layout/style/nsAnimationManager.cpp
author Nika Layzell <nika@thelayzells.com>
Tue, 25 Sep 2018 17:34:53 +0200
changeset 507828 5e6dae0c1e5a4939ccd406f14607f7fafffd45a7
parent 501690 0a73fd515a35eb7337d4c8d91aa70275c542efa4
child 508163 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1448426 - Wrap windows.h to avoid problematic define statements, r=froydnj,glandium By default, windows.h exposes a large number of problematic define statements which are UpperCamelCase, such as a define from `CreateWindow` to `CreateWindow{A,W}`. As many of these names are generic (e.g. CreateFile, CreateWindow), they can mess up Gecko code that may legitimately have its own methods with the same names. The header also defines some traditional SCREAMING_SNAKE_CASE defines which can mess up our code by conflicting with local values. This patch adds a simple code generator which generates wrappers for these defines, and uses them to wrap the windows.h wrapper using the `stl_wrappers` mechanism, allowing us to use windows.h in more places. Differential Revision: https://phabricator.services.mozilla.com/D10932

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "nsAnimationManager.h"
#include "nsTransitionManager.h"
#include "mozilla/dom/CSSAnimationBinding.h"

#include "mozilla/AnimationEventDispatcher.h"
#include "mozilla/AnimationTarget.h"
#include "mozilla/EffectCompositor.h"
#include "mozilla/EffectSet.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/ServoStyleSet.h"
#include "mozilla/StyleAnimationValue.h"
#include "mozilla/dom/AnimationEffect.h"
#include "mozilla/dom/DocumentTimeline.h"
#include "mozilla/dom/KeyframeEffect.h"

#include "nsPresContext.h"
#include "nsStyleChangeList.h"
#include "nsLayoutUtils.h"
#include "nsIFrame.h"
#include "nsIDocument.h"
#include "nsDOMMutationObserver.h"
#include "nsIPresShell.h"
#include "nsIPresShellInlines.h"
#include "nsRFPService.h"
#include <algorithm> // std::stable_sort
#include <math.h>

using namespace mozilla;
using namespace mozilla::css;
using mozilla::dom::Animation;
using mozilla::dom::AnimationEffect;
using mozilla::dom::AnimationPlayState;
using mozilla::dom::KeyframeEffect;
using mozilla::dom::CSSAnimation;

typedef mozilla::ComputedTiming::AnimationPhase AnimationPhase;

////////////////////////// CSSAnimation ////////////////////////////

JSObject*
CSSAnimation::WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto)
{
  return dom::CSSAnimation_Binding::Wrap(aCx, this, aGivenProto);
}

mozilla::dom::Promise*
CSSAnimation::GetReady(ErrorResult& aRv)
{
  FlushUnanimatedStyle();
  return Animation::GetReady(aRv);
}

void
CSSAnimation::Play(ErrorResult &aRv, LimitBehavior aLimitBehavior)
{
  mPauseShouldStick = false;
  Animation::Play(aRv, aLimitBehavior);
}

void
CSSAnimation::Pause(ErrorResult& aRv)
{
  mPauseShouldStick = true;
  Animation::Pause(aRv);
}

AnimationPlayState
CSSAnimation::PlayStateFromJS() const
{
  // Flush style to ensure that any properties controlling animation state
  // (e.g. animation-play-state) are fully updated.
  FlushUnanimatedStyle();
  return Animation::PlayStateFromJS();
}

bool
CSSAnimation::PendingFromJS() const
{
  // Flush style since, for example, if the animation-play-state was just
  // changed its possible we should now be pending.
  FlushUnanimatedStyle();
  return Animation::PendingFromJS();
}

void
CSSAnimation::PlayFromJS(ErrorResult& aRv)
{
  // Note that flushing style below might trigger calls to
  // PlayFromStyle()/PauseFromStyle() on this object.
  FlushUnanimatedStyle();
  Animation::PlayFromJS(aRv);
}

void
CSSAnimation::PlayFromStyle()
{
  mIsStylePaused = false;
  if (!mPauseShouldStick) {
    ErrorResult rv;
    Animation::Play(rv, Animation::LimitBehavior::Continue);
    // play() should not throw when LimitBehavior is Continue
    MOZ_ASSERT(!rv.Failed(), "Unexpected exception playing animation");
  }
}

void
CSSAnimation::PauseFromStyle()
{
  // Check if the pause state is being overridden
  if (mIsStylePaused) {
    return;
  }

  mIsStylePaused = true;
  ErrorResult rv;
  Animation::Pause(rv);
  // pause() should only throw when *all* of the following conditions are true:
  // - we are in the idle state, and
  // - we have a negative playback rate, and
  // - we have an infinitely repeating animation
  // The first two conditions will never happen under regular style processing
  // but could happen if an author made modifications to the Animation object
  // and then updated animation-play-state. It's an unusual case and there's
  // no obvious way to pass on the exception information so we just silently
  // fail for now.
  if (rv.Failed()) {
    NS_WARNING("Unexpected exception pausing animation - silently failing");
  }
}

void
CSSAnimation::Tick()
{
  Animation::Tick();
  QueueEvents();
}

bool
CSSAnimation::HasLowerCompositeOrderThan(const CSSAnimation& aOther) const
{
  MOZ_ASSERT(IsTiedToMarkup() && aOther.IsTiedToMarkup(),
             "Should only be called for CSS animations that are sorted "
             "as CSS animations (i.e. tied to CSS markup)");

  // 0. Object-equality case
  if (&aOther == this) {
    return false;
  }

  // 1. Sort by document order
  if (!mOwningElement.Equals(aOther.mOwningElement)) {
    return mOwningElement.LessThan(
      const_cast<CSSAnimation*>(this)->CachedChildIndexRef(),
      aOther.mOwningElement,
      const_cast<CSSAnimation*>(&aOther)->CachedChildIndexRef());
  }

  // 2. (Same element and pseudo): Sort by position in animation-name
  return mAnimationIndex < aOther.mAnimationIndex;
}

void
CSSAnimation::QueueEvents(const StickyTimeDuration& aActiveTime)
{
  // If the animation is pending, we ignore animation events until we finish
  // pending.
  if (mPendingState != PendingState::NotPending) {
    return;
  }

  // CSS animations dispatch events at their owning element. This allows
  // script to repurpose a CSS animation to target a different element,
  // to use a group effect (which has no obvious "target element"), or
  // to remove the animation effect altogether whilst still getting
  // animation events.
  //
  // It does mean, however, that for a CSS animation that has no owning
  // element (e.g. it was created using the CSSAnimation constructor or
  // disassociated from CSS) no events are fired. If it becomes desirable
  // for these animations to still fire events we should spec the concept
  // of the "original owning element" or "event target" and allow script
  // to set it when creating a CSSAnimation object.
  if (!mOwningElement.IsSet()) {
    return;
  }

  nsPresContext* presContext = mOwningElement.GetPresContext();
  if (!presContext) {
    return;
  }

  uint64_t currentIteration = 0;
  ComputedTiming::AnimationPhase currentPhase;
  StickyTimeDuration intervalStartTime;
  StickyTimeDuration intervalEndTime;
  StickyTimeDuration iterationStartTime;

  if (!mEffect) {
    currentPhase = GetAnimationPhaseWithoutEffect
      <ComputedTiming::AnimationPhase>(*this);
    if (currentPhase == mPreviousPhase) {
      return;
    }
  } else {
    ComputedTiming computedTiming = mEffect->GetComputedTiming();
    currentPhase = computedTiming.mPhase;
    currentIteration = computedTiming.mCurrentIteration;
    if (currentPhase == mPreviousPhase &&
        currentIteration == mPreviousIteration) {
      return;
    }
    intervalStartTime = IntervalStartTime(computedTiming.mActiveDuration);
    intervalEndTime = IntervalEndTime(computedTiming.mActiveDuration);

    uint64_t iterationBoundary = mPreviousIteration > currentIteration
                                 ? currentIteration + 1
                                 : currentIteration;
    iterationStartTime  =
      computedTiming.mDuration.MultDouble(
        (iterationBoundary - computedTiming.mIterationStart));
  }

  TimeStamp startTimeStamp     = ElapsedTimeToTimeStamp(intervalStartTime);
  TimeStamp endTimeStamp       = ElapsedTimeToTimeStamp(intervalEndTime);
  TimeStamp iterationTimeStamp = ElapsedTimeToTimeStamp(iterationStartTime);

  AutoTArray<AnimationEventInfo, 2> events;

  auto appendAnimationEvent = [&](EventMessage aMessage,
                                  const StickyTimeDuration& aElapsedTime,
                                  const TimeStamp& aScheduledEventTimeStamp) {
    double elapsedTime = aElapsedTime.ToSeconds();
    if (aMessage == eAnimationCancel) {
      // 0 is an inappropriate value for this callsite. What we need to do is
      // use a single random value for all increasing times reportable.
      // That is to say, whenever elapsedTime goes negative (because an
      // animation restarts, something rewinds the animation, or otherwise)
      // a new random value for the mix-in must be generated.
      elapsedTime = nsRFPService::ReduceTimePrecisionAsSecs(elapsedTime, 0, TimerPrecisionType::RFPOnly);
    }
    events.AppendElement(AnimationEventInfo(mAnimationName,
                                            mOwningElement.Target(),
                                            aMessage,
                                            elapsedTime,
                                            aScheduledEventTimeStamp,
                                            this));
  };

  // Handle cancel event first
  if ((mPreviousPhase != AnimationPhase::Idle &&
       mPreviousPhase != AnimationPhase::After) &&
      currentPhase == AnimationPhase::Idle) {
    appendAnimationEvent(eAnimationCancel,
                         aActiveTime,
                         GetTimelineCurrentTimeAsTimeStamp());
  }

  switch (mPreviousPhase) {
    case AnimationPhase::Idle:
    case AnimationPhase::Before:
      if (currentPhase == AnimationPhase::Active) {
        appendAnimationEvent(eAnimationStart,
                             intervalStartTime,
                             startTimeStamp);
      } else if (currentPhase == AnimationPhase::After) {
        appendAnimationEvent(eAnimationStart,
                             intervalStartTime,
                             startTimeStamp);
        appendAnimationEvent(eAnimationEnd, intervalEndTime, endTimeStamp);
      }
      break;
    case AnimationPhase::Active:
      if (currentPhase == AnimationPhase::Before) {
        appendAnimationEvent(eAnimationEnd, intervalStartTime, startTimeStamp);
      } else if (currentPhase == AnimationPhase::Active) {
        // The currentIteration must have changed or element we would have
        // returned early above.
        MOZ_ASSERT(currentIteration != mPreviousIteration);
        appendAnimationEvent(eAnimationIteration,
                             iterationStartTime,
                             iterationTimeStamp);
      } else if (currentPhase == AnimationPhase::After) {
        appendAnimationEvent(eAnimationEnd, intervalEndTime, endTimeStamp);
      }
      break;
    case AnimationPhase::After:
      if (currentPhase == AnimationPhase::Before) {
        appendAnimationEvent(eAnimationStart, intervalEndTime, startTimeStamp);
        appendAnimationEvent(eAnimationEnd, intervalStartTime, endTimeStamp);
      } else if (currentPhase == AnimationPhase::Active) {
        appendAnimationEvent(eAnimationStart, intervalEndTime, endTimeStamp);
      }
      break;
  }
  mPreviousPhase = currentPhase;
  mPreviousIteration = currentIteration;

  if (!events.IsEmpty()) {
    presContext->AnimationEventDispatcher()->QueueEvents(std::move(events));
  }
}

void
CSSAnimation::UpdateTiming(SeekFlag aSeekFlag, SyncNotifyFlag aSyncNotifyFlag)
{
  if (mNeedsNewAnimationIndexWhenRun &&
      PlayState() != AnimationPlayState::Idle) {
    mAnimationIndex = sNextAnimationIndex++;
    mNeedsNewAnimationIndexWhenRun = false;
  }

  Animation::UpdateTiming(aSeekFlag, aSyncNotifyFlag);
}

////////////////////////// nsAnimationManager ////////////////////////////

// Find the matching animation by |aName| in the old list
// of animations and remove the matched animation from the list.
static already_AddRefed<CSSAnimation>
PopExistingAnimation(const nsAtom* aName,
                     nsAnimationManager::CSSAnimationCollection* aCollection)
{
  if (!aCollection) {
    return nullptr;
  }

  // Animations are stored in reverse order to how they appear in the
  // animation-name property. However, we want to match animations beginning
  // from the end of the animation-name list, so we iterate *forwards*
  // through the collection.
  for (size_t idx = 0, length = aCollection->mAnimations.Length();
       idx != length; ++ idx) {
    CSSAnimation* cssAnim = aCollection->mAnimations[idx];
    if (cssAnim->AnimationName() == aName) {
      RefPtr<CSSAnimation> match = cssAnim;
      aCollection->mAnimations.RemoveElementAt(idx);
      return match.forget();
    }
  }

  return nullptr;
}


class MOZ_STACK_CLASS ServoCSSAnimationBuilder final {
public:
  explicit ServoCSSAnimationBuilder(const ComputedStyle* aComputedStyle)
    : mComputedStyle(aComputedStyle)
  {
    MOZ_ASSERT(aComputedStyle);
  }

  bool BuildKeyframes(const Element& aElement,
                      nsPresContext* aPresContext,
                      nsAtom* aName,
                      const nsTimingFunction& aTimingFunction,
                      nsTArray<Keyframe>& aKeyframes)
  {
    return aPresContext->StyleSet()->GetKeyframesForName(
        aElement,
        *mComputedStyle,
        aName,
        aTimingFunction,
        aKeyframes);
  }
  void SetKeyframes(KeyframeEffect& aEffect, nsTArray<Keyframe>&& aKeyframes)
  {
    aEffect.SetKeyframes(std::move(aKeyframes), mComputedStyle);
  }

  // Currently all the animation building code in this file is based on
  // assumption that creating and removing animations should *not* trigger
  // additional restyles since those changes will be handled within the same
  // restyle.
  //
  // While that is true for the Gecko style backend, it is not true for the
  // Servo style backend where we want restyles to be triggered so that we
  // perform a second animation restyle where we will incorporate the changes
  // arising from creating and removing animations.
  //
  // Fortunately, our attempts to avoid posting extra restyles as part of the
  // processing here are imperfect and most of the time we happen to post
  // them anyway. Occasionally, however, we don't. For example, we don't post
  // a restyle when we create a new animation whose an animation index matches
  // the default value it was given already (which is typically only true when
  // the CSSAnimation we create is the first Animation created in a particular
  // content process).
  //
  // As a result, when we are using the Servo backend, whenever we have an added
  // or removed animation we need to explicitly trigger a restyle.
  //
  // This code should eventually disappear along with the Gecko style backend
  // and we should simply call Play() / Pause() / Cancel() etc. which will
  // post the required restyles.
  void NotifyNewOrRemovedAnimation(const Animation& aAnimation)
  {
    dom::AnimationEffect* effect = aAnimation.GetEffect();
    if (!effect) {
      return;
    }

    KeyframeEffect* keyframeEffect = effect->AsKeyframeEffect();
    if (!keyframeEffect) {
      return;
    }

    keyframeEffect->RequestRestyle(EffectCompositor::RestyleType::Standard);
  }

private:
  const ComputedStyle* mComputedStyle;
};


static void
UpdateOldAnimationPropertiesWithNew(
    CSSAnimation& aOld,
    TimingParams&& aNewTiming,
    nsTArray<Keyframe>&& aNewKeyframes,
    bool aNewIsStylePaused,
    ServoCSSAnimationBuilder& aBuilder)
{
  bool animationChanged = false;

  // Update the old from the new so we can keep the original object
  // identity (and any expando properties attached to it).
  if (aOld.GetEffect()) {
    dom::AnimationEffect* oldEffect = aOld.GetEffect();
    animationChanged = oldEffect->SpecifiedTiming() != aNewTiming;
    oldEffect->SetSpecifiedTiming(std::move(aNewTiming));

    KeyframeEffect* oldKeyframeEffect = oldEffect->AsKeyframeEffect();
    if (oldKeyframeEffect) {
      aBuilder.SetKeyframes(*oldKeyframeEffect, std::move(aNewKeyframes));
    }
  }

  // Handle changes in play state. If the animation is idle, however,
  // changes to animation-play-state should *not* restart it.
  if (aOld.PlayState() != AnimationPlayState::Idle) {
    // CSSAnimation takes care of override behavior so that,
    // for example, if the author has called pause(), that will
    // override the animation-play-state.
    // (We should check aNew->IsStylePaused() but that requires
    //  downcasting to CSSAnimation and we happen to know that
    //  aNew will only ever be paused by calling PauseFromStyle
    //  making IsPausedOrPausing synonymous in this case.)
    if (!aOld.IsStylePaused() && aNewIsStylePaused) {
      aOld.PauseFromStyle();
      animationChanged = true;
    } else if (aOld.IsStylePaused() && !aNewIsStylePaused) {
      aOld.PlayFromStyle();
      animationChanged = true;
    }
  }

  // Updating the effect timing above might already have caused the
  // animation to become irrelevant so only add a changed record if
  // the animation is still relevant.
  if (animationChanged && aOld.IsRelevant()) {
    nsNodeUtils::AnimationChanged(&aOld);
  }
}

// Returns a new animation set up with given StyleAnimation.
// Or returns an existing animation matching StyleAnimation's name updated
// with the new StyleAnimation.
static already_AddRefed<CSSAnimation>
BuildAnimation(nsPresContext* aPresContext,
               const NonOwningAnimationTarget& aTarget,
               const nsStyleDisplay& aStyleDisplay,
               uint32_t animIdx,
               ServoCSSAnimationBuilder& aBuilder,
               nsAnimationManager::CSSAnimationCollection* aCollection)
{
  MOZ_ASSERT(aPresContext);

  nsAtom* animationName = aStyleDisplay.GetAnimationName(animIdx);
  nsTArray<Keyframe> keyframes;
  if (!aBuilder.BuildKeyframes(*aTarget.mElement,
                               aPresContext,
                               animationName,
                               aStyleDisplay.GetAnimationTimingFunction(animIdx),
                               keyframes)) {
    return nullptr;
  }

  TimingParams timing =
    TimingParamsFromCSSParams(aStyleDisplay.GetAnimationDuration(animIdx),
                              aStyleDisplay.GetAnimationDelay(animIdx),
                              aStyleDisplay.GetAnimationIterationCount(animIdx),
                              aStyleDisplay.GetAnimationDirection(animIdx),
                              aStyleDisplay.GetAnimationFillMode(animIdx));

  bool isStylePaused =
    aStyleDisplay.GetAnimationPlayState(animIdx) ==
      StyleAnimationPlayState::Paused;

  // Find the matching animation with animation name in the old list
  // of animations and remove the matched animation from the list.
  RefPtr<CSSAnimation> oldAnim =
    PopExistingAnimation(animationName, aCollection);

  if (oldAnim) {
    // Copy over the start times and (if still paused) pause starts
    // for each animation (matching on name only) that was also in the
    // old list of animations.
    // This means that we honor dynamic changes, which isn't what the
    // spec says to do, but WebKit seems to honor at least some of
    // them.  See
    // http://lists.w3.org/Archives/Public/www-style/2011Apr/0079.html
    // In order to honor what the spec said, we'd copy more data over.
    UpdateOldAnimationPropertiesWithNew(*oldAnim,
                                        std::move(timing),
                                        std::move(keyframes),
                                        isStylePaused,
                                        aBuilder);
    return oldAnim.forget();
  }

  // mTarget is non-null here, so we emplace it directly.
  Maybe<OwningAnimationTarget> target;
  target.emplace(aTarget.mElement, aTarget.mPseudoType);
  KeyframeEffectParams effectOptions;
  RefPtr<KeyframeEffect> effect =
    new KeyframeEffect(aPresContext->Document(), target, std::move(timing), effectOptions);

  aBuilder.SetKeyframes(*effect, std::move(keyframes));

  RefPtr<CSSAnimation> animation =
    new CSSAnimation(aPresContext->Document()->GetScopeObject(), animationName);
  animation->SetOwningElement(
    OwningElementRef(*aTarget.mElement, aTarget.mPseudoType));

  animation->SetTimelineNoUpdate(aTarget.mElement->OwnerDoc()->Timeline());
  animation->SetEffectNoUpdate(effect);

  if (isStylePaused) {
    animation->PauseFromStyle();
  } else {
    animation->PlayFromStyle();
  }

  aBuilder.NotifyNewOrRemovedAnimation(*animation);

  return animation.forget();
}


static nsAnimationManager::OwningCSSAnimationPtrArray
BuildAnimations(nsPresContext* aPresContext,
                const NonOwningAnimationTarget& aTarget,
                const nsStyleDisplay& aStyleDisplay,
                ServoCSSAnimationBuilder& aBuilder,
                nsAnimationManager::CSSAnimationCollection* aCollection,
                nsTHashtable<nsRefPtrHashKey<nsAtom>>& aReferencedAnimations)
{
  nsAnimationManager::OwningCSSAnimationPtrArray result;

  for (size_t animIdx = aStyleDisplay.mAnimationNameCount; animIdx-- != 0;) {
    nsAtom* name = aStyleDisplay.GetAnimationName(animIdx);
    // CSS Animations whose animation-name does not match a @keyframes rule do
    // not generate animation events. This includes when the animation-name is
    // "none" which is represented by an empty name in the StyleAnimation.
    // Since such animations neither affect style nor dispatch events, we do
    // not generate a corresponding CSSAnimation for them.
    if (name == nsGkAtoms::_empty) {
      continue;
    }

    aReferencedAnimations.PutEntry(name);
    RefPtr<CSSAnimation> dest = BuildAnimation(aPresContext,
                                               aTarget,
                                               aStyleDisplay,
                                               animIdx,
                                               aBuilder,
                                               aCollection);
    if (!dest) {
      continue;
    }

    dest->SetAnimationIndex(static_cast<uint64_t>(animIdx));
    result.AppendElement(dest);
  }
  return result;
}


void
nsAnimationManager::UpdateAnimations(
  dom::Element* aElement,
  CSSPseudoElementType aPseudoType,
  const ComputedStyle* aComputedStyle)
{
  MOZ_ASSERT(mPresContext->IsDynamic(),
             "Should not update animations for print or print preview");
  MOZ_ASSERT(aElement->IsInComposedDoc(),
             "Should not update animations that are not attached to the "
             "document tree");

  const nsStyleDisplay* disp = aComputedStyle
    ? aComputedStyle->ComputedData()->GetStyleDisplay()
    : nullptr;

  if (!disp || disp->mDisplay == StyleDisplay::None) {
    // If we are in a display:none subtree we will have no computed values.
    // However, if we are on the root of display:none subtree, the computed
    // values might not have been cleared yet.
    // In either case, since CSS animations should not run in display:none
    // subtrees we should stop (actually, destroy) any animations on this
    // element here.
    StopAnimationsForElement(aElement, aPseudoType);
    return;
  }

  NonOwningAnimationTarget target(aElement, aPseudoType);
  ServoCSSAnimationBuilder builder(aComputedStyle);

  DoUpdateAnimations(target, *disp, builder);
}

void
nsAnimationManager::DoUpdateAnimations(
  const NonOwningAnimationTarget& aTarget,
  const nsStyleDisplay& aStyleDisplay,
  ServoCSSAnimationBuilder& aBuilder)
{
  // Everything that causes our animation data to change triggers a
  // style change, which in turn triggers a non-animation restyle.
  // Likewise, when we initially construct frames, we're not in a
  // style change, but also not in an animation restyle.

  CSSAnimationCollection* collection =
    CSSAnimationCollection::GetAnimationCollection(aTarget.mElement,
                                                   aTarget.mPseudoType);
  if (!collection &&
      aStyleDisplay.mAnimationNameCount == 1 &&
      aStyleDisplay.mAnimations[0].GetName() == nsGkAtoms::_empty) {
    return;
  }

  nsAutoAnimationMutationBatch mb(aTarget.mElement->OwnerDoc());

  // Build the updated animations list, extracting matching animations from
  // the existing collection as we go.
  OwningCSSAnimationPtrArray newAnimations =
    BuildAnimations(mPresContext,
                    aTarget,
                    aStyleDisplay,
                    aBuilder,
                    collection,
                    mMaybeReferencedAnimations);

  if (newAnimations.IsEmpty()) {
    if (collection) {
      collection->Destroy();
    }
    return;
  }

  if (!collection) {
    bool createdCollection = false;
    collection =
      CSSAnimationCollection::GetOrCreateAnimationCollection(
        aTarget.mElement, aTarget.mPseudoType, &createdCollection);
    if (!collection) {
      MOZ_ASSERT(!createdCollection, "outparam should agree with return value");
      NS_WARNING("allocating collection failed");
      return;
    }

    if (createdCollection) {
      AddElementCollection(collection);
    }
  }
  collection->mAnimations.SwapElements(newAnimations);

  // Cancel removed animations
  for (size_t newAnimIdx = newAnimations.Length(); newAnimIdx-- != 0; ) {
    aBuilder.NotifyNewOrRemovedAnimation(*newAnimations[newAnimIdx]);
    newAnimations[newAnimIdx]->CancelFromStyle();
  }
}