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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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4
components/layout/display_list/stacking_context.rs
View file

@ -618,7 +618,7 @@ impl StackingContext {
// If it’s larger, we also want to paint areas reachable after scrolling.
let painting_area = fragment_tree
.initial_containing_block
.union(&fragment_tree.scrollable_overflow)
.union(&fragment_tree.scrollable_overflow())
.to_webrender();
let background_color =
@ -1346,7 +1346,7 @@ impl BoxFragment {
let position = self.style.get_box().position;
// https://drafts.csswg.org/css2/#clipping
// The clip property applies only to absolutely positioned elements
if position != ComputedPosition::Absolute && position != ComputedPosition::Fixed {
if !position.is_absolutely_positioned() {
return None;
}

24
components/layout/flow/root.rs
View file

@ -29,7 +29,7 @@ use crate::flow::inline::InlineItem;
use crate::flow::{BlockContainer, BlockFormattingContext, BlockLevelBox};
use crate::formatting_contexts::IndependentFormattingContext;
use crate::fragment_tree::FragmentTree;
use crate::geom::{LogicalVec2, PhysicalRect, PhysicalSize};
use crate::geom::{LogicalVec2, PhysicalSize};
use crate::positioned::{AbsolutelyPositionedBox, PositioningContext};
use crate::replaced::ReplacedContents;
use crate::style_ext::{Display, DisplayGeneratingBox, DisplayInside};
@ -392,31 +392,9 @@ impl BoxTree {
&mut root_fragments,
);
let scrollable_overflow = root_fragments
.iter()
.fold(PhysicalRect::zero(), |acc, child| {
let child_overflow = child.scrollable_overflow_for_parent();
// https://drafts.csswg.org/css-overflow/#scrolling-direction
// We want to clip scrollable overflow on box-start and inline-start
// sides of the scroll container.
//
// FIXME(mrobinson, bug 25564): This should take into account writing
// mode.
let child_overflow = PhysicalRect::new(
euclid::Point2D::zero(),
euclid::Size2D::new(
child_overflow.size.width + child_overflow.origin.x,
child_overflow.size.height + child_overflow.origin.y,
),
);
acc.union(&child_overflow)
});
FragmentTree::new(
layout_context,
root_fragments,
scrollable_overflow,
physical_containing_block,
self.viewport_scroll_sensitivity,
)

44
components/layout/fragment_tree/box_fragment.rs
View file

@ -89,7 +89,7 @@ pub(crate) struct BoxFragment {
block_margins_collapsed_with_children: Option<Box<CollapsedBlockMargins>>,
/// The scrollable overflow of this box fragment.
pub scrollable_overflow_from_children: PhysicalRect<Au>,
scrollable_overflow: Option<PhysicalRect<Au>>,
/// The resolved box insets if this box is `position: sticky`. These are calculated
/// during `StackingContextTree` construction because they rely on the size of the
@ -114,11 +114,6 @@ impl BoxFragment {
margin: PhysicalSides<Au>,
clearance: Option<Au>,
) -> BoxFragment {
let scrollable_overflow_from_children =
children.iter().fold(PhysicalRect::zero(), |acc, child| {
acc.union(&child.scrollable_overflow_for_parent())
});
BoxFragment {
base: base_fragment_info.into(),
style,
@ -131,7 +126,7 @@ impl BoxFragment {
clearance,
baselines: Baselines::default(),
block_margins_collapsed_with_children: None,
scrollable_overflow_from_children,
scrollable_overflow: None,
resolved_sticky_insets: AtomicRefCell::default(),
background_mode: BackgroundMode::Normal,
specific_layout_info: None,
@ -203,13 +198,23 @@ impl BoxFragment {
/// Get the scrollable overflow for this [`BoxFragment`] relative to its
/// containing block.
pub fn scrollable_overflow(&self) -> PhysicalRect<Au> {
self.scrollable_overflow
.expect("Should only call `scrollable_overflow()` after calculating overflow")
}
pub(crate) fn calculate_scrollable_overflow(&mut self) {
let scrollable_overflow_from_children = self
.children
.iter()
.fold(PhysicalRect::zero(), |acc, child| {
acc.union(&child.calculate_scrollable_overflow_for_parent())
});
let physical_padding_rect = self.padding_rect();
let content_origin = self.content_rect.origin.to_vector();
physical_padding_rect.union(
&self
.scrollable_overflow_from_children
.translate(content_origin),
)
self.scrollable_overflow = Some(
physical_padding_rect
.union(&scrollable_overflow_from_children.translate(content_origin)),
);
}
pub(crate) fn set_containing_block(&mut self, containing_block: &PhysicalRect<Au>) {
@ -275,7 +280,12 @@ impl BoxFragment {
tree.end_level();
}
pub fn scrollable_overflow_for_parent(&self) -> PhysicalRect<Au> {
pub(crate) fn scrollable_overflow_for_parent(&self) -> PhysicalRect<Au> {
// TODO: Properly handle absolutely positioned fragments.
if self.style.get_box().position.is_absolutely_positioned() {
return PhysicalRect::zero();
}
let mut overflow = self.border_rect();
if !self.style.establishes_scroll_container(self.base.flags) {
// https://www.w3.org/TR/css-overflow-3/#scrollable
@ -328,7 +338,7 @@ impl BoxFragment {
///
/// Return the clipped the scrollable overflow based on its scroll origin, determined by overflow direction.
/// For an element, the clip rect is the padding rect and for viewport, it is the initial containing block.
pub fn clip_unreachable_scrollable_overflow_region(
pub(crate) fn clip_unreachable_scrollable_overflow_region(
&self,
scrollable_overflow: PhysicalRect<Au>,
clipping_rect: PhysicalRect<Au>,
@ -362,7 +372,7 @@ impl BoxFragment {
///
/// Return the clipped the scrollable overflow based on its scroll origin, determined by overflow direction.
/// This will coincides with the scrollport if the fragment is a scroll container.
pub fn reachable_scrollable_overflow_region(&self) -> PhysicalRect<Au> {
pub(crate) fn reachable_scrollable_overflow_region(&self) -> PhysicalRect<Au> {
self.clip_unreachable_scrollable_overflow_region(
self.scrollable_overflow(),
self.padding_rect(),
@ -421,9 +431,7 @@ impl BoxFragment {
return convert_to_au_or_auto(PhysicalSides::new(top, right, bottom, left));
}
debug_assert!(
position == ComputedPosition::Fixed || position == ComputedPosition::Absolute
);
debug_assert!(position.is_absolutely_positioned());
let margin_rect = self.margin_rect();
let (top, bottom) = match (&insets.top, &insets.bottom) {

23
components/layout/fragment_tree/fragment.rs
View file

@ -183,19 +183,36 @@ impl Fragment {
}
}
pub fn scrollable_overflow_for_parent(&self) -> PhysicalRect<Au> {
pub(crate) fn scrollable_overflow_for_parent(&self) -> PhysicalRect<Au> {
match self {
Fragment::Box(fragment) | Fragment::Float(fragment) => {
fragment.borrow().scrollable_overflow_for_parent()
return fragment.borrow().scrollable_overflow_for_parent();
},
Fragment::AbsoluteOrFixedPositioned(_) => PhysicalRect::zero(),
Fragment::Positioning(fragment) => fragment.borrow().scrollable_overflow,
Fragment::Positioning(fragment) => fragment.borrow().scrollable_overflow_for_parent(),
Fragment::Text(fragment) => fragment.borrow().rect,
Fragment::Image(fragment) => fragment.borrow().rect,
Fragment::IFrame(fragment) => fragment.borrow().rect,
}
}
pub(crate) fn calculate_scrollable_overflow_for_parent(&self) -> PhysicalRect<Au> {
self.calculate_scrollable_overflow();
self.scrollable_overflow_for_parent()
}
pub(crate) fn calculate_scrollable_overflow(&self) {
match self {
Fragment::Box(fragment) | Fragment::Float(fragment) => {
fragment.borrow_mut().calculate_scrollable_overflow()
},
Fragment::Positioning(fragment) => {
fragment.borrow_mut().calculate_scrollable_overflow()
},
_ => {},
}
}
pub(crate) fn cumulative_border_box_rect(&self) -> Option<PhysicalRect<Au>> {
match self {
Fragment::Box(fragment) | Fragment::Float(fragment) => {

43
components/layout/fragment_tree/fragment_tree.rs
View file

@ -2,14 +2,14 @@
* 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 std::cell::Cell;
use app_units::Au;
use base::print_tree::PrintTree;
use compositing_traits::display_list::AxesScrollSensitivity;
use euclid::default::Size2D;
use fxhash::FxHashSet;
use malloc_size_of_derive::MallocSizeOf;
use style::animation::AnimationSetKey;
use webrender_api::units;
use super::{BoxFragment, ContainingBlockManager, Fragment};
use crate::ArcRefCell;
@ -30,7 +30,7 @@ pub struct FragmentTree {
/// The scrollable overflow rectangle for the entire tree
/// <https://drafts.csswg.org/css-overflow/#scrollable>
pub(crate) scrollable_overflow: PhysicalRect<Au>,
scrollable_overflow: Cell<Option<PhysicalRect<Au>>>,
/// The containing block used in the layout of this fragment tree.
pub(crate) initial_containing_block: PhysicalRect<Au>,
@ -43,13 +43,12 @@ impl FragmentTree {
pub(crate) fn new(
layout_context: &LayoutContext,
root_fragments: Vec<Fragment>,
scrollable_overflow: PhysicalRect<Au>,
initial_containing_block: PhysicalRect<Au>,
viewport_scroll_sensitivity: AxesScrollSensitivity,
) -> Self {
let fragment_tree = Self {
root_fragments,
scrollable_overflow,
scrollable_overflow: Cell::default(),
initial_containing_block,
viewport_scroll_sensitivity,
};
@ -97,11 +96,35 @@ impl FragmentTree {
}
}
pub fn scrollable_overflow(&self) -> units::LayoutSize {
units::LayoutSize::from_untyped(Size2D::new(
self.scrollable_overflow.size.width.to_f32_px(),
self.scrollable_overflow.size.height.to_f32_px(),
))
pub(crate) fn scrollable_overflow(&self) -> PhysicalRect<Au> {
self.scrollable_overflow
.get()
.expect("Should only call `scrollable_overflow()` after calculating overflow")
}
pub(crate) fn calculate_scrollable_overflow(&self) {
self.scrollable_overflow
.set(Some(self.root_fragments.iter().fold(
PhysicalRect::zero(),
|acc, child| {
let child_overflow = child.calculate_scrollable_overflow_for_parent();
// https://drafts.csswg.org/css-overflow/#scrolling-direction
// We want to clip scrollable overflow on box-start and inline-start
// sides of the scroll container.
//
// FIXME(mrobinson, bug 25564): This should take into account writing
// mode.
let child_overflow = PhysicalRect::new(
euclid::Point2D::zero(),
euclid::Size2D::new(
child_overflow.size.width + child_overflow.origin.x,
child_overflow.size.height + child_overflow.origin.y,
),
);
acc.union(&child_overflow)
},
)));
}
pub(crate) fn find<T>(

31
components/layout/fragment_tree/positioning_fragment.rs
View file

@ -22,7 +22,7 @@ pub(crate) struct PositioningFragment {
pub children: Vec<Fragment>,
/// The scrollable overflow of this anonymous fragment's children.
pub scrollable_overflow: PhysicalRect<Au>,
scrollable_overflow: Option<PhysicalRect<Au>>,
/// The style of the fragment.
pub style: ServoArc<ComputedValues>,
@ -55,20 +55,12 @@ impl PositioningFragment {
rect: PhysicalRect<Au>,
children: Vec<Fragment>,
) -> ArcRefCell<Self> {
let content_origin = rect.origin;
let scrollable_overflow = children.iter().fold(PhysicalRect::zero(), |acc, child| {
acc.union(
&child
.scrollable_overflow_for_parent()
.translate(content_origin.to_vector()),
)
});
ArcRefCell::new(PositioningFragment {
base,
style,
rect,
children,
scrollable_overflow,
scrollable_overflow: None,
cumulative_containing_block_rect: PhysicalRect::zero(),
})
}
@ -81,6 +73,25 @@ impl PositioningFragment {
rect.translate(self.cumulative_containing_block_rect.origin.to_vector())
}
pub(crate) fn calculate_scrollable_overflow(&mut self) {
self.scrollable_overflow = Some(self.children.iter().fold(
PhysicalRect::zero(),
|acc, child| {
acc.union(
&child
.calculate_scrollable_overflow_for_parent()
.translate(self.rect.origin.to_vector()),
)
},
));
}
pub(crate) fn scrollable_overflow_for_parent(&self) -> PhysicalRect<Au> {
self.scrollable_overflow.expect(
"Should only call `scrollable_overflow_for_parent()` after calculating overflow",
)
}
pub fn print(&self, tree: &mut PrintTree) {
tree.new_level(format!(
"PositioningFragment\

38
components/layout/layout_impl.rs
View file

@ -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(),

7
components/layout/positioned.rs
View file

@ -305,10 +305,7 @@ impl PositioningContext {
}
pub(crate) fn push(&mut self, hoisted_box: HoistedAbsolutelyPositionedBox) {
debug_assert!(matches!(
hoisted_box.position(),
Position::Absolute | Position::Fixed
));
debug_assert!(hoisted_box.position().is_absolutely_positioned());
self.absolutes.push(hoisted_box);
}
@ -380,7 +377,7 @@ impl HoistedAbsolutelyPositionedBox {
.context
.style()
.clone_position();
assert!(position == Position::Fixed || position == Position::Absolute);
assert!(position.is_absolutely_positioned());
position
}

4
components/layout/query.rs
View file

@ -3,7 +3,7 @@
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
//! Utilities for querying the layout, as needed by layout.
use std::sync::Arc;
use std::rc::Rc;
use app_units::Au;
use euclid::default::{Point2D, Rect};
@ -80,7 +80,7 @@ pub fn process_client_rect_request(node: ServoLayoutNode<'_>) -> Rect<i32> {
/// <https://drafts.csswg.org/cssom-view/#scrolling-area>
pub fn process_node_scroll_area_request(
requested_node: Option<ServoLayoutNode<'_>>,
fragment_tree: Option<Arc<FragmentTree>>,
fragment_tree: Option<Rc<FragmentTree>>,
) -> Rect<i32> {
let Some(tree) = fragment_tree else {
return Rect::zero();