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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 */
#ifndef mozilla_RestyleManager_h
#define mozilla_RestyleManager_h
#include "mozilla/AutoRestore.h"
#include "mozilla/Maybe.h"
#include "mozilla/OverflowChangedTracker.h"
#include "mozilla/ServoElementSnapshot.h"
#include "mozilla/ServoElementSnapshotTable.h"
#include "nsChangeHint.h"
#include "nsPresContext.h"
#include "nsPresContextInlines.h" // XXX Shouldn't be included by header though
#include "nsStringFwd.h"
#include "nsTHashSet.h"
class nsAttrValue;
class nsAtom;
class nsIFrame;
class nsStyleChangeList;
class nsStyleChangeList;
namespace mozilla {
class ServoStyleSet;
namespace dom {
class Element;
* A stack class used to pass some common restyle state in a slightly more
* comfortable way than a bunch of individual arguments, and that also checks
* that the change hint used for optimization is correctly used in debug mode.
class ServoRestyleState {
ServoStyleSet& aStyleSet, nsStyleChangeList& aChangeList,
nsTArray<nsIFrame*>& aPendingWrapperRestyles,
nsTArray<RefPtr<dom::Element>>& aPendingScrollAnchorSuppressions)
: mStyleSet(aStyleSet),
#ifdef DEBUG
// If !mOwner, then we wouldn't have processed our wrapper restyles,
// because we only process those when handling an element with a frame.
// But that's OK, because if we started our traversal at an element with
// no frame (e.g. it's display:contents), that means the wrapper frames
// in our list actually inherit from one of its ancestors, not from it,
// and hence not restyling them is OK.
#endif // DEBUG
// We shouldn't assume that changes handled from our parent are handled for
// our children too if we're out of flow since they aren't necessarily
// parented in DOM order, and thus a change handled by a DOM ancestor doesn't
// necessarily mean that it's handled for an ancestor frame.
enum class CanUseHandledHints : bool { No = false, Yes };
ServoRestyleState(const nsIFrame& aOwner, ServoRestyleState& aParentState,
nsChangeHint aHintForThisFrame,
CanUseHandledHints aCanUseHandledHints,
bool aAssertWrapperRestyleLength = true)
: mStyleSet(aParentState.mStyleSet),
? aParentState.mChangesHandled | aHintForThisFrame
: aHintForThisFrame)
#ifdef DEBUG
if (bool(aCanUseHandledHints)) {
~ServoRestyleState() {
!mAssertWrapperRestyleLength ||
mPendingWrapperRestyles.Length() == mPendingWrapperRestyleOffset,
"Someone forgot to call ProcessWrapperRestyles!");
nsStyleChangeList& ChangeList() { return mChangeList; }
ServoStyleSet& StyleSet() { return mStyleSet; }
#ifdef DEBUG
void AssertOwner(const ServoRestyleState& aParentState) const;
nsChangeHint ChangesHandledFor(const nsIFrame*) const;
void AssertOwner(const ServoRestyleState&) const {}
nsChangeHint ChangesHandledFor(const nsIFrame*) const {
return mChangesHandled;
// Add a pending wrapper restyle. We don't have to do anything if the thing
// being added is already last in the list, but otherwise we do want to add
// it, in order for ProcessWrapperRestyles to work correctly.
void AddPendingWrapperRestyle(nsIFrame* aWrapperFrame);
// Process wrapper restyles for this restyle state. This should be done
// before it comes off the stack.
void ProcessWrapperRestyles(nsIFrame* aParentFrame);
// Get the table-aware parent for the given child. This will walk through
// outer table and cellcontent frames.
static nsIFrame* TableAwareParentFor(const nsIFrame* aChild);
// When the value of the position property changes such as we stop or start
// being absolutely or fixed positioned, we need to suppress scroll anchoring
// adjustments to avoid breaking websites.
// We do need to process all this once we're done with all our reframes,
// to handle correctly the cases where we reconstruct an ancestor, like when
// you reframe an ib-split (see bug 1559627 for example).
// This doesn't handle nested reframes. We'd need to rework quite some code to
// do that, and so far it doesn't seem to be a problem in practice.
void AddPendingScrollAnchorSuppression(dom::Element* aElement) {
// Process a wrapper restyle at the given index, and restyles for any
// wrappers nested in it. Returns the number of entries from
// mPendingWrapperRestyles that we processed. The return value is always at
// least 1.
size_t ProcessMaybeNestedWrapperRestyle(nsIFrame* aParent, size_t aIndex);
ServoStyleSet& mStyleSet;
nsStyleChangeList& mChangeList;
// A list of pending wrapper restyles. Anonymous box wrapper frames that need
// restyling are added to this list when their non-anonymous kids are
// restyled. This avoids us having to do linear searches along the frame tree
// for these anonymous boxes. The problem then becomes that we can have
// multiple kids all with the same anonymous parent, and we don't want to
// restyle it more than once. We use mPendingWrapperRestyles to track which
// anonymous wrapper boxes we've requested be restyled and which of them have
// already been restyled. We use a single array propagated through
// ServoRestyleStates by reference, because in a situation like this:
// <div style="display: table"><span></span></div>
// We have multiple wrappers to restyle (cell, row, table-row-group) and we
// want to add them in to the list all at once but restyle them using
// different ServoRestyleStates with different owners. When this situation
// occurs, the relevant frames will be placed in the array with ancestors
// before descendants.
nsTArray<nsIFrame*>& mPendingWrapperRestyles;
nsTArray<RefPtr<dom::Element>>& mPendingScrollAnchorSuppressions;
// Since we're given a possibly-nonempty mPendingWrapperRestyles to start
// with, we need to keep track of where the part of it we're responsible for
// starts.
size_t mPendingWrapperRestyleOffset;
const nsChangeHint mChangesHandled;
// We track the "owner" frame of this restyle state, that is, the frame that
// generated the last change that is stored in mChangesHandled, in order to
// verify that we only use mChangesHandled for actual descendants of that
// frame (given DOM order isn't always frame order, and that there are a few
// special cases for stuff like wrapper frames, ::backdrop, and so on).
#ifdef DEBUG
const nsIFrame* mOwner{nullptr};
// Whether we should assert in our destructor that we've processed all of the
// relevant wrapper restyles.
#ifdef DEBUG
const bool mAssertWrapperRestyleLength;
#endif // DEBUG
enum class ServoPostTraversalFlags : uint32_t;
class RestyleManager {
friend class ServoStyleSet;
typedef ServoElementSnapshotTable SnapshotTable;
typedef mozilla::dom::Element Element;
// Get an integer that increments every time we process pending restyles.
// The value is never 0.
uint64_t GetRestyleGeneration() const { return mRestyleGeneration; }
// Unlike GetRestyleGeneration, which means the actual restyling count,
// GetUndisplayedRestyleGeneration represents any possible DOM changes that
// can cause restyling. This is needed for getComputedStyle to work with
// non-styled (e.g. display: none) elements.
uint64_t GetUndisplayedRestyleGeneration() const {
return mUndisplayedRestyleGeneration;
void Disconnect() { mPresContext = nullptr; }
~RestyleManager() {
"leaving dangling pointers from AnimationsWithDestroyedFrame");
#ifdef DEBUG
static nsCString ChangeHintToString(nsChangeHint aHint);
* DEBUG ONLY method to verify integrity of style tree versus frame tree
void DebugVerifyStyleTree(nsIFrame* aFrame);
void FlushOverflowChangedTracker() { mOverflowChangedTracker.Flush(); }
// Should be called when a frame is going to be destroyed and
// WillDestroyFrameTree hasn't been called yet.
void NotifyDestroyingFrame(nsIFrame* aFrame) {
// If ProcessRestyledFrames is tracking frames which have been
// destroyed (to avoid re-visiting them), add this one to its set.
if (mDestroyedFrames) {
// Note: It's the caller's responsibility to make sure to wrap a
// ProcessRestyledFrames call in a view update batch and a script blocker.
// This function does not call ProcessAttachedQueue() on the binding manager.
// If the caller wants that to happen synchronously, it needs to handle that
// itself.
void ProcessRestyledFrames(nsStyleChangeList& aChangeList);
bool IsInStyleRefresh() const { return mInStyleRefresh; }
// AnimationsWithDestroyedFrame is used to stop animations and transitions
// on elements that have no frame at the end of the restyling process.
// It only lives during the restyling process.
class MOZ_STACK_CLASS AnimationsWithDestroyedFrame final {
// Construct a AnimationsWithDestroyedFrame object. The caller must
// ensure that aRestyleManager lives at least as long as the
// object. (This is generally easy since the caller is typically a
// method of RestyleManager.)
explicit AnimationsWithDestroyedFrame(RestyleManager* aRestyleManager);
// This method takes the content node for the generated content for
// animation/transition on ::before and ::after, rather than the
// content node for the real element.
void Put(nsIContent* aContent, ComputedStyle* aComputedStyle) {
PseudoStyleType pseudoType = aComputedStyle->GetPseudoType();
if (pseudoType == PseudoStyleType::NotPseudo) {
} else if (pseudoType == PseudoStyleType::before) {
MOZ_ASSERT(aContent->NodeInfo()->NameAtom() ==
} else if (pseudoType == PseudoStyleType::after) {
MOZ_ASSERT(aContent->NodeInfo()->NameAtom() ==
} else if (pseudoType == PseudoStyleType::marker) {
MOZ_ASSERT(aContent->NodeInfo()->NameAtom() ==
void StopAnimationsForElementsWithoutFrames();
void StopAnimationsWithoutFrame(nsTArray<RefPtr<nsIContent>>& aArray,
PseudoStyleType aPseudoType);
RestyleManager* mRestyleManager;
AutoRestore<AnimationsWithDestroyedFrame*> mRestorePointer;
// Below three arrays might include elements that have already had their
// animations or transitions stopped.
// mBeforeContents, mAfterContents and mMarkerContents hold the real element
// rather than the content node for the generated content (which might
// change during a reframe)
nsTArray<RefPtr<nsIContent>> mContents;
nsTArray<RefPtr<nsIContent>> mBeforeContents;
nsTArray<RefPtr<nsIContent>> mAfterContents;
nsTArray<RefPtr<nsIContent>> mMarkerContents;
* Return the current AnimationsWithDestroyedFrame struct, or null if we're
* not currently in a restyling operation.
AnimationsWithDestroyedFrame* GetAnimationsWithDestroyedFrame() {
return mAnimationsWithDestroyedFrame;
void ContentInserted(nsIContent* aChild);
void ContentAppended(nsIContent* aFirstNewContent);
// This would be have the same logic as RestyleForInsertOrChange if we got the
// notification before the removal. However, we get it after, so we need the
// following sibling in addition to the old child.
// aFollowingSibling is the sibling that used to come after aOldChild before
// the removal.
void ContentRemoved(nsIContent* aOldChild, nsIContent* aFollowingSibling);
// Restyling for a ContentInserted (notification after insertion) or
// for some CharacterDataChanged.
void RestyleForInsertOrChange(nsIContent* aChild);
// Restyle for a CharacterDataChanged notification. In practice this can only
// affect :empty / :-moz-only-whitespace / :-moz-first-node / :-moz-last-node.
void CharacterDataChanged(nsIContent*, const CharacterDataChangeInfo&);
void PostRestyleEvent(dom::Element*, RestyleHint,
nsChangeHint aMinChangeHint);
* Posts restyle hints for animations.
* This is only called for the second traversal for CSS animations during
* updating CSS animations in a SequentialTask.
* This function does neither register a refresh observer nor flag that a
* style flush is needed since this function is supposed to be called during
* restyling process and this restyle event will be processed in the second
* traversal of the same restyling process.
void PostRestyleEventForAnimations(dom::Element*, PseudoStyleType,
void NextRestyleIsForCSSRuleChanges() { mRestyleForCSSRuleChanges = true; }
void RebuildAllStyleData(nsChangeHint aExtraHint, RestyleHint);
void ProcessPendingRestyles();
void ProcessAllPendingAttributeAndStateInvalidations();
void ElementStateChanged(Element*, dom::ElementState);
void CustomStatesWillChange(Element&);
void CustomStateChanged(Element&, nsAtom* aState);
void MaybeRestyleForNthOfCustomState(ServoStyleSet&, Element&,
nsAtom* aState);
* Posts restyle hints for siblings of an element and their descendants if the
* element's parent has NODE_HAS_SLOW_SELECTOR_NTH_OF and the element has a
* relevant state dependency.
void MaybeRestyleForNthOfState(ServoStyleSet& aStyleSet, dom::Element* aChild,
dom::ElementState aChangedBits);
void AttributeWillChange(Element* aElement, int32_t aNameSpaceID,
nsAtom* aAttribute, int32_t aModType);
void ClassAttributeWillBeChangedBySMIL(dom::Element* aElement);
void AttributeChanged(dom::Element* aElement, int32_t aNameSpaceID,
nsAtom* aAttribute, int32_t aModType,
const nsAttrValue* aOldValue);
* Restyle an element's previous and/or next siblings.
void RestyleSiblingsForNthOf(dom::Element* aChild,
NodeSelectorFlags aParentFlags);
* Posts restyle hints for siblings of an element and their descendants if the
* element's parent has NODE_HAS_SLOW_SELECTOR_NTH_OF and the element has a
* relevant attribute dependency.
void MaybeRestyleForNthOfAttribute(dom::Element* aChild, nsAtom* aAttribute,
const nsAttrValue* aOldValue);
void MaybeRestyleForRelativeSelectorAttribute(dom::Element* aElement,
nsAtom* aAttribute,
const nsAttrValue* aOldValue);
void MaybeRestyleForRelativeSelectorState(ServoStyleSet& aStyleSet,
dom::Element* aElement,
dom::ElementState aChangedBits);
// This is only used to reparent things when moving them in/out of the
// ::first-line.
void ReparentComputedStyleForFirstLine(nsIFrame*);
* Performs a Servo animation-only traversal to compute style for all nodes
* with the animation-only dirty bit in the document.
* This processes just the traversal for animation-only restyles and skips the
* normal traversal for other restyles unrelated to animations.
* This is used to bring throttled animations up-to-date such as when we need
* to get correct position for transform animations that are throttled because
* they are running on the compositor.
* This will traverse all of the document's style roots (that is, its document
* element, and the roots of the document-level native anonymous content).
void UpdateOnlyAnimationStyles();
// Get a counter that increments on every style change, that we use to
// track whether off-main-thread animations are up-to-date.
uint64_t GetAnimationGeneration() const { return mAnimationGeneration; }
// Typically only style frames have animations associated with them so this
// will likely return zero for anything that is not a style frame.
static uint64_t GetAnimationGenerationForFrame(nsIFrame* aStyleFrame);
// Update the animation generation count to mark that animation state
// has changed.
// This is normally performed automatically by ProcessPendingRestyles
// but it is also called when we have out-of-band changes to animations
// such as changes made through the Web Animations API.
void IncrementAnimationGeneration();
// Apply change hints for animations on the compositor.
// There are some cases where we forcibly apply change hints for animations
// even if there is no change hint produced in order to synchronize with
// animations running on the compositor.
// For example:
// a) Pausing animations via the Web Animations API
// b) When the style before sending the animation to the compositor exactly
// the same as the current style
static void AddLayerChangesForAnimation(
nsIFrame* aStyleFrame, nsIFrame* aPrimaryFrame, Element* aElement,
nsChangeHint aHintForThisFrame, nsStyleChangeList& aChangeListToProcess);
* Whether to clear all the style data (including the element itself), or just
* the descendants' data.
enum class IncludeRoot {
* Clears the ServoElementData and HasDirtyDescendants from all elements
* in the subtree rooted at aElement.
static void ClearServoDataFromSubtree(Element*,
IncludeRoot = IncludeRoot::Yes);
* Clears HasDirtyDescendants and RestyleData from all elements in the
* subtree rooted at aElement.
static void ClearRestyleStateFromSubtree(Element* aElement);
explicit RestyleManager(nsPresContext* aPresContext);
* Reparent the descendants of aFrame. This is used by ReparentComputedStyle
* and shouldn't be called by anyone else. aProviderChild, if non-null, is a
* child that was the style parent for aFrame and hence shouldn't be
* reparented.
void ReparentFrameDescendants(nsIFrame* aFrame, nsIFrame* aProviderChild,
ServoStyleSet& aStyleSet);
* Performs post-Servo-traversal processing on this element and its
* descendants.
* Returns whether any style did actually change. There may be cases where we
* didn't need to change any style after all, for example, when a content
* attribute changes that happens not to have any effect on the style of that
* element or any descendant or sibling.
bool ProcessPostTraversal(Element* aElement, ServoRestyleState& aRestyleState,
ServoPostTraversalFlags aFlags);
struct TextPostTraversalState;
bool ProcessPostTraversalForText(nsIContent* aTextNode,
TextPostTraversalState& aState,
ServoRestyleState& aRestyleState,
ServoPostTraversalFlags aFlags);
ServoStyleSet* StyleSet() const { return PresContext()->StyleSet(); }
void RestylePreviousSiblings(nsIContent* aStartingSibling);
void RestyleSiblingsStartingWith(nsIContent* aStartingSibling);
void RestyleForEmptyChange(Element* aContainer);
void MaybeRestyleForEdgeChildChange(nsINode* aContainer,
nsIContent* aChangedChild);
bool IsDisconnected() const { return !mPresContext; }
void IncrementRestyleGeneration() {
if (++mRestyleGeneration == 0) {
// Keep mRestyleGeneration from being 0, since that's what
// nsPresContext::GetRestyleGeneration returns when it no
// longer has a RestyleManager.
void IncrementUndisplayedRestyleGeneration() {
if (++mUndisplayedRestyleGeneration == 0) {
// Ensure mUndisplayedRestyleGeneration > 0, for the same reason as
// IncrementRestyleGeneration.
nsPresContext* PresContext() const {
return mPresContext;
nsPresContext* mPresContext; // weak, can be null after Disconnect().
uint64_t mRestyleGeneration;
uint64_t mUndisplayedRestyleGeneration;
// Used to keep track of frames that have been destroyed during
// ProcessRestyledFrames, so we don't try to touch them again even if
// they're referenced again later in the changelist.
mozilla::UniquePtr<nsTHashSet<const nsIFrame*>> mDestroyedFrames;
// True if we're in the middle of a nsRefreshDriver refresh
bool mInStyleRefresh;
// The total number of animation flushes by this frame constructor.
// Used to keep the layer and animation manager in sync.
uint64_t mAnimationGeneration;
OverflowChangedTracker mOverflowChangedTracker;
AnimationsWithDestroyedFrame* mAnimationsWithDestroyedFrame = nullptr;
const SnapshotTable& Snapshots() const { return mSnapshots; }
void ClearSnapshots();
ServoElementSnapshot& SnapshotFor(Element&);
void TakeSnapshotForAttributeChange(Element&, int32_t aNameSpaceID,
nsAtom* aAttribute);
void DoProcessPendingRestyles(ServoTraversalFlags aFlags);
// Function to do the actual (recursive) work of
// ReparentComputedStyleForFirstLine, once we have asserted the invariants
// that only hold on the initial call.
void DoReparentComputedStyleForFirstLine(nsIFrame*, ServoStyleSet&);
// We use a separate data structure from nsStyleChangeList because we need a
// frame to create nsStyleChangeList entries, and the primary frame may not be
// attached yet.
struct ReentrantChange {
nsCOMPtr<nsIContent> mContent;
nsChangeHint mHint;
typedef AutoTArray<ReentrantChange, 10> ReentrantChangeList;
// Only non-null while processing change hints. See the comment in
// ProcessPendingRestyles.
ReentrantChangeList* mReentrantChanges = nullptr;
// We use this flag to track if the current restyle contains any non-animation
// update, which triggers a normal restyle, and so there might be any new
// transition created later. Therefore, if this flag is true, we need to
// increase mAnimationGeneration before creating new transitions, so their
// creation sequence will be correct.
bool mHaveNonAnimationRestyles = false;
// Set to true when posting restyle events triggered by CSS rule changes.
// This flag is cleared once ProcessPendingRestyles has completed.
// When we process a traversal all descendants elements of the document
// triggered by CSS rule changes, we will need to update all elements with
// CSS animations. We propagate TraversalRestyleBehavior::ForCSSRuleChanges
// to traversal function if this flag is set.
bool mRestyleForCSSRuleChanges = false;
// A hashtable with the elements that have changed state or attributes, in
// order to calculate restyle hints during the traversal.
SnapshotTable mSnapshots;
} // namespace mozilla