compositor/layout: Rely on layout for fine-grained input event hit testing (#38480)

Before, the compositor was responsible for doing the hit testing during
input events within a page. This change moves that hit testing to
layout.  With this change, epoch mismatches are no longer a bit deal and
we can simply ignore them, as the Constellation and Script will take
care of ignoring hit tests against scroll nodes and browsing contexts
that no longer exist. This means that hit testing retry support can be
removed.

Add the concept of a Script `HitTest` that transforms the coarse-grained
renderer hit test into one that hit tests against the actual layout
items.

Testing: Currently we do not have good tests for verifying the behavior
of
input events, but WebDriver tests should cover this.
Fixes: This is part of #37932.
Fixes: #26608.
Fixes: #25282.
Fixes: #38090.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
Co-authored-by: kongbai1996 <1782765876@qq.com>

components/script/dom/window.rs

@@ -8,6 +8,7 @@ use std::cmp;
 use std::collections::hash_map::Entry;
 use std::collections::{HashMap, HashSet};
 use std::default::Default;
+use std::ffi::c_void;
 use std::io::{Write, stderr, stdout};
 use std::rc::Rc;
 use std::sync::{Arc, Mutex};
@@ -33,8 +34,8 @@ use dom_struct::dom_struct;
 use embedder_traits::user_content_manager::{UserContentManager, UserScript};
 use embedder_traits::{
     AlertResponse, ConfirmResponse, EmbedderMsg, GamepadEvent, GamepadSupportedHapticEffects,
-    GamepadUpdateType, PromptResponse, SimpleDialog, Theme, ViewportDetails, WebDriverJSError,
-    WebDriverJSResult, WebDriverLoadStatus,
+    GamepadUpdateType, PromptResponse, SimpleDialog, Theme, UntrustedNodeAddress, ViewportDetails,
+    WebDriverJSError, WebDriverJSResult, WebDriverLoadStatus,
 };
 use euclid::default::{Point2D as UntypedPoint2D, Rect as UntypedRect, Size2D as UntypedSize2D};
 use euclid::{Point2D, Scale, Size2D, Vector2D};
@@ -51,9 +52,10 @@ use js::rust::{
     MutableHandleValue,
 };
 use layout_api::{
-    FragmentType, Layout, PendingImage, PendingImageState, PendingRasterizationImage, QueryMsg,
-    ReflowGoal, ReflowPhasesRun, ReflowRequest, ReflowRequestRestyle, RestyleReason,
-    TrustedNodeAddress, combine_id_with_fragment_type,
+    ElementsFromPointFlags, ElementsFromPointResult, FragmentType, Layout, PendingImage,
+    PendingImageState, PendingRasterizationImage, QueryMsg, ReflowGoal, ReflowPhasesRun,
+    ReflowRequest, ReflowRequestRestyle, RestyleReason, TrustedNodeAddress,
+    combine_id_with_fragment_type,
 };
 use malloc_size_of::MallocSizeOf;
 use media::WindowGLContext;
@@ -72,7 +74,7 @@ use script_bindings::codegen::GenericBindings::PerformanceBinding::PerformanceMe
 use script_bindings::conversions::SafeToJSValConvertible;
 use script_bindings::interfaces::WindowHelpers;
 use script_bindings::root::Root;
-use script_traits::ScriptThreadMessage;
+use script_traits::{ConstellationInputEvent, ScriptThreadMessage};
 use selectors::attr::CaseSensitivity;
 use servo_arc::Arc as ServoArc;
 use servo_config::{opts, pref};
@@ -88,7 +90,7 @@ use style_traits::CSSPixel;
 use stylo_atoms::Atom;
 use url::Position;
 use webrender_api::ExternalScrollId;
-use webrender_api::units::{DeviceIntSize, DevicePixel, LayoutPixel};
+use webrender_api::units::{DeviceIntSize, DevicePixel, LayoutPixel, LayoutPoint};
 
 use super::bindings::codegen::Bindings::MessagePortBinding::StructuredSerializeOptions;
 use super::bindings::trace::HashMapTracedValues;
@@ -138,6 +140,7 @@ use crate::dom::history::History;
 use crate::dom::htmlcollection::{CollectionFilter, HTMLCollection};
 use crate::dom::htmliframeelement::HTMLIFrameElement;
 use crate::dom::idbfactory::IDBFactory;
+use crate::dom::inputevent::HitTestResult;
 use crate::dom::location::Location;
 use crate::dom::medialist::MediaList;
 use crate::dom::mediaquerylist::{MediaQueryList, MediaQueryListMatchState};
@@ -2589,6 +2592,41 @@ impl Window {
             .query_text_indext(node.to_opaque(), point_in_node)
     }
 
+    pub(crate) fn elements_from_point_query(
+        &self,
+        point: LayoutPoint,
+        flags: ElementsFromPointFlags,
+    ) -> Vec<ElementsFromPointResult> {
+        self.layout_reflow(QueryMsg::ElementsFromPoint);
+        self.layout().query_elements_from_point(point, flags)
+    }
+
+    #[allow(unsafe_code)]
+    pub(crate) fn hit_test_from_input_event(
+        &self,
+        input_event: &ConstellationInputEvent,
+    ) -> Option<HitTestResult> {
+        let compositor_hit_test_result = input_event.hit_test_result.as_ref()?;
+        let result = self
+            .elements_from_point_query(
+                compositor_hit_test_result.point_in_viewport.cast_unit(),
+                ElementsFromPointFlags::empty(),
+            )
+            .into_iter()
+            .nth(0)?;
+
+        // SAFETY: This is safe because `Window::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);
+        Some(HitTestResult {
+            node: unsafe { from_untrusted_node_address(address) },
+            point_in_node: result.point_in_target,
+            point_in_frame: compositor_hit_test_result.point_in_viewport,
+            point_relative_to_initial_containing_block: compositor_hit_test_result
+                .point_relative_to_initial_containing_block,
+        })
+    }
+
     #[allow(unsafe_code)]
     pub(crate) fn init_window_proxy(&self, window_proxy: &WindowProxy) {
         assert!(self.window_proxy.get().is_none());