/* 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 http://mozilla.org/MPL/2.0/. */
//! Traversing the DOM tree; the bloom filter.
use context::{ElementCascadeInputs, StyleContext, SharedStyleContext};
use data::{ElementData, ElementStyles};
use dom::{NodeInfo, OpaqueNode, TElement, TNode};
use invalidation::element::restyle_hints::RestyleHint;
use matching::{ChildCascadeRequirement, MatchMethods};
use selector_parser::PseudoElement;
use selectors::NthIndexCache;
use sharing::StyleSharingTarget;
use smallvec::SmallVec;
use style_resolver::{PseudoElementResolution, StyleResolverForElement};
use stylist::RuleInclusion;
use traversal_flags::TraversalFlags;
/// A per-traversal-level chunk of data. This is sent down by the traversal, and
/// currently only holds the dom depth for the bloom filter.
///
/// NB: Keep this as small as possible, please!
#[derive(Clone, Debug)]
pub struct PerLevelTraversalData {
/// The current dom depth.
///
/// This is kept with cooperation from the traversal code and the bloom
/// filter.
pub current_dom_depth: usize,
}
/// We use this structure, rather than just returning a boolean from pre_traverse,
/// to enfore that callers process root invalidations before starting the traversal.
pub struct PreTraverseToken<E: TElement>(Option<E>);
impl<E: TElement> PreTraverseToken<E> {
/// Whether we should traverse children.
pub fn should_traverse(&self) -> bool {
self.0.is_some()
}
/// Returns the traversal root for the current traversal.
pub(crate) fn traversal_root(self) -> Option<E> {
self.0
}
}
#[cfg(feature = "servo")]
#[inline]
fn is_servo_nonincremental_layout() -> bool {
use servo_config::opts;
opts::get().nonincremental_layout
}
#[cfg(not(feature = "servo"))]
#[inline]
fn is_servo_nonincremental_layout() -> bool {
false
}
/// A DOM Traversal trait, that is used to generically implement styling for
/// Gecko and Servo.
pub trait DomTraversal<E: TElement> : Sync {
/// Process `node` on the way down, before its children have been processed.
///
/// The callback is invoked for each child node that should be processed by
/// the traversal.
fn process_preorder<F>(&self,
data: &PerLevelTraversalData,
context: &mut StyleContext<E>,
node: E::ConcreteNode,
note_child: F)
where F: FnMut(E::ConcreteNode);
/// Process `node` on the way up, after its children have been processed.
///
/// This is only executed if `needs_postorder_traversal` returns true.
fn process_postorder(&self,
contect: &mut StyleContext<E>,
node: E::ConcreteNode);
/// Boolean that specifies whether a bottom up traversal should be
/// performed.
///
/// If it's false, then process_postorder has no effect at all.
fn needs_postorder_traversal() -> bool { true }
/// Handles the postorder step of the traversal, if it exists, by bubbling
/// up the parent chain.
///
/// If we are the last child that finished processing, recursively process
/// our parent. Else, stop. Also, stop at the root.
///
/// Thus, if we start with all the leaves of a tree, we end up traversing
/// the whole tree bottom-up because each parent will be processed exactly
/// once (by the last child that finishes processing).
///
/// The only communication between siblings is that they both
/// fetch-and-subtract the parent's children count. This makes it safe to
/// call durign the parallel traversal.
fn handle_postorder_traversal(
&self,
context: &mut StyleContext<E>,
root: OpaqueNode,
mut node: E::ConcreteNode,
children_to_process: isize
) {
// If the postorder step is a no-op, don't bother.
if !Self::needs_postorder_traversal() {
return;
}
if children_to_process == 0 {
// We are a leaf. Walk up the chain.
loop {
self.process_postorder(context, node);
if node.opaque() == root {
break;
}
let parent = node.traversal_parent().unwrap();
let remaining = parent.did_process_child();
if remaining != 0 {
// The parent has other unprocessed descendants. We only
// perform postorder processing after the last descendant
// has been processed.
break
}
node = parent.as_node();
}
} else {
// Otherwise record the number of children to process when the time
// comes.
node.as_element().unwrap()
.store_children_to_process(children_to_process);
}
}
/// Style invalidations happen when traversing from a parent to its children.
/// However, this mechanism can't handle style invalidations on the root. As
/// such, we have a pre-traversal step to handle that part and determine whether
/// a full traversal is needed.
fn pre_traverse(
root: E,
shared_context: &SharedStyleContext,
) -> PreTraverseToken<E> {
let traversal_flags = shared_context.traversal_flags;
let mut data = root.mutate_data();
let mut data = data.as_mut().map(|d| &mut **d);
if let Some(ref mut data) = data {
if !traversal_flags.for_animation_only() {
// Invalidate our style, and that of our siblings and
// descendants as needed.
let invalidation_result = data.invalidate_style_if_needed(
root,
shared_context,
None,
&mut NthIndexCache::default(),
);
if invalidation_result.has_invalidated_siblings() {
let actual_root = root.traversal_parent()
.expect("How in the world can you invalidate \
siblings without a parent?");
unsafe { actual_root.set_dirty_descendants() }
return PreTraverseToken(Some(actual_root));
}
}
}
let should_traverse = Self::element_needs_traversal(
root,
traversal_flags,
data.as_mut().map(|d| &**d),
);
// If we're not going to traverse at all, we may need to clear some state
// off the root (which would normally be done at the end of recalc_style_at).
if !should_traverse && data.is_some() {
clear_state_after_traversing(root, data.unwrap(), traversal_flags);
}
PreTraverseToken(if should_traverse { Some(root) } else { None })
}
/// Returns true if traversal should visit a text node. The style system
/// never processes text nodes, but Servo overrides this to visit them for
/// flow construction when necessary.
fn text_node_needs_traversal(node: E::ConcreteNode, _parent_data: &ElementData) -> bool {
debug_assert!(node.is_text_node());
false
}
/// Returns true if traversal is needed for the given element and subtree.
fn element_needs_traversal(
el: E,
traversal_flags: TraversalFlags,
data: Option<&ElementData>,
) -> bool {
debug!("element_needs_traversal({:?}, {:?}, {:?})",
el, traversal_flags, data);
// In case of animation-only traversal we need to traverse the element
// if the element has animation only dirty descendants bit,
// animation-only restyle hint or recascade.
if traversal_flags.for_animation_only() {
return data.map_or(false, |d| d.has_styles()) &&
(el.has_animation_only_dirty_descendants() ||
data.as_ref().unwrap().hint.has_animation_hint_or_recascade());
}
// Non-incremental layout visits every node.
if is_servo_nonincremental_layout() {
return true;
}
// Unwrap the data.
let data = match data {
Some(d) if d.has_styles() => d,
_ => return true,
};
// If the dirty descendants bit is set, we need to traverse no matter
// what. Skip examining the ElementData.
if el.has_dirty_descendants() {
return true;
}
// If we have a restyle hint or need to recascade, we need to visit the
// element.
//
// Note that this is different than checking has_current_styles_for_traversal(),
// since that can return true even if we have a restyle hint indicating
// that the element's descendants (but not necessarily the element) need
// restyling.
if !data.hint.is_empty() {
return true;
}
// Servo uses the post-order traversal for flow construction, so we need
// to traverse any element with damage so that we can perform fixup /
// reconstruction on our way back up the tree.
if cfg!(feature = "servo") && !data.damage.is_empty() {
return true;
}
trace!("{:?} doesn't need traversal", el);
false
}
/// Returns true if we want to cull this subtree from the travesal.
fn should_cull_subtree(
&self,
context: &mut StyleContext<E>,
parent: E,
parent_data: &ElementData,
is_initial_style: bool,
) -> bool {
debug_assert!(parent.has_current_styles_for_traversal(
parent_data,
context.shared.traversal_flags,
));
// If the parent computed display:none, we don't style the subtree.
if parent_data.styles.is_display_none() {
debug!("Parent {:?} is display:none, culling traversal", parent);
return true;
}
// Gecko-only XBL handling.
//
// When we apply the XBL binding during frame construction, we restyle
// the whole subtree again if the binding is valid, so assuming it's
// likely to load valid bindings, we avoid wasted work here, which may
// be a very big perf hit when elements with bindings are nested
// heavily.
if cfg!(feature = "gecko") &&
is_initial_style &&
parent_data.styles.primary().has_moz_binding()
{
debug!("Parent {:?} has XBL binding, deferring traversal", parent);
return true;
}
return false;
}
/// Return the shared style context common to all worker threads.
fn shared_context(&self) -> &SharedStyleContext;
}
/// Manually resolve style by sequentially walking up the parent chain to the
/// first styled Element, ignoring pending restyles. The resolved style is made
/// available via a callback, and can be dropped by the time this function
/// returns in the display:none subtree case.
pub fn resolve_style<E>(
context: &mut StyleContext<E>,
element: E,
rule_inclusion: RuleInclusion,
pseudo: Option<&PseudoElement>,
) -> ElementStyles
where
E: TElement,
{
use style_resolver::StyleResolverForElement;
debug_assert!(rule_inclusion == RuleInclusion::DefaultOnly ||
pseudo.map_or(false, |p| p.is_before_or_after()) ||
element.borrow_data().map_or(true, |d| !d.has_styles()),
"Why are we here?");
let mut ancestors_requiring_style_resolution = SmallVec::<[E; 16]>::new();
// Clear the bloom filter, just in case the caller is reusing TLS.
context.thread_local.bloom_filter.clear();
let mut style = None;
let mut ancestor = element.traversal_parent();
while let Some(current) = ancestor {
if rule_inclusion == RuleInclusion::All {
if let Some(data) = current.borrow_data() {
if let Some(ancestor_style) = data.styles.get_primary() {
style = Some(ancestor_style.clone());
break;
}
}
}
ancestors_requiring_style_resolution.push(current);
ancestor = current.traversal_parent();
}
if let Some(ancestor) = ancestor {
context.thread_local.bloom_filter.rebuild(ancestor);
context.thread_local.bloom_filter.push(ancestor);
}
let mut layout_parent_style = style.clone();
while let Some(style) = layout_parent_style.take() {
if !style.is_display_contents() {
layout_parent_style = Some(style);
break;
}
ancestor = ancestor.unwrap().traversal_parent();
layout_parent_style = ancestor.map(|a| {
a.borrow_data().unwrap().styles.primary().clone()
});
}
for ancestor in ancestors_requiring_style_resolution.iter().rev() {
context.thread_local.bloom_filter.assert_complete(*ancestor);
// Actually `PseudoElementResolution` doesn't really matter here.
// (but it does matter below!).
let primary_style =
StyleResolverForElement::new(*ancestor, context, rule_inclusion, PseudoElementResolution::IfApplicable)
.resolve_primary_style(
style.as_ref().map(|s| &**s),
layout_parent_style.as_ref().map(|s| &**s)
);
let is_display_contents = primary_style.style().is_display_contents();
style = Some(primary_style.style.0);
if !is_display_contents {
layout_parent_style = style.clone();
}
context.thread_local.bloom_filter.push(*ancestor);
}
context.thread_local.bloom_filter.assert_complete(element);
StyleResolverForElement::new(element, context, rule_inclusion, PseudoElementResolution::Force)
.resolve_style(
style.as_ref().map(|s| &**s),
layout_parent_style.as_ref().map(|s| &**s)
).into()
}
/// Calculates the style for a single node.
#[inline]
#[allow(unsafe_code)]
pub fn recalc_style_at<E, D, F>(
traversal: &D,
traversal_data: &PerLevelTraversalData,
context: &mut StyleContext<E>,
element: E,
data: &mut ElementData,
note_child: F,
)
where
E: TElement,
D: DomTraversal<E>,
F: FnMut(E::ConcreteNode),
{
use std::cmp;
use traversal_flags::TraversalFlags;
let flags = context.shared.traversal_flags;
let is_initial_style = !data.has_styles();
context.thread_local.statistics.elements_traversed += 1;
debug_assert!(flags.intersects(TraversalFlags::AnimationOnly) ||
!element.has_snapshot() || element.handled_snapshot(),
"Should've handled snapshots here already");
let compute_self = !element.has_current_styles_for_traversal(data, flags);
debug!("recalc_style_at: {:?} (compute_self={:?}, \
dirty_descendants={:?}, data={:?})",
element, compute_self, element.has_dirty_descendants(), data);
let mut child_cascade_requirement = ChildCascadeRequirement::CanSkipCascade;
// Compute style for this element if necessary.
if compute_self {
child_cascade_requirement =
compute_style(traversal_data, context, element, data);
if element.is_native_anonymous() {
// We must always cascade native anonymous subtrees, since they inherit
// styles from their first non-NAC ancestor.
child_cascade_requirement = cmp::max(
child_cascade_requirement,
ChildCascadeRequirement::MustCascadeChildren,
);
}
// If we're restyling this element to display:none, throw away all style
// data in the subtree, notify the caller to early-return.
if data.styles.is_display_none() {
debug!("{:?} style is display:none - clearing data from descendants.",
element);
unsafe { clear_descendant_data(element); }
}
// Inform any paint worklets of changed style, to speculatively
// evaluate the worklet code. In the case that the size hasn't changed,
// this will result in increased concurrency between script and layout.
notify_paint_worklet(context, data);
} else {
debug_assert!(data.has_styles());
data.set_traversed_without_styling();
}
// Now that matching and cascading is done, clear the bits corresponding to
// those operations and compute the propagated restyle hint (unless we're
// not processing invalidations, in which case don't need to propagate it
// and must avoid clearing it).
debug_assert!(flags.for_animation_only() ||
!data.hint.has_animation_hint(),
"animation restyle hint should be handled during \
animation-only restyles");
let propagated_hint = data.hint.propagate(&flags);
trace!("propagated_hint={:?}, cascade_requirement={:?}, \
is_display_none={:?}, implementing_pseudo={:?}",
propagated_hint,
child_cascade_requirement,
data.styles.is_display_none(),
element.implemented_pseudo_element());
debug_assert!(element.has_current_styles_for_traversal(data, flags),
"Should have computed style or haven't yet valid computed \
style in case of animation-only restyle");
let has_dirty_descendants_for_this_restyle =
if flags.for_animation_only() {
element.has_animation_only_dirty_descendants()
} else {
element.has_dirty_descendants()
};
// Before examining each child individually, try to prove that our children
// don't need style processing. They need processing if any of the following
// conditions hold:
//
// * We have the dirty descendants bit.
// * We're propagating a restyle hint.
// * We can't skip the cascade.
// * This is a servo non-incremental traversal.
//
// Additionally, there are a few scenarios where we avoid traversing the
// subtree even if descendant styles are out of date. These cases are
// enumerated in should_cull_subtree().
let mut traverse_children =
has_dirty_descendants_for_this_restyle ||
!propagated_hint.is_empty() ||
!child_cascade_requirement.can_skip_cascade() ||
is_servo_nonincremental_layout();
traverse_children =
traverse_children &&
!traversal.should_cull_subtree(context, element, &data, is_initial_style);
// Examine our children, and enqueue the appropriate ones for traversal.
if traverse_children {
note_children::<E, D, F>(
context,
element,
data,
propagated_hint,
child_cascade_requirement,
is_initial_style,
note_child
);
}
// FIXME(bholley): Make these assertions pass for servo.
if cfg!(feature = "gecko") && cfg!(debug_assertions) && data.styles.is_display_none() {
debug_assert!(!element.has_dirty_descendants());
debug_assert!(!element.has_animation_only_dirty_descendants());
}
debug_assert!(flags.for_animation_only() ||
!flags.contains(TraversalFlags::ClearDirtyBits) ||
!element.has_animation_only_dirty_descendants(),
"Should have cleared animation bits already");
clear_state_after_traversing(element, data, flags);
}
fn clear_state_after_traversing<E>(
element: E,
data: &mut ElementData,
flags: TraversalFlags
)
where
E: TElement,
{
// If we are in a forgetful traversal, drop the existing restyle
// data here, since we won't need to perform a post-traversal to pick up
// any change hints.
if flags.contains(TraversalFlags::Forgetful) {
data.clear_restyle_flags_and_damage();
}
// Clear dirty bits as appropriate.
if flags.for_animation_only() {
if flags.intersects(TraversalFlags::ClearDirtyBits | TraversalFlags::ClearAnimationOnlyDirtyDescendants) {
unsafe { element.unset_animation_only_dirty_descendants(); }
}
} else if flags.contains(TraversalFlags::ClearDirtyBits) {
// The animation traversal happens first, so we don't need to guard against
// clearing the animation bit on the regular traversal.
unsafe { element.clear_dirty_bits(); }
}
}
fn compute_style<E>(
traversal_data: &PerLevelTraversalData,
context: &mut StyleContext<E>,
element: E,
data: &mut ElementData
) -> ChildCascadeRequirement
where
E: TElement,
{
use data::RestyleKind::*;
context.thread_local.statistics.elements_styled += 1;
let kind = data.restyle_kind(context.shared);
debug!("compute_style: {:?} (kind={:?})", element, kind);
if data.has_styles() {
data.set_restyled();
}
let mut important_rules_changed = false;
let new_styles = match kind {
MatchAndCascade => {
debug_assert!(!context.shared.traversal_flags.for_animation_only(),
"MatchAndCascade shouldn't be processed during \
animation-only traversal");
// Ensure the bloom filter is up to date.
context.thread_local.bloom_filter
.insert_parents_recovering(element,
traversal_data.current_dom_depth);
context.thread_local.bloom_filter.assert_complete(element);
debug_assert_eq!(
context.thread_local.bloom_filter.matching_depth(),
traversal_data.current_dom_depth
);
// This is only relevant for animations as of right now.
important_rules_changed = true;
let mut target = StyleSharingTarget::new(element);
// Now that our bloom filter is set up, try the style sharing
// cache.
match target.share_style_if_possible(context) {
Some(shared_styles) => {
context.thread_local.statistics.styles_shared += 1;
shared_styles
}
None => {
context.thread_local.statistics.elements_matched += 1;
// Perform the matching and cascading.
let new_styles = {
let mut resolver =
StyleResolverForElement::new(
element,
context,
RuleInclusion::All,
PseudoElementResolution::IfApplicable
);
resolver.resolve_style_with_default_parents()
};
context.thread_local.sharing_cache.insert_if_possible(
&element,
&new_styles.primary,
Some(&mut target),
traversal_data.current_dom_depth,
);
new_styles
}
}
}
CascadeWithReplacements(flags) => {
// Skipping full matching, load cascade inputs from previous values.
let mut cascade_inputs =
ElementCascadeInputs::new_from_element_data(data);
important_rules_changed =
element.replace_rules(flags, context, &mut cascade_inputs);
let mut resolver =
StyleResolverForElement::new(
element,
context,
RuleInclusion::All,
PseudoElementResolution::IfApplicable
);
resolver.cascade_styles_with_default_parents(cascade_inputs)
}
CascadeOnly => {
// Skipping full matching, load cascade inputs from previous values.
let cascade_inputs =
ElementCascadeInputs::new_from_element_data(data);
let new_styles = {
let mut resolver =
StyleResolverForElement::new(
element,
context,
RuleInclusion::All,
PseudoElementResolution::IfApplicable
);
resolver.cascade_styles_with_default_parents(cascade_inputs)
};
// Insert into the cache, but only if this style isn't reused from a
// sibling or cousin. Otherwise, recascading a bunch of identical
// elements would unnecessarily flood the cache with identical entries.
//
// This is analagous to the obvious "don't insert an element that just
// got a hit in the style sharing cache" behavior in the MatchAndCascade
// handling above.
//
// Note that, for the MatchAndCascade path, we still insert elements that
// shared styles via the rule node, because we know that there's something
// different about them that caused them to miss the sharing cache before
// selector matching. If we didn't, we would still end up with the same
// number of eventual styles, but would potentially miss out on various
// opportunities for skipping selector matching, which could hurt
// performance.
if !new_styles.primary.reused_via_rule_node {
context.thread_local.sharing_cache.insert_if_possible(
&element,
&new_styles.primary,
None,
traversal_data.current_dom_depth,
);
}
new_styles
}
};
element.finish_restyle(
context,
data,
new_styles,
important_rules_changed
)
}
#[cfg(feature = "servo")]
fn notify_paint_worklet<E>(context: &StyleContext<E>, data: &ElementData)
where
E: TElement,
{
use style_traits::ToCss;
use values::Either;
use values::generics::image::Image;
// We speculatively evaluate any paint worklets during styling.
// This allows us to run paint worklets in parallel with style and layout.
// Note that this is wasted effort if the size of the node has
// changed, but in may cases it won't have.
if let Some(ref values) = data.styles.primary {
for image in &values.get_background().background_image.0 {
let (name, arguments) = match *image {
Either::Second(Image::PaintWorklet(ref worklet)) => (&worklet.name, &worklet.arguments),
_ => continue,
};
let painter = match context.shared.registered_speculative_painters.get(name) {
Some(painter) => painter,
None => continue,
};
let properties = painter.properties().iter()
.filter_map(|(name, id)| id.as_shorthand().err().map(|id| (name, id)))
.map(|(name, id)| (name.clone(), values.computed_value_to_string(id)))
.collect();
let arguments = arguments.iter()
.map(|argument| argument.to_css_string())
.collect();
debug!("Notifying paint worklet {}.", painter.name());
painter.speculatively_draw_a_paint_image(properties, arguments);
}
}
}
#[cfg(feature = "gecko")]
fn notify_paint_worklet<E>(_context: &StyleContext<E>, _data: &ElementData)
where
E: TElement,
{
// The CSS paint API is Servo-only at the moment
}
fn note_children<E, D, F>(
context: &mut StyleContext<E>,
element: E,
data: &ElementData,
propagated_hint: RestyleHint,
cascade_requirement: ChildCascadeRequirement,
is_initial_style: bool,
mut note_child: F,
)
where
E: TElement,
D: DomTraversal<E>,
F: FnMut(E::ConcreteNode),
{
trace!("note_children: {:?}", element);
let flags = context.shared.traversal_flags;
// Loop over all the traversal children.
for child_node in element.traversal_children() {
let child = match child_node.as_element() {
Some(el) => el,
None => {
if is_servo_nonincremental_layout() ||
D::text_node_needs_traversal(child_node, data) {
note_child(child_node);
}
continue;
},
};
let mut child_data = child.mutate_data();
let mut child_data = child_data.as_mut().map(|d| &mut **d);
trace!(" > {:?} -> {:?} + {:?}, pseudo: {:?}",
child,
child_data.as_ref().map(|d| d.hint),
propagated_hint,
child.implemented_pseudo_element());
if let Some(ref mut child_data) = child_data {
let mut child_hint = propagated_hint;
match cascade_requirement {
ChildCascadeRequirement::CanSkipCascade => {}
ChildCascadeRequirement::MustCascadeDescendants => {
child_hint |= RestyleHint::RECASCADE_SELF | RestyleHint::RECASCADE_DESCENDANTS;
}
ChildCascadeRequirement::MustCascadeChildrenIfInheritResetStyle => {
use properties::computed_value_flags::ComputedValueFlags;
if child_data.styles.primary().flags.contains(ComputedValueFlags::INHERITS_RESET_STYLE) {
child_hint |= RestyleHint::RECASCADE_SELF;
}
}
ChildCascadeRequirement::MustCascadeChildren => {
child_hint |= RestyleHint::RECASCADE_SELF;
}
}
child_data.hint.insert(child_hint);
// Handle element snapshots and invalidation of descendants and siblings
// as needed.
//
// NB: This will be a no-op if there's no snapshot.
child_data.invalidate_style_if_needed(
child,
&context.shared,
Some(&context.thread_local.stack_limit_checker),
&mut context.thread_local.nth_index_cache,
);
}
if D::element_needs_traversal(child, flags, child_data.map(|d| &*d)) {
note_child(child_node);
// Set the dirty descendants bit on the parent as needed, so that we
// can find elements during the post-traversal.
//
// Note that these bits may be cleared again at the bottom of
// recalc_style_at if requested by the caller.
if !is_initial_style {
if flags.for_animation_only() {
unsafe { element.set_animation_only_dirty_descendants(); }
} else {
unsafe { element.set_dirty_descendants(); }
}
}
}
}
}
/// Clear style data for all the subtree under `root` (but not for root itself).
///
/// We use a list to avoid unbounded recursion, which we need to avoid in the
/// parallel traversal because the rayon stacks are small.
pub unsafe fn clear_descendant_data<E>(root: E)
where
E: TElement,
{
let mut parents = SmallVec::<[E; 32]>::new();
parents.push(root);
while let Some(p) = parents.pop() {
for kid in p.traversal_children() {
if let Some(kid) = kid.as_element() {
// We maintain an invariant that, if an element has data, all its
// ancestors have data as well.
//
// By consequence, any element without data has no descendants with
// data.
if kid.get_data().is_some() {
kid.clear_data();
parents.push(kid);
}
}
}
}
// Make sure not to clear NODE_NEEDS_FRAME on the root.
root.clear_descendant_bits();
}