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layout: Simplify effective_overflow() a little (#39172)

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This implements the Default trait for `AxesOverflow`, to avoid having to
manually set both axes to `Overflow::Visible`.

Also implements the conversion from `&ComputedValues` to `AxesOverflow`,
which is the also used for overflow viewport propagation.

And moves the `is_inline_box()` checkinto the `ignores_overflow` logic.

Testing: Not needed, no change in behavior

Signed-off-by: Oriol Brufau <obrufau@igalia.com>
This commit is contained in:
Oriol Brufau 2025-09-06 11:10:15 +02:00 • committed by GitHub
parent c490033c52
commit 506e186d03
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2 changed files with 55 additions and 58 deletions
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16
components/layout/flow/root.rs
View file

@ -31,7 +31,7 @@ use crate::fragment_tree::{FragmentFlags, FragmentTree};
use crate::geom::{LogicalVec2, PhysicalSize};
use crate::positioned::{AbsolutelyPositionedBox, PositioningContext};
use crate::replaced::ReplacedContents;
use crate::style_ext::{Display, DisplayGeneratingBox, DisplayInside};
use crate::style_ext::{AxesOverflow, Display, DisplayGeneratingBox, DisplayInside};
use crate::taffy::{TaffyItemBox, TaffyItemBoxInner};
use crate::{DefiniteContainingBlock, PropagatedBoxTreeData};
@ -60,11 +60,10 @@ impl BoxTree {
// > used overflow value of visible.
let root_style = root_element.style(&context.style_context);
let mut viewport_overflow_x = root_style.clone_overflow_x();
let mut viewport_overflow_y = root_style.clone_overflow_y();
let mut viewport_overflow = AxesOverflow::from(&*root_style);
let mut element_propagating_overflow = root_element;
if viewport_overflow_x == Overflow::Visible &&
viewport_overflow_y == Overflow::Visible &&
if viewport_overflow.x == Overflow::Visible &&
viewport_overflow.y == Overflow::Visible &&
!root_style.get_box().display.is_none()
{
for child in root_element.children() {
@ -77,8 +76,7 @@ impl BoxTree {
let style = child.style(&context.style_context);
if !style.get_box().display.is_none() {
viewport_overflow_x = style.clone_overflow_x();
viewport_overflow_y = style.clone_overflow_y();
viewport_overflow = AxesOverflow::from(&*style);
element_propagating_overflow = child;
break;
@ -112,8 +110,8 @@ impl BoxTree {
// > If visible is applied to the viewport, it must be interpreted as auto.
// > If clip is applied to the viewport, it must be interpreted as hidden.
viewport_scroll_sensitivity: AxesScrollSensitivity {
x: viewport_overflow_x.to_scrollable().into(),
y: viewport_overflow_y.to_scrollable().into(),
x: viewport_overflow.x.to_scrollable().into(),
y: viewport_overflow.y.to_scrollable().into(),
},
}
}

97
components/layout/style_ext.rs
View file

@ -64,6 +64,24 @@ pub struct AxesOverflow {
pub y: Overflow,
}
impl Default for AxesOverflow {
fn default() -> Self {
Self {
x: Overflow::Visible,
y: Overflow::Visible,
}
}
}
impl From<&ComputedValues> for AxesOverflow {
fn from(style: &ComputedValues) -> Self {
Self {
x: style.clone_overflow_x(),
y: style.clone_overflow_y(),
}
}
}
impl DisplayGeneratingBox {
pub(crate) fn display_inside(&self) -> DisplayInside {
match *self {
@ -594,79 +612,60 @@ impl ComputedValuesExt for ComputedValues {
/// flex containers, and grid containers. And some box types only accept a few values.
/// <https://www.w3.org/TR/css-overflow-3/#overflow-control>
fn effective_overflow(&self, fragment_flags: FragmentFlags) -> AxesOverflow {
let style_box = self.get_box();
let mut overflow_x = style_box.overflow_x;
let mut overflow_y = style_box.overflow_y;
// Inline boxes should never establish scroll containers.
if self.is_inline_box(fragment_flags) {
return AxesOverflow {
x: Overflow::Visible,
y: Overflow::Visible,
};
}
// https://www.w3.org/TR/css-overflow-3/#overflow-propagation
// The element from which the value is propagated must then have a used overflow value of visible.
if fragment_flags.contains(FragmentFlags::PROPAGATED_OVERFLOW_TO_VIEWPORT) {
return AxesOverflow {
x: Overflow::Visible,
y: Overflow::Visible,
};
return AxesOverflow::default();
}
let mut overflow = AxesOverflow::from(self);
// From <https://www.w3.org/TR/css-overflow-4/#overflow-control>:
// "On replaced elements, the used values of all computed values other than visible is clip."
if fragment_flags.contains(FragmentFlags::IS_REPLACED) {
if overflow_x != Overflow::Visible {
overflow_x = Overflow::Clip;
if overflow.x != Overflow::Visible {
overflow.x = Overflow::Clip;
}
if overflow_y != Overflow::Visible {
overflow_y = Overflow::Clip;
if overflow.y != Overflow::Visible {
overflow.y = Overflow::Clip;
}
return AxesOverflow {
x: overflow_x,
y: overflow_y,
};
return overflow;
}
let ignores_overflow = match style_box.display.inside() {
let ignores_overflow = match self.get_box().display.inside() {
// <https://drafts.csswg.org/css-overflow-3/#overflow-control>
// `overflow` doesn't apply to inline boxes.
stylo::DisplayInside::Flow => self.is_inline_box(fragment_flags),
// According to <https://drafts.csswg.org/css-tables/#global-style-overrides>,
// - overflow applies to table-wrapper boxes and not to table grid boxes.
// That's what Blink and WebKit do, however Firefox matches a CSSWG resolution that says
// the opposite: <https://lists.w3.org/Archives/Public/www-style/2012Aug/0298.html>
// Due to the way that we implement table-wrapper boxes, it's easier to align with Firefox.
// - Tables ignore overflow values different than visible, clip and hidden.
// This affects both axes, to ensure they have the same scrollability.
stylo::DisplayInside::Table => {
// According to <https://drafts.csswg.org/css-tables/#global-style-overrides>,
// - overflow applies to table-wrapper boxes and not to table grid boxes.
// That's what Blink and WebKit do, however Firefox matches a CSSWG resolution that says
// the opposite: <https://lists.w3.org/Archives/Public/www-style/2012Aug/0298.html>
// Due to the way that we implement table-wrapper boxes, it's easier to align with Firefox.
// - Tables ignore overflow values different than visible, clip and hidden.
// This affects both axes, to ensure they have the same scrollability.
!matches!(self.pseudo(), Some(PseudoElement::ServoTableGrid)) ||
matches!(overflow_x, Overflow::Auto | Overflow::Scroll) ||
matches!(overflow_y, Overflow::Auto | Overflow::Scroll)
matches!(overflow.x, Overflow::Auto | Overflow::Scroll) ||
matches!(overflow.y, Overflow::Auto | Overflow::Scroll)
},
// <https://drafts.csswg.org/css-tables/#global-style-overrides>
// Table-track and table-track-group boxes ignore overflow.
stylo::DisplayInside::TableColumn |
stylo::DisplayInside::TableColumnGroup |
stylo::DisplayInside::TableRow |
stylo::DisplayInside::TableRowGroup |
stylo::DisplayInside::TableHeaderGroup |
stylo::DisplayInside::TableFooterGroup => {
// <https://drafts.csswg.org/css-tables/#global-style-overrides>
// Table-track and table-track-group boxes ignore overflow.
true
},
stylo::DisplayInside::TableFooterGroup => true,
_ => false,
};
if ignores_overflow {
AxesOverflow {
x: Overflow::Visible,
y: Overflow::Visible,
}
} else {
AxesOverflow {
x: overflow_x,
y: overflow_y,
}
return AxesOverflow::default();
}
overflow
}
/// Return true if this style is a normal block and establishes