We want to move the newly-introduced RequestRestyle call from FlushAnimations
to Animation::Tick. However, nsAnimationManager::CheckAnimationRule calls
Animation::Tick so this would cause us to start posting animation restyles
within a restyle.
Typically, Animations have an effect (currently there is only one type of
effect: KeyframeEffectReadOnly) and when there is any change in timing they
pass it down to their effect. However, the Animation is dependent on the
duration of the effect for determining if it is "finished" or not. As a result,
when an effect's timing changes, the owning Animation needs to know.
(The way this *should* work is that effects should tell their animation or
trigger some chain of events that causes animation's to update themselves.
However, the current implementation of effects is fairly primitive and does
not do this or even have a reference to the owning Animation. When we
implement the script API for updating the timing properties of effects we will
have to fix this but for now it is up to code in layout/style to update the
Animation when it touches the corresponding effect's timing.)
nsAnimationManager::CheckAnimationRule currently does this by calling
Animation::Tick() which ensures the Animation's finished state is updated
accordingly.
Ultimately we want to ensure that Animation::Tick is called exactly once per
frame (and at the appropriate point in that frame) so we'd like to remove this
call from CheckAnimationRule.
This patch achieves that by:
* Making Animation::SetEffect update the animation's timing - this is necessary
for animations that are created by CheckAnimationRule and will be
necessary when once we make Animation.effect writeable from script anyway.
* Calling Animation::SetEffect even for the case when we are updating the
existing effect.
Another side-effect of calling Animation::Tick within
nsAnimationManager::CheckAnimationRule is that CSSAnimation::Tick queues
events. There are some tests (e.g. layout/style/test/test_animations.html) that
assume that animationstart events are dispatched immediately when new
animations are created. That will change with bug 1134163 but for now we
should maintain this existing behavior since changing this might introduce
compatibility issues that are best dealt with as a separate bug rather than
blocking this refactoring. To that end, this patch also explicitly queues
animationstart events for newly-created animations.
nsTransitionManager::WillRefresh and nsAnimationManager::WillRefresh are now
identical and all methods they call exist on CommonAnimationManager so we
can unify them there.
The implementations of FlushAnimations and FlushTransitions should now be all
but equivalent so this patch combines them into a single implementation on
CommonAnimationManager.
Regarding some of the minor differences between the two methods:
* The combined implementation drops the check for an empty list of collections
found only in FlushTransitions. This seems like a very minor optimization
that could possibly cause us to fail to unregister from the refresh driver
if we forgot to do so when removing the last collection.
* The combined implementation uses the loop implementation from FlushAnimations
since it is more compact.
This patch also removes the extra nested scope since it doesn't seem necessary.
There are a couple of assertions that only exist in FlushTransitions (and not
FlushAnimations). This patch moves them to RequestRestyle since they appear to
apply to either transitions or animations equally. By eliminating this
difference between FlushTransitions and FlushAnimations we should then be
in a position to combine them into a common method on the base class.
This patch moves the additional checks (beyond those of Animation::CanThrottle)
from FlushAnimations/FlushTransitions to AnimationCollection::RequestRestyle.
These checks are on a per-collection basis hence it makes sense for the
collection to perform them. This also moves logic out of the managers which is
needed if we want to support script-based animations without introducing another
manager.
Ultimately we want to move throttling logic to AnimationCollection and
Animation::Tick (and later to KeyframeEffect::SetParentTime). This is so that
we can support script-generated animations without having to introduce yet
another manager.
To that end this patch introduces a method on AnimationCollection that can be
called from Animation::Tick to perform the necessary notifications needed to
update style.
Later in this patch series we will extend RequestRestyle to incorporate more of
the throttling logic and further extend it to cover some of the other
notifications such as updating layers.
This patch tracks whether or not we have already posted a restyle for animation
to avoid making redundant calls. Calls to nsIDocument::SetNeedStyleFlush are
cheap and more difficult to detect when they have completed so we don't filter
redundant calls in the Restyle::Throttled case.
If mHasPendingAnimationRestyle is set and AnimationCommon::EnsureStyleRuleFor
is *never* called then we could arrive at situation where we fail to make post
further restyles for animation.
I have verified that if we fail to reset mHasPendingAnimationRestyle at the
appropriate point (e.g. resetting it at the end of EnsureStyleRuleFor *after*
the early-returns) then a number of existing tests fail.
Furthermore, I have observed that it is reset by the beginning of each tick
in almost every case except for a few instances of browser mochitests such as
browser/components/customizableui/test/browser_1007336_lwthemes_in_customize_mode.js.
In this case, during the async cleanup of the test, we have an opacity
transition on a vbox element that becomes display:none and appears to be skipped
during restyling. However, even in this case, EnsureStyleRuleFor is called
within one or at most two ticks and mHasPendingAnimationRestyle flag is cleared
(i.e. it does not get stuck).
In FlushTransitions and FlushAnimations we use different mechanisms to see if a
transition/animation can be throttled on the current tick.
FlushTransitions calls Animation::CanThrottle whilst FlushAnimations calls
EnsureStyleRuleFor and checks if the rule has changed or not. These are not as
completely different as they might seem at first since, internally,
EnsureStyleRuleFor calls Animation::CanThrottle.
We would like to unify this behavior and simply use Animation::CanThrottle in
FlushAnimations as we do in FlushTransitions.
First, however, we have to account for the differences in these approaches:
1. Using the result of EnsureStyleRuleFor means we may *not* call
PostRestyleForAnimation if an animation collection's mNeedsRefreshes member
is false.
This member is false when all animations have finished (or there are no
animations in the collection). In this case EnsureStyleRuleFor will not
update the style rule and we will end up assuming the tick can be throttled.
*However*, in the case that all animations are finished
Animation::CanThrottle will *also* return true (technically it will return
false until we compose style for the first time after becoming finished but
beyond that one moment it will return true) so skipping this check by using
Animation::CanThrottle instead of EnsureStyleRuleFor should not
make a significant difference.
2. Using the result of EnsureStyleRuleFor will mean that if we have already
updated the style rule within a given tick we will avoid calling
PostRestyleForAnimation (and call SetNeedStyleFlush instead). This can
happen the first time we call FlushAnimations from
PresShell::FlushPendingNotifications. (When we call FlushAnimations from
nsAnimationManager::WillRefresh mStyleRuleRefreshTime will be stale and we
won't apply this optimization. Furthermore after the first call to
PresShell::FlushPendingNotifications we will typically skip calling
FlushAnimations since PresShell::StyleUpdateForAllAnimationsIsUpToDate will
typically return true).
This seems like a possibly useful optimization although it is surprising we
don't do the same for transitions. Note that this optimization applies
regardless of whether we are performing a throttleable flush or not. That is,
even if we pass CommonAnimationManager::Cannot_Throttle we will still end up
throttling the tick in this case. Furthermore, we will mark the document as
needing a style flush even though this does not appear to be necessary.
This patch copies this optimization (checking if mStyleRuleRefreshTime) to
FlushAnimations so we can maintain this behavior when calling
Animation::CanThrottle instead of EnsureStyleRuleFor. It also applies the
same behavior to FlushTransitions for consistency (and so we can later
combine FlushAnimations and FlushTransitions).
Note that we apply this optimization *before* calling Tick since it should
only apply once we have already Tick'ed the animations in the collection.
We will first hit FlushAnimations as a result of the refresh driver calling
nsAnimationManager/nsTransitionManager::WillRefresh at which point
mStyleRuleRefreshTime should be stale. Using this order not only saves
redundant work but also makes moving the restyle code to Animation later on
more straightforward.
(In future we will divorce WillRefresh and FlushAnimations and only call
Tick in WillRefresh and only perform this optimization FlushAnimations.)
3. Using the result of EnsureStyleRuleFor means that while checking if we can
throttle or not we also update the style rule in FlushAnimations. That seems
like an odd side-effect particularly since FlushTransitions doesn't do the
same thing.
There is no longer anything in FlushTransitions that modifies the set of
transitions. I believe this changed as of bug 960465, specifically changeset
https://hg.mozilla.org/mozilla-central/rev/b2ee72589c18, so that this code is
no longer needed.
By removing this we can further align FlushAnimations and FlushTransitions.
