Bug 1923208 - Store animation index into AnimationEventDispatcher. r=layout-reviewers,birtles,jwatt,emilio

We need this information when comparing the cancelled transitions/animations
in the following patches.

Note that we have to reorder the calling of `Animation::Cancel()` and
the update of `mAnimationIndex` to make sure we enqueue the cancel event
with the correct `mAnimationIndex`.

Differential Revision: https://phabricator.services.mozilla.com/D227110

dom/animation/AnimationEventDispatcher.h

@@ -29,6 +29,12 @@ struct AnimationEventInfo {
     OwningAnimationTarget mTarget;
     const EventMessage mMessage;
     const double mElapsedTime;
+    // The transition generation or animation relative position in the global
+    // animation list. We use this information to determine the order of
+    // cancelled transitions or animations. (i.e. We override the animation
+    // index of the cancelled transitions/animations because their animation
+    // indexes have been changed.)
+    const uint64_t mAnimationIndex;
     // FIXME(emilio): is this needed? This preserves behavior from before
     // bug 1847200, but it's unclear what the timeStamp of the event should be.
     // See also https://github.com/w3c/csswg-drafts/issues/9167
@@ -73,13 +79,14 @@ struct AnimationEventInfo {
   AnimationEventInfo(RefPtr<nsAtom> aAnimationName,
                      const NonOwningAnimationTarget& aTarget,
                      EventMessage aMessage, double aElapsedTime,
+                     uint64_t aAnimationIndex,
                      const TimeStamp& aScheduledEventTimeStamp,
                      dom::Animation* aAnimation)
       : mAnimation(aAnimation),
         mScheduledEventTimeStamp(aScheduledEventTimeStamp),
         mData(CssAnimationData{
             {OwningAnimationTarget(aTarget.mElement, aTarget.mPseudoType),
-             aMessage, aElapsedTime},
+             aMessage, aElapsedTime, aAnimationIndex},
             std::move(aAnimationName)}) {
     if (profiler_thread_is_being_profiled_for_markers()) {
       MaybeAddMarker();
@@ -90,13 +97,14 @@ struct AnimationEventInfo {
   AnimationEventInfo(const AnimatedPropertyID& aProperty,
                      const NonOwningAnimationTarget& aTarget,
                      EventMessage aMessage, double aElapsedTime,
+                     uint64_t aTransitionGeneration,
                      const TimeStamp& aScheduledEventTimeStamp,
                      dom::Animation* aAnimation)
       : mAnimation(aAnimation),
         mScheduledEventTimeStamp(aScheduledEventTimeStamp),
         mData(CssTransitionData{
             {OwningAnimationTarget(aTarget.mElement, aTarget.mPseudoType),
-             aMessage, aElapsedTime},
+             aMessage, aElapsedTime, aTransitionGeneration},
             aProperty}) {
     if (profiler_thread_is_being_profiled_for_markers()) {
       MaybeAddMarker();

dom/animation/CSSAnimation.cpp

@@ -230,9 +230,9 @@ void CSSAnimation::QueueEvents(const StickyTimeDuration& aActiveTime) {
       elapsedTime = nsRFPService::ReduceTimePrecisionAsSecsRFPOnly(
           elapsedTime, 0, mRTPCallerType);
     }
-    events.AppendElement(
-        AnimationEventInfo(mAnimationName, mOwningElement.Target(), aMessage,
-                           elapsedTime, aScheduledEventTimeStamp, this));
+    events.AppendElement(AnimationEventInfo(
+        mAnimationName, mOwningElement.Target(), aMessage, elapsedTime,
+        mAnimationIndex, aScheduledEventTimeStamp, this));
   };
 
   // Handle cancel event first

dom/animation/CSSAnimation.h

@@ -84,6 +84,8 @@ class CSSAnimation final : public Animation {
   void PlayFromStyle();
   void PauseFromStyle();
   void CancelFromStyle(PostRestyleMode aPostRestyle) {
+    Animation::Cancel(aPostRestyle);
+
     // When an animation is disassociated with style it enters an odd state
     // where its composite order is undefined until it first transitions
     // out of the idle state.
@@ -94,11 +96,13 @@ class CSSAnimation final : public Animation {
     // if it had been added to the end of the global animation list so that
     // its sort order is defined. We'll update this index again once the
     // animation leaves the idle state.
+    //
+    // Note: We have to update |mAnimationIndex| after calling
+    // Animation::Cancel(), which enqueues animationcancel event, to make sure
+    // we have the correct |mAnimationIndex| in AnimationEventInfo.
     mAnimationIndex = sNextAnimationIndex++;
     mNeedsNewAnimationIndexWhenRun = true;
 
-    Animation::Cancel(aPostRestyle);
-
     // We need to do this *after* calling Cancel() since
     // Cancel() might synchronously trigger a cancel event for which
     // we need an owning element to target the event at.

dom/animation/CSSTransition.cpp

@@ -120,7 +120,7 @@ void CSSTransition::QueueEvents(const StickyTimeDuration& aActiveTime) {
     }
     events.AppendElement(AnimationEventInfo(
         TransitionProperty(), mOwningElement.Target(), aMessage, elapsedTime,
-        aScheduledEventTimeStamp, this));
+        mAnimationIndex, aScheduledEventTimeStamp, this));
   };
 
   // Handle cancel events first

dom/animation/CSSTransition.h

@@ -51,17 +51,21 @@ class CSSTransition final : public Animation {
   }
 
   void CancelFromStyle(PostRestyleMode aPostRestyle) {
+    Animation::Cancel(aPostRestyle);
+
     // The animation index to use for compositing will be established when
     // this transition next transitions out of the idle state but we still
     // update it now so that the sort order of this transition remains
     // defined until that moment.
     //
     // See longer explanation in CSSAnimation::CancelFromStyle.
+    //
+    // Note: We have to update |mAnimationIndex| after calling
+    // Animation::Cancel(), which enqueues transitioncancel event, to make sure
+    // we have the correct |mAnimationIndex| in AnimationEventInfo.
     mAnimationIndex = sNextAnimationIndex++;
     mNeedsNewAnimationIndexWhenRun = true;
 
-    Animation::Cancel(aPostRestyle);
-
     // It is important we do this *after* calling Cancel().
     // This is because Cancel() will end up posting a restyle and
     // that restyle should target the *transitions* level of the cascade.