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layout: Add a repaint-only incremental layout mode (#36978)

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This change adds the simplest kind of incremental layout. When Servo
detects that all style changes only require a repaint, only run stacking
context tree and WebRender display list generation. This means that
these kind of restyles do not need a re-layout. Instead, the existing
box and fragment trees will be used and the styles of damaged nodes will
be updated in their box and fragment tree nodes.

This requires a new style repair DOM traversal for nodes that have had
their style damaged. In addition, careful accounting of all the places
where we store style must happen in order ot update those styles.

Testing: This is covered by existing WPT tests as it should not change
observable behavior.

We have created a test case which shows a 50% speedup when run
in Servo, even though there still a long way to go to match the speed
of other browsers:
https://gist.github.com/mrobinson/44ec87d028c0198917a7715a06dd98a0

Co-authored-by: Oriol Brufau <obrufau@igalia.com>
Signed-off-by: Martin Robinson <mrobinson@igalia.com>

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
This commit is contained in:
Martin Robinson 2025-05-12 19:03:50 +02:00 • committed by GitHub
parent 51fa6cdcb6
commit 8808f9a468
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GPG key ID: B5690EEEBB952194
20 changed files with 467 additions and 72 deletions
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71
components/layout/dom.rs
View file

@ -19,11 +19,11 @@ use script_layout_interface::{
GenericLayoutDataTrait, LayoutElementType, LayoutNodeType as ScriptLayoutNodeType,
};
use servo_arc::Arc as ServoArc;
use style::context::SharedStyleContext;
use style::properties::ComputedValues;
use style::selector_parser::PseudoElement;
use crate::cell::ArcRefCell;
use crate::context::LayoutContext;
use crate::flexbox::FlexLevelBox;
use crate::flow::BlockLevelBox;
use crate::flow::inline::{InlineItem, SharedInlineStyles};
@ -102,6 +102,41 @@ impl LayoutBox {
LayoutBox::TableLevelBox(table_box) => table_box.fragments(),
}
}
fn repair_style(
&self,
context: &SharedStyleContext,
node: &ServoLayoutNode,
new_style: &ServoArc<ComputedValues>,
) {
match self {
LayoutBox::DisplayContents(inline_shared_styles) => {
*inline_shared_styles.style.borrow_mut() = new_style.clone();
*inline_shared_styles.selected.borrow_mut() = node.to_threadsafe().selected_style();
},
LayoutBox::BlockLevel(block_level_box) => {
block_level_box
.borrow_mut()
.repair_style(context, node, new_style);
},
LayoutBox::InlineLevel(inline_items) => {
for inline_item in inline_items {
inline_item
.borrow_mut()
.repair_style(context, node, new_style);
}
},
LayoutBox::FlexLevel(flex_level_box) => {
flex_level_box.borrow_mut().repair_style(context, new_style)
},
LayoutBox::TableLevelBox(table_level_box) => {
table_level_box.repair_style(context, new_style)
},
LayoutBox::TaffyItemBox(taffy_item_box) => {
taffy_item_box.borrow_mut().repair_style(context, new_style)
},
}
}
}
/// A wrapper for [`InnerDOMLayoutData`]. This is necessary to give the entire data
@ -167,7 +202,7 @@ pub(crate) trait NodeExt<'dom> {
fn as_iframe(&self) -> Option<(PipelineId, BrowsingContextId)>;
fn as_video(&self) -> Option<(Option<webrender_api::ImageKey>, Option<PhysicalSize<f64>>)>;
fn as_typeless_object_with_data_attribute(&self) -> Option<String>;
fn style(&self, context: &LayoutContext) -> ServoArc<ComputedValues>;
fn style(&self, context: &SharedStyleContext) -> ServoArc<ComputedValues>;
fn layout_data_mut(&self) -> AtomicRefMut<'dom, InnerDOMLayoutData>;
fn layout_data(&self) -> Option<AtomicRef<'dom, InnerDOMLayoutData>>;
@ -180,6 +215,8 @@ pub(crate) trait NodeExt<'dom> {
fn fragments_for_pseudo(&self, pseudo_element: Option<PseudoElement>) -> Vec<Fragment>;
fn invalidate_cached_fragment(&self);
fn repair_style(&self, context: &SharedStyleContext);
}
impl<'dom> NodeExt<'dom> for ServoLayoutNode<'dom> {
@ -253,8 +290,8 @@ impl<'dom> NodeExt<'dom> for ServoLayoutNode<'dom> {
.map(|string| string.to_owned())
}
fn style(&self, context: &LayoutContext) -> ServoArc<ComputedValues> {
self.to_threadsafe().style(context.shared_context())
fn style(&self, context: &SharedStyleContext) -> ServoArc<ComputedValues> {
self.to_threadsafe().style(context)
}
fn layout_data_mut(&self) -> AtomicRefMut<'dom, InnerDOMLayoutData> {
@ -339,4 +376,30 @@ impl<'dom> NodeExt<'dom> for ServoLayoutNode<'dom> {
})
.unwrap_or_default()
}
fn repair_style(&self, context: &SharedStyleContext) {
let data = self.layout_data_mut();
if let Some(layout_object) = &*data.self_box.borrow() {
let style = self.to_threadsafe().style(context);
layout_object.repair_style(context, self, &style);
}
if let Some(layout_object) = &*data.pseudo_before_box.borrow() {
if let Some(node) = self.to_threadsafe().with_pseudo(PseudoElement::Before) {
layout_object.repair_style(context, self, &node.style(context));
}
}
if let Some(layout_object) = &*data.pseudo_after_box.borrow() {
if let Some(node) = self.to_threadsafe().with_pseudo(PseudoElement::After) {
layout_object.repair_style(context, self, &node.style(context));
}
}
if let Some(layout_object) = &*data.pseudo_marker_box.borrow() {
if let Some(node) = self.to_threadsafe().with_pseudo(PseudoElement::Marker) {
layout_object.repair_style(context, self, &node.style(context));
}
}
}
}