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/* -*- 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 */
/* Code to start and animate CSS transitions. */
#include "nsTransitionManager.h"
#include "mozilla/dom/Document.h"
#include "nsAnimationManager.h"
#include "nsIContent.h"
#include "AnimatedPropertyID.h"
#include "AnimatedPropertyIDSet.h"
#include "mozilla/ComputedStyle.h"
#include "mozilla/MemoryReporting.h"
#include "nsCSSPropertyIDSet.h"
#include "mozilla/EffectSet.h"
#include "mozilla/ElementAnimationData.h"
#include "mozilla/EventDispatcher.h"
#include "mozilla/ServoBindings.h"
#include "mozilla/StyleAnimationValue.h"
#include "mozilla/dom/DocumentTimeline.h"
#include "mozilla/dom/Element.h"
#include "nsIFrame.h"
#include "nsCSSProps.h"
#include "nsCSSPseudoElements.h"
#include "nsDisplayList.h"
#include "nsRFPService.h"
#include "nsStyleChangeList.h"
#include "mozilla/RestyleManager.h"
using mozilla::dom::CSSTransition;
using mozilla::dom::DocumentTimeline;
using mozilla::dom::KeyframeEffect;
using namespace mozilla;
using namespace mozilla::css;
bool nsTransitionManager::UpdateTransitions(dom::Element* aElement,
PseudoStyleType aPseudoType,
const ComputedStyle& aOldStyle,
const ComputedStyle& aNewStyle) {
if (mPresContext->Medium() == nsGkAtoms::print) {
// For print or print preview, ignore transitions.
return false;
if (aNewStyle.StyleDisplay()->mDisplay == StyleDisplay::None) {
StopAnimationsForElement(aElement, aPseudoType);
return false;
auto* collection = CSSTransitionCollection::Get(aElement, aPseudoType);
return DoUpdateTransitions(*aNewStyle.StyleUIReset(), aElement, aPseudoType,
collection, aOldStyle, aNewStyle);
// This function expands the shorthands and "all" keyword specified in
// transition-property, and then execute |aHandler| on the expanded longhand.
// |aHandler| should be a lamda function which accepts nsCSSPropertyID.
template <typename T>
static void ExpandTransitionProperty(const StyleTransitionProperty& aProperty,
T aHandler) {
switch (aProperty.tag) {
case StyleTransitionProperty::Tag::Unsupported:
case StyleTransitionProperty::Tag::Custom: {
AnimatedPropertyID property(aProperty.AsCustom().AsAtom());
case StyleTransitionProperty::Tag::NonCustom: {
nsCSSPropertyID id = nsCSSPropertyID(aProperty.AsNonCustom()._0);
if (nsCSSProps::IsShorthand(id)) {
CSSEnabledState::ForAllContent) {
AnimatedPropertyID property(*subprop);
} else {
AnimatedPropertyID property(id);
bool nsTransitionManager::DoUpdateTransitions(
const nsStyleUIReset& aStyle, dom::Element* aElement,
PseudoStyleType aPseudoType, CSSTransitionCollection*& aElementTransitions,
const ComputedStyle& aOldStyle, const ComputedStyle& aNewStyle) {
MOZ_ASSERT(!aElementTransitions || &aElementTransitions->mElement == aElement,
"Element mismatch");
// I'll consider only the transitions from the number of items in
// 'transition-property' on down, and later ones will override earlier
// ones (tracked using |propertiesChecked|).
bool startedAny = false;
AnimatedPropertyIDSet propertiesChecked;
for (uint32_t i = aStyle.mTransitionPropertyCount; i--;) {
const float delay = aStyle.GetTransitionDelay(i).ToMilliseconds();
// The spec says a negative duration is treated as zero.
const float duration =
std::max(aStyle.GetTransitionDuration(i).ToMilliseconds(), 0.0f);
// If the combined duration of this transition is 0 or less we won't start a
// transition, we can avoid even looking at transition-property if we're the
// last one.
if (i == 0 && delay + duration <= 0.0f) {
const auto behavior = aStyle.GetTransitionBehavior(i);
[&](const AnimatedPropertyID& aProperty) {
// We might have something to transition. See if
// any of the properties in question changed and
// are animatable.
startedAny |= ConsiderInitiatingTransition(
aProperty, aStyle, i, delay, duration,
behavior, aElement, aPseudoType,
aElementTransitions, aOldStyle, aNewStyle,
// Stop any transitions for properties that are no longer in
// 'transition-property', including finished transitions.
// Also stop any transitions (and remove any finished transitions)
// for properties that just changed (and are still in the set of
// properties to transition), but for which we didn't just start the
// transition. This can happen delay and duration are both zero, or
// because the new value is not interpolable.
if (aElementTransitions) {
const bool checkProperties = !aStyle.GetTransitionProperty(0).IsAll();
AnimatedPropertyIDSet allTransitionProperties;
if (checkProperties) {
for (uint32_t i = aStyle.mTransitionPropertyCount; i-- != 0;) {
[&](const AnimatedPropertyID& aProperty) {
OwningCSSTransitionPtrArray& animations = aElementTransitions->mAnimations;
size_t i = animations.Length();
MOZ_ASSERT(i != 0, "empty transitions list?");
AnimationValue currentValue;
do {
CSSTransition* anim = animations[i];
const AnimatedPropertyID& property = anim->TransitionProperty();
if (
// Properties no longer in `transition-property`.
(checkProperties && !allTransitionProperties.HasProperty(property)) ||
// Properties whose computed values changed but for which we did not
// start a new transition (because delay and duration are both zero,
// or because the new value is not interpolable); a new transition
// would have anim->ToValue() matching currentValue.
&aNewStyle, &property, anim->ToValue().mServo.get())) {
// Stop the transition.
DoCancelTransition(aElement, aPseudoType, aElementTransitions, i);
} while (i != 0);
return startedAny;
static Keyframe& AppendKeyframe(double aOffset,
const AnimatedPropertyID& aProperty,
AnimationValue&& aValue,
nsTArray<Keyframe>& aKeyframes) {
Keyframe& frame = *aKeyframes.AppendElement();
RefPtr<StyleLockedDeclarationBlock> decl =
PropertyValuePair(aProperty, std::move(decl)));
return frame;
static nsTArray<Keyframe> GetTransitionKeyframes(
const AnimatedPropertyID& aProperty, AnimationValue&& aStartValue,
AnimationValue&& aEndValue) {
nsTArray<Keyframe> keyframes(2);
AppendKeyframe(0.0, aProperty, std::move(aStartValue), keyframes);
AppendKeyframe(1.0, aProperty, std::move(aEndValue), keyframes);
return keyframes;
static Maybe<CSSTransition::ReplacedTransitionProperties>
GetReplacedTransitionProperties(const CSSTransition* aTransition,
const DocumentTimeline* aTimelineToMatch) {
Maybe<CSSTransition::ReplacedTransitionProperties> result;
// Transition needs to be currently running on the compositor to be
// replaceable.
if (!aTransition || !aTransition->HasCurrentEffect() ||
!aTransition->IsRunningOnCompositor() ||
aTransition->GetStartTime().IsNull()) {
return result;
// Transition needs to be running on the same timeline.
if (aTransition->GetTimeline() != aTimelineToMatch) {
return result;
// The transition needs to have a keyframe effect.
const KeyframeEffect* keyframeEffect =
aTransition->GetEffect() ? aTransition->GetEffect()->AsKeyframeEffect()
: nullptr;
if (!keyframeEffect) {
return result;
// The keyframe effect needs to be a simple transition of the original
// transition property (i.e. not replaced with something else).
if (keyframeEffect->Properties().Length() != 1 ||
keyframeEffect->Properties()[0].mSegments.Length() != 1 ||
keyframeEffect->Properties()[0].mProperty !=
aTransition->TransitionProperty()) {
return result;
const AnimationPropertySegment& segment =
{aTransition->GetStartTime().Value(), aTransition->PlaybackRate(),
keyframeEffect->SpecifiedTiming(), segment.mTimingFunction,
segment.mFromValue, segment.mToValue}));
return result;
bool nsTransitionManager::ConsiderInitiatingTransition(
const AnimatedPropertyID& aProperty, const nsStyleUIReset& aStyle,
uint32_t aTransitionIndex, float aDelay, float aDuration,
mozilla::StyleTransitionBehavior aBehavior, dom::Element* aElement,
PseudoStyleType aPseudoType, CSSTransitionCollection*& aElementTransitions,
const ComputedStyle& aOldStyle, const ComputedStyle& aNewStyle,
AnimatedPropertyIDSet& aPropertiesChecked) {
// IsShorthand itself will assert if aProperty is not a property.
MOZ_ASSERT(aProperty.IsCustom() || !nsCSSProps::IsShorthand(aProperty.mID),
"property out of range");
!aElementTransitions || &aElementTransitions->mElement == aElement,
"Element mismatch");
AnimatedPropertyID property = aProperty.ToPhysical(aNewStyle);
// A later item in transition-property already specified a transition for
// this property, so we ignore this one.
if (aPropertiesChecked.HasProperty(property)) {
return false;
if (aDuration + aDelay <= 0.0f) {
return false;
size_t currentIndex = nsTArray<KeyframeEffect>::NoIndex;
const auto* oldTransition = [&]() -> const CSSTransition* {
if (!aElementTransitions) {
return nullptr;
const OwningCSSTransitionPtrArray& animations =
for (size_t i = 0, i_end = animations.Length(); i < i_end; ++i) {
if (animations[i]->TransitionProperty() == property) {
currentIndex = i;
return animations[i];
return nullptr;
AnimationValue startValue, endValue;
const StyleShouldTransitionResult result =
&aOldStyle, &aNewStyle, &property, aBehavior,
oldTransition ? oldTransition->ToValue().mServo.get() : nullptr,
&startValue.mServo, &endValue.mServo);
// If we got a style change that changed the value to the endpoint
// of the currently running transition, we don't want to interrupt
// its timing function.
// This needs to be before the !shouldAnimate && haveCurrentTransition
// case below because we might be close enough to the end of the
// transition that the current value rounds to the final value. In
// this case, we'll end up with shouldAnimate as false (because
// there's no value change), but we need to return early here rather
// than cancel the running transition because shouldAnimate is false!
// Likewise, if we got a style change that changed the value to the
// endpoint of our finished transition, we also don't want to start
// a new transition for the reasons described in
if (result.old_transition_value_matches) {
// GetAnimationRule already called RestyleForAnimation.
return false;
if (!result.should_animate) {
if (oldTransition) {
// We're in the middle of a transition, and just got a non-transition
// style change to something that we can't animate. This might happen
// because we got a non-transition style change changing to the current
// in-progress value (which is particularly easy to cause when we're
// currently in the 'transition-delay'). It also might happen because we
// just got a style change to a value that can't be interpolated.
DoCancelTransition(aElement, aPseudoType, aElementTransitions,
return false;
AnimationValue startForReversingTest = startValue;
double reversePortion = 1.0;
// If the new transition reverses an existing one, we'll need to
// handle the timing differently.
if (oldTransition && oldTransition->HasCurrentEffect() &&
oldTransition->StartForReversingTest() == endValue) {
// Compute the appropriate negative transition-delay such that right
// now we'd end up at the current position.
double valuePortion =
oldTransition->CurrentValuePortion() * oldTransition->ReversePortion() +
(1.0 - oldTransition->ReversePortion());
// A timing function with negative y1 (or y2!) might make
// valuePortion negative. In this case, we still want to apply our
// reversing logic based on relative distances, not make duration
// negative.
if (valuePortion < 0.0) {
valuePortion = -valuePortion;
// A timing function with y2 (or y1!) greater than one might
// advance past its terminal value. It's probably a good idea to
// clamp valuePortion to be at most one to preserve the invariant
// that a transition will complete within at most its specified
// time.
if (valuePortion > 1.0) {
valuePortion = 1.0;
// Negative delays are essentially part of the transition
// function, so reduce them along with the duration, but don't
// reduce positive delays.
if (aDelay < 0.0f && std::isfinite(aDelay)) {
aDelay *= valuePortion;
if (std::isfinite(aDuration)) {
aDuration *= valuePortion;
startForReversingTest = oldTransition->ToValue();
reversePortion = valuePortion;
TimingParams timing = TimingParamsFromCSSParams(
aDuration, aDelay, 1.0 /* iteration count */,
StyleAnimationDirection::Normal, StyleAnimationFillMode::Backwards);
const StyleComputedTimingFunction& tf =
if (!tf.IsLinearKeyword()) {
RefPtr<CSSTransition> transition = DoCreateTransition(
property, aElement, aPseudoType, aNewStyle, aElementTransitions,
std::move(timing), std::move(startValue), std::move(endValue),
std::move(startForReversingTest), reversePortion);
if (!transition) {
return false;
OwningCSSTransitionPtrArray& transitions = aElementTransitions->mAnimations;
#ifdef DEBUG
for (size_t i = 0, i_end = transitions.Length(); i < i_end; ++i) {
i == currentIndex || transitions[i]->TransitionProperty() != property,
"duplicate transitions for property");
if (oldTransition) {
// If this new transition is replacing an existing transition that is
// running on the compositor, we store select parameters from the replaced
// transition so that later, once all scripts have run, we can update the
// start value of the transition using TimeStamp::Now(). This allows us to
// avoid a large jump when starting a new transition when the main thread
// lags behind the compositor.
const dom::DocumentTimeline* timeline = aElement->OwnerDoc()->Timeline();
auto replacedTransitionProperties =
GetReplacedTransitionProperties(oldTransition, timeline);
if (replacedTransitionProperties) {
oldTransition = nullptr; // Clear pointer so it doesn't dangle
transitions[currentIndex] = transition;
} else {
// XXX(Bug 1631371) Check if this should use a fallible operation as it
// pretended earlier.
if (auto* effectSet = EffectSet::Get(aElement, aPseudoType)) {
return true;
already_AddRefed<CSSTransition> nsTransitionManager::DoCreateTransition(
const AnimatedPropertyID& aProperty, dom::Element* aElement,
PseudoStyleType aPseudoType, const mozilla::ComputedStyle& aNewStyle,
CSSTransitionCollection*& aElementTransitions, TimingParams&& aTiming,
AnimationValue&& aStartValue, AnimationValue&& aEndValue,
AnimationValue&& aStartForReversingTest, double aReversePortion) {
dom::DocumentTimeline* timeline = aElement->OwnerDoc()->Timeline();
KeyframeEffectParams effectOptions;
auto keyframeEffect = MakeRefPtr<KeyframeEffect>(
aElement->OwnerDoc(), OwningAnimationTarget(aElement, aPseudoType),
std::move(aTiming), effectOptions);
GetTransitionKeyframes(aProperty, std::move(aStartValue),
&aNewStyle, timeline);
if (NS_WARN_IF(MOZ_UNLIKELY(!keyframeEffect->IsValidTransition()))) {
return nullptr;
auto animation = MakeRefPtr<CSSTransition>(
mPresContext->Document()->GetScopeObject(), aProperty);
animation->SetOwningElement(OwningElementRef(*aElement, aPseudoType));
if (!aElementTransitions) {
aElementTransitions =
*aElement, aPseudoType);
if (!aElementTransitions->isInList()) {
return animation.forget();
void nsTransitionManager::DoCancelTransition(
dom::Element* aElement, PseudoStyleType aPseudoType,
CSSTransitionCollection*& aElementTransitions, size_t aIndex) {
OwningCSSTransitionPtrArray& transitions = aElementTransitions->mAnimations;
CSSTransition* transition = transitions[aIndex];
if (transition->HasCurrentEffect()) {
if (auto* effectSet = EffectSet::Get(aElement, aPseudoType)) {
if (transitions.IsEmpty()) {
// |aElementTransitions| is now a dangling pointer!
aElementTransitions = nullptr;