Source/WebCore/rendering/RenderCombineText.cpp

/*
 * Copyright (C) 2011 Apple Inc. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public License
 * along with this library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 *
 */

#include "config.h"
#include "RenderCombineText.h"

#include "RenderBlock.h"
#include "StyleInheritedData.h"
#include <wtf/IsoMallocInlines.h>
#include <wtf/NeverDestroyed.h>

namespace WebCore {

WTF_MAKE_ISO_ALLOCATED_IMPL(RenderCombineText);

const float textCombineMargin = 1.15f; // Allow em + 15% margin

RenderCombineText::RenderCombineText(Text& textNode, const String& string)
    : RenderText(textNode, string)
    , m_isCombined(false)
    , m_needsFontUpdate(false)
{
}

void RenderCombineText::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle)
{
    // FIXME: This is pretty hackish.
    // Only cache a new font style if our old one actually changed. We do this to avoid
    // clobbering width variants and shrink-to-fit changes, since we won't recombine when
    // the font doesn't change.
    if (!oldStyle || oldStyle->fontCascade() != style().fontCascade())
        m_combineFontStyle = RenderStyle::clonePtr(style());

    RenderText::styleDidChange(diff, oldStyle);

    if (m_isCombined && selfNeedsLayout()) {
        // Layouts cause the text to be recombined; therefore, only only un-combine when the style diff causes a layout.
        RenderText::setRenderedText(originalText()); // This RenderCombineText has been combined once. Restore the original text for the next combineText().
        m_isCombined = false;
    }

    m_needsFontUpdate = true;
    combineTextIfNeeded();
}

void RenderCombineText::setRenderedText(const String& text)
{
    RenderText::setRenderedText(text);

    m_needsFontUpdate = true;
    combineTextIfNeeded();
}

float RenderCombineText::width(unsigned from, unsigned length, const FontCascade& font, float xPosition, HashSet<const Font*>* fallbackFonts, GlyphOverflow* glyphOverflow) const
{
    if (m_isCombined)
        return !length ? 0 : font.size();

    return RenderText::width(from, length, font, xPosition, fallbackFonts, glyphOverflow);
}

std::optional<FloatPoint> RenderCombineText::computeTextOrigin(const FloatRect& boxRect) const
{
    if (!m_isCombined)
        return std::nullopt;

    // Visually center m_combinedTextWidth/Ascent/Descent within boxRect
    FloatPoint result = boxRect.minXMaxYCorner();
    FloatSize combinedTextSize(m_combinedTextWidth, m_combinedTextAscent + m_combinedTextDescent);
    result.move((boxRect.size().transposedSize() - combinedTextSize) / 2);
    result.move(0, m_combinedTextAscent);
    return result;
}

String RenderCombineText::combinedStringForRendering() const
{
    if (m_isCombined) {
        auto originalText = this->originalText();
        ASSERT(!originalText.isNull());
        return originalText;
    }
 
    return { };
}

void RenderCombineText::combineTextIfNeeded()
{
    if (!m_needsFontUpdate)
        return;

    // An ancestor element may trigger us to lay out again, even when we're already combined.
    if (m_isCombined)
        RenderText::setRenderedText(originalText());

    m_isCombined = false;
    m_needsFontUpdate = false;

    // CSS3 spec says text-combine works only in vertical writing mode.
    if (style().isHorizontalWritingMode())
        return;

    auto description = originalFont().fontDescription();
    float emWidth = description.computedSize() * textCombineMargin;
    bool shouldUpdateFont = false;

    FontSelector* fontSelector = style().fontCascade().fontSelector();

    description.setOrientation(Horizontal); // We are going to draw combined text horizontally.

    FontCascade horizontalFont(description, style().fontCascade().letterSpacing(), style().fontCascade().wordSpacing());
    horizontalFont.update(fontSelector);
    
    GlyphOverflow glyphOverflow;
    glyphOverflow.computeBounds = true;
    float combinedTextWidth = width(0, text().length(), horizontalFont, 0, nullptr, &glyphOverflow);

    float bestFitDelta = combinedTextWidth - emWidth;
    auto bestFitDescription = description;

    m_isCombined = combinedTextWidth <= emWidth;
    
    if (m_isCombined)
        shouldUpdateFont = m_combineFontStyle->setFontDescription(description); // Need to change font orientation to horizontal.
    else {
        // Need to try compressed glyphs.
        static const FontWidthVariant widthVariants[] = { HalfWidth, ThirdWidth, QuarterWidth };
        for (auto widthVariant : widthVariants) {
            description.setWidthVariant(widthVariant); // When modifying this, make sure to keep it in sync with FontPlatformData::isForTextCombine()!

            FontCascade compressedFont(description, style().fontCascade().letterSpacing(), style().fontCascade().wordSpacing());
            compressedFont.update(fontSelector);
            
            glyphOverflow.left = glyphOverflow.top = glyphOverflow.right = glyphOverflow.bottom = 0;
            float runWidth = RenderText::width(0, text().length(), compressedFont, 0, nullptr, &glyphOverflow);
            if (runWidth <= emWidth) {
                combinedTextWidth = runWidth;
                m_isCombined = true;

                // Replace my font with the new one.
                shouldUpdateFont = m_combineFontStyle->setFontDescription(description);
                break;
            }
            
            float widthDelta = runWidth - emWidth;
            if (widthDelta < bestFitDelta) {
                bestFitDelta = widthDelta;
                bestFitDescription = description;
            }
        }
    }

    if (!m_isCombined) {
        float scaleFactor = std::max(0.4f, emWidth / (emWidth + bestFitDelta));
        float originalSize = bestFitDescription.computedSize();
        do {
            float computedSize = originalSize * scaleFactor;
            bestFitDescription.setComputedSize(computedSize);
            shouldUpdateFont = m_combineFontStyle->setFontDescription(bestFitDescription);
        
            FontCascade compressedFont(bestFitDescription, style().fontCascade().letterSpacing(), style().fontCascade().wordSpacing());
            compressedFont.update(fontSelector);
            
            glyphOverflow.left = glyphOverflow.top = glyphOverflow.right = glyphOverflow.bottom = 0;
            float runWidth = RenderText::width(0, text().length(), compressedFont, 0, nullptr, &glyphOverflow);
            if (runWidth <= emWidth) {
                combinedTextWidth = runWidth;
                m_isCombined = true;
                break;
            }
            scaleFactor -= 0.05f;
        } while (scaleFactor >= 0.4f);
    }

    if (shouldUpdateFont)
        m_combineFontStyle->fontCascade().update(fontSelector);

    if (m_isCombined) {
        static NeverDestroyed<String> objectReplacementCharacterString(&objectReplacementCharacter, 1);
        RenderText::setRenderedText(objectReplacementCharacterString.get());
        m_combinedTextWidth = combinedTextWidth;
        m_combinedTextAscent = glyphOverflow.top;
        m_combinedTextDescent = glyphOverflow.bottom;
        m_lineBoxes.dirtyRange(*this, 0, originalText().length(), originalText().length());
        setNeedsLayout();
    }
}

} // namespace WebCore