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layout: Split overflow calculation after fragment tree construction (#37203)

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Instead of computing scrollable overflow while constructing the fragment
tree, we will now do it later. In the future this will also allow to
only recalculate the overflow without rebuilding the tree when transform
properties change, but that's left for a follow-up.

Stylo PR: https://github.com/servo/stylo/pull/194

Testing: One test is now passing (more investigation is needed), but
otherwise this isn't expected to have any effect.

Signed-off-by: Oriol Brufau <obrufau@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>
This commit is contained in:
Oriol Brufau 2025-05-30 21:41:05 +02:00 • committed by GitHub
parent 079198c898
commit de2da3b1e1
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GPG key ID: B5690EEEBB952194
11 changed files with 148 additions and 96 deletions
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38
components/layout/layout_impl.rs
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@ -8,6 +8,7 @@ use std::cell::{Cell, RefCell};
use std::collections::HashMap;
use std::fmt::Debug;
use std::process;
use std::rc::Rc;
use std::sync::{Arc, LazyLock};
use app_units::Au;
@ -142,7 +143,7 @@ pub struct LayoutThread {
box_tree: RefCell<Option<Arc<BoxTree>>>,
/// The fragment tree.
fragment_tree: RefCell<Option<Arc<FragmentTree>>>,
fragment_tree: RefCell<Option<Rc<FragmentTree>>>,
/// The [`StackingContextTree`] cached from previous layouts.
stacking_context_tree: RefCell<Option<StackingContextTree>>,
@ -656,7 +657,7 @@ impl LayoutThread {
&mut layout_context,
viewport_changed,
);
self.calculate_overflow(damage);
self.build_stacking_context_tree(&reflow_request, damage);
self.build_display_list(&reflow_request, &mut layout_context);
@ -773,8 +774,11 @@ impl LayoutThread {
driver::traverse_dom(&recalc_style_traversal, token, rayon_pool).as_node();
let root_node = root_element.as_node();
let damage = compute_damage_and_repair_style(layout_context.shared_context(), root_node);
if !viewport_changed && !damage.contains(RestyleDamage::REBUILD_BOX) {
let mut damage =
compute_damage_and_repair_style(layout_context.shared_context(), root_node);
if viewport_changed {
damage = RestyleDamage::REBUILD_BOX;
} else if !damage.contains(RestyleDamage::REBUILD_BOX) {
layout_context.style_context.stylist.rule_tree().maybe_gc();
return damage;
}
@ -802,15 +806,12 @@ impl LayoutThread {
.unwrap()
.layout(recalc_style_traversal.context(), viewport_size)
};
let fragment_tree = Arc::new(if let Some(pool) = rayon_pool {
let fragment_tree = Rc::new(if let Some(pool) = rayon_pool {
pool.install(run_layout)
} else {
run_layout()
});
if self.debug.dump_flow_tree {
fragment_tree.print();
}
*self.fragment_tree.borrow_mut() = Some(fragment_tree);
// The FragmentTree has been updated, so any existing StackingContext tree that layout
@ -837,6 +838,19 @@ impl LayoutThread {
damage
}
fn calculate_overflow(&self, damage: RestyleDamage) {
if !damage.contains(RestyleDamage::RECALCULATE_OVERFLOW) {
return;
}
if let Some(fragment_tree) = &*self.fragment_tree.borrow() {
fragment_tree.calculate_scrollable_overflow();
if self.debug.dump_flow_tree {
fragment_tree.print();
}
}
}
fn build_stacking_context_tree(&self, reflow_request: &ReflowRequest, damage: RestyleDamage) {
if !reflow_request.reflow_goal.needs_display_list() &&
!reflow_request.reflow_goal.needs_display()
@ -858,13 +872,19 @@ impl LayoutThread {
viewport_size.height.to_f32_px(),
);
let scrollable_overflow = fragment_tree.scrollable_overflow();
let scrollable_overflow = LayoutSize::from_untyped(Size2D::new(
scrollable_overflow.size.width.to_f32_px(),
scrollable_overflow.size.height.to_f32_px(),
));
// Build the StackingContextTree. This turns the `FragmentTree` into a
// tree of fragments in CSS painting order and also creates all
// applicable spatial and clip nodes.
*self.stacking_context_tree.borrow_mut() = Some(StackingContextTree::new(
fragment_tree,
viewport_size,
fragment_tree.scrollable_overflow(),
scrollable_overflow,
self.id.into(),
fragment_tree.viewport_scroll_sensitivity,
self.first_reflow.get(),