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layout: Add a first pass at incremental box tree construction (#37751)

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This change:

- Adds a new type of LayoutDamage that signifies that a box needs its
  children recollected, because one or more of them need to be rebuilt.
- During restyle damage propagation, propagate this new damage upward in
  the tree. Then box tree construction should be able to preserve any
  still-valid box tree nodes from box slots.
- During BlockLevelBox job finalization, if a box slot is valid and
  there is not LayoutDamage to the element, use the old box slot,
  ensuring that its fragment cache is invalidated.

Testing: This should not change observable behavior and thus is covered
by existing WPT tests.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
Co-authored-by: coding-joedow <ibluegalaxy_taoj@163.com>
This commit is contained in:
Martin Robinson 2025-07-03 10:13:20 +02:00 • committed by GitHub
parent 9aa06b2c17
commit 6dafeb7a59
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GPG key ID: B5690EEEBB952194
9 changed files with 156 additions and 78 deletions
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40
components/layout/traversal.rs
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@ -2,6 +2,7 @@
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
use layout_api::LayoutDamage;
use layout_api::wrapper_traits::LayoutNode;
use script::layout_dom::ServoLayoutNode;
use style::context::{SharedStyleContext, StyleContext};
@ -103,39 +104,48 @@ pub(crate) fn compute_damage_and_repair_style(
pub(crate) fn compute_damage_and_repair_style_inner(
context: &SharedStyleContext,
node: ServoLayoutNode<'_>,
parent_restyle_damage: RestyleDamage,
damage_from_parent: RestyleDamage,
) -> RestyleDamage {
let element_damage;
let mut element_damage;
let element_data = &node
.style_data()
.expect("Should not run `compute_damage` before styling.")
.element_data;
{
let mut element_data = node
.style_data()
.expect("Should not run `compute_damage` before styling.")
.element_data
.borrow_mut();
element_damage = std::mem::take(&mut element_data.damage);
let mut element_data = element_data.borrow_mut();
element_data.damage.insert(damage_from_parent);
element_damage = element_data.damage;
if let Some(ref style) = element_data.styles.primary {
if style.get_box().display == Display::None {
return element_damage | parent_restyle_damage;
return element_damage;
}
}
}
let element_and_parent_damage = element_damage | parent_restyle_damage;
// If we are reconstructing this node, then all of the children should be reconstructed as well.
let damage_for_children = element_damage | damage_from_parent;
let mut damage_from_children = RestyleDamage::empty();
for child in iter_child_nodes(node) {
if child.is_element() {
damage_from_children |=
compute_damage_and_repair_style_inner(context, child, element_and_parent_damage);
compute_damage_and_repair_style_inner(context, child, damage_for_children);
}
}
let damage_for_parent = damage_from_children | element_and_parent_damage;
if !damage_for_parent.contains(RestyleDamage::RELAYOUT) && !element_damage.is_empty() {
if element_damage != RestyleDamage::reconstruct() && !element_damage.is_empty() {
node.repair_style(context);
}
damage_for_parent
// If one of our children needed to be reconstructed, we need to recollect children
// during box tree construction.
if damage_from_children.contains(LayoutDamage::recollect_box_tree_children()) {
element_damage.insert(LayoutDamage::recollect_box_tree_children());
element_data.borrow_mut().damage.insert(element_damage);
}
// Only propagate up layout phases from children, as other types of damage are
// incorporated into `element_damage` above.
element_damage | (damage_from_children & RestyleDamage::RELAYOUT)
}