bool
KeyframeEffectReadOnly::CanThrottle() const
{
// Unthrottle if we are not in effect or current. This will be the case when
// our owning animation has finished, is idle, or when we are in the delay
// phase (but without a backwards fill). In each case the computed progress
// value produced on each tick will be the same so we will skip requesting
// unnecessary restyles in NotifyAnimationTimingUpdated. Any calls we *do* get
// here will be because of a change in state (e.g. we are newly finished or
// newly no longer in effect) in which case we shouldn't throttle the sample.
if (!IsInEffect() || !IsCurrent()) {
return false;
}
nsIFrame* frame = GetAnimationFrame();
if (!frame) {
// There are two possible cases here.
// a) No target element
// b) The target element has no frame, e.g. because it is in a display:none
// subtree.
// In either case we can throttle the animation because there is no
// need to update on the main thread.
return true;
}
// We can throttle the animation if the animation is paint only and
// the target frame is out of view or the document is in background tabs.
if (CanIgnoreIfNotVisible()) {
nsIPresShell* presShell = GetPresShell();
if ((presShell && !presShell->IsActive()) ||
frame->IsScrolledOutOfView()) {
return true;
}
}
// First we need to check layer generation and transform overflow
// prior to the property.mIsRunningOnCompositor check because we should
// occasionally unthrottle these animations even if the animations are
// already running on compositor.
for (const LayerAnimationInfo::Record& record :
LayerAnimationInfo::sRecords) {
// Skip properties that are overridden by !important rules.
// (GetEffectiveAnimationOfProperty, as called by
// HasEffectiveAnimationOfProperty, only returns a property which is
// neither overridden by !important rules nor overridden by other
// animation.)
if (!HasEffectiveAnimationOfProperty(record.mProperty)) {
continue;
}
EffectSet* effectSet = EffectSet::GetEffectSet(mTarget->mElement,
mTarget->mPseudoType);
MOZ_ASSERT(effectSet, "CanThrottle should be called on an effect "
"associated with a target element");
layers::Layer* layer =
FrameLayerBuilder::GetDedicatedLayer(frame, record.mLayerType);
// Unthrottle if the layer needs to be brought up to date
if (!layer ||
effectSet->GetAnimationGeneration() !=
layer->GetAnimationGeneration()) {
return false;
}
// If this is a transform animation that affects the overflow region,
// we should unthrottle the animation periodically.
if (record.mProperty == eCSSProperty_transform &&
!CanThrottleTransformChanges(*frame)) {
return false;
}
}
for (const AnimationProperty& property : mProperties) {
if (!property.mIsRunningOnCompositor) {
return false;
}
}
return true;
}
void
Animation::ComposeStyle(RefPtr<AnimValuesStyleRule>& aStyleRule,
nsCSSPropertySet& aSetProperties,
bool& aStyleChanging)
{
if (!mEffect) {
return;
}
AnimationPlayState playState = PlayState();
if (playState == AnimationPlayState::Running ||
playState == AnimationPlayState::Pending) {
aStyleChanging = true;
}
if (!IsInEffect()) {
return;
}
// In order to prevent flicker, there are a few cases where we want to use
// a different time for rendering that would otherwise be returned by
// GetCurrentTime. These are:
//
// (a) For animations that are pausing but which are still running on the
// compositor. In this case we send a layer transaction that removes the
// animation but which also contains the animation values calculated on
// the main thread. To prevent flicker when this occurs we want to ensure
// the timeline time used to calculate the main thread animation values
// does not lag far behind the time used on the compositor. Ideally we
// would like to use the "animation ready time" calculated at the end of
// the layer transaction as the timeline time but it will be too late to
// update the style rule at that point so instead we just use the current
// wallclock time.
//
// (b) For animations that are pausing that we have already taken off the
// compositor. In this case we record a pending ready time but we don't
// apply it until the next tick. However, while waiting for the next tick,
// we should still use the pending ready time as the timeline time. If we
// use the regular timeline time the animation may appear jump backwards
// if the main thread's timeline time lags behind the compositor.
//
// (c) For animations that are play-pending due to an aborted pause operation
// (i.e. a pause operation that was interrupted before we entered the
// paused state). When we cancel a pending pause we might momentarily take
// the animation off the compositor, only to re-add it moments later. In
// that case the compositor might have been ahead of the main thread so we
// should use the current wallclock time to ensure the animation doesn't
// temporarily jump backwards.
//
// To address each of these cases we temporarily tweak the hold time
// immediately before updating the style rule and then restore it immediately
// afterwards. This is purely to prevent visual flicker. Other behavior
// such as dispatching events continues to rely on the regular timeline time.
bool updatedHoldTime = false;
{
AutoRestore<Nullable<TimeDuration>> restoreHoldTime(mHoldTime);
if (playState == AnimationPlayState::Pending &&
mHoldTime.IsNull() &&
!mStartTime.IsNull()) {
Nullable<TimeDuration> timeToUse = mPendingReadyTime;
if (timeToUse.IsNull() &&
mTimeline &&
mTimeline->TracksWallclockTime()) {
timeToUse = mTimeline->ToTimelineTime(TimeStamp::Now());
}
if (!timeToUse.IsNull()) {
mHoldTime.SetValue((timeToUse.Value() - mStartTime.Value())
.MultDouble(mPlaybackRate));
// Push the change down to the effect
UpdateEffect();
updatedHoldTime = true;
}
}
mEffect->ComposeStyle(aStyleRule, aSetProperties);
}
// Now that the hold time has been restored, update the effect
if (updatedHoldTime) {
UpdateEffect();
}
MOZ_ASSERT(playState == PlayState(),
"Play state should not change during the course of compositing");
mFinishedAtLastComposeStyle = (playState == AnimationPlayState::Finished);
}
