Source/WebCore/rendering/RenderVTTCue.cpp - external/github.com/WebKit/webkit - Git at Google

 /*
  * Copyright (C) 2012 Victor Carbune ([email protected])
  * Copyright (C) 2014-2025 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``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
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #include "config.h"

 #if ENABLE(VIDEO)
 #include "RenderVTTCue.h"

 #include "FrameInlines.h"
 #include "InlineIteratorBoxInlines.h"
 #include "RenderBoxInlines.h"
 #include "RenderBoxModelObjectInlines.h"
 #include "RenderInline.h"
 #include "RenderLayoutState.h"
 #include "RenderView.h"
 #include "TextTrackCueGeneric.h"
 #include "VTTCue.h"
 #include <wtf/Ref.h>
 #include <wtf/StackStats.h>
 #include <wtf/TZoneMallocInlines.h>

 namespace WebCore {

 WTF_MAKE_TZONE_ALLOCATED_IMPL(RenderVTTCue);

 RenderVTTCue::RenderVTTCue(VTTCueBox& element, RenderStyle&& style)
     : RenderBlockFlow(Type::VTTCue, element, WTF::move(style))
     , m_cue(downcast<VTTCue>(element.getCue()))
 {
     ASSERT(m_cue);
     ASSERT(isRenderVTTCue());
 }

 RenderVTTCue::~RenderVTTCue() = default;

 void RenderVTTCue::layout()
 {
     StackStats::LayoutCheckPoint layoutCheckPoint;
     RenderBlockFlow::layout();

     // If WebVTT Regions are used, the regular WebVTT layout algorithm is no
     // longer necessary, since cues having the region parameter set do not have
     // any positioning parameters. Also, in this case, the regions themselves
     // have positioning information.
     RefPtr cue = m_cue.get();
     if (!cue || !cue->regionId().isEmpty())
         return;

     LayoutStateMaintainer statePusher(*this, locationOffset(), true);

     if (cue->cueType()== TextTrackCue::WebVTT) {
         if (cue->snapToLines())
             repositionCueSnapToLinesSet();
         else
             repositionCueSnapToLinesNotSet();
     } else
         repositionGenericCue();
 }

 bool RenderVTTCue::initializeLayoutParameters(LayoutUnit& step, LayoutUnit& position)
 {
     if (!firstChild())
         return false;

     auto* box = cueBox();
     if (!box)
         return false;

     auto firstInlineBox = InlineIterator::lineLeftmostInlineBoxFor(*box) ? : InlineIterator::firstRootInlineBoxFor(*this);
     if (!firstInlineBox)
         return false;

     auto* backdropBox = this->backdropBox();
     if (!backdropBox)
         return false;

     // 1. Horizontal: Let step be the height of the first line box in boxes.
     //    Vertical: Let step be the width of the first line box in boxes.
     auto firstInlineBoxSize = firstInlineBox->visualRectIgnoringBlockDirection().size();
     step = m_cue->vertical() == VTTCue::DirectionSetting::Horizontal ? firstInlineBoxSize.height() : firstInlineBoxSize.width();

     // Note: the previous rules in initializeLayoutParameters() only account for
     // the height of the line boxes contained within the cue, and not the cue's height
     // nor its padding, nor its borders. Ignoring these will lead to errors
     // in the initial placement of cues, as the resulting placement will result in
     // the cue always being partially outside its containing block, rather than at
     // its initial position. Correct the initial position by subtracting from
     // position the difference between the the logicalHeight of the cue and its
     // first line box.
     auto inlineBoxHeights = LayoutUnit { };
     for (auto inlineBox = firstInlineBox; inlineBox; inlineBox = inlineBox->nextInlineBoxLineRightward())
         inlineBoxHeights += inlineBox->logicalHeight();
     auto logicalHeightDelta = backdropBox->logicalHeight() - inlineBoxHeights;
     if (logicalHeightDelta > 0)
         step += logicalHeightDelta;

     // 2. If step is zero, then jump to the step labeled done positioning below.
     if (!step)
         return false;

     // 3. Let line position be the text track cue computed line position.
     RefPtr cue = m_cue.get();
     if (!cue)
         return false;

     int linePosition = cue->calculateComputedLinePosition();

     // 4. Vertical Growing Left: Add one to line position then negate it.
     if (cue->vertical() == VTTCue::DirectionSetting::VerticalGrowingLeft)
         linePosition = -(linePosition + 1);

     // 5. Let position be the result of multiplying step and line position.
     position = step * linePosition;

     // 6. Vertical Growing Left: Decrease position by the width of the
     // bounding box of the boxes in boxes, then increase position by step.
     if (cue->vertical() == VTTCue::DirectionSetting::VerticalGrowingLeft) {
         position -= width();
         position += step;
     }

     // 7. If line position is less than zero...
     if (linePosition < 0) {
         // Horizontal / Vertical: ... then increase position by the
         // height / width of the video's rendering area ...
         position += cue->vertical() == VTTCue::DirectionSetting::Horizontal ? containingBlock()->height() : containingBlock()->width();

         // ... and negate step.
         step = -step;
     }

     return true;
 }

 void RenderVTTCue::placeBoxInDefaultPosition(LayoutUnit position, bool& switched)
 {
     // 8. Move all boxes in boxes ...
     if (m_cue->vertical() == VTTCue::DirectionSetting::Horizontal) {
         // Horizontal: ... down by the distance given by position
         setY(y() + position);
     } else {
         // Vertical: ... right by the distance given by position
         setX(x() + position);
     }

     // 9. Default: Remember the position of all the boxes in boxes as their
     // default position.
     m_fallbackPosition = FloatPoint(x(), y());

     // 10. Let switched be false.
     switched = false;
 }

 bool RenderVTTCue::isOutside() const
 {
     if (!firstChild())
         return false;

     if (auto* backdropBox = this->backdropBox())
         return !rectIsWithinContainer(backdropBox->absoluteBoundingBoxRect());
     return false;
 }

 bool RenderVTTCue::rectIsWithinContainer(const IntRect& rect) const
 {
     return containingBlock()->absoluteBoundingBoxRect().contains(rect);
 }


 bool RenderVTTCue::isOverlapping() const
 {
     if (!firstChild())
         return false;

     return overlappingObject();
 }

 RenderVTTCue* RenderVTTCue::overlappingObject() const
 {
     ASSERT(firstChild());

     if (auto* backdropBox = this->backdropBox())
         return overlappingObjectForRect(backdropBox->absoluteBoundingBoxRect());
     return nullptr;
 }

 RenderVTTCue* RenderVTTCue::overlappingObjectForRect(const IntRect& rect) const
 {
     for (RenderObject* sibling = previousSibling(); sibling; sibling = sibling->previousSibling()) {
         auto* previousCue = downcast<RenderVTTCue>(sibling);
         if (!previousCue || !previousCue->firstChild())
             continue;

         auto* previousCueBackdropBox = previousCue->backdropBox();
         if (previousCueBackdropBox && rect.intersects(previousCueBackdropBox->absoluteBoundingBoxRect()))
             return previousCue;
     }

     return 0;
 }

 bool RenderVTTCue::shouldSwitchDirection(const InlineIterator::InlineBox& firstInlineBox, LayoutUnit step) const
 {
     auto firstInlineBoxSize = firstInlineBox.visualRectIgnoringBlockDirection().size();
     LayoutUnit top = y();
     LayoutUnit left = x();
     LayoutUnit bottom { top + firstInlineBoxSize.height() };
     LayoutUnit right { left + firstInlineBoxSize.width() };

     // 12. Horizontal: If step is negative and the top of the first line
     // box in boxes is now above the top of the video's rendering area,
     // or if step is positive and the bottom of the first line box in
     // boxes is now below the bottom of the video's rendering area, jump
     // to the step labeled switch direction.
     LayoutUnit parentHeight = containingBlock()->height();
     if (m_cue->vertical() == VTTCue::DirectionSetting::Horizontal && ((step < 0 && top < 0) || (step > 0 && bottom > parentHeight)))
         return true;

     // 12. Vertical: If step is negative and the left edge of the first line
     // box in boxes is now to the left of the left edge of the video's
     // rendering area, or if step is positive and the right edge of the
     // first line box in boxes is now to the right of the right edge of
     // the video's rendering area, jump to the step labeled switch direction.
     LayoutUnit parentWidth = containingBlock()->width();
     if (m_cue->vertical() != VTTCue::DirectionSetting::Horizontal && ((step < 0 && left < 0) || (step > 0 && right > parentWidth)))
         return true;

     return false;
 }

 void RenderVTTCue::moveBoxesByStep(LayoutUnit step)
 {
     // 13. Horizontal: Move all the boxes in boxes down by the distance
     // given by step. (If step is negative, then this will actually
     // result in an upwards movement of the boxes in absolute terms.)
     if (m_cue->vertical() == VTTCue::DirectionSetting::Horizontal)
         setY(y() + step);

     // 13. Vertical: Move all the boxes in boxes right by the distance
     // given by step. (If step is negative, then this will actually
     // result in a leftwards movement of the boxes in absolute terms.)
     else
         setX(x() + step);
 }

 bool RenderVTTCue::switchDirection(bool& switched, LayoutUnit& step)
 {
     // 15. Switch direction: Move all the boxes in boxes back to their
     // default position as determined in the step above labeled default.
     setX(m_fallbackPosition.x());
     setY(m_fallbackPosition.y());

     // 16. If switched is true, jump to the step labeled done
     // positioning below.
     if (switched)
         return false;

     // 17. Negate step.
     step = -step;

     // 18. Set switched to true.
     switched = true;
     return true;
 }

 void RenderVTTCue::moveIfNecessaryToKeepWithinContainer()
 {
     if (!firstChild())
         return;

     auto* backdropBox = this->backdropBox();
     if (!backdropBox)
         return;

     IntRect containerRect = containingBlock()->absoluteBoundingBoxRect();
     IntRect cueRect = backdropBox->absoluteBoundingBoxRect();

     int topOverflow = cueRect.y() - containerRect.y();
     int bottomOverflow = containerRect.maxY() - cueRect.maxY();

     int verticalAdjustment = 0;
     if (topOverflow < 0)
         verticalAdjustment = -topOverflow;
     else if (bottomOverflow < 0)
         verticalAdjustment = bottomOverflow;

     if (verticalAdjustment)
         setY(y() + verticalAdjustment);

     int leftOverflow = cueRect.x() - containerRect.x();
     int rightOverflow = containerRect.maxX() - cueRect.maxX();

     int horizontalAdjustment = 0;
     if (leftOverflow < 0)
         horizontalAdjustment = -leftOverflow;
     else if (rightOverflow < 0)
         horizontalAdjustment = rightOverflow;

     if (horizontalAdjustment)
         setX(x() + horizontalAdjustment);
 }

 bool RenderVTTCue::findNonOverlappingPosition(int& newX, int& newY) const
 {
     if (!firstChild())
         return false;

     auto* backdropBox = this->backdropBox();
     if (!backdropBox)
         return false;

     newX = x();
     newY = y();
     IntRect srcRect = backdropBox->absoluteBoundingBoxRect();
     IntRect destRect = srcRect;

     // Move the box up, looking for a non-overlapping position:
     while (RenderVTTCue* cue = overlappingObjectForRect(destRect)) {
         auto* cueBackdropBox = cue->backdropBox();
         if (!cueBackdropBox)
             continue;
         if (m_cue->vertical() == VTTCue::DirectionSetting::Horizontal)
             destRect.setY(cueBackdropBox->absoluteBoundingBoxRect().y() - destRect.height());
         else
             destRect.setX(cueBackdropBox->absoluteBoundingBoxRect().x() - destRect.width());
     }

     if (rectIsWithinContainer(destRect)) {
         newX += destRect.x() - srcRect.x();
         newY += destRect.y() - srcRect.y();
         return true;
     }

     destRect = srcRect;

     // Move the box down, looking for a non-overlapping position:
     while (RenderVTTCue* cue = overlappingObjectForRect(destRect)) {
         auto* cueBackdropBox = cue->backdropBox();
         if (!cueBackdropBox)
             continue;
         if (m_cue->vertical() == VTTCue::DirectionSetting::Horizontal)
             destRect.setY(cueBackdropBox->absoluteBoundingBoxRect().maxY());
         else
             destRect.setX(cueBackdropBox->absoluteBoundingBoxRect().maxX());
     }

     if (rectIsWithinContainer(destRect)) {
         newX += destRect.x() - srcRect.x();
         newY += destRect.y() - srcRect.y();
         return true;
     }

     return false;
 }

 void RenderVTTCue::repositionCueSnapToLinesSet()
 {
     LayoutUnit step;
     LayoutUnit position;
     if (!initializeLayoutParameters(step, position))
         return;

     if (!firstChild())
         return;

     bool switched;
     placeBoxInDefaultPosition(position, switched);

     auto* box = cueBox();
     if (!box)
         return;

     auto firstInlineBox = InlineIterator::lineLeftmostInlineBoxFor(*box) ? : InlineIterator::firstRootInlineBoxFor(*this);
     ASSERT(firstInlineBox);
     // 11. Step loop: If none of the boxes in boxes would overlap any of the boxes
     // in output and all the boxes in output are within the video's rendering area
     // then jump to the step labeled done positioning.
     while (isOutside() || isOverlapping()) {
         if (!shouldSwitchDirection(*firstInlineBox, step)) {
             // 13. Move all the boxes in boxes ...
             // 14. Jump back to the step labeled step loop.
             moveBoxesByStep(step);
         } else if (!switchDirection(switched, step))
             break;

         // 19. Jump back to the step labeled step loop.
     }

     // Acommodate extra top and bottom padding, border or margin.
     // Note: this is supported only for internal UA styling, not through the cue selector.
     if (hasInlineDirectionBordersPaddingOrMargin())
         moveIfNecessaryToKeepWithinContainer();
 }

 void RenderVTTCue::repositionGenericCue()
 {
     if (!firstChild())
         return;

     auto* box = cueBox();
     if (!box)
         return;

     auto firstInlineBox = InlineIterator::lineLeftmostInlineBoxFor(*box);
     if (downcast<TextTrackCueGeneric>(*m_cue).useDefaultPosition() && firstInlineBox) {
         LayoutUnit parentWidth = containingBlock()->logicalWidth();
         LayoutUnit width { firstInlineBox->visualRectIgnoringBlockDirection().width() };
         LayoutUnit right = (parentWidth / 2) - (width / 2);
         setX(right);
     }
     repositionCueSnapToLinesNotSet();
 }

 void RenderVTTCue::repositionCueSnapToLinesNotSet()
 {
     if (!firstChild())
         return;

     auto* backdropBox = this->backdropBox();
     if (!backdropBox)
         return;

     // https://w3c.github.io/webvtt/#processing-cue-settings
     // 7.2.28 Adjust the positions of boxes according to the appropriate steps from the following list:

     // ↳ If cue’s WebVTT cue snap-to-lines flag is false
     // 1. Let bounding box be the bounding box of the boxes in boxes.
     auto boundingBox = backdropBox->absoluteBoundingBoxRect();

     // 2. Run the appropriate steps from the following list:
     switch (m_cue->vertical()) {
     case VTTCue::DirectionSetting::Horizontal:
         // ↳ If the WebVTT cue writing direction is horizontal
         if (m_cue->lineAlign() == VTTCue::LineAlignSetting::Center) {
             // ↳ If the WebVTT cue line alignment is center alignment
             // Move all the boxes in boxes up by half of the height of bounding box.
             setY(y() - boundingBox.height() / 2);
         } else if (m_cue->lineAlign() == VTTCue::LineAlignSetting::End) {
             // ↳ If the WebVTT cue line alignment is end alignment
             // Move all the boxes in boxes up by the height of bounding box.
             setY(y() - boundingBox.height());
         }
         break;
     case VTTCue::DirectionSetting::VerticalGrowingLeft:
     case VTTCue::DirectionSetting::VerticalGrowingRight:
         // ↳ If the WebVTT cue writing direction is vertical growing left or
         // vertical growing right
         if (m_cue->lineAlign() == VTTCue::LineAlignSetting::Center) {
             // ↳ If the WebVTT cue line alignment is center alignment
             // Move all the boxes in boxes left by half of the width of bounding box.
             setX(x() - boundingBox.width() / 2);
         } else if (m_cue->lineAlign() == VTTCue::LineAlignSetting::End) {
             // ↳ If the WebVTT cue line alignment is end alignment
             // Move all the boxes in boxes left by the width of bounding box.
             setX(x() - boundingBox.width());
         }
         break;
     default:
         ASSERT_NOT_REACHED();
     }

     // 9. If none of the boxes in boxes would overlap any of the boxes in output, and all the boxes in
     // output are within the video's rendering area, then jump to the step labeled done positioning below.
     if (!isOutside() && !isOverlapping())
         return;

     // 10. If there is a position to which the boxes in boxes can be moved while maintaining the relative
     // positions of the boxes in boxes to each other such that none of the boxes in boxes would overlap
     // any of the boxes in output, and all the boxes in output would be within the video's rendering area,
     // then move the boxes in boxes to the closest such position to their current position, and then jump
     // to the step labeled done positioning below. If there are multiple such positions that are equidistant
     // from their current position, use the highest one amongst them; if there are several at that height,
     // then use the leftmost one amongst them.
     moveIfNecessaryToKeepWithinContainer();
     int x = 0;
     int y = 0;
     if (findNonOverlappingPosition(x, y)) {
         setX(x);
         setY(y);
     }

     // 11. Otherwise, jump to the step labeled done positioning below. (The
     // boxes will unfortunately overlap.)
 }

 RenderBlockFlow* RenderVTTCue::backdropBox() const
 {
     // firstChild() returns the wrapping (backdrop) <div>. The cue object is
     // the <div>'s first child.
     auto* firstChild = this->firstChild();
     ASSERT(firstChild);
     ASSERT(is<RenderBlockFlow>(firstChild));
     return dynamicDowncast<RenderBlockFlow>(firstChild);
 }

 RenderInline* RenderVTTCue::cueBox() const
 {
     auto* backdropBox = this->backdropBox();
     if (!backdropBox)
         return nullptr;

     auto* firstChild = backdropBox->firstChild();
     ASSERT(firstChild);
     ASSERT(is<RenderInline>(firstChild));
     return dynamicDowncast<RenderInline>(firstChild);
 }

 } // namespace WebCore

 #endif
	/*
	* Copyright (C) 2012 Victor Carbune ([email protected])
	* Copyright (C) 2014-2025 Apple Inc. All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``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
	* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
	* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
	* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
	* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
	* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#include "config.h"

	#if ENABLE(VIDEO)
	#include "RenderVTTCue.h"

	#include "FrameInlines.h"
	#include "InlineIteratorBoxInlines.h"
	#include "RenderBoxInlines.h"
	#include "RenderBoxModelObjectInlines.h"
	#include "RenderInline.h"
	#include "RenderLayoutState.h"
	#include "RenderView.h"
	#include "TextTrackCueGeneric.h"
	#include "VTTCue.h"
	#include <wtf/Ref.h>
	#include <wtf/StackStats.h>
	#include <wtf/TZoneMallocInlines.h>

	namespace WebCore {

	WTF_MAKE_TZONE_ALLOCATED_IMPL(RenderVTTCue);

	RenderVTTCue::RenderVTTCue(VTTCueBox& element, RenderStyle&& style)
	: RenderBlockFlow(Type::VTTCue, element, WTF::move(style))
	, m_cue(downcast<VTTCue>(element.getCue()))
	{
	ASSERT(m_cue);
	ASSERT(isRenderVTTCue());
	}

	RenderVTTCue::~RenderVTTCue() = default;

	void RenderVTTCue::layout()
	{
	StackStats::LayoutCheckPoint layoutCheckPoint;
	RenderBlockFlow::layout();

	// If WebVTT Regions are used, the regular WebVTT layout algorithm is no
	// longer necessary, since cues having the region parameter set do not have
	// any positioning parameters. Also, in this case, the regions themselves
	// have positioning information.
	RefPtr cue = m_cue.get();
	if (!cue \|\| !cue->regionId().isEmpty())
	return;

	LayoutStateMaintainer statePusher(*this, locationOffset(), true);

	if (cue->cueType()== TextTrackCue::WebVTT) {
	if (cue->snapToLines())
	repositionCueSnapToLinesSet();
	else
	repositionCueSnapToLinesNotSet();
	} else
	repositionGenericCue();
	}

	bool RenderVTTCue::initializeLayoutParameters(LayoutUnit& step, LayoutUnit& position)
	{
	if (!firstChild())
	return false;

	auto* box = cueBox();
	if (!box)
	return false;

	auto firstInlineBox = InlineIterator::lineLeftmostInlineBoxFor(box) ? : InlineIterator::firstRootInlineBoxFor(this);
	if (!firstInlineBox)
	return false;

	auto* backdropBox = this->backdropBox();
	if (!backdropBox)
	return false;

	// 1. Horizontal: Let step be the height of the first line box in boxes.
	// Vertical: Let step be the width of the first line box in boxes.
	auto firstInlineBoxSize = firstInlineBox->visualRectIgnoringBlockDirection().size();
	step = m_cue->vertical() == VTTCue::DirectionSetting::Horizontal ? firstInlineBoxSize.height() : firstInlineBoxSize.width();

	// Note: the previous rules in initializeLayoutParameters() only account for
	// the height of the line boxes contained within the cue, and not the cue's height
	// nor its padding, nor its borders. Ignoring these will lead to errors
	// in the initial placement of cues, as the resulting placement will result in
	// the cue always being partially outside its containing block, rather than at
	// its initial position. Correct the initial position by subtracting from
	// position the difference between the the logicalHeight of the cue and its
	// first line box.
	auto inlineBoxHeights = LayoutUnit { };
	for (auto inlineBox = firstInlineBox; inlineBox; inlineBox = inlineBox->nextInlineBoxLineRightward())
	inlineBoxHeights += inlineBox->logicalHeight();
	auto logicalHeightDelta = backdropBox->logicalHeight() - inlineBoxHeights;
	if (logicalHeightDelta > 0)
	step += logicalHeightDelta;

	// 2. If step is zero, then jump to the step labeled done positioning below.
	if (!step)
	return false;

	// 3. Let line position be the text track cue computed line position.
	RefPtr cue = m_cue.get();
	if (!cue)
	return false;

	int linePosition = cue->calculateComputedLinePosition();

	// 4. Vertical Growing Left: Add one to line position then negate it.
	if (cue->vertical() == VTTCue::DirectionSetting::VerticalGrowingLeft)
	linePosition = -(linePosition + 1);

	// 5. Let position be the result of multiplying step and line position.
	position = step * linePosition;

	// 6. Vertical Growing Left: Decrease position by the width of the
	// bounding box of the boxes in boxes, then increase position by step.
	if (cue->vertical() == VTTCue::DirectionSetting::VerticalGrowingLeft) {
	position -= width();
	position += step;
	}

	// 7. If line position is less than zero...
	if (linePosition < 0) {
	// Horizontal / Vertical: ... then increase position by the
	// height / width of the video's rendering area ...
	position += cue->vertical() == VTTCue::DirectionSetting::Horizontal ? containingBlock()->height() : containingBlock()->width();

	// ... and negate step.
	step = -step;
	}

	return true;
	}

	void RenderVTTCue::placeBoxInDefaultPosition(LayoutUnit position, bool& switched)
	{
	// 8. Move all boxes in boxes ...
	if (m_cue->vertical() == VTTCue::DirectionSetting::Horizontal) {
	// Horizontal: ... down by the distance given by position
	setY(y() + position);
	} else {
	// Vertical: ... right by the distance given by position
	setX(x() + position);
	}

	// 9. Default: Remember the position of all the boxes in boxes as their
	// default position.
	m_fallbackPosition = FloatPoint(x(), y());

	// 10. Let switched be false.
	switched = false;
	}

	bool RenderVTTCue::isOutside() const
	{
	if (!firstChild())
	return false;

	if (auto* backdropBox = this->backdropBox())
	return !rectIsWithinContainer(backdropBox->absoluteBoundingBoxRect());
	return false;
	}

	bool RenderVTTCue::rectIsWithinContainer(const IntRect& rect) const
	{
	return containingBlock()->absoluteBoundingBoxRect().contains(rect);
	}


	bool RenderVTTCue::isOverlapping() const
	{
	if (!firstChild())
	return false;

	return overlappingObject();
	}

	RenderVTTCue* RenderVTTCue::overlappingObject() const
	{
	ASSERT(firstChild());

	if (auto* backdropBox = this->backdropBox())
	return overlappingObjectForRect(backdropBox->absoluteBoundingBoxRect());
	return nullptr;
	}

	RenderVTTCue* RenderVTTCue::overlappingObjectForRect(const IntRect& rect) const
	{
	for (RenderObject* sibling = previousSibling(); sibling; sibling = sibling->previousSibling()) {
	auto* previousCue = downcast<RenderVTTCue>(sibling);
	if (!previousCue \|\| !previousCue->firstChild())
	continue;

	auto* previousCueBackdropBox = previousCue->backdropBox();
	if (previousCueBackdropBox && rect.intersects(previousCueBackdropBox->absoluteBoundingBoxRect()))
	return previousCue;
	}

	return 0;
	}

	bool RenderVTTCue::shouldSwitchDirection(const InlineIterator::InlineBox& firstInlineBox, LayoutUnit step) const
	{
	auto firstInlineBoxSize = firstInlineBox.visualRectIgnoringBlockDirection().size();
	LayoutUnit top = y();
	LayoutUnit left = x();
	LayoutUnit bottom { top + firstInlineBoxSize.height() };
	LayoutUnit right { left + firstInlineBoxSize.width() };

	// 12. Horizontal: If step is negative and the top of the first line
	// box in boxes is now above the top of the video's rendering area,
	// or if step is positive and the bottom of the first line box in
	// boxes is now below the bottom of the video's rendering area, jump
	// to the step labeled switch direction.
	LayoutUnit parentHeight = containingBlock()->height();
	if (m_cue->vertical() == VTTCue::DirectionSetting::Horizontal && ((step < 0 && top < 0) \|\| (step > 0 && bottom > parentHeight)))
	return true;

	// 12. Vertical: If step is negative and the left edge of the first line
	// box in boxes is now to the left of the left edge of the video's
	// rendering area, or if step is positive and the right edge of the
	// first line box in boxes is now to the right of the right edge of
	// the video's rendering area, jump to the step labeled switch direction.
	LayoutUnit parentWidth = containingBlock()->width();
	if (m_cue->vertical() != VTTCue::DirectionSetting::Horizontal && ((step < 0 && left < 0) \|\| (step > 0 && right > parentWidth)))
	return true;

	return false;
	}

	void RenderVTTCue::moveBoxesByStep(LayoutUnit step)
	{
	// 13. Horizontal: Move all the boxes in boxes down by the distance
	// given by step. (If step is negative, then this will actually
	// result in an upwards movement of the boxes in absolute terms.)
	if (m_cue->vertical() == VTTCue::DirectionSetting::Horizontal)
	setY(y() + step);

	// 13. Vertical: Move all the boxes in boxes right by the distance
	// given by step. (If step is negative, then this will actually
	// result in a leftwards movement of the boxes in absolute terms.)
	else
	setX(x() + step);
	}

	bool RenderVTTCue::switchDirection(bool& switched, LayoutUnit& step)
	{
	// 15. Switch direction: Move all the boxes in boxes back to their
	// default position as determined in the step above labeled default.
	setX(m_fallbackPosition.x());
	setY(m_fallbackPosition.y());

	// 16. If switched is true, jump to the step labeled done
	// positioning below.
	if (switched)
	return false;

	// 17. Negate step.
	step = -step;

	// 18. Set switched to true.
	switched = true;
	return true;
	}

	void RenderVTTCue::moveIfNecessaryToKeepWithinContainer()
	{
	if (!firstChild())
	return;

	auto* backdropBox = this->backdropBox();
	if (!backdropBox)
	return;

	IntRect containerRect = containingBlock()->absoluteBoundingBoxRect();
	IntRect cueRect = backdropBox->absoluteBoundingBoxRect();

	int topOverflow = cueRect.y() - containerRect.y();
	int bottomOverflow = containerRect.maxY() - cueRect.maxY();

	int verticalAdjustment = 0;
	if (topOverflow < 0)
	verticalAdjustment = -topOverflow;
	else if (bottomOverflow < 0)
	verticalAdjustment = bottomOverflow;

	if (verticalAdjustment)
	setY(y() + verticalAdjustment);

	int leftOverflow = cueRect.x() - containerRect.x();
	int rightOverflow = containerRect.maxX() - cueRect.maxX();

	int horizontalAdjustment = 0;
	if (leftOverflow < 0)
	horizontalAdjustment = -leftOverflow;
	else if (rightOverflow < 0)
	horizontalAdjustment = rightOverflow;

	if (horizontalAdjustment)
	setX(x() + horizontalAdjustment);
	}

	bool RenderVTTCue::findNonOverlappingPosition(int& newX, int& newY) const
	{
	if (!firstChild())
	return false;

	auto* backdropBox = this->backdropBox();
	if (!backdropBox)
	return false;

	newX = x();
	newY = y();
	IntRect srcRect = backdropBox->absoluteBoundingBoxRect();
	IntRect destRect = srcRect;

	// Move the box up, looking for a non-overlapping position:
	while (RenderVTTCue* cue = overlappingObjectForRect(destRect)) {
	auto* cueBackdropBox = cue->backdropBox();
	if (!cueBackdropBox)
	continue;
	if (m_cue->vertical() == VTTCue::DirectionSetting::Horizontal)
	destRect.setY(cueBackdropBox->absoluteBoundingBoxRect().y() - destRect.height());
	else
	destRect.setX(cueBackdropBox->absoluteBoundingBoxRect().x() - destRect.width());
	}

	if (rectIsWithinContainer(destRect)) {
	newX += destRect.x() - srcRect.x();
	newY += destRect.y() - srcRect.y();
	return true;
	}

	destRect = srcRect;

	// Move the box down, looking for a non-overlapping position:
	while (RenderVTTCue* cue = overlappingObjectForRect(destRect)) {
	auto* cueBackdropBox = cue->backdropBox();
	if (!cueBackdropBox)
	continue;
	if (m_cue->vertical() == VTTCue::DirectionSetting::Horizontal)
	destRect.setY(cueBackdropBox->absoluteBoundingBoxRect().maxY());
	else
	destRect.setX(cueBackdropBox->absoluteBoundingBoxRect().maxX());
	}

	if (rectIsWithinContainer(destRect)) {
	newX += destRect.x() - srcRect.x();
	newY += destRect.y() - srcRect.y();
	return true;
	}

	return false;
	}

	void RenderVTTCue::repositionCueSnapToLinesSet()
	{
	LayoutUnit step;
	LayoutUnit position;
	if (!initializeLayoutParameters(step, position))
	return;

	if (!firstChild())
	return;

	bool switched;
	placeBoxInDefaultPosition(position, switched);

	auto* box = cueBox();
	if (!box)
	return;

	auto firstInlineBox = InlineIterator::lineLeftmostInlineBoxFor(box) ? : InlineIterator::firstRootInlineBoxFor(this);
	ASSERT(firstInlineBox);
	// 11. Step loop: If none of the boxes in boxes would overlap any of the boxes
	// in output and all the boxes in output are within the video's rendering area
	// then jump to the step labeled done positioning.
	while (isOutside() \|\| isOverlapping()) {
	if (!shouldSwitchDirection(*firstInlineBox, step)) {
	// 13. Move all the boxes in boxes ...
	// 14. Jump back to the step labeled step loop.
	moveBoxesByStep(step);
	} else if (!switchDirection(switched, step))
	break;

	// 19. Jump back to the step labeled step loop.
	}

	// Acommodate extra top and bottom padding, border or margin.
	// Note: this is supported only for internal UA styling, not through the cue selector.
	if (hasInlineDirectionBordersPaddingOrMargin())
	moveIfNecessaryToKeepWithinContainer();
	}

	void RenderVTTCue::repositionGenericCue()
	{
	if (!firstChild())
	return;

	auto* box = cueBox();
	if (!box)
	return;

	auto firstInlineBox = InlineIterator::lineLeftmostInlineBoxFor(*box);
	if (downcast<TextTrackCueGeneric>(*m_cue).useDefaultPosition() && firstInlineBox) {
	LayoutUnit parentWidth = containingBlock()->logicalWidth();
	LayoutUnit width { firstInlineBox->visualRectIgnoringBlockDirection().width() };
	LayoutUnit right = (parentWidth / 2) - (width / 2);
	setX(right);
	}
	repositionCueSnapToLinesNotSet();
	}

	void RenderVTTCue::repositionCueSnapToLinesNotSet()
	{
	if (!firstChild())
	return;

	auto* backdropBox = this->backdropBox();
	if (!backdropBox)
	return;

	// https://w3c.github.io/webvtt/#processing-cue-settings
	// 7.2.28 Adjust the positions of boxes according to the appropriate steps from the following list:

	// ↳ If cue’s WebVTT cue snap-to-lines flag is false
	// 1. Let bounding box be the bounding box of the boxes in boxes.
	auto boundingBox = backdropBox->absoluteBoundingBoxRect();

	// 2. Run the appropriate steps from the following list:
	switch (m_cue->vertical()) {
	case VTTCue::DirectionSetting::Horizontal:
	// ↳ If the WebVTT cue writing direction is horizontal
	if (m_cue->lineAlign() == VTTCue::LineAlignSetting::Center) {
	// ↳ If the WebVTT cue line alignment is center alignment
	// Move all the boxes in boxes up by half of the height of bounding box.
	setY(y() - boundingBox.height() / 2);
	} else if (m_cue->lineAlign() == VTTCue::LineAlignSetting::End) {
	// ↳ If the WebVTT cue line alignment is end alignment
	// Move all the boxes in boxes up by the height of bounding box.
	setY(y() - boundingBox.height());
	}
	break;
	case VTTCue::DirectionSetting::VerticalGrowingLeft:
	case VTTCue::DirectionSetting::VerticalGrowingRight:
	// ↳ If the WebVTT cue writing direction is vertical growing left or
	// vertical growing right
	if (m_cue->lineAlign() == VTTCue::LineAlignSetting::Center) {
	// ↳ If the WebVTT cue line alignment is center alignment
	// Move all the boxes in boxes left by half of the width of bounding box.
	setX(x() - boundingBox.width() / 2);
	} else if (m_cue->lineAlign() == VTTCue::LineAlignSetting::End) {
	// ↳ If the WebVTT cue line alignment is end alignment
	// Move all the boxes in boxes left by the width of bounding box.
	setX(x() - boundingBox.width());
	}
	break;
	default:
	ASSERT_NOT_REACHED();
	}

	// 9. If none of the boxes in boxes would overlap any of the boxes in output, and all the boxes in
	// output are within the video's rendering area, then jump to the step labeled done positioning below.
	if (!isOutside() && !isOverlapping())
	return;

	// 10. If there is a position to which the boxes in boxes can be moved while maintaining the relative
	// positions of the boxes in boxes to each other such that none of the boxes in boxes would overlap
	// any of the boxes in output, and all the boxes in output would be within the video's rendering area,
	// then move the boxes in boxes to the closest such position to their current position, and then jump
	// to the step labeled done positioning below. If there are multiple such positions that are equidistant
	// from their current position, use the highest one amongst them; if there are several at that height,
	// then use the leftmost one amongst them.
	moveIfNecessaryToKeepWithinContainer();
	int x = 0;
	int y = 0;
	if (findNonOverlappingPosition(x, y)) {
	setX(x);
	setY(y);
	}

	// 11. Otherwise, jump to the step labeled done positioning below. (The
	// boxes will unfortunately overlap.)
	}

	RenderBlockFlow* RenderVTTCue::backdropBox() const
	{
	// firstChild() returns the wrapping (backdrop) <div>. The cue object is
	// the <div>'s first child.
	auto* firstChild = this->firstChild();
	ASSERT(firstChild);
	ASSERT(is<RenderBlockFlow>(firstChild));
	return dynamicDowncast<RenderBlockFlow>(firstChild);
	}

	RenderInline* RenderVTTCue::cueBox() const
	{
	auto* backdropBox = this->backdropBox();
	if (!backdropBox)
	return nullptr;

	auto* firstChild = backdropBox->firstChild();
	ASSERT(firstChild);
	ASSERT(is<RenderInline>(firstChild));
	return dynamicDowncast<RenderInline>(firstChild);
	}

	} // namespace WebCore

	#endif