Source/WebCore/html/shadow/MediaControlTextTrackContainerElement.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 2008-2020 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Google 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.
  * 3.  Neither the name of Apple Inc. ("Apple") nor the names of
  *     its contributors may be used to endorse or promote products derived
  *     from this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "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 OR ITS 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"
 #include "MediaControlTextTrackContainerElement.h"

 #if ENABLE(VIDEO)

 #include "DOMTokenList.h"
 #include "ElementChildIterator.h"
 #include "EventHandler.h"
 #include "EventLoop.h"
 #include "EventNames.h"
 #include "Frame.h"
 #include "FullscreenManager.h"
 #include "GraphicsContext.h"
 #include "HTMLVideoElement.h"
 #include "ImageBuffer.h"
 #include "LocalizedStrings.h"
 #include "Logging.h"
 #include "PODInterval.h"
 #include "Page.h"
 #include "PageGroup.h"
 #include "RenderLayer.h"
 #include "RenderVideo.h"
 #include "RenderView.h"
 #include "Settings.h"
 #include "ShadowPseudoIds.h"
 #include "ShadowRoot.h"
 #include "StyleProperties.h"
 #include "TextTrackCueGeneric.h"
 #include "TextTrackList.h"
 #include "VTTRegionList.h"
 #include <wtf/IsoMallocInlines.h>
 #include <wtf/Language.h>

 namespace WebCore {

 WTF_MAKE_ISO_ALLOCATED_IMPL(MediaControlTextTrackContainerElement);

 using namespace HTMLNames;

 Ref<MediaControlTextTrackContainerElement> MediaControlTextTrackContainerElement::create(Document& document, HTMLMediaElement& mediaElement)
 {
     auto element = adoptRef(*new MediaControlTextTrackContainerElement(document, mediaElement));
     element->setPseudo(ShadowPseudoIds::webkitMediaTextTrackContainer());
     element->hide();
     return element;
 }

 MediaControlTextTrackContainerElement::MediaControlTextTrackContainerElement(Document& document, HTMLMediaElement& element)
     : HTMLDivElement(divTag, document)
     , m_mediaElement(element)
 {
 }

 RenderPtr<RenderElement> MediaControlTextTrackContainerElement::createElementRenderer(RenderStyle&& style, const RenderTreePosition&)
 {
     return createRenderer<RenderBlockFlow>(*this, WTFMove(style));
 }

 static bool compareCueIntervalForDisplay(const CueInterval& one, const CueInterval& two)
 {
     return one.data()->isPositionedAbove(two.data());
 };

 void MediaControlTextTrackContainerElement::updateDisplay()
 {
     if (m_mediaElement && !m_mediaElement->closedCaptionsVisible())
         removeChildren();

     // 1. If the media element is an audio element, or is another playback
     // mechanism with no rendering area, abort these steps. There is nothing to
     // render.
     if (!m_mediaElement || !m_mediaElement->isVideo() || m_videoDisplaySize.size().isEmpty())
         return;

     // 2. Let video be the media element or other playback mechanism.
     HTMLVideoElement& video = downcast<HTMLVideoElement>(*m_mediaElement);

     // 3. Let output be an empty list of absolutely positioned CSS block boxes.

     // 4. If the user agent is exposing a user interface for video, add to
     // output one or more completely transparent positioned CSS block boxes that
     // cover the same region as the user interface.

     // 5. If the last time these rules were run, the user agent was not exposing
     // a user interface for video, but now it is, let reset be true. Otherwise,
     // let reset be false.

     // There is nothing to be done explicitly for 4th and 5th steps, as
     // everything is handled through CSS. The caption box is on top of the
     // controls box, in a container set with the -webkit-box display property.

     // 6. Let tracks be the subset of video's list of text tracks that have as
     // their rules for updating the text track rendering these rules for
     // updating the display of WebVTT text tracks, and whose text track mode is
     // showing or showing by default.
     // 7. Let cues be an empty list of text track cues.
     // 8. For each track track in tracks, append to cues all the cues from
     // track's list of cues that have their text track cue active flag set.
     CueList activeCues = video.currentlyActiveCues();

     // 9. If reset is false, then, for each text track cue cue in cues: if cue's
     // text track cue display state has a set of CSS boxes, then add those boxes
     // to output, and remove cue from cues.

     // There is nothing explicitly to be done here, as all the caching occurs
     // within the TextTrackCue instance itself. If parameters of the cue change,
     // the display tree is cleared.

     // If the number of CSS boxes in the output is less than the number of cues
     // we wish to render (e.g., we are adding another cue in a set of roll-up
     // cues), remove all the existing CSS boxes representing the cues and re-add
     // them so that the new cue is at the bottom.
     // FIXME: Calling countChildNodes() here is inefficient. We don't need to
     // traverse all children just to check if there are less children than cues.
     if (countChildNodes() < activeCues.size())
         removeChildren();

     activeCues.removeAllMatching([] (CueInterval& cueInterval) {
         RefPtr<TextTrackCue> cue = cueInterval.data();
         return !cue->track()
             || !cue->track()->isRendered()
             || cue->track()->mode() == TextTrack::Mode::Disabled
             || !cue->isActive()
             || !cue->isRenderable();
     });

     // Sort the active cues for the appropriate display order. For example, for roll-up
     // or paint-on captions, we need to add the cues in reverse chronological order,
     // so that the newest captions appear at the bottom.
     std::sort(activeCues.begin(), activeCues.end(), &compareCueIntervalForDisplay);

     if (m_mediaElement->closedCaptionsVisible()) {
         // 10. For each text track cue in cues that has not yet had
         // corresponding CSS boxes added to output, in text track cue order, run the
         // following substeps:
         for (auto& interval : activeCues) {
             auto cue = interval.data();
             cue->setFontSize(m_fontSize, m_videoDisplaySize.size(), m_fontSizeIsImportant);
             if (is<VTTCue>(*cue))
                 processActiveVTTCue(downcast<VTTCue>(*cue));
             else {
                 auto displayBox = cue->getDisplayTree(m_videoDisplaySize.size(), m_fontSize);
                 if (displayBox->hasChildNodes() && !contains(displayBox.get()))
                     appendChild(*displayBox);
             }
         }
     }

     // 11. Return output.
     if (hasChildNodes())
         show();
     else
         hide();

     updateTextTrackRepresentationIfNeeded();
     updateTextTrackStyle();
 }

 void MediaControlTextTrackContainerElement::updateTextTrackRepresentationImageIfNeeded()
 {
     if (!m_needsToGenerateTextTrackRepresentation)
         return;

     m_needsToGenerateTextTrackRepresentation = false;

     // We should call m_textTrackRepresentation->update() to paint the subtree of
     // the RenderTextTrackContainerElement after the layout is clean.
     if (m_textTrackRepresentation) {
         m_textTrackRepresentation->update();
         m_textTrackRepresentation->setHidden(false);
     }
 }

 void MediaControlTextTrackContainerElement::processActiveVTTCue(VTTCue& cue)
 {
     DEBUG_LOG(LOGIDENTIFIER, "adding and positioning cue: \"", cue.text(), "\", start=", cue.startTime(), ", end=", cue.endTime());
     Ref<TextTrackCueBox> displayBox = *cue.getDisplayTree(m_videoDisplaySize.size(), m_fontSize);

     if (auto region = cue.track()->regions()->getRegionById(cue.regionId())) {
         // Let region be the WebVTT region whose region identifier
         // matches the text track cue region identifier of cue.
         Ref<HTMLDivElement> regionNode = region->getDisplayTree();

         if (!contains(regionNode.ptr()))
             appendChild(region->getDisplayTree());

         region->appendTextTrackCueBox(WTFMove(displayBox));
     } else {
         // If cue has an empty text track cue region identifier or there is no
         // WebVTT region whose region identifier is identical to cue's text
         // track cue region identifier, run the following substeps:
         if (displayBox->hasChildNodes() && !contains(displayBox.ptr())) {
             // Note: the display tree of a cue is removed when the active flag of the cue is unset.
             appendChild(displayBox);
         }
     }
 }

 void MediaControlTextTrackContainerElement::updateActiveCuesFontSize()
 {
     if (!document().page())
         return;

     if (!m_mediaElement)
         return;

     float smallestDimension = std::min(m_videoDisplaySize.size().height(), m_videoDisplaySize.size().width());
     float fontScale = document().page()->group().ensureCaptionPreferences().captionFontSizeScaleAndImportance(m_fontSizeIsImportant);
     m_fontSize = lroundf(smallestDimension * fontScale);

     for (auto& activeCue : m_mediaElement->currentlyActiveCues()) {
         RefPtr<TextTrackCue> cue = activeCue.data();
         if (cue->isRenderable())
             cue->setFontSize(m_fontSize, m_videoDisplaySize.size(), m_fontSizeIsImportant);
     }
 }

 void MediaControlTextTrackContainerElement::updateTextStrokeStyle()
 {
     if (!document().page())
         return;

     if (!m_mediaElement)
         return;

     String language;

     // FIXME: Since it is possible to have more than one text track enabled, the following code may not find the correct language.
     // The default UI only allows a user to enable one track at a time, so it should be OK for now, but we should consider doing
     // this differently, see <https://bugs.webkit.org/show_bug.cgi?id=169875>.
     if (auto* tracks = m_mediaElement->textTracks()) {
         for (unsigned i = 0; i < tracks->length(); ++i) {
             auto track = tracks->item(i);
             if (track && track->mode() == TextTrack::Mode::Showing) {
                 language = track->validBCP47Language();
                 break;
             }
         }
     }

     float strokeWidth;
     bool important;

     // FIXME: find a way to set this property in the stylesheet like the other user style preferences, see <https://bugs.webkit.org/show_bug.cgi?id=169874>.
     if (document().page()->group().ensureCaptionPreferences().captionStrokeWidthForFont(m_fontSize, language, strokeWidth, important))
         setInlineStyleProperty(CSSPropertyStrokeWidth, strokeWidth, CSSUnitType::CSS_PX, important);
 }

 void MediaControlTextTrackContainerElement::updateTextTrackRepresentationIfNeeded()
 {
     if (!m_mediaElement)
         return;

     auto requiresTextTrackRepresentation = m_mediaElement->requiresTextTrackRepresentation();
     if (!hasChildNodes() || !requiresTextTrackRepresentation) {
         if (m_textTrackRepresentation) {
             if (!requiresTextTrackRepresentation)
                 clearTextTrackRepresentation();
             else
                 m_textTrackRepresentation->setHidden(true);
         }
         return;
     }

     if (!m_textTrackRepresentation) {
         ALWAYS_LOG(LOGIDENTIFIER);

         m_textTrackRepresentation = TextTrackRepresentation::create(*this);
         if (document().page())
             m_textTrackRepresentation->setContentScale(document().page()->deviceScaleFactor());
         m_mediaElement->setTextTrackRepresentation(m_textTrackRepresentation.get());
     }

     m_needsToGenerateTextTrackRepresentation = true;
 }

 void MediaControlTextTrackContainerElement::clearTextTrackRepresentation()
 {
     if (!m_textTrackRepresentation)
         return;

     ALWAYS_LOG(LOGIDENTIFIER);

     m_textTrackRepresentation = nullptr;
     if (m_mediaElement)
         m_mediaElement->setTextTrackRepresentation(nullptr);
 }

 void MediaControlTextTrackContainerElement::updateTextTrackStyle()
 {
     if (m_textTrackRepresentation) {
         setInlineStyleProperty(CSSPropertyPosition, CSSValueAbsolute);
         setInlineStyleProperty(CSSPropertyWidth, m_videoDisplaySize.size().width(), CSSUnitType::CSS_PX);
         setInlineStyleProperty(CSSPropertyHeight, m_videoDisplaySize.size().height(), CSSUnitType::CSS_PX);
         setInlineStyleProperty(CSSPropertyLeft, 0, CSSUnitType::CSS_PX);
         setInlineStyleProperty(CSSPropertyTop, 0, CSSUnitType::CSS_PX);
         return;
     }

     removeInlineStyleProperty(CSSPropertyPosition);
     removeInlineStyleProperty(CSSPropertyWidth);
     removeInlineStyleProperty(CSSPropertyHeight);
     removeInlineStyleProperty(CSSPropertyLeft);
     removeInlineStyleProperty(CSSPropertyTop);
 }

 void MediaControlTextTrackContainerElement::enteredFullscreen()
 {
     updateTextTrackRepresentationIfNeeded();
     updateSizes(ForceUpdate::Yes);
 }

 void MediaControlTextTrackContainerElement::exitedFullscreen()
 {
     clearTextTrackRepresentation();
     updateSizes(ForceUpdate::Yes);
 }

 bool MediaControlTextTrackContainerElement::updateVideoDisplaySize()
 {
     if (!document().page())
         return false;

     if (!m_mediaElement)
         return false;

     IntRect videoBox;
     if (m_textTrackRepresentation) {
         videoBox = m_textTrackRepresentation->bounds();
         float deviceScaleFactor = document().page()->deviceScaleFactor();
         videoBox.setWidth(videoBox.width() * deviceScaleFactor);
         videoBox.setHeight(videoBox.height() * deviceScaleFactor);
     } else {
         if (!is<RenderVideo>(m_mediaElement->renderer()))
             return false;
         videoBox = downcast<RenderVideo>(*m_mediaElement->renderer()).videoBox();
     }

     if (m_videoDisplaySize == videoBox)
         return false;

     m_videoDisplaySize = videoBox;
     return true;
 }

 void MediaControlTextTrackContainerElement::updateSizes(ForceUpdate force)
 {
     if (!updateVideoDisplaySize() && force != ForceUpdate::Yes)
         return;

     if (!document().page() || !m_mediaElement)
         return;

     m_mediaElement->syncTextTrackBounds();

     updateActiveCuesFontSize();
     updateTextStrokeStyle();
     for (auto& activeCue : m_mediaElement->currentlyActiveCues())
         activeCue.data()->recalculateStyles();

     document().eventLoop().queueTask(TaskSource::MediaElement, [weakThis = WeakPtr { *this }] () {
         if (weakThis)
             weakThis->updateDisplay();
     });
 }

 RefPtr<Image> MediaControlTextTrackContainerElement::createTextTrackRepresentationImage()
 {
     if (!hasChildNodes())
         return nullptr;

     RefPtr<Frame> frame = document().frame();
     if (!frame)
         return nullptr;

     document().updateLayout();

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

     if (!renderer->hasLayer())
         return nullptr;

     RenderLayer* layer = downcast<RenderLayerModelObject>(*renderer).layer();

     float deviceScaleFactor = 1;
     if (Page* page = document().page())
         deviceScaleFactor = page->deviceScaleFactor();

     IntRect paintingRect = IntRect(IntPoint(), layer->size());

     // FIXME (149422): This buffer should not be unconditionally unaccelerated.
     auto buffer = ImageBuffer::create(paintingRect.size(), RenderingPurpose::Unspecified, deviceScaleFactor, DestinationColorSpace::SRGB(), PixelFormat::BGRA8);
     if (!buffer)
         return nullptr;

     auto paintFlags = RenderLayer::paintLayerPaintingCompositingAllPhasesFlags();
     paintFlags.add(RenderLayer::PaintLayerFlag::TemporaryClipRects);
     layer->paint(buffer->context(), paintingRect, LayoutSize(), { PaintBehavior::FlattenCompositingLayers, PaintBehavior::Snapshotting }, nullptr, paintFlags);

     return ImageBuffer::sinkIntoImage(WTFMove(buffer));
 }

 void MediaControlTextTrackContainerElement::textTrackRepresentationBoundsChanged(const IntRect&)
 {
     updateTextTrackRepresentationIfNeeded();
     updateSizes();
 }

 void MediaControlTextTrackContainerElement::hide()
 {
     setInlineStyleProperty(CSSPropertyDisplay, CSSValueNone);
 }

 void MediaControlTextTrackContainerElement::show()
 {
     removeInlineStyleProperty(CSSPropertyDisplay);
 }

 bool MediaControlTextTrackContainerElement::isShowing() const
 {
     const StyleProperties* propertySet = inlineStyle();

     // Following the code from show() and hide() above, we only have
     // to check for the presense of inline display.
     return (!propertySet || !propertySet->getPropertyCSSValue(CSSPropertyDisplay));
 }


 #if !RELEASE_LOG_DISABLED
 const Logger& MediaControlTextTrackContainerElement::logger() const
 {
     if (!m_logger)
         m_logger = &document().logger();

     return *m_logger;
 }

 const void* MediaControlTextTrackContainerElement::logIdentifier() const
 {
     if (!m_logIdentifier && m_mediaElement)
         m_logIdentifier = m_mediaElement->logIdentifier();

     return m_logIdentifier;
 }

 WTFLogChannel& MediaControlTextTrackContainerElement::logChannel() const
 {
     return LogMedia;
 }
 #endif // !RELEASE_LOG_DISABLED

 // ----------------------------

 } // namespace WebCore

 #endif // ENABLE(VIDEO)
	/*
	* Copyright (C) 2008-2020 Apple Inc. All rights reserved.
	* Copyright (C) 2012 Google 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.
	* 3. Neither the name of Apple Inc. ("Apple") nor the names of
	* its contributors may be used to endorse or promote products derived
	* from this software without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "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 OR ITS 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"
	#include "MediaControlTextTrackContainerElement.h"

	#if ENABLE(VIDEO)

	#include "DOMTokenList.h"
	#include "ElementChildIterator.h"
	#include "EventHandler.h"
	#include "EventLoop.h"
	#include "EventNames.h"
	#include "Frame.h"
	#include "FullscreenManager.h"
	#include "GraphicsContext.h"
	#include "HTMLVideoElement.h"
	#include "ImageBuffer.h"
	#include "LocalizedStrings.h"
	#include "Logging.h"
	#include "PODInterval.h"
	#include "Page.h"
	#include "PageGroup.h"
	#include "RenderLayer.h"
	#include "RenderVideo.h"
	#include "RenderView.h"
	#include "Settings.h"
	#include "ShadowPseudoIds.h"
	#include "ShadowRoot.h"
	#include "StyleProperties.h"
	#include "TextTrackCueGeneric.h"
	#include "TextTrackList.h"
	#include "VTTRegionList.h"
	#include <wtf/IsoMallocInlines.h>
	#include <wtf/Language.h>

	namespace WebCore {

	WTF_MAKE_ISO_ALLOCATED_IMPL(MediaControlTextTrackContainerElement);

	using namespace HTMLNames;

	Ref<MediaControlTextTrackContainerElement> MediaControlTextTrackContainerElement::create(Document& document, HTMLMediaElement& mediaElement)
	{
	auto element = adoptRef(*new MediaControlTextTrackContainerElement(document, mediaElement));
	element->setPseudo(ShadowPseudoIds::webkitMediaTextTrackContainer());
	element->hide();
	return element;
	}

	MediaControlTextTrackContainerElement::MediaControlTextTrackContainerElement(Document& document, HTMLMediaElement& element)
	: HTMLDivElement(divTag, document)
	, m_mediaElement(element)
	{
	}

	RenderPtr<RenderElement> MediaControlTextTrackContainerElement::createElementRenderer(RenderStyle&& style, const RenderTreePosition&)
	{
	return createRenderer<RenderBlockFlow>(*this, WTFMove(style));
	}

	static bool compareCueIntervalForDisplay(const CueInterval& one, const CueInterval& two)
	{
	return one.data()->isPositionedAbove(two.data());
	};

	void MediaControlTextTrackContainerElement::updateDisplay()
	{
	if (m_mediaElement && !m_mediaElement->closedCaptionsVisible())
	removeChildren();

	// 1. If the media element is an audio element, or is another playback
	// mechanism with no rendering area, abort these steps. There is nothing to
	// render.
	if (!m_mediaElement \|\| !m_mediaElement->isVideo() \|\| m_videoDisplaySize.size().isEmpty())
	return;

	// 2. Let video be the media element or other playback mechanism.
	HTMLVideoElement& video = downcast<HTMLVideoElement>(*m_mediaElement);

	// 3. Let output be an empty list of absolutely positioned CSS block boxes.

	// 4. If the user agent is exposing a user interface for video, add to
	// output one or more completely transparent positioned CSS block boxes that
	// cover the same region as the user interface.

	// 5. If the last time these rules were run, the user agent was not exposing
	// a user interface for video, but now it is, let reset be true. Otherwise,
	// let reset be false.

	// There is nothing to be done explicitly for 4th and 5th steps, as
	// everything is handled through CSS. The caption box is on top of the
	// controls box, in a container set with the -webkit-box display property.

	// 6. Let tracks be the subset of video's list of text tracks that have as
	// their rules for updating the text track rendering these rules for
	// updating the display of WebVTT text tracks, and whose text track mode is
	// showing or showing by default.
	// 7. Let cues be an empty list of text track cues.
	// 8. For each track track in tracks, append to cues all the cues from
	// track's list of cues that have their text track cue active flag set.
	CueList activeCues = video.currentlyActiveCues();

	// 9. If reset is false, then, for each text track cue cue in cues: if cue's
	// text track cue display state has a set of CSS boxes, then add those boxes
	// to output, and remove cue from cues.

	// There is nothing explicitly to be done here, as all the caching occurs
	// within the TextTrackCue instance itself. If parameters of the cue change,
	// the display tree is cleared.

	// If the number of CSS boxes in the output is less than the number of cues
	// we wish to render (e.g., we are adding another cue in a set of roll-up
	// cues), remove all the existing CSS boxes representing the cues and re-add
	// them so that the new cue is at the bottom.
	// FIXME: Calling countChildNodes() here is inefficient. We don't need to
	// traverse all children just to check if there are less children than cues.
	if (countChildNodes() < activeCues.size())
	removeChildren();

	activeCues.removeAllMatching([] (CueInterval& cueInterval) {
	RefPtr<TextTrackCue> cue = cueInterval.data();
	return !cue->track()
	\|\| !cue->track()->isRendered()
	\|\| cue->track()->mode() == TextTrack::Mode::Disabled
	\|\| !cue->isActive()
	\|\| !cue->isRenderable();
	});

	// Sort the active cues for the appropriate display order. For example, for roll-up
	// or paint-on captions, we need to add the cues in reverse chronological order,
	// so that the newest captions appear at the bottom.
	std::sort(activeCues.begin(), activeCues.end(), &compareCueIntervalForDisplay);

	if (m_mediaElement->closedCaptionsVisible()) {
	// 10. For each text track cue in cues that has not yet had
	// corresponding CSS boxes added to output, in text track cue order, run the
	// following substeps:
	for (auto& interval : activeCues) {
	auto cue = interval.data();
	cue->setFontSize(m_fontSize, m_videoDisplaySize.size(), m_fontSizeIsImportant);
	if (is<VTTCue>(*cue))
	processActiveVTTCue(downcast<VTTCue>(*cue));
	else {
	auto displayBox = cue->getDisplayTree(m_videoDisplaySize.size(), m_fontSize);
	if (displayBox->hasChildNodes() && !contains(displayBox.get()))
	appendChild(*displayBox);
	}
	}
	}

	// 11. Return output.
	if (hasChildNodes())
	show();
	else
	hide();

	updateTextTrackRepresentationIfNeeded();
	updateTextTrackStyle();
	}

	void MediaControlTextTrackContainerElement::updateTextTrackRepresentationImageIfNeeded()
	{
	if (!m_needsToGenerateTextTrackRepresentation)
	return;

	m_needsToGenerateTextTrackRepresentation = false;

	// We should call m_textTrackRepresentation->update() to paint the subtree of
	// the RenderTextTrackContainerElement after the layout is clean.
	if (m_textTrackRepresentation) {
	m_textTrackRepresentation->update();
	m_textTrackRepresentation->setHidden(false);
	}
	}

	void MediaControlTextTrackContainerElement::processActiveVTTCue(VTTCue& cue)
	{
	DEBUG_LOG(LOGIDENTIFIER, "adding and positioning cue: \"", cue.text(), "\", start=", cue.startTime(), ", end=", cue.endTime());
	Ref<TextTrackCueBox> displayBox = *cue.getDisplayTree(m_videoDisplaySize.size(), m_fontSize);

	if (auto region = cue.track()->regions()->getRegionById(cue.regionId())) {
	// Let region be the WebVTT region whose region identifier
	// matches the text track cue region identifier of cue.
	Ref<HTMLDivElement> regionNode = region->getDisplayTree();

	if (!contains(regionNode.ptr()))
	appendChild(region->getDisplayTree());

	region->appendTextTrackCueBox(WTFMove(displayBox));
	} else {
	// If cue has an empty text track cue region identifier or there is no
	// WebVTT region whose region identifier is identical to cue's text
	// track cue region identifier, run the following substeps:
	if (displayBox->hasChildNodes() && !contains(displayBox.ptr())) {
	// Note: the display tree of a cue is removed when the active flag of the cue is unset.
	appendChild(displayBox);
	}
	}
	}

	void MediaControlTextTrackContainerElement::updateActiveCuesFontSize()
	{
	if (!document().page())
	return;

	if (!m_mediaElement)
	return;

	float smallestDimension = std::min(m_videoDisplaySize.size().height(), m_videoDisplaySize.size().width());
	float fontScale = document().page()->group().ensureCaptionPreferences().captionFontSizeScaleAndImportance(m_fontSizeIsImportant);
	m_fontSize = lroundf(smallestDimension * fontScale);

	for (auto& activeCue : m_mediaElement->currentlyActiveCues()) {
	RefPtr<TextTrackCue> cue = activeCue.data();
	if (cue->isRenderable())
	cue->setFontSize(m_fontSize, m_videoDisplaySize.size(), m_fontSizeIsImportant);
	}
	}

	void MediaControlTextTrackContainerElement::updateTextStrokeStyle()
	{
	if (!document().page())
	return;

	if (!m_mediaElement)
	return;

	String language;

	// FIXME: Since it is possible to have more than one text track enabled, the following code may not find the correct language.
	// The default UI only allows a user to enable one track at a time, so it should be OK for now, but we should consider doing
	// this differently, see <https://bugs.webkit.org/show_bug.cgi?id=169875>.
	if (auto* tracks = m_mediaElement->textTracks()) {
	for (unsigned i = 0; i < tracks->length(); ++i) {
	auto track = tracks->item(i);
	if (track && track->mode() == TextTrack::Mode::Showing) {
	language = track->validBCP47Language();
	break;
	}
	}
	}

	float strokeWidth;
	bool important;

	// FIXME: find a way to set this property in the stylesheet like the other user style preferences, see <https://bugs.webkit.org/show_bug.cgi?id=169874>.
	if (document().page()->group().ensureCaptionPreferences().captionStrokeWidthForFont(m_fontSize, language, strokeWidth, important))
	setInlineStyleProperty(CSSPropertyStrokeWidth, strokeWidth, CSSUnitType::CSS_PX, important);
	}

	void MediaControlTextTrackContainerElement::updateTextTrackRepresentationIfNeeded()
	{
	if (!m_mediaElement)
	return;

	auto requiresTextTrackRepresentation = m_mediaElement->requiresTextTrackRepresentation();
	if (!hasChildNodes() \|\| !requiresTextTrackRepresentation) {
	if (m_textTrackRepresentation) {
	if (!requiresTextTrackRepresentation)
	clearTextTrackRepresentation();
	else
	m_textTrackRepresentation->setHidden(true);
	}
	return;
	}

	if (!m_textTrackRepresentation) {
	ALWAYS_LOG(LOGIDENTIFIER);

	m_textTrackRepresentation = TextTrackRepresentation::create(*this);
	if (document().page())
	m_textTrackRepresentation->setContentScale(document().page()->deviceScaleFactor());
	m_mediaElement->setTextTrackRepresentation(m_textTrackRepresentation.get());
	}

	m_needsToGenerateTextTrackRepresentation = true;
	}

	void MediaControlTextTrackContainerElement::clearTextTrackRepresentation()
	{
	if (!m_textTrackRepresentation)
	return;

	ALWAYS_LOG(LOGIDENTIFIER);

	m_textTrackRepresentation = nullptr;
	if (m_mediaElement)
	m_mediaElement->setTextTrackRepresentation(nullptr);
	}

	void MediaControlTextTrackContainerElement::updateTextTrackStyle()
	{
	if (m_textTrackRepresentation) {
	setInlineStyleProperty(CSSPropertyPosition, CSSValueAbsolute);
	setInlineStyleProperty(CSSPropertyWidth, m_videoDisplaySize.size().width(), CSSUnitType::CSS_PX);
	setInlineStyleProperty(CSSPropertyHeight, m_videoDisplaySize.size().height(), CSSUnitType::CSS_PX);
	setInlineStyleProperty(CSSPropertyLeft, 0, CSSUnitType::CSS_PX);
	setInlineStyleProperty(CSSPropertyTop, 0, CSSUnitType::CSS_PX);
	return;
	}

	removeInlineStyleProperty(CSSPropertyPosition);
	removeInlineStyleProperty(CSSPropertyWidth);
	removeInlineStyleProperty(CSSPropertyHeight);
	removeInlineStyleProperty(CSSPropertyLeft);
	removeInlineStyleProperty(CSSPropertyTop);
	}

	void MediaControlTextTrackContainerElement::enteredFullscreen()
	{
	updateTextTrackRepresentationIfNeeded();
	updateSizes(ForceUpdate::Yes);
	}

	void MediaControlTextTrackContainerElement::exitedFullscreen()
	{
	clearTextTrackRepresentation();
	updateSizes(ForceUpdate::Yes);
	}

	bool MediaControlTextTrackContainerElement::updateVideoDisplaySize()
	{
	if (!document().page())
	return false;

	if (!m_mediaElement)
	return false;

	IntRect videoBox;
	if (m_textTrackRepresentation) {
	videoBox = m_textTrackRepresentation->bounds();
	float deviceScaleFactor = document().page()->deviceScaleFactor();
	videoBox.setWidth(videoBox.width() * deviceScaleFactor);
	videoBox.setHeight(videoBox.height() * deviceScaleFactor);
	} else {
	if (!is<RenderVideo>(m_mediaElement->renderer()))
	return false;
	videoBox = downcast<RenderVideo>(*m_mediaElement->renderer()).videoBox();
	}

	if (m_videoDisplaySize == videoBox)
	return false;

	m_videoDisplaySize = videoBox;
	return true;
	}

	void MediaControlTextTrackContainerElement::updateSizes(ForceUpdate force)
	{
	if (!updateVideoDisplaySize() && force != ForceUpdate::Yes)
	return;

	if (!document().page() \|\| !m_mediaElement)
	return;

	m_mediaElement->syncTextTrackBounds();

	updateActiveCuesFontSize();
	updateTextStrokeStyle();
	for (auto& activeCue : m_mediaElement->currentlyActiveCues())
	activeCue.data()->recalculateStyles();

	document().eventLoop().queueTask(TaskSource::MediaElement, [weakThis = WeakPtr { *this }] () {
	if (weakThis)
	weakThis->updateDisplay();
	});
	}

	RefPtr<Image> MediaControlTextTrackContainerElement::createTextTrackRepresentationImage()
	{
	if (!hasChildNodes())
	return nullptr;

	RefPtr<Frame> frame = document().frame();
	if (!frame)
	return nullptr;

	document().updateLayout();

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

	if (!renderer->hasLayer())
	return nullptr;

	RenderLayer* layer = downcast<RenderLayerModelObject>(*renderer).layer();

	float deviceScaleFactor = 1;
	if (Page* page = document().page())
	deviceScaleFactor = page->deviceScaleFactor();

	IntRect paintingRect = IntRect(IntPoint(), layer->size());

	// FIXME (149422): This buffer should not be unconditionally unaccelerated.
	auto buffer = ImageBuffer::create(paintingRect.size(), RenderingPurpose::Unspecified, deviceScaleFactor, DestinationColorSpace::SRGB(), PixelFormat::BGRA8);
	if (!buffer)
	return nullptr;

	auto paintFlags = RenderLayer::paintLayerPaintingCompositingAllPhasesFlags();
	paintFlags.add(RenderLayer::PaintLayerFlag::TemporaryClipRects);
	layer->paint(buffer->context(), paintingRect, LayoutSize(), { PaintBehavior::FlattenCompositingLayers, PaintBehavior::Snapshotting }, nullptr, paintFlags);

	return ImageBuffer::sinkIntoImage(WTFMove(buffer));
	}

	void MediaControlTextTrackContainerElement::textTrackRepresentationBoundsChanged(const IntRect&)
	{
	updateTextTrackRepresentationIfNeeded();
	updateSizes();
	}

	void MediaControlTextTrackContainerElement::hide()
	{
	setInlineStyleProperty(CSSPropertyDisplay, CSSValueNone);
	}

	void MediaControlTextTrackContainerElement::show()
	{
	removeInlineStyleProperty(CSSPropertyDisplay);
	}

	bool MediaControlTextTrackContainerElement::isShowing() const
	{
	const StyleProperties* propertySet = inlineStyle();

	// Following the code from show() and hide() above, we only have
	// to check for the presense of inline display.
	return (!propertySet \|\| !propertySet->getPropertyCSSValue(CSSPropertyDisplay));
	}


	#if !RELEASE_LOG_DISABLED
	const Logger& MediaControlTextTrackContainerElement::logger() const
	{
	if (!m_logger)
	m_logger = &document().logger();

	return *m_logger;
	}

	const void* MediaControlTextTrackContainerElement::logIdentifier() const
	{
	if (!m_logIdentifier && m_mediaElement)
	m_logIdentifier = m_mediaElement->logIdentifier();

	return m_logIdentifier;
	}

	WTFLogChannel& MediaControlTextTrackContainerElement::logChannel() const
	{
	return LogMedia;
	}
	#endif // !RELEASE_LOG_DISABLED

	// ----------------------------

	} // namespace WebCore

	#endif // ENABLE(VIDEO)