from - segment.start, to - from, m_style.font, xPosition, nullptr, nullptr);
    return segment.text.is8Bit() ? runWidth<LChar>(segment, from, to, xPosition) : runWidth<UChar>(segment, from, to, xPosition);
}

unsigned TextFragmentIterator::skipToNextPosition(PositionType positionType, unsigned startPosition, float& width, float xPosition, bool& overlappingFragment)
{
    overlappingFragment = false;
    unsigned currentPosition = startPosition;
    unsigned nextPosition = currentPosition;
    // Collapsed whitespace has constant width. Do not measure it.
    if (positionType == NonWhitespace)
        nextPosition = m_currentSegment->text.is8Bit() ? nextNonWhitespacePosition<LChar>(*m_currentSegment, currentPosition) : nextNonWhitespacePosition<UChar>(*m_currentSegment, currentPosition);
    else if (positionType == Breakable) {
        // nextBreakablePosition returns the same position for certain characters such as hyphens. Call next again with modified position unless it's the end of the segment.
        nextPosition = m_currentSegment->text.is8Bit() ? nextBreakablePosition<LChar>(*m_currentSegment, currentPosition) : nextBreakablePosition<UChar>(*m_currentSegment, currentPosition);
        // We need to know whether the word actually finishes at the end of this renderer or not.
        if (nextPosition == m_currentSegment->end) {
            const auto nextSegment = m_currentSegment + 1;
            if (nextSegment != m_flowContents.end() && !isHardLineBreak(nextSegment))
                overlappingFragment = nextPosition < (nextSegment->text.is8Bit() ? nextBreakablePosition<LChar>(*nextSegment, nextPosition) : nextBreakablePosition<UChar>(*nextSegment, nextPosition));
        } else if (nextPosition == currentPosition) {
            if (++nextPosition < m_currentSegment->end)
                nextPosition = m_currentSegment->text.is8Bit() ? nextBreakablePosition<LChar>(*m_currentSegment, currentPosition + 1) : nextBreakablePosition<UChar>(*m_currentSegment, currentPosition + 1);
        }
    }
    width = 0;
    if (nextPosition == currentPosition)
        return currentPosition;
    bool measureText = positionType != NonWhitespace || !m_style.collapseWhitespace;
    if (measureText) {
        float textWidth = this->textWidth(currentPosition, nextPosition, xPosition);
        width += textWidth;
    } else if (startPosition < nextPosition)
        width = m_style.spaceWidth;
    return nextPosition;
}

template <typename CharacterType>
float TextFragmentIterator::runWidth(const FlowContents::Segment& segment, unsigned startPosition, unsigned endPosition, float xPosition) const
{
    ASSERT(startPosition <= endPosition);
    if (startPosition == endPosition)
        return 0;
    unsigned segmentFrom = startPosition - segment.start;
    unsigned segmentTo = endPosition - segment.start;
    bool measureWithEndSpace = m_style.collapseWhitespace && segmentTo < segment.text.length() && segment.text[segmentTo] == ' ';
    if (measureWithEndSpace)
        ++segmentTo;
    TextRun run(StringView(segment.text).substring(segmentFrom, segmentTo - segmentFrom));
    run.setXPos(xPosition);
    run.setTabSize(!!m_style.tabWidth, m_style.tabWidth);
    float width = m_style.font.width(run);
    if (measureWithEndSpace)
        width -= m_style.spaceWidth;
    return width;
}

}
}