Source/WebCore/rendering/svg/SVGTextQuery.cpp - WebKit - Git at Google

 /*
  * Copyright (C) Research In Motion Limited 2010-2012. 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 "SVGTextQuery.h"

 #include "FloatConversion.h"
 #include "InlineFlowBox.h"
 #include "RenderBlockFlow.h"
 #include "RenderInline.h"
 #include "RenderSVGText.h"
 #include "SVGInlineTextBox.h"
 #include "VisiblePosition.h"

 #include <wtf/MathExtras.h>

 namespace WebCore {

 // Base structure for callback user data
 struct SVGTextQuery::Data {
     Data()
         : isVerticalText(false)
         , processedCharacters(0)
         , textRenderer(0)
         , textBox(0)
     {
     }

     bool isVerticalText;
     unsigned processedCharacters;
     RenderSVGInlineText* textRenderer;
     const SVGInlineTextBox* textBox;
 };

 static inline InlineFlowBox* flowBoxForRenderer(RenderObject* renderer)
 {
     if (!renderer)
         return nullptr;

     if (is<RenderBlockFlow>(*renderer)) {
         // If we're given a block element, it has to be a RenderSVGText.
         ASSERT(is<RenderSVGText>(*renderer));
         RenderBlockFlow& renderBlock = downcast<RenderBlockFlow>(*renderer);

         // RenderSVGText only ever contains a single line box.
         auto flowBox = renderBlock.firstRootBox();
         ASSERT(flowBox == renderBlock.lastRootBox());
         return flowBox;
     }

     if (is<RenderInline>(*renderer)) {
         // We're given a RenderSVGInline or objects that derive from it (RenderSVGTSpan / RenderSVGTextPath)
         RenderInline& renderInline = downcast<RenderInline>(*renderer);

         // RenderSVGInline only ever contains a single line box.
         InlineFlowBox* flowBox = renderInline.firstLineBox();
         ASSERT(flowBox == renderInline.lastLineBox());
         return flowBox;
     }

     ASSERT_NOT_REACHED();
     return nullptr;
 }

 SVGTextQuery::SVGTextQuery(RenderObject* renderer)
 {
     collectTextBoxesInFlowBox(flowBoxForRenderer(renderer));
 }

 void SVGTextQuery::collectTextBoxesInFlowBox(InlineFlowBox* flowBox)
 {
     if (!flowBox)
         return;

     for (InlineBox* child = flowBox->firstChild(); child; child = child->nextOnLine()) {
         if (is<InlineFlowBox>(*child)) {
             // Skip generated content.
             if (!child->renderer().node())
                 continue;

             collectTextBoxesInFlowBox(downcast<InlineFlowBox>(child));
             continue;
         }

         if (is<SVGInlineTextBox>(*child))
             m_textBoxes.append(downcast<SVGInlineTextBox>(child));
     }
 }

 bool SVGTextQuery::executeQuery(Data* queryData, ProcessTextFragmentCallback fragmentCallback) const
 {
     ASSERT(!m_textBoxes.isEmpty());

     unsigned processedCharacters = 0;
     unsigned textBoxCount = m_textBoxes.size();

     // Loop over all text boxes
     for (unsigned textBoxPosition = 0; textBoxPosition < textBoxCount; ++textBoxPosition) {
         queryData->textBox = m_textBoxes.at(textBoxPosition);
         queryData->textRenderer = &queryData->textBox->renderer();

         queryData->isVerticalText = queryData->textRenderer->style().isVerticalWritingMode();
         const Vector<SVGTextFragment>& fragments = queryData->textBox->textFragments();

         // Loop over all text fragments in this text box, firing a callback for each.
         unsigned fragmentCount = fragments.size();
         for (unsigned i = 0; i < fragmentCount; ++i) {
             const SVGTextFragment& fragment = fragments.at(i);
             if ((this->*fragmentCallback)(queryData, fragment))
                 return true;

             processedCharacters += fragment.length;
         }

         queryData->processedCharacters = processedCharacters;
     }

     return false;
 }

 bool SVGTextQuery::mapStartEndPositionsIntoFragmentCoordinates(Data* queryData, const SVGTextFragment& fragment, unsigned& startPosition, unsigned& endPosition) const
 {
     // Reuse the same logic used for text selection & painting, to map our query start/length into start/endPositions of the current text fragment.
     ASSERT(startPosition >= queryData->processedCharacters);
     ASSERT(endPosition >= queryData->processedCharacters);
     startPosition -= queryData->processedCharacters;
     endPosition -= queryData->processedCharacters;

     if (startPosition >= endPosition)
         return false;

     modifyStartEndPositionsRespectingLigatures(queryData, startPosition, endPosition);
     if (!queryData->textBox->mapStartEndPositionsIntoFragmentCoordinates(fragment, startPosition, endPosition))
         return false;

     ASSERT_WITH_SECURITY_IMPLICATION(startPosition < endPosition);
     return true;
 }

 void SVGTextQuery::modifyStartEndPositionsRespectingLigatures(Data* queryData, unsigned& startPosition, unsigned& endPosition) const
 {
     SVGTextLayoutAttributes* layoutAttributes = queryData->textRenderer->layoutAttributes();
     Vector<SVGTextMetrics>& textMetricsValues = layoutAttributes->textMetricsValues();
     unsigned boxStart = queryData->textBox->start();
     unsigned boxLength = queryData->textBox->len();

     unsigned textMetricsOffset = 0;
     unsigned textMetricsSize = textMetricsValues.size();

     unsigned positionOffset = 0;
     unsigned positionSize = layoutAttributes->context().text().length();

     bool alterStartPosition = true;
     bool alterEndPosition = true;

     Optional<unsigned> lastPositionOffset;
     for (; textMetricsOffset < textMetricsSize && positionOffset < positionSize; ++textMetricsOffset) {
         SVGTextMetrics& metrics = textMetricsValues[textMetricsOffset];

         // Advance to text box start location.
         if (positionOffset < boxStart) {
             positionOffset += metrics.length();
             continue;
         }

         // Stop if we've finished processing this text box.
         if (positionOffset >= boxStart + boxLength)
             break;

         // If the start position maps to a character in the metrics list, we don't need to modify it.
         if (startPosition == positionOffset)
             alterStartPosition = false;

         // If the start position maps to a character in the metrics list, we don't need to modify it.
         if (endPosition == positionOffset)
             alterEndPosition = false;

         // Detect ligatures.
         if (lastPositionOffset && lastPositionOffset.value() - positionOffset > 1) {
             if (alterStartPosition && startPosition > lastPositionOffset.value() && startPosition < positionOffset) {
                 startPosition = lastPositionOffset.value();
                 alterStartPosition = false;
             }

             if (alterEndPosition && endPosition > lastPositionOffset.value() && endPosition < positionOffset) {
                 endPosition = positionOffset;
                 alterEndPosition = false;
             }
         }

         if (!alterStartPosition && !alterEndPosition)
             break;

         lastPositionOffset = positionOffset;
         positionOffset += metrics.length();
     }

     if (!alterStartPosition && !alterEndPosition)
         return;

     if (lastPositionOffset && lastPositionOffset.value() - positionOffset > 1) {
         if (alterStartPosition && startPosition > lastPositionOffset.value() && startPosition < positionOffset)
             startPosition = lastPositionOffset.value();

         if (alterEndPosition && endPosition > lastPositionOffset.value() && endPosition < positionOffset)
             endPosition = positionOffset;
     }
 }

 // numberOfCharacters() implementation
 bool SVGTextQuery::numberOfCharactersCallback(Data*, const SVGTextFragment&) const
 {
     // no-op
     return false;
 }

 unsigned SVGTextQuery::numberOfCharacters() const
 {
     if (m_textBoxes.isEmpty())
         return 0;

     Data data;
     executeQuery(&data, &SVGTextQuery::numberOfCharactersCallback);
     return data.processedCharacters;
 }

 // textLength() implementation
 struct TextLengthData : SVGTextQuery::Data {
     TextLengthData()
         : textLength(0)
     {
     }

     float textLength;
 };

 bool SVGTextQuery::textLengthCallback(Data* queryData, const SVGTextFragment& fragment) const
 {
     TextLengthData* data = static_cast<TextLengthData*>(queryData);
     data->textLength += queryData->isVerticalText ? fragment.height : fragment.width;
     return false;
 }

 float SVGTextQuery::textLength() const
 {
     if (m_textBoxes.isEmpty())
         return 0;

     TextLengthData data;
     executeQuery(&data, &SVGTextQuery::textLengthCallback);
     return data.textLength;
 }

 // subStringLength() implementation
 struct SubStringLengthData : SVGTextQuery::Data {
     SubStringLengthData(unsigned queryStartPosition, unsigned queryLength)
         : startPosition(queryStartPosition)
         , length(queryLength)
         , subStringLength(0)
     {
     }

     unsigned startPosition;
     unsigned length;

     float subStringLength;
 };

 bool SVGTextQuery::subStringLengthCallback(Data* queryData, const SVGTextFragment& fragment) const
 {
     SubStringLengthData* data = static_cast<SubStringLengthData*>(queryData);

     unsigned startPosition = data->startPosition;
     unsigned endPosition = startPosition + data->length;
     if (!mapStartEndPositionsIntoFragmentCoordinates(queryData, fragment, startPosition, endPosition))
         return false;

     SVGTextMetrics metrics = SVGTextMetrics::measureCharacterRange(*queryData->textRenderer, fragment.characterOffset + startPosition, endPosition - startPosition);
     data->subStringLength += queryData->isVerticalText ? metrics.height() : metrics.width();
     return false;
 }

 float SVGTextQuery::subStringLength(unsigned startPosition, unsigned length) const
 {
     if (m_textBoxes.isEmpty())
         return 0;

     SubStringLengthData data(startPosition, length);
     executeQuery(&data, &SVGTextQuery::subStringLengthCallback);
     return data.subStringLength;
 }

 // startPositionOfCharacter() implementation
 struct StartPositionOfCharacterData : SVGTextQuery::Data {
     StartPositionOfCharacterData(unsigned queryPosition)
         : position(queryPosition)
     {
     }

     unsigned position;
     FloatPoint startPosition;
 };

 bool SVGTextQuery::startPositionOfCharacterCallback(Data* queryData, const SVGTextFragment& fragment) const
 {
     StartPositionOfCharacterData* data = static_cast<StartPositionOfCharacterData*>(queryData);

     unsigned startPosition = data->position;
     unsigned endPosition = startPosition + 1;
     if (!mapStartEndPositionsIntoFragmentCoordinates(queryData, fragment, startPosition, endPosition))
         return false;

     data->startPosition = FloatPoint(fragment.x, fragment.y);

     if (startPosition) {
         SVGTextMetrics metrics = SVGTextMetrics::measureCharacterRange(*queryData->textRenderer, fragment.characterOffset, startPosition);
         if (queryData->isVerticalText)
             data->startPosition.move(0, metrics.height());
         else
             data->startPosition.move(metrics.width(), 0);
     }

     AffineTransform fragmentTransform;
     fragment.buildFragmentTransform(fragmentTransform, SVGTextFragment::TransformIgnoringTextLength);
     if (fragmentTransform.isIdentity())
         return true;

     data->startPosition = fragmentTransform.mapPoint(data->startPosition);
     return true;
 }

 FloatPoint SVGTextQuery::startPositionOfCharacter(unsigned position) const
 {
     if (m_textBoxes.isEmpty())
         return { };

     StartPositionOfCharacterData data(position);
     executeQuery(&data, &SVGTextQuery::startPositionOfCharacterCallback);
     return data.startPosition;
 }

 // endPositionOfCharacter() implementation
 struct EndPositionOfCharacterData : SVGTextQuery::Data {
     EndPositionOfCharacterData(unsigned queryPosition)
         : position(queryPosition)
     {
     }

     unsigned position;
     FloatPoint endPosition;
 };

 bool SVGTextQuery::endPositionOfCharacterCallback(Data* queryData, const SVGTextFragment& fragment) const
 {
     EndPositionOfCharacterData* data = static_cast<EndPositionOfCharacterData*>(queryData);

     unsigned startPosition = data->position;
     unsigned endPosition = startPosition + 1;
     if (!mapStartEndPositionsIntoFragmentCoordinates(queryData, fragment, startPosition, endPosition))
         return false;

     data->endPosition = FloatPoint(fragment.x, fragment.y);

     SVGTextMetrics metrics = SVGTextMetrics::measureCharacterRange(*queryData->textRenderer, fragment.characterOffset, startPosition + 1);
     if (queryData->isVerticalText)
         data->endPosition.move(0, metrics.height());
     else
         data->endPosition.move(metrics.width(), 0);

     AffineTransform fragmentTransform;
     fragment.buildFragmentTransform(fragmentTransform, SVGTextFragment::TransformIgnoringTextLength);
     if (fragmentTransform.isIdentity())
         return true;

     data->endPosition = fragmentTransform.mapPoint(data->endPosition);
     return true;
 }

 FloatPoint SVGTextQuery::endPositionOfCharacter(unsigned position) const
 {
     if (m_textBoxes.isEmpty())
         return { };

     EndPositionOfCharacterData data(position);
     executeQuery(&data, &SVGTextQuery::endPositionOfCharacterCallback);
     return data.endPosition;
 }

 // rotationOfCharacter() implementation
 struct RotationOfCharacterData : SVGTextQuery::Data {
     RotationOfCharacterData(unsigned queryPosition)
         : position(queryPosition)
         , rotation(0)
     {
     }

     unsigned position;
     float rotation;
 };

 bool SVGTextQuery::rotationOfCharacterCallback(Data* queryData, const SVGTextFragment& fragment) const
 {
     RotationOfCharacterData* data = static_cast<RotationOfCharacterData*>(queryData);

     unsigned startPosition = data->position;
     unsigned endPosition = startPosition + 1;
     if (!mapStartEndPositionsIntoFragmentCoordinates(queryData, fragment, startPosition, endPosition))
         return false;

     AffineTransform fragmentTransform;
     fragment.buildFragmentTransform(fragmentTransform, SVGTextFragment::TransformIgnoringTextLength);
     if (fragmentTransform.isIdentity())
         data->rotation = 0;
     else {
         fragmentTransform.scale(1 / fragmentTransform.xScale(), 1 / fragmentTransform.yScale());
         data->rotation = narrowPrecisionToFloat(rad2deg(atan2(fragmentTransform.b(), fragmentTransform.a())));
     }

     return true;
 }

 float SVGTextQuery::rotationOfCharacter(unsigned position) const
 {
     if (m_textBoxes.isEmpty())
         return 0;

     RotationOfCharacterData data(position);
     executeQuery(&data, &SVGTextQuery::rotationOfCharacterCallback);
     return data.rotation;
 }

 // extentOfCharacter() implementation
 struct ExtentOfCharacterData : SVGTextQuery::Data {
     ExtentOfCharacterData(unsigned queryPosition)
         : position(queryPosition)
     {
     }

     unsigned position;
     FloatRect extent;
 };

 static inline void calculateGlyphBoundaries(SVGTextQuery::Data* queryData, const SVGTextFragment& fragment, unsigned startPosition, FloatRect& extent)
 {
     float scalingFactor = queryData->textRenderer->scalingFactor();
     ASSERT(scalingFactor);

     extent.setLocation(FloatPoint(fragment.x, fragment.y - queryData->textRenderer->scaledFont().fontMetrics().floatAscent() / scalingFactor));

     if (startPosition) {
         SVGTextMetrics metrics = SVGTextMetrics::measureCharacterRange(*queryData->textRenderer, fragment.characterOffset, startPosition);
         if (queryData->isVerticalText)
             extent.move(0, metrics.height());
         else
             extent.move(metrics.width(), 0);
     }

     SVGTextMetrics metrics = SVGTextMetrics::measureCharacterRange(*queryData->textRenderer, fragment.characterOffset + startPosition, 1);
     extent.setSize(FloatSize(metrics.width(), metrics.height()));

     AffineTransform fragmentTransform;
     fragment.buildFragmentTransform(fragmentTransform, SVGTextFragment::TransformIgnoringTextLength);
     if (fragmentTransform.isIdentity())
         return;

     extent = fragmentTransform.mapRect(extent);
 }

 bool SVGTextQuery::extentOfCharacterCallback(Data* queryData, const SVGTextFragment& fragment) const
 {
     ExtentOfCharacterData* data = static_cast<ExtentOfCharacterData*>(queryData);

     unsigned startPosition = data->position;
     unsigned endPosition = startPosition + 1;
     if (!mapStartEndPositionsIntoFragmentCoordinates(queryData, fragment, startPosition, endPosition))
         return false;

     calculateGlyphBoundaries(queryData, fragment, startPosition, data->extent);
     return true;
 }

 FloatRect SVGTextQuery::extentOfCharacter(unsigned position) const
 {
     if (m_textBoxes.isEmpty())
         return FloatRect();

     ExtentOfCharacterData data(position);
     executeQuery(&data, &SVGTextQuery::extentOfCharacterCallback);
     return data.extent;
 }

 // characterNumberAtPosition() implementation
 struct CharacterNumberAtPositionData : SVGTextQuery::Data {
     CharacterNumberAtPositionData(const FloatPoint& queryPosition)
         : position(queryPosition)
     {
     }

     FloatPoint position;
 };

 bool SVGTextQuery::characterNumberAtPositionCallback(Data* queryData, const SVGTextFragment& fragment) const
 {
     CharacterNumberAtPositionData* data = static_cast<CharacterNumberAtPositionData*>(queryData);

     FloatRect extent;
     for (unsigned i = 0; i < fragment.length; ++i) {
         unsigned startPosition = data->processedCharacters + i;
         unsigned endPosition = startPosition + 1;
         if (!mapStartEndPositionsIntoFragmentCoordinates(queryData, fragment, startPosition, endPosition))
             continue;

         calculateGlyphBoundaries(queryData, fragment, startPosition, extent);
         if (extent.contains(data->position)) {
             data->processedCharacters += i;
             return true;
         }
     }

     return false;
 }

 int SVGTextQuery::characterNumberAtPosition(const FloatPoint& position) const
 {
     if (m_textBoxes.isEmpty())
         return -1;

     CharacterNumberAtPositionData data(position);
     if (!executeQuery(&data, &SVGTextQuery::characterNumberAtPositionCallback))
         return -1;

     return data.processedCharacters;
 }

 }
	/*
	* Copyright (C) Research In Motion Limited 2010-2012. 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 "SVGTextQuery.h"

	#include "FloatConversion.h"
	#include "InlineFlowBox.h"
	#include "RenderBlockFlow.h"
	#include "RenderInline.h"
	#include "RenderSVGText.h"
	#include "SVGInlineTextBox.h"
	#include "VisiblePosition.h"

	#include <wtf/MathExtras.h>

	namespace WebCore {

	// Base structure for callback user data
	struct SVGTextQuery::Data {
	Data()
	: isVerticalText(false)
	, processedCharacters(0)
	, textRenderer(0)
	, textBox(0)
	{
	}

	bool isVerticalText;
	unsigned processedCharacters;
	RenderSVGInlineText* textRenderer;
	const SVGInlineTextBox* textBox;
	};

	static inline InlineFlowBox* flowBoxForRenderer(RenderObject* renderer)
	{
	if (!renderer)
	return nullptr;

	if (is<RenderBlockFlow>(*renderer)) {
	// If we're given a block element, it has to be a RenderSVGText.
	ASSERT(is<RenderSVGText>(*renderer));
	RenderBlockFlow& renderBlock = downcast<RenderBlockFlow>(*renderer);

	// RenderSVGText only ever contains a single line box.
	auto flowBox = renderBlock.firstRootBox();
	ASSERT(flowBox == renderBlock.lastRootBox());
	return flowBox;
	}

	if (is<RenderInline>(*renderer)) {
	// We're given a RenderSVGInline or objects that derive from it (RenderSVGTSpan / RenderSVGTextPath)
	RenderInline& renderInline = downcast<RenderInline>(*renderer);

	// RenderSVGInline only ever contains a single line box.
	InlineFlowBox* flowBox = renderInline.firstLineBox();
	ASSERT(flowBox == renderInline.lastLineBox());
	return flowBox;
	}

	ASSERT_NOT_REACHED();
	return nullptr;
	}

	SVGTextQuery::SVGTextQuery(RenderObject* renderer)
	{
	collectTextBoxesInFlowBox(flowBoxForRenderer(renderer));
	}

	void SVGTextQuery::collectTextBoxesInFlowBox(InlineFlowBox* flowBox)
	{
	if (!flowBox)
	return;

	for (InlineBox* child = flowBox->firstChild(); child; child = child->nextOnLine()) {
	if (is<InlineFlowBox>(*child)) {
	// Skip generated content.
	if (!child->renderer().node())
	continue;

	collectTextBoxesInFlowBox(downcast<InlineFlowBox>(child));
	continue;
	}

	if (is<SVGInlineTextBox>(*child))
	m_textBoxes.append(downcast<SVGInlineTextBox>(child));
	}
	}

	bool SVGTextQuery::executeQuery(Data* queryData, ProcessTextFragmentCallback fragmentCallback) const
	{
	ASSERT(!m_textBoxes.isEmpty());

	unsigned processedCharacters = 0;
	unsigned textBoxCount = m_textBoxes.size();

	// Loop over all text boxes
	for (unsigned textBoxPosition = 0; textBoxPosition < textBoxCount; ++textBoxPosition) {
	queryData->textBox = m_textBoxes.at(textBoxPosition);
	queryData->textRenderer = &queryData->textBox->renderer();

	queryData->isVerticalText = queryData->textRenderer->style().isVerticalWritingMode();
	const Vector<SVGTextFragment>& fragments = queryData->textBox->textFragments();

	// Loop over all text fragments in this text box, firing a callback for each.
	unsigned fragmentCount = fragments.size();
	for (unsigned i = 0; i < fragmentCount; ++i) {
	const SVGTextFragment& fragment = fragments.at(i);
	if ((this->*fragmentCallback)(queryData, fragment))
	return true;

	processedCharacters += fragment.length;
	}

	queryData->processedCharacters = processedCharacters;
	}

	return false;
	}

	bool SVGTextQuery::mapStartEndPositionsIntoFragmentCoordinates(Data* queryData, const SVGTextFragment& fragment, unsigned& startPosition, unsigned& endPosition) const
	{
	// Reuse the same logic used for text selection & painting, to map our query start/length into start/endPositions of the current text fragment.
	ASSERT(startPosition >= queryData->processedCharacters);
	ASSERT(endPosition >= queryData->processedCharacters);
	startPosition -= queryData->processedCharacters;
	endPosition -= queryData->processedCharacters;

	if (startPosition >= endPosition)
	return false;

	modifyStartEndPositionsRespectingLigatures(queryData, startPosition, endPosition);
	if (!queryData->textBox->mapStartEndPositionsIntoFragmentCoordinates(fragment, startPosition, endPosition))
	return false;

	ASSERT_WITH_SECURITY_IMPLICATION(startPosition < endPosition);
	return true;
	}

	void SVGTextQuery::modifyStartEndPositionsRespectingLigatures(Data* queryData, unsigned& startPosition, unsigned& endPosition) const
	{
	SVGTextLayoutAttributes* layoutAttributes = queryData->textRenderer->layoutAttributes();
	Vector<SVGTextMetrics>& textMetricsValues = layoutAttributes->textMetricsValues();
	unsigned boxStart = queryData->textBox->start();
	unsigned boxLength = queryData->textBox->len();

	unsigned textMetricsOffset = 0;
	unsigned textMetricsSize = textMetricsValues.size();

	unsigned positionOffset = 0;
	unsigned positionSize = layoutAttributes->context().text().length();

	bool alterStartPosition = true;
	bool alterEndPosition = true;

	Optional<unsigned> lastPositionOffset;
	for (; textMetricsOffset < textMetricsSize && positionOffset < positionSize; ++textMetricsOffset) {
	SVGTextMetrics& metrics = textMetricsValues[textMetricsOffset];

	// Advance to text box start location.
	if (positionOffset < boxStart) {
	positionOffset += metrics.length();
	continue;
	}

	// Stop if we've finished processing this text box.
	if (positionOffset >= boxStart + boxLength)
	break;

	// If the start position maps to a character in the metrics list, we don't need to modify it.
	if (startPosition == positionOffset)
	alterStartPosition = false;

	// If the start position maps to a character in the metrics list, we don't need to modify it.
	if (endPosition == positionOffset)
	alterEndPosition = false;

	// Detect ligatures.
	if (lastPositionOffset && lastPositionOffset.value() - positionOffset > 1) {
	if (alterStartPosition && startPosition > lastPositionOffset.value() && startPosition < positionOffset) {
	startPosition = lastPositionOffset.value();
	alterStartPosition = false;
	}

	if (alterEndPosition && endPosition > lastPositionOffset.value() && endPosition < positionOffset) {
	endPosition = positionOffset;
	alterEndPosition = false;
	}
	}

	if (!alterStartPosition && !alterEndPosition)
	break;

	lastPositionOffset = positionOffset;
	positionOffset += metrics.length();
	}

	if (!alterStartPosition && !alterEndPosition)
	return;

	if (lastPositionOffset && lastPositionOffset.value() - positionOffset > 1) {
	if (alterStartPosition && startPosition > lastPositionOffset.value() && startPosition < positionOffset)
	startPosition = lastPositionOffset.value();

	if (alterEndPosition && endPosition > lastPositionOffset.value() && endPosition < positionOffset)
	endPosition = positionOffset;
	}
	}

	// numberOfCharacters() implementation
	bool SVGTextQuery::numberOfCharactersCallback(Data*, const SVGTextFragment&) const
	{
	// no-op
	return false;
	}

	unsigned SVGTextQuery::numberOfCharacters() const
	{
	if (m_textBoxes.isEmpty())
	return 0;

	Data data;
	executeQuery(&data, &SVGTextQuery::numberOfCharactersCallback);
	return data.processedCharacters;
	}

	// textLength() implementation
	struct TextLengthData : SVGTextQuery::Data {
	TextLengthData()
	: textLength(0)
	{
	}

	float textLength;
	};

	bool SVGTextQuery::textLengthCallback(Data* queryData, const SVGTextFragment& fragment) const
	{
	TextLengthData* data = static_cast<TextLengthData*>(queryData);
	data->textLength += queryData->isVerticalText ? fragment.height : fragment.width;
	return false;
	}

	float SVGTextQuery::textLength() const
	{
	if (m_textBoxes.isEmpty())
	return 0;

	TextLengthData data;
	executeQuery(&data, &SVGTextQuery::textLengthCallback);
	return data.textLength;
	}

	// subStringLength() implementation
	struct SubStringLengthData : SVGTextQuery::Data {
	SubStringLengthData(unsigned queryStartPosition, unsigned queryLength)
	: startPosition(queryStartPosition)
	, length(queryLength)
	, subStringLength(0)
	{
	}

	unsigned startPosition;
	unsigned length;

	float subStringLength;
	};

	bool SVGTextQuery::subStringLengthCallback(Data* queryData, const SVGTextFragment& fragment) const
	{
	SubStringLengthData* data = static_cast<SubStringLengthData*>(queryData);

	unsigned startPosition = data->startPosition;
	unsigned endPosition = startPosition + data->length;
	if (!mapStartEndPositionsIntoFragmentCoordinates(queryData, fragment, startPosition, endPosition))
	return false;

	SVGTextMetrics metrics = SVGTextMetrics::measureCharacterRange(*queryData->textRenderer, fragment.characterOffset + startPosition, endPosition - startPosition);
	data->subStringLength += queryData->isVerticalText ? metrics.height() : metrics.width();
	return false;
	}

	float SVGTextQuery::subStringLength(unsigned startPosition, unsigned length) const
	{
	if (m_textBoxes.isEmpty())
	return 0;

	SubStringLengthData data(startPosition, length);
	executeQuery(&data, &SVGTextQuery::subStringLengthCallback);
	return data.subStringLength;
	}

	// startPositionOfCharacter() implementation
	struct StartPositionOfCharacterData : SVGTextQuery::Data {
	StartPositionOfCharacterData(unsigned queryPosition)
	: position(queryPosition)
	{
	}

	unsigned position;
	FloatPoint startPosition;
	};

	bool SVGTextQuery::startPositionOfCharacterCallback(Data* queryData, const SVGTextFragment& fragment) const
	{
	StartPositionOfCharacterData* data = static_cast<StartPositionOfCharacterData*>(queryData);

	unsigned startPosition = data->position;
	unsigned endPosition = startPosition + 1;
	if (!mapStartEndPositionsIntoFragmentCoordinates(queryData, fragment, startPosition, endPosition))
	return false;

	data->startPosition = FloatPoint(fragment.x, fragment.y);

	if (startPosition) {
	SVGTextMetrics metrics = SVGTextMetrics::measureCharacterRange(*queryData->textRenderer, fragment.characterOffset, startPosition);
	if (queryData->isVerticalText)
	data->startPosition.move(0, metrics.height());
	else
	data->startPosition.move(metrics.width(), 0);
	}

	AffineTransform fragmentTransform;
	fragment.buildFragmentTransform(fragmentTransform, SVGTextFragment::TransformIgnoringTextLength);
	if (fragmentTransform.isIdentity())
	return true;

	data->startPosition = fragmentTransform.mapPoint(data->startPosition);
	return true;
	}

	FloatPoint SVGTextQuery::startPositionOfCharacter(unsigned position) const
	{
	if (m_textBoxes.isEmpty())
	return { };

	StartPositionOfCharacterData data(position);
	executeQuery(&data, &SVGTextQuery::startPositionOfCharacterCallback);
	return data.startPosition;
	}

	// endPositionOfCharacter() implementation
	struct EndPositionOfCharacterData : SVGTextQuery::Data {
	EndPositionOfCharacterData(unsigned queryPosition)
	: position(queryPosition)
	{
	}

	unsigned position;
	FloatPoint endPosition;
	};

	bool SVGTextQuery::endPositionOfCharacterCallback(Data* queryData, const SVGTextFragment& fragment) const
	{
	EndPositionOfCharacterData* data = static_cast<EndPositionOfCharacterData*>(queryData);

	unsigned startPosition = data->position;
	unsigned endPosition = startPosition + 1;
	if (!mapStartEndPositionsIntoFragmentCoordinates(queryData, fragment, startPosition, endPosition))
	return false;

	data->endPosition = FloatPoint(fragment.x, fragment.y);

	SVGTextMetrics metrics = SVGTextMetrics::measureCharacterRange(*queryData->textRenderer, fragment.characterOffset, startPosition + 1);
	if (queryData->isVerticalText)
	data->endPosition.move(0, metrics.height());
	else
	data->endPosition.move(metrics.width(), 0);

	AffineTransform fragmentTransform;
	fragment.buildFragmentTransform(fragmentTransform, SVGTextFragment::TransformIgnoringTextLength);
	if (fragmentTransform.isIdentity())
	return true;

	data->endPosition = fragmentTransform.mapPoint(data->endPosition);
	return true;
	}

	FloatPoint SVGTextQuery::endPositionOfCharacter(unsigned position) const
	{
	if (m_textBoxes.isEmpty())
	return { };

	EndPositionOfCharacterData data(position);
	executeQuery(&data, &SVGTextQuery::endPositionOfCharacterCallback);
	return data.endPosition;
	}

	// rotationOfCharacter() implementation
	struct RotationOfCharacterData : SVGTextQuery::Data {
	RotationOfCharacterData(unsigned queryPosition)
	: position(queryPosition)
	, rotation(0)
	{
	}

	unsigned position;
	float rotation;
	};

	bool SVGTextQuery::rotationOfCharacterCallback(Data* queryData, const SVGTextFragment& fragment) const
	{
	RotationOfCharacterData* data = static_cast<RotationOfCharacterData*>(queryData);

	unsigned startPosition = data->position;
	unsigned endPosition = startPosition + 1;
	if (!mapStartEndPositionsIntoFragmentCoordinates(queryData, fragment, startPosition, endPosition))
	return false;

	AffineTransform fragmentTransform;
	fragment.buildFragmentTransform(fragmentTransform, SVGTextFragment::TransformIgnoringTextLength);
	if (fragmentTransform.isIdentity())
	data->rotation = 0;
	else {
	fragmentTransform.scale(1 / fragmentTransform.xScale(), 1 / fragmentTransform.yScale());
	data->rotation = narrowPrecisionToFloat(rad2deg(atan2(fragmentTransform.b(), fragmentTransform.a())));
	}

	return true;
	}

	float SVGTextQuery::rotationOfCharacter(unsigned position) const
	{
	if (m_textBoxes.isEmpty())
	return 0;

	RotationOfCharacterData data(position);
	executeQuery(&data, &SVGTextQuery::rotationOfCharacterCallback);
	return data.rotation;
	}

	// extentOfCharacter() implementation
	struct ExtentOfCharacterData : SVGTextQuery::Data {
	ExtentOfCharacterData(unsigned queryPosition)
	: position(queryPosition)
	{
	}

	unsigned position;
	FloatRect extent;
	};

	static inline void calculateGlyphBoundaries(SVGTextQuery::Data* queryData, const SVGTextFragment& fragment, unsigned startPosition, FloatRect& extent)
	{
	float scalingFactor = queryData->textRenderer->scalingFactor();
	ASSERT(scalingFactor);

	extent.setLocation(FloatPoint(fragment.x, fragment.y - queryData->textRenderer->scaledFont().fontMetrics().floatAscent() / scalingFactor));

	if (startPosition) {
	SVGTextMetrics metrics = SVGTextMetrics::measureCharacterRange(*queryData->textRenderer, fragment.characterOffset, startPosition);
	if (queryData->isVerticalText)
	extent.move(0, metrics.height());
	else
	extent.move(metrics.width(), 0);
	}

	SVGTextMetrics metrics = SVGTextMetrics::measureCharacterRange(*queryData->textRenderer, fragment.characterOffset + startPosition, 1);
	extent.setSize(FloatSize(metrics.width(), metrics.height()));

	AffineTransform fragmentTransform;
	fragment.buildFragmentTransform(fragmentTransform, SVGTextFragment::TransformIgnoringTextLength);
	if (fragmentTransform.isIdentity())
	return;

	extent = fragmentTransform.mapRect(extent);
	}

	bool SVGTextQuery::extentOfCharacterCallback(Data* queryData, const SVGTextFragment& fragment) const
	{
	ExtentOfCharacterData* data = static_cast<ExtentOfCharacterData*>(queryData);

	unsigned startPosition = data->position;
	unsigned endPosition = startPosition + 1;
	if (!mapStartEndPositionsIntoFragmentCoordinates(queryData, fragment, startPosition, endPosition))
	return false;

	calculateGlyphBoundaries(queryData, fragment, startPosition, data->extent);
	return true;
	}

	FloatRect SVGTextQuery::extentOfCharacter(unsigned position) const
	{
	if (m_textBoxes.isEmpty())
	return FloatRect();

	ExtentOfCharacterData data(position);
	executeQuery(&data, &SVGTextQuery::extentOfCharacterCallback);
	return data.extent;
	}

	// characterNumberAtPosition() implementation
	struct CharacterNumberAtPositionData : SVGTextQuery::Data {
	CharacterNumberAtPositionData(const FloatPoint& queryPosition)
	: position(queryPosition)
	{
	}

	FloatPoint position;
	};

	bool SVGTextQuery::characterNumberAtPositionCallback(Data* queryData, const SVGTextFragment& fragment) const
	{
	CharacterNumberAtPositionData* data = static_cast<CharacterNumberAtPositionData*>(queryData);

	FloatRect extent;
	for (unsigned i = 0; i < fragment.length; ++i) {
	unsigned startPosition = data->processedCharacters + i;
	unsigned endPosition = startPosition + 1;
	if (!mapStartEndPositionsIntoFragmentCoordinates(queryData, fragment, startPosition, endPosition))
	continue;

	calculateGlyphBoundaries(queryData, fragment, startPosition, extent);
	if (extent.contains(data->position)) {
	data->processedCharacters += i;
	return true;
	}
	}

	return false;
	}

	int SVGTextQuery::characterNumberAtPosition(const FloatPoint& position) const
	{
	if (m_textBoxes.isEmpty())
	return -1;

	CharacterNumberAtPositionData data(position);
	if (!executeQuery(&data, &SVGTextQuery::characterNumberAtPositionCallback))
	return -1;

	return data.processedCharacters;
	}

	}