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layout: Add a layout hit test and use it for document.elementsFromPoint (#38463)

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In #18933, hit testing was moved from layout to WebRender. This presents
some issues. For instance, the DOM can change at the same time that hit
test is happening. This can mean that hit test returns references to
defunct DOM nodes, introducing memory safety issues. Currently, Servo
will try to ensure that the epochs used for testing and those recorded
in the DOM match, but this is not very reliable and has led to code that
retries failed hit tests.

This change reintroduces (8 years later) a layout hit tester and turns
it on for `document.elementFromPoint` and `document.elementsFromPoint`.
The idea is that this hit tester will gradually replace the majority of
the WebRender hit testing happening in the renderer.

Testing: This shouldn't really change the behavior hit testing, but it
seems to improve one WPT test.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
Co-authored-by: kongbai1996 <1782765876@qq.com>
This commit is contained in:
Martin Robinson 2025-08-05 11:48:21 +02:00 • committed by GitHub
parent 3e856cbf11
commit 11844ca5af
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GPG key ID: B5690EEEBB952194
11 changed files with 539 additions and 113 deletions
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40
components/script/dom/documentorshadowroot.rs
View file

@ -3,12 +3,12 @@
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
use std::collections::HashSet;
use std::ffi::c_void;
use std::fmt;
use embedder_traits::UntrustedNodeAddress;
use euclid::default::Point2D;
use js::rust::HandleValue;
use layout_api::{NodesFromPointQueryType, QueryMsg};
use layout_api::{ElementsFromPointFlags, ElementsFromPointResult, QueryMsg};
use script_bindings::error::{Error, ErrorResult};
use script_bindings::script_runtime::JSContext;
use servo_arc::Arc;
@ -19,6 +19,7 @@ use style::shared_lock::{SharedRwLock as StyleSharedRwLock, SharedRwLockReadGuar
use style::stylesheets::scope_rule::ImplicitScopeRoot;
use style::stylesheets::{Stylesheet, StylesheetContents};
use stylo_atoms::Atom;
use webrender_api::units::LayoutPoint;
use super::bindings::trace::HashMapTracedValues;
use crate::dom::bindings::cell::DomRefCell;
@ -136,15 +137,13 @@ impl DocumentOrShadowRoot {
}
}
pub(crate) fn nodes_from_point(
pub(crate) fn query_elements_from_point(
&self,
client_point: &Point2D<f32>,
query_type: NodesFromPointQueryType,
) -> Vec<UntrustedNodeAddress> {
self.window.layout_reflow(QueryMsg::NodesFromPointQuery);
self.window
.layout()
.query_nodes_from_point(*client_point, query_type)
point: LayoutPoint,
flags: ElementsFromPointFlags,
) -> Vec<ElementsFromPointResult> {
self.window.layout_reflow(QueryMsg::ElementsFromPoint);
self.window.layout().query_elements_from_point(point, flags)
}
#[allow(unsafe_code)]
@ -158,7 +157,6 @@ impl DocumentOrShadowRoot {
) -> Option<DomRoot<Element>> {
let x = *x as f32;
let y = *y as f32;
let point = &Point2D::new(x, y);
let viewport = self.window.viewport_details().size;
if !has_browsing_context {
@ -170,11 +168,14 @@ impl DocumentOrShadowRoot {
}
match self
.nodes_from_point(point, NodesFromPointQueryType::Topmost)
.query_elements_from_point(LayoutPoint::new(x, y), ElementsFromPointFlags::empty())
.first()
{
Some(address) => {
let node = unsafe { node::from_untrusted_node_address(*address) };
Some(result) => {
// SAFETY: This is safe because `Self::query_elements_from_point` has ensured that
// layout has run and any OpaqueNodes that no longer refer to real nodes are gone.
let address = UntrustedNodeAddress(result.node.0 as *const c_void);
let node = unsafe { node::from_untrusted_node_address(address) };
let parent_node = node.GetParentNode().unwrap();
let shadow_host = parent_node
.downcast::<ShadowRoot>()
@ -205,7 +206,6 @@ impl DocumentOrShadowRoot {
) -> Vec<DomRoot<Element>> {
let x = *x as f32;
let y = *y as f32;
let point = &Point2D::new(x, y);
let viewport = self.window.viewport_details().size;
if !has_browsing_context {
@ -218,11 +218,15 @@ impl DocumentOrShadowRoot {
}
// Step 1 and Step 3
let nodes = self.nodes_from_point(point, NodesFromPointQueryType::All);
let nodes =
self.query_elements_from_point(LayoutPoint::new(x, y), ElementsFromPointFlags::FindAll);
let mut elements: Vec<DomRoot<Element>> = nodes
.iter()
.flat_map(|&untrusted_node_address| {
let node = unsafe { node::from_untrusted_node_address(untrusted_node_address) };
.flat_map(|result| {
// SAFETY: This is safe because `Self::query_elements_from_point` has ensured that
// layout has run and any OpaqueNodes that no longer refer to real nodes are gone.
let address = UntrustedNodeAddress(result.node.0 as *const c_void);
let node = unsafe { node::from_untrusted_node_address(address) };
DomRoot::downcast::<Element>(node)
})
.collect();