When updating the cascade results between transitions and animations, if we
detect a change we force an update by taking the following steps:
a. Updating the animation generation on the restyle manager
b. Updating the animation generation on the collection
c. Iterating over all the properties animated by the collection and, for
each property that we can animate on the compositor, posting a restyle
event with the appropriate change hint (nsChangeHint_UpdateTransformLayer
or nsChangeHint_UpdateTransformOpacity)
d. Marking the collection as needing refreshes
e. Clearing the style rule refresh time so we generate a new style rule in
EnsureStyleRuleFor
As it turns out, the newly-added
AnimationCollection::RequestRestyle(RestyleType::Layer) already performs a, b,
d, and e. It also:
* Ensures we are observing the refresh driver if need be (should have no effect
in this case)
* Clears the last animation style update time on the pres context so that
subsequent calls to FlushPendingNotifications will update animation style
(it seems like we probably should have been doing this for changes to cascade
results anyway)
* Posts a restyle event with restyle hint eRestyle_CSSTransitions or
eRestyle_CSSAnimations
* Marks the document as needing a style flush (irrelevant since posting
a restyle event does this anyway)
The only missing piece that would prevent using RequestRestyle in place of this
code when updating cascade results is (c) from the list above. However, (c)
should not be necessary since ElementRestyler::AddLayerChangesForAnimation()
explicitly checks for out-of-date layer animation generation numbers and adds
the appropriate change hints (nsChangeHint_UpdateTransformLayer etc.) to the
change list.
We currently have a series of methods that clobber various bits of animation
state to force animations on layers to be updated. This aligns closely with
the restyle code introduced in this patch series.
By re-using RequestRestyle when updating animations on layers, not only should
we be able to simplify the code somewhat but, in future, we should also be able
to have Animation objects use the same mechanism to update layers during
a regular tick.
For example, currently we have a bug where when an animation starts after
a delay with the same value as the backwards fill then we don't send the
animation to the compositor right away (see
https://dxr.mozilla.org/mozilla-central/rev/d6ea652c579992daa9041cc9718bb7c6abefbc91/layout/style/test/test_animations_omta.html#287).
By adding this Restyle::Layer value we should be able to fix that in future.
EnsureStyleRuleFor contains logic for performing throttled updates to the style
rule but it is only used in one case: inside
nsTransitionManager::UpdateCascadeResults to determine what properties are
being animated by CSS animations.
We would like to remove throttling logic from EnsureStyleRuleFor altogether but
if that one case where it is currently used is run on every tick then removing
this logic could effectively mean we end up updating the style rule on every
tick. Fortunately nsTransitionManager::UpdateCascadeResults is only called
in the following cases:
1. From nsTransitionManager::StyleContextChanged (via
TransitionManager::UpdateCascadeResultsWithTransitions), when we are
processing style changes for transitions.
2. From AnimationCollection::EnsureStyleRuleFor (via
nsAnimationManager::MaybeUpdateCascadeResults and
nsTransitionManager::UpdateCascadeResultsWithAnimations), when we are
updating the animation style rule from CSS animations.
3. From nsAnimationManager::CheckAnimationRule (via
TransitionManager::UpdateCascadeResultsWithAnimationsToBeDestroyed), when
we are processing style changes for CSS animations.
None of these things should be happenning on a regular throttle-able tick so by
removing this logic we shouldn't be causing any additional work.
I have verified, using a test case that combines transitions and animations on
the same property, that we have the same behavior with regard to calling
EnsureStyleRuleFor both before and after this patch (specifically we avoid
calling it altogether while running only the transition but when the animation
starts and clobbers the transition we end up calling EnsureStyleRuleFor once on
each tick).
In preparation for ultimately being able to run animations without a manager,
this patch moves the request restyle code from FlushAnimations to
Animation::Tick. (Ultimately most of this functionality should move to the
KeyframeEffect but for now Animation is fine.)
