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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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54
components/layout/layout_impl.rs
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@ -17,7 +17,7 @@ use base::id::{PipelineId, WebViewId};
use bitflags::bitflags;
use compositing_traits::CrossProcessCompositorApi;
use compositing_traits::display_list::ScrollType;
use embedder_traits::{Theme, UntrustedNodeAddress, ViewportDetails};
use embedder_traits::{Theme, ViewportDetails};
use euclid::default::{Point2D as UntypedPoint2D, Rect as UntypedRect};
use euclid::{Point2D, Scale, Size2D};
use fnv::FnvHashMap;
@ -26,9 +26,9 @@ use fonts_traits::StylesheetWebFontLoadFinishedCallback;
use fxhash::FxHashMap;
use ipc_channel::ipc::IpcSender;
use layout_api::{
IFrameSizes, Layout, LayoutConfig, LayoutDamage, LayoutFactory, NodesFromPointQueryType,
OffsetParentResponse, QueryMsg, ReflowGoal, ReflowPhasesRun, ReflowRequest,
ReflowRequestRestyle, ReflowResult, TrustedNodeAddress,
IFrameSizes, Layout, LayoutConfig, LayoutDamage, LayoutFactory, OffsetParentResponse, QueryMsg,
ReflowGoal, ReflowPhasesRun, ReflowRequest, ReflowRequestRestyle, ReflowResult,
TrustedNodeAddress,
};
use log::{debug, error, warn};
use malloc_size_of::{MallocConditionalSizeOf, MallocSizeOf, MallocSizeOfOps};
@ -75,11 +75,11 @@ use style::{Zero, driver};
use style_traits::{CSSPixel, SpeculativePainter};
use stylo_atoms::Atom;
use url::Url;
use webrender_api::units::{DevicePixel, DevicePoint, LayoutVector2D};
use webrender_api::{ExternalScrollId, HitTestFlags};
use webrender_api::ExternalScrollId;
use webrender_api::units::{DevicePixel, LayoutVector2D};
use crate::context::{CachedImageOrError, ImageResolver, LayoutContext};
use crate::display_list::{DisplayListBuilder, StackingContextTree};
use crate::display_list::{DisplayListBuilder, HitTest, StackingContextTree};
use crate::query::{
get_the_text_steps, process_client_rect_request, process_content_box_request,
process_content_boxes_request, process_node_scroll_area_request, process_offset_parent_query,
@ -294,30 +294,6 @@ impl Layout for LayoutThread {
let node = unsafe { ServoLayoutNode::new(&node) };
get_the_text_steps(node)
}
#[servo_tracing::instrument(skip_all)]
fn query_nodes_from_point(
&self,
point: UntypedPoint2D<f32>,
query_type: NodesFromPointQueryType,
) -> Vec<UntrustedNodeAddress> {
let mut flags = match query_type {
NodesFromPointQueryType::Topmost => HitTestFlags::empty(),
NodesFromPointQueryType::All => HitTestFlags::FIND_ALL,
};
// The point we get is not relative to the entire WebRender scene, but to this
// particular pipeline, so we need to tell WebRender about that.
flags.insert(HitTestFlags::POINT_RELATIVE_TO_PIPELINE_VIEWPORT);
let client_point = DevicePoint::from_untyped(point);
let results = self
.compositor_api
.hit_test(Some(self.id.into()), client_point, flags);
results.iter().map(|result| result.node).collect()
}
#[servo_tracing::instrument(skip_all)]
fn query_offset_parent(&self, node: TrustedNodeAddress) -> OffsetParentResponse {
let node = unsafe { ServoLayoutNode::new(&node) };
@ -405,6 +381,19 @@ impl Layout for LayoutThread {
process_text_index_request(node, point_in_node)
}
#[servo_tracing::instrument(skip_all)]
fn query_elements_from_point(
&self,
point: webrender_api::units::LayoutPoint,
flags: layout_api::ElementsFromPointFlags,
) -> Vec<layout_api::ElementsFromPointResult> {
self.stacking_context_tree
.borrow_mut()
.as_mut()
.map(|tree| HitTest::run(tree, point, flags))
.unwrap_or_default()
}
fn exit_now(&mut self) {}
fn collect_reports(&self, reports: &mut Vec<Report>, ops: &mut MallocSizeOfOps) {
@ -1486,7 +1475,8 @@ impl ReflowPhases {
QueryMsg::ContentBox |
QueryMsg::ContentBoxes |
QueryMsg::ResolvedStyleQuery |
QueryMsg::ScrollingAreaOrOffsetQuery => Self::StackingContextTreeConstruction,
QueryMsg::ScrollingAreaOrOffsetQuery |
QueryMsg::ElementsFromPoint => Self::StackingContextTreeConstruction,
QueryMsg::ClientRectQuery |
QueryMsg::ElementInnerOuterTextQuery |
QueryMsg::InnerWindowDimensionsQuery |