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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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44
components/layout/fragment_tree/box_fragment.rs
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@ -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) {