Source/WebCore/layout/inlineformatting/InlineLineBreaker.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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 *
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 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
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#include "config.h"
#include "InlineLineBreaker.h"

#if ENABLE(LAYOUT_FORMATTING_CONTEXT)

#include "Hyphenation.h"
#include "InlineItem.h"
#include "InlineTextItem.h"

namespace WebCore {
namespace Layout {

static inline bool isContentWrappingAllowed(const RenderStyle& style)
{
    return style.whiteSpace() != WhiteSpace::Pre && style.whiteSpace() != WhiteSpace::NoWrap;
}

static inline bool isTrailingWhitespaceWithPreWrap(const InlineItem& trailingInlineItem)
{
    if (!trailingInlineItem.isText())
        return false;
    return trailingInlineItem.style().whiteSpace() == WhiteSpace::PreWrap && downcast<InlineTextItem>(trailingInlineItem).isWhitespace();
}

LineBreaker::BreakingContext LineBreaker::breakingContextForInlineContent(const Vector<LineLayout::Run>& runs, LayoutUnit logicalWidth, LayoutUnit availableWidth, bool lineIsEmpty)
{
    if (logicalWidth <= availableWidth)
        return { BreakingContext::ContentBreak::Keep, { } };

    auto isTextContent = [](auto& runs) {
        // <span>text</span> is considered a text run even with the [container start][container end] inline items.
        for (auto& run : runs) {
            auto& inlineItem = run.inlineItem;
            // Skip "typeless" inline items.
            if (inlineItem.isContainerStart() || inlineItem.isContainerEnd())
                continue;
            return inlineItem.isText();
        }
        return false;
    };
    if (isTextContent(runs)) {
        if (auto trailingPartialContent = wordBreakingBehavior(runs, availableWidth))
            return { BreakingContext::ContentBreak::Split, trailingPartialContent };
        // If we did not manage to break this content, we still need to decide whether keep it or wrap it to the next line.
        // FIXME: Keep tracking the last breaking opportunity where we can wrap the content:
        // <span style="white-space: pre;">this fits</span> <span style="white-space: pre;">this does not fit but does not wrap either</span>
        // ^^ could wrap at the whitespace position between the 2 inline containers.
        auto contentShouldWrap = !lineIsEmpty && isContentWrappingAllowed(runs[0].inlineItem.style());
        // FIXME: white-space: pre-wrap needs clarification. According to CSS Text Module Level 3, content wrapping is as 'normal' but apparently
        // we need to keep the overlapping whitespace on the line (and hang it I'd assume).
        if (isTrailingWhitespaceWithPreWrap(runs.last().inlineItem))
            contentShouldWrap = false;
        return { contentShouldWrap ? BreakingContext::ContentBreak::Wrap : BreakingContext::ContentBreak::Keep, { } };
    }

    // First non-text inline content always stays on line.
    return { lineIsEmpty ? BreakingContext::ContentBreak::Keep : BreakingContext::ContentBreak::Wrap, { } };
}

bool LineBreaker::shouldWrapFloatBox(LayoutUnit floatLogicalWidth, LayoutUnit availableWidth, bool lineIsEmpty)
{
    return !lineIsEmpty && floatLogicalWidth > availableWidth;
}

Optional<LineBreaker::BreakingContext::TrailingPartialContent> LineBreaker::wordBreakingBehavior(const Vector<LineLayout::Run>& runs, LayoutUnit availableWidth) const
{
    // Check where the overflow occurs and use the corresponding style to figure out the breaking behaviour.
    // <span style="word-break: normal">first</span><span style="word-break: break-all">second</span><span style="word-break: normal">third</span>
    LayoutUnit runsWidth;
    for (unsigned i = 0; i < runs.size(); ++i) {
        auto& run = runs[i];
        ASSERT(run.inlineItem.isText() || run.inlineItem.isContainerStart() || run.inlineItem.isContainerEnd());
        runsWidth += run.logicalWidth;
        // FIXME: In case of multiple inline items, we might not be able to split the content where it overflows (<span style="white-space: normal">this still fits the line</span<span style="white-space: pre">this is not anymore, but can't split</span)
        // so we need to look for split positions even runsWidth <= availableWidth.
        if (runsWidth <= availableWidth)
            continue;
        // Let's find the first breaking opportunity starting from this overflown inline item.
        if (!run.inlineItem.isText()) {
            // Can't split horizontal spacing -> e.g. <span style="padding-right: 100px;">textcontent</span>, if the [container end] is the overflown inline item
            // we need to check if there's another inline item beyond the [container end] to split.
            continue;
        }
        // Do not try to split 'pre' and 'no-wrap' content.
        if (!isContentWrappingAllowed(run.inlineItem.style()))
            continue;
        // At this point the available width can very well be negative e.g. when some part of the continuous text content can not be broken into parts ->
        // <span style="word-break: keep-all">textcontentwithnobreak</span><span>textcontentwithyesbreak</span>
        // When the first span computes longer than the available space, by the time we get to the second span, the adjusted available space becomes negative.
        auto adjustedAvailableWidth = std::max(LayoutUnit { }, availableWidth - runsWidth + run.logicalWidth);
        if (auto splitLengthAndWidth = tryBreakingTextRun(run, adjustedAvailableWidth))
            return BreakingContext::TrailingPartialContent { i, splitLengthAndWidth->length, splitLengthAndWidth->leftLogicalWidth };
    }
    // We did not manage to break in this sequence of runs.
    return { };
}

Optional<LineBreaker::SplitLengthAndWidth> LineBreaker::tryBreakingTextRun(const LineLayout::Run overflowRun, LayoutUnit availableWidth) const
{
    ASSERT(overflowRun.inlineItem.isText());
    auto breakWords = overflowRun.inlineItem.style().wordBreak();
    if (breakWords == WordBreak::KeepAll)
        return { };
    auto& inlineTextItem = downcast<InlineTextItem>(overflowRun.inlineItem);
    if (breakWords == WordBreak::BreakAll) {
        // FIXME: Pass in the content logical left to be able to measure tabs.
        auto splitData = TextUtil::split(inlineTextItem.layoutBox(), inlineTextItem.start(), inlineTextItem.length(), overflowRun.logicalWidth, availableWidth, { });
        return SplitLengthAndWidth { splitData.length, splitData.logicalWidth };
    }
    // FIXME: Find first soft wrap opportunity (e.g. hyphenation)
    return { };
}

}
}
#endif