Source/WebCore/layout/inlineformatting/InlineTextItem.cpp

/*
 * Copyright (C) 2018 Apple Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *
 * 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
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#include "config.h"
#include "InlineTextItem.h"

#if ENABLE(LAYOUT_FORMATTING_CONTEXT)

#include "FontCascade.h"
#include "InlineSoftLineBreakItem.h"
#include "TextUtil.h"
#include <wtf/unicode/CharacterNames.h>

namespace WebCore {
namespace Layout {

static_assert(sizeof(InlineItem) == sizeof(InlineTextItem), "");

static inline bool isWhitespaceCharacter(UChar character, bool preserveNewline)
{
    return character == ' ' || character == '\t' || (character == '\n' && !preserveNewline);
}

static unsigned moveToNextNonWhitespacePosition(const StringView& textContent, unsigned startPosition, bool preserveNewline)
{
    auto nextNonWhiteSpacePosition = startPosition;
    while (nextNonWhiteSpacePosition < textContent.length() && isWhitespaceCharacter(textContent[nextNonWhiteSpacePosition], preserveNewline))
        ++nextNonWhiteSpacePosition;
    return nextNonWhiteSpacePosition - startPosition;
}

static unsigned moveToNextBreakablePosition(unsigned startPosition, LazyLineBreakIterator& lineBreakIterator, const RenderStyle& style)
{
    auto textLength = lineBreakIterator.stringView().length();
    auto startPositionForNextBreakablePosition = startPosition;
    while (startPositionForNextBreakablePosition < textLength) {
        auto nextBreakablePosition = TextUtil::findNextBreakablePosition(lineBreakIterator, startPositionForNextBreakablePosition, style);
        // Oftentimes the next breakable position comes back as the start position (most notably hyphens).
        if (nextBreakablePosition != startPosition)
            return nextBreakablePosition - startPosition;
        ++startPositionForNextBreakablePosition;
    }
    return textLength - startPosition;
}

void InlineTextItem::createAndAppendTextItems(InlineItems& inlineContent, const Box& inlineBox)
{
    auto& textContext = *inlineBox.textContext();
    auto text = textContext.content;
    if (!text.length())
        return inlineContent.append(InlineTextItem::createEmptyItem(inlineBox));

    auto& style = inlineBox.style();
    auto& font = style.fontCascade();
    LazyLineBreakIterator lineBreakIterator(text);
    unsigned currentPosition = 0;

    auto inlineItemWidth = [&](auto startPosition, auto length) -> Optional<InlineLayoutUnit> {
        if (!textContext.canUseSimplifiedContentMeasuring)
            return { };
        return TextUtil::width(inlineBox, startPosition, startPosition + length);
    };

    while (currentPosition < text.length()) {
        auto isSegmentBreakCandidate = [](auto character) {
            return character == '\n';
        };

        // Segment breaks with preserve new line style (white-space: pre, pre-wrap, break-spaces and pre-line) compute to forced line break.
        if (isSegmentBreakCandidate(text[currentPosition]) && style.preserveNewline()) {
            inlineContent.append(InlineSoftLineBreakItem::createSoftLineBreakItem(inlineBox, currentPosition));
            ++currentPosition;
            continue;
        }

        if (isWhitespaceCharacter(text[currentPosition], style.preserveNewline())) {
            auto appendWhitespaceItem = [&] (auto startPosition, auto itemLength) {
                auto simpleSingleWhitespaceContent = textContext.canUseSimplifiedContentMeasuring && (itemLength == 1 || style.collapseWhiteSpace());
                auto width = simpleSingleWhitespaceContent ? makeOptional(InlineLayoutUnit { font.spaceWidth() }) : inlineItemWidth(startPosition, itemLength);
                inlineContent.append(InlineTextItem::createWhitespaceItem(inlineBox, startPosition, itemLength, width));
            };

            auto length = moveToNextNonWhitespacePosition(text, currentPosition, style.preserveNewline());
            if (style.whiteSpace() == WhiteSpace::BreakSpaces) {
                // https://www.w3.org/TR/css-text-3/#white-space-phase-1
                // For break-spaces, a soft wrap opportunity exists after every space and every tab.
                // FIXME: if this turns out to be a perf hit with too many individual whitespace inline items, we should transition this logic to line breaking.
                for (unsigned i = 0; i < length; ++i)
                    appendWhitespaceItem(currentPosition + i, 1);
            } else
                appendWhitespaceItem(currentPosition, length);
            currentPosition += length;
            continue;
        }

        auto length = moveToNextBreakablePosition(currentPosition, lineBreakIterator, style);
        inlineContent.append(InlineTextItem::createNonWhitespaceItem(inlineBox, currentPosition, length, inlineItemWidth(currentPosition, length)));
        currentPosition += length;
    }
}

bool InlineTextItem::isEmptyContent() const
{
    // FIXME: We should check for more zero width content and not just U+200B.
    return !m_length || (m_length == 1 && layoutBox().textContext()->content[start()] == zeroWidthSpace); 
}

std::unique_ptr<InlineTextItem> InlineTextItem::left(unsigned length) const
{
    RELEASE_ASSERT(length <= this->length());
    ASSERT(m_textItemType != TextItemType::Undefined);
    ASSERT(length);
    return makeUnique<InlineTextItem>(layoutBox(), start(), length, WTF::nullopt, m_textItemType);
}

std::unique_ptr<InlineTextItem> InlineTextItem::right(unsigned length) const
{
    RELEASE_ASSERT(length <= this->length());
    ASSERT(m_textItemType != TextItemType::Undefined);
    ASSERT(length);
    return makeUnique<InlineTextItem>(layoutBox(), end() - length, length, WTF::nullopt, m_textItemType);
}

}
}
#endif