third_party/WebKit/Source/core/layout/svg/SVGTextChunkBuilder.cpp

/*
 * Copyright (C) Research In Motion Limited 2010. 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 "core/layout/svg/SVGTextChunkBuilder.h"

#include "core/layout/api/LineLayoutSVGInlineText.h"
#include "core/layout/svg/line/SVGInlineTextBox.h"
#include "core/svg/SVGLengthContext.h"
#include "core/svg/SVGTextContentElement.h"

namespace blink {

namespace {

float calculateTextAnchorShift(const ComputedStyle& style, float length) {
  bool isLTR = style.isLeftToRightDirection();
  switch (style.svgStyle().textAnchor()) {
    default:
      ASSERT_NOT_REACHED();
    case TA_START:
      return isLTR ? 0 : -length;
    case TA_MIDDLE:
      return -length / 2;
    case TA_END:
      return isLTR ? -length : 0;
  }
}

bool needsTextAnchorAdjustment(const ComputedStyle& style) {
  bool isLTR = style.isLeftToRightDirection();
  switch (style.svgStyle().textAnchor()) {
    default:
      ASSERT_NOT_REACHED();
    case TA_START:
      return !isLTR;
    case TA_MIDDLE:
      return true;
    case TA_END:
      return isLTR;
  }
}

class ChunkLengthAccumulator {
 public:
  ChunkLengthAccumulator(bool isVertical)
      : m_numCharacters(0), m_length(0), m_isVertical(isVertical) {}

  typedef Vector<SVGInlineTextBox*>::const_iterator BoxListConstIterator;

  void processRange(BoxListConstIterator boxStart, BoxListConstIterator boxEnd);
  void reset() {
    m_numCharacters = 0;
    m_length = 0;
  }

  float length() const { return m_length; }
  unsigned numCharacters() const { return m_numCharacters; }

 private:
  unsigned m_numCharacters;
  float m_length;
  const bool m_isVertical;
};

void ChunkLengthAccumulator::processRange(BoxListConstIterator boxStart,
                                          BoxListConstIterator boxEnd) {
  SVGTextFragment* lastFragment = nullptr;
  for (auto boxIter = boxStart; boxIter != boxEnd; ++boxIter) {
    for (SVGTextFragment& fragment : (*boxIter)->textFragments()) {
      m_numCharacters += fragment.length;

      if (m_isVertical)
        m_length += fragment.height;
      else
        m_length += fragment.width;

      if (!lastFragment) {
        lastFragment = &fragment;
        continue;
      }

      // Respect gap between chunks.
      if (m_isVertical)
        m_length += fragment.y - (lastFragment->y + lastFragment->height);
      else
        m_length += fragment.x - (lastFragment->x + lastFragment->width);

      lastFragment = &fragment;
    }
  }
}

}  // namespace

SVGTextChunkBuilder::SVGTextChunkBuilder() {}

void SVGTextChunkBuilder::processTextChunks(
    const Vector<SVGInlineTextBox*>& lineLayoutBoxes) {
  if (lineLayoutBoxes.isEmpty())
    return;

  bool foundStart = false;
  auto boxIter = lineLayoutBoxes.begin();
  auto endBox = lineLayoutBoxes.end();
  auto chunkStartBox = boxIter;
  for (; boxIter != endBox; ++boxIter) {
    if (!(*boxIter)->startsNewTextChunk())
      continue;

    if (!foundStart) {
      foundStart = true;
    } else {
      ASSERT(boxIter != chunkStartBox);
      handleTextChunk(chunkStartBox, boxIter);
    }
    chunkStartBox = boxIter;
  }

  if (!foundStart)
    return;

  if (boxIter != chunkStartBox)
    handleTextChunk(chunkStartBox, boxIter);
}

SVGTextPathChunkBuilder::SVGTextPathChunkBuilder()
    : SVGTextChunkBuilder(),
      m_totalLength(0),
      m_totalCharacters(0),
      m_totalTextAnchorShift(0) {}

void SVGTextPathChunkBuilder::handleTextChunk(BoxListConstIterator boxStart,
                                              BoxListConstIterator boxEnd) {
  const ComputedStyle& style = (*boxStart)->getLineLayoutItem().styleRef();

  ChunkLengthAccumulator lengthAccumulator(!style.isHorizontalWritingMode());
  lengthAccumulator.processRange(boxStart, boxEnd);

  // Handle text-anchor as additional start offset for text paths.
  m_totalTextAnchorShift +=
      calculateTextAnchorShift(style, lengthAccumulator.length());

  m_totalLength += lengthAccumulator.length();
  m_totalCharacters += lengthAccumulator.numCharacters();
}

static float computeTextLengthBias(const SVGTextFragment& fragment,
                                   float scale) {
  float initialPosition = fragment.isVertical ? fragment.y : fragment.x;
  return initialPosition + scale * -initialPosition;
}

void SVGTextChunkBuilder::handleTextChunk(BoxListConstIterator boxStart,
                                          BoxListConstIterator boxEnd) {
  ASSERT(*boxStart);

  const LineLayoutSVGInlineText textLineLayout =
      LineLayoutSVGInlineText((*boxStart)->getLineLayoutItem());
  const ComputedStyle& style = textLineLayout.styleRef();

  // Handle 'lengthAdjust' property.
  float desiredTextLength = 0;
  SVGLengthAdjustType lengthAdjust = SVGLengthAdjustUnknown;
  if (SVGTextContentElement* textContentElement =
          SVGTextContentElement::elementFromLineLayoutItem(
              textLineLayout.parent())) {
    lengthAdjust =
        textContentElement->lengthAdjust()->currentValue()->enumValue();

    SVGLengthContext lengthContext(textContentElement);
    if (textContentElement->textLengthIsSpecifiedByUser())
      desiredTextLength =
          textContentElement->textLength()->currentValue()->value(
              lengthContext);
    else
      desiredTextLength = 0;
  }

  bool processTextLength = desiredTextLength > 0;
  bool processTextAnchor = needsTextAnchorAdjustment(style);
  if (!processTextAnchor && !processTextLength)
    return;

  bool isVerticalText = !style.isHorizontalWritingMode();

  // Calculate absolute length of whole text chunk (starting from text box
  // 'start', spanning 'length' text boxes).
  ChunkLengthAccumulator lengthAccumulator(isVerticalText);
  lengthAccumulator.processRange(boxStart, boxEnd);

  if (processTextLength) {
    float chunkLength = lengthAccumulator.length();
    if (lengthAdjust == SVGLengthAdjustSpacing) {
      float textLengthShift =
          (desiredTextLength - chunkLength) / lengthAccumulator.numCharacters();
      unsigned atCharacter = 0;
      for (auto boxIter = boxStart; boxIter != boxEnd; ++boxIter) {
        Vector<SVGTextFragment>& fragments = (*boxIter)->textFragments();
        if (fragments.isEmpty())
          continue;
        processTextLengthSpacingCorrection(isVerticalText, textLengthShift,
                                           fragments, atCharacter);
      }

      // Fragments have been adjusted, we have to recalculate the chunk
      // length, to be able to apply the text-anchor shift.
      if (processTextAnchor) {
        lengthAccumulator.reset();
        lengthAccumulator.processRange(boxStart, boxEnd);
      }
    } else {
      ASSERT(lengthAdjust == SVGLengthAdjustSpacingAndGlyphs);
      float textLengthScale = desiredTextLength / chunkLength;
      float textLengthBias = 0;

      bool foundFirstFragment = false;
      for (auto boxIter = boxStart; boxIter != boxEnd; ++boxIter) {
        SVGInlineTextBox* textBox = *boxIter;
        Vector<SVGTextFragment>& fragments = textBox->textFragments();
        if (fragments.isEmpty())
          continue;

        if (!foundFirstFragment) {
          foundFirstFragment = true;
          textLengthBias =
              computeTextLengthBias(fragments.first(), textLengthScale);
        }

        applyTextLengthScaleAdjustment(textLengthScale, textLengthBias,
                                       fragments);
      }
    }
  }

  if (!processTextAnchor)
    return;

  float textAnchorShift =
      calculateTextAnchorShift(style, lengthAccumulator.length());
  for (auto boxIter = boxStart; boxIter != boxEnd; ++boxIter) {
    Vector<SVGTextFragment>& fragments = (*boxIter)->textFragments();
    if (fragments.isEmpty())
      continue;
    processTextAnchorCorrection(isVerticalText, textAnchorShift, fragments);
  }
}

void SVGTextChunkBuilder::processTextLengthSpacingCorrection(
    bool isVerticalText,
    float textLengthShift,
    Vector<SVGTextFragment>& fragments,
    unsigned& atCharacter) {
  for (SVGTextFragment& fragment : fragments) {
    if (isVerticalText)
      fragment.y += textLengthShift * atCharacter;
    else
      fragment.x += textLengthShift * atCharacter;

    atCharacter += fragment.length;
  }
}

void SVGTextChunkBuilder::applyTextLengthScaleAdjustment(
    float textLengthScale,
    float textLengthBias,
    Vector<SVGTextFragment>& fragments) {
  for (SVGTextFragment& fragment : fragments) {
    ASSERT(fragment.lengthAdjustScale == 1);
    fragment.lengthAdjustScale = textLengthScale;
    fragment.lengthAdjustBias = textLengthBias;
  }
}

void SVGTextChunkBuilder::processTextAnchorCorrection(
    bool isVerticalText,
    float textAnchorShift,
    Vector<SVGTextFragment>& fragments) {
  for (SVGTextFragment& fragment : fragments) {
    if (isVerticalText)
      fragment.y += textAnchorShift;
    else
      fragment.x += textAnchorShift;
  }
}

}  // namespace blink