script: Move point_in_initial_containing_block calculation to script (#38520)

Instead of calculating this value in the compositor, calculate it in
`ScriptThread` now that it is straightforward to get this value from the
layout spatial tree. This allows removing some tricky callback code in
the Compositor.

Testing: This shouldn't change any observable behavior so is covered by
existing tests.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/compositing/compositor.rs

@@ -259,20 +259,15 @@ impl ServoRenderer {
         self.shutdown_state.get()
     }
 
-    pub(crate) fn hit_test_at_point<'a>(
-        &self,
-        point: DevicePoint,
-        details_for_pipeline: impl Fn(PipelineId) -> Option<&'a PipelineDetails>,
-    ) -> Vec<CompositorHitTestResult> {
-        self.hit_test_at_point_with_flags(point, HitTestFlags::empty(), details_for_pipeline)
+    pub(crate) fn hit_test_at_point(&self, point: DevicePoint) -> Vec<CompositorHitTestResult> {
+        self.hit_test_at_point_with_flags(point, HitTestFlags::empty())
     }
 
     // TODO: split this into first half (global) and second half (one for whole compositor, one for webview)
-    pub(crate) fn hit_test_at_point_with_flags<'a>(
+    pub(crate) fn hit_test_at_point_with_flags(
         &self,
         point: DevicePoint,
         flags: HitTestFlags,
-        details_for_pipeline: impl Fn(PipelineId) -> Option<&'a PipelineDetails>,
     ) -> Vec<CompositorHitTestResult> {
         // DevicePoint and WorldPoint are the same for us.
         let world_point = WorldPoint::from_untyped(point.to_untyped());
@@ -286,26 +281,14 @@ impl ServoRenderer {
         results
             .items
             .iter()
-            .filter_map(|item| {
+            .map(|item| {
                 let pipeline_id = item.pipeline.into();
-                let details = details_for_pipeline(pipeline_id)?;
-
-                let offset = details
-                    .scroll_tree
-                    .scroll_offset(pipeline_id.root_scroll_id())
-                    .unwrap_or_default();
-                let point_in_initial_containing_block =
-                    (item.point_in_viewport + offset).to_untyped();
-
                 let external_scroll_id = ExternalScrollId(item.tag.0, item.pipeline);
-                Some(CompositorHitTestResult {
+                CompositorHitTestResult {
                     pipeline_id,
                     point_in_viewport: Point2D::from_untyped(item.point_in_viewport.to_untyped()),
-                    point_relative_to_initial_containing_block: Point2D::from_untyped(
-                        point_in_initial_containing_block,
-                    ),
                     external_scroll_id,
-                })
+                }
             })
             .collect()
     }
@@ -1112,19 +1095,6 @@ impl IOCompositor {
         }
     }
 
-    fn details_for_pipeline(&self, pipeline_id: PipelineId) -> Option<&PipelineDetails> {
-        let webview_id = self
-            .global
-            .borrow()
-            .pipeline_to_webview_map
-            .get(&pipeline_id)
-            .cloned()?;
-        self.webview_renderers
-            .get(webview_id)?
-            .pipelines
-            .get(&pipeline_id)
-    }
-
     /// Returns true if any animation callbacks (ie `requestAnimationFrame`) are waiting for a response.
     fn animation_callbacks_running(&self) -> bool {
         self.webview_renderers
@@ -1604,9 +1574,8 @@ impl IOCompositor {
             return;
         };
 
-        let details_for_pipeline = |pipeline_id| self.details_for_pipeline(pipeline_id);
         let Some(hit_test_result) = global
-            .hit_test_at_point(last_mouse_move_position, details_for_pipeline)
+            .hit_test_at_point(last_mouse_move_position)
             .first()
             .cloned()
         else {

components/compositing/webview_renderer.rs

@@ -337,11 +337,10 @@ impl WebViewRenderer {
         };
 
         // If we can't find a pipeline to send this event to, we cannot continue.
-        let get_pipeline_details = |pipeline_id| self.pipelines.get(&pipeline_id);
         let Some(result) = self
             .global
             .borrow()
-            .hit_test_at_point(point, get_pipeline_details)
+            .hit_test_at_point(point)
             .into_iter()
             .nth(0)
         else {
@@ -852,12 +851,10 @@ impl WebViewRenderer {
             ScrollLocation::Start | ScrollLocation::End => scroll_location,
         };
 
-        let get_pipeline_details = |pipeline_id| self.pipelines.get(&pipeline_id);
-        let hit_test_results = self.global.borrow().hit_test_at_point_with_flags(
-            cursor,
-            HitTestFlags::FIND_ALL,
-            get_pipeline_details,
-        );
+        let hit_test_results = self
+            .global
+            .borrow()
+            .hit_test_at_point_with_flags(cursor, HitTestFlags::FIND_ALL);
 
         // Iterate through all hit test results, processing only the first node of each pipeline.
         // This is needed to propagate the scroll events from a pipeline representing an iframe to

components/script/dom/window.rs

@@ -2611,6 +2611,10 @@ impl Window {
             .into_iter()
             .nth(0)?;
 
+        let point_in_frame = compositor_hit_test_result.point_in_viewport;
+        let point_relative_to_initial_containing_block =
+            point_in_frame + self.scroll_offset().cast_unit();
+
         // 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);
@@ -2618,9 +2622,8 @@ impl Window {
             node: unsafe { from_untrusted_node_address(address) },
             cursor: result.cursor,
             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,
+            point_in_frame,
+            point_relative_to_initial_containing_block,
         })
     }
 

components/shared/embedder/lib.rs

@@ -884,10 +884,6 @@ pub struct CompositorHitTestResult {
     /// The hit test point in the item's viewport.
     pub point_in_viewport: Point2D<f32, CSSPixel>,
 
-    /// The hit test point relative to the root scroll node content origin / initial
-    /// containing block.
-    pub point_relative_to_initial_containing_block: Point2D<f32, CSSPixel>,
-
     /// The [`ExternalScrollId`] of the scroll tree node associated with this hit test item.
     pub external_scroll_id: ExternalScrollId,
 }