constellation: Proxy ScrollState through the Constellation (#36062)

This will allow removing the dependency of the compositor on
`script_traits`, which should make our internal dependency chain a lot
easier to deal with.

Part of #35984.

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

components/compositing/webview.rs

@@ -16,13 +16,13 @@ use embedder_traits::{
 use euclid::{Point2D, Scale, Vector2D};
 use fnv::FnvHashSet;
 use log::{debug, warn};
-use script_traits::{AnimationState, ScriptThreadMessage, ScrollState, TouchEventResult};
+use script_traits::{AnimationState, ScriptThreadMessage, TouchEventResult};
 use webrender::Transaction;
 use webrender_api::units::{DeviceIntPoint, DevicePoint, DeviceRect, LayoutVector2D};
 use webrender_api::{
     ExternalScrollId, HitTestFlags, RenderReasons, SampledScrollOffset, ScrollLocation,
 };
-use webrender_traits::CompositorHitTestResult;
+use webrender_traits::{CompositorHitTestResult, ScrollState};
 
 use crate::IOCompositor;
 use crate::compositor::{PipelineDetails, ServoRenderer};

components/constellation/constellation.rs

@@ -160,7 +160,7 @@ use webgpu::{self, WebGPU, WebGPURequest, WebGPUResponse};
 use webrender::RenderApi;
 use webrender::RenderApiSender;
 use webrender_api::{DocumentId, ImageKey};
-use webrender_traits::{CompositorHitTestResult, WebrenderExternalImageRegistry};
+use webrender_traits::{CompositorHitTestResult, ScrollState, WebrenderExternalImageRegistry};
 
 use crate::browsingcontext::{
     AllBrowsingContextsIterator, BrowsingContext, FullyActiveBrowsingContextsIterator,
@@ -1406,6 +1406,9 @@ where
             FromCompositorMsg::SetWebViewThrottled(webview_id, throttled) => {
                 self.set_webview_throttled(webview_id, throttled);
             },
+            FromCompositorMsg::SetScrollStates(pipeline_id, scroll_states) => {
+                self.handle_set_scroll_states(pipeline_id, scroll_states)
+            },
         }
     }
 
@@ -5562,4 +5565,24 @@ where
             error!("Got a media session action but no active media session is registered");
         }
     }
+
+    #[cfg_attr(
+        feature = "tracing",
+        tracing::instrument(skip_all, fields(servo_profiling = true), level = "trace")
+    )]
+    fn handle_set_scroll_states(&self, pipeline_id: PipelineId, scroll_states: Vec<ScrollState>) {
+        let Some(pipeline) = self.pipelines.get(&pipeline_id) else {
+            warn!("Discarding scroll offset update for unknown pipeline");
+            return;
+        };
+        if let Err(error) = pipeline
+            .event_loop
+            .send(ScriptThreadMessage::SetScrollStates(
+                pipeline_id,
+                scroll_states,
+            ))
+        {
+            warn!("Could not send scroll offsets to pipeline: {pipeline_id:?}: {error:?}");
+        }
+    }
 }

components/constellation/tracing.rs

@@ -86,6 +86,7 @@ mod from_compositor {
                 Self::ExitFullScreen(_) => target!("ExitFullScreen"),
                 Self::MediaSessionAction(_) => target!("MediaSessionAction"),
                 Self::SetWebViewThrottled(_, _) => target!("SetWebViewThrottled"),
+                Self::SetScrollStates(..) => target!("SetScrollStates"),
             }
         }
     }

components/layout_thread_2020/lib.rs

@@ -51,8 +51,8 @@ use script_layout_interface::{
     ReflowRequest, ReflowResult, TrustedNodeAddress,
 };
 use script_traits::{
-    DrawAPaintImageResult, PaintWorkletError, Painter, ScriptThreadMessage, ScrollState,
-    UntrustedNodeAddress, WindowSizeData,
+    DrawAPaintImageResult, PaintWorkletError, Painter, ScriptThreadMessage, UntrustedNodeAddress,
+    WindowSizeData,
 };
 use servo_arc::Arc as ServoArc;
 use servo_config::opts::{self, DebugOptions};
@@ -90,7 +90,7 @@ use stylo_atoms::Atom;
 use url::Url;
 use webrender_api::units::{DevicePixel, LayoutPixel};
 use webrender_api::{ExternalScrollId, HitTestFlags, units};
-use webrender_traits::CrossProcessCompositorApi;
+use webrender_traits::{CrossProcessCompositorApi, ScrollState};
 
 // This mutex is necessary due to syncronisation issues between two different types of thread-local storage
 // which manifest themselves when the layout thread tries to layout iframes in parallel with the main page
@@ -456,7 +456,7 @@ impl Layout for LayoutThread {
     ) {
     }
 
-    fn set_scroll_states(&mut self, scroll_states: &[ScrollState]) {
+    fn set_scroll_offsets(&mut self, scroll_states: &[ScrollState]) {
         *self.scroll_offsets.borrow_mut() = scroll_states
             .iter()
             .map(|scroll_state| (scroll_state.scroll_id, scroll_state.scroll_offset))

components/script/dom/window.rs

@@ -61,8 +61,7 @@ use script_layout_interface::{
 };
 use script_traits::{
     DocumentState, LoadData, LoadOrigin, NavigationHistoryBehavior, ScriptMsg, ScriptThreadMessage,
-    ScriptToConstellationChan, ScrollState, StructuredSerializedData, WindowSizeData,
-    WindowSizeType,
+    ScriptToConstellationChan, StructuredSerializedData, WindowSizeData, WindowSizeType,
 };
 use selectors::attr::CaseSensitivity;
 use servo_arc::Arc as ServoArc;
@@ -84,7 +83,7 @@ use stylo_atoms::Atom;
 use url::Position;
 use webrender_api::units::{DevicePixel, LayoutPixel};
 use webrender_api::{DocumentId, ExternalScrollId};
-use webrender_traits::CrossProcessCompositorApi;
+use webrender_traits::{CrossProcessCompositorApi, ScrollState};
 
 use super::bindings::codegen::Bindings::MessagePortBinding::StructuredSerializeOptions;
 use super::bindings::trace::HashMapTracedValues;

components/script/script_thread.rs

@@ -81,7 +81,7 @@ use script_traits::{
     ConstellationInputEvent, DiscardBrowsingContext, DocumentActivity, InitialScriptState,
     JsEvalResult, LoadData, LoadOrigin, NavigationHistoryBehavior, NewLayoutInfo, Painter,
     ProgressiveWebMetricType, ScriptMsg, ScriptThreadMessage, ScriptToConstellationChan,
-    ScrollState, StructuredSerializedData, UpdatePipelineIdReason, WindowSizeData, WindowSizeType,
+    StructuredSerializedData, UpdatePipelineIdReason, WindowSizeData, WindowSizeType,
 };
 use servo_config::opts;
 use servo_url::{ImmutableOrigin, MutableOrigin, ServoUrl};
@@ -93,7 +93,7 @@ use url::Position;
 #[cfg(feature = "webgpu")]
 use webgpu::{WebGPUDevice, WebGPUMsg};
 use webrender_api::DocumentId;
-use webrender_traits::{CompositorHitTestResult, CrossProcessCompositorApi};
+use webrender_traits::{CompositorHitTestResult, CrossProcessCompositorApi, ScrollState};
 
 use crate::document_collection::DocumentCollection;
 use crate::document_loader::DocumentLoader;
@@ -1870,7 +1870,7 @@ impl ScriptThread {
                 panic!("should have handled {:?} already", msg)
             },
             ScriptThreadMessage::SetScrollStates(pipeline_id, scroll_states) => {
-                self.handle_set_scroll_states_msg(pipeline_id, scroll_states)
+                self.handle_set_scroll_states_offsets(pipeline_id, scroll_states)
             },
             ScriptThreadMessage::SetEpochPaintTime(pipeline_id, epoch, time) => {
                 self.handle_set_epoch_paint_time(pipeline_id, epoch, time)
@@ -1878,7 +1878,7 @@ impl ScriptThread {
         }
     }
 
-    fn handle_set_scroll_states_msg(
+    fn handle_set_scroll_states_offsets(
         &self,
         pipeline_id: PipelineId,
         scroll_states: Vec<ScrollState>,
@@ -1892,7 +1892,7 @@ impl ScriptThread {
             ScriptThreadEventCategory::SetScrollState,
             Some(pipeline_id),
             || {
-                window.layout_mut().set_scroll_states(&scroll_states);
+                window.layout_mut().set_scroll_offsets(&scroll_states);
 
                 let mut scroll_offsets = HashMap::new();
                 for scroll_state in scroll_states.into_iter() {

components/shared/compositing/constellation_msg.rs

@@ -15,7 +15,7 @@ use ipc_channel::ipc::IpcSender;
 use script_traits::{AnimationTickType, LogEntry, WindowSizeData, WindowSizeType};
 use servo_url::ServoUrl;
 use strum_macros::IntoStaticStr;
-use webrender_traits::CompositorHitTestResult;
+use webrender_traits::{CompositorHitTestResult, ScrollState};
 
 /// Messages to the constellation.
 #[derive(IntoStaticStr)]
@@ -69,6 +69,9 @@ pub enum ConstellationMsg {
     MediaSessionAction(MediaSessionActionType),
     /// Set whether to use less resources, by stopping animations and running timers at a heavily limited rate.
     SetWebViewThrottled(WebViewId, bool),
+    /// The Servo renderer scrolled and is updating the scroll states of the nodes in the
+    /// given pipeline via the constellation.
+    SetScrollStates(PipelineId, Vec<ScrollState>),
 }
 
 impl fmt::Debug for ConstellationMsg {

components/shared/script/lib.rs

@@ -33,7 +33,7 @@ use crossbeam_channel::{RecvTimeoutError, Sender};
 use devtools_traits::{DevtoolScriptControlMsg, ScriptToDevtoolsControlMsg, WorkerId};
 use embedder_traits::input_events::InputEvent;
 use embedder_traits::{MediaSessionActionType, Theme, WebDriverScriptCommand};
-use euclid::{Rect, Scale, Size2D, UnknownUnit, Vector2D};
+use euclid::{Rect, Scale, Size2D, UnknownUnit};
 use http::{HeaderMap, Method};
 use ipc_channel::Error as IpcError;
 use ipc_channel::ipc::{IpcReceiver, IpcSender};
@@ -56,10 +56,10 @@ use style_traits::{CSSPixel, SpeculativePainter};
 use stylo_atoms::Atom;
 #[cfg(feature = "webgpu")]
 use webgpu::WebGPUMsg;
-use webrender_api::units::{DevicePixel, LayoutPixel};
-use webrender_api::{DocumentId, ExternalScrollId, ImageKey};
+use webrender_api::units::DevicePixel;
+use webrender_api::{DocumentId, ImageKey};
 use webrender_traits::{
-    CompositorHitTestResult, CrossProcessCompositorApi,
+    CompositorHitTestResult, CrossProcessCompositorApi, ScrollState,
     UntrustedNodeAddress as WebRenderUntrustedNodeAddress,
 };
 
@@ -593,15 +593,6 @@ bitflags! {
     }
 }
 
-/// The scroll state of a stacking context.
-#[derive(Clone, Copy, Debug, Deserialize, PartialEq, Serialize)]
-pub struct ScrollState {
-    /// The ID of the scroll root.
-    pub scroll_id: ExternalScrollId,
-    /// The scrolling offset of this stacking context.
-    pub scroll_offset: Vector2D<f32, LayoutPixel>,
-}
-
 /// Data about the window size.
 #[derive(Clone, Copy, Debug, Deserialize, MallocSizeOf, PartialEq, Serialize)]
 pub struct WindowSizeData {

components/shared/script_layout/lib.rs

@@ -33,7 +33,7 @@ use net_traits::image_cache::{ImageCache, PendingImageId};
 use profile_traits::mem::Report;
 use profile_traits::time;
 use script_traits::{
-    InitialScriptState, LoadData, Painter, ScriptThreadMessage, ScrollState, UntrustedNodeAddress,
+    InitialScriptState, LoadData, Painter, ScriptThreadMessage, UntrustedNodeAddress,
     WindowSizeData,
 };
 use serde::{Deserialize, Serialize};
@@ -53,7 +53,7 @@ use style::selector_parser::{PseudoElement, RestyleDamage, Snapshot};
 use style::stylesheets::Stylesheet;
 use style_traits::CSSPixel;
 use webrender_api::ImageKey;
-use webrender_traits::CrossProcessCompositorApi;
+use webrender_traits::{CrossProcessCompositorApi, ScrollState};
 
 pub type GenericLayoutData = dyn Any + Send + Sync;
 
@@ -243,7 +243,7 @@ pub trait Layout {
     );
 
     /// Set the scroll states of this layout after a compositor scroll.
-    fn set_scroll_states(&mut self, scroll_states: &[ScrollState]);
+    fn set_scroll_offsets(&mut self, scroll_states: &[ScrollState]);
 
     /// Set the paint time for a specific epoch.
     fn set_epoch_paint_time(&mut self, epoch: Epoch, paint_time: CrossProcessInstant);

components/shared/webrender/lib.rs

@@ -14,13 +14,14 @@ use std::sync::{Arc, Mutex};
 use base::id::{PipelineId, WebViewId};
 use display_list::{CompositorDisplayListInfo, ScrollTreeNodeId};
 use embedder_traits::Cursor;
+use euclid::Vector2D;
 use euclid::default::Size2D as UntypedSize2D;
 use ipc_channel::ipc::{self, IpcSender, IpcSharedMemory};
 use libc::c_void;
 use log::warn;
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use servo_geometry::{DeviceIndependentIntRect, DeviceIndependentIntSize};
-use webrender_api::units::{DevicePoint, LayoutPoint, TexelRect};
+use webrender_api::units::{DevicePoint, LayoutPixel, LayoutPoint, TexelRect};
 use webrender_api::{
     BuiltDisplayList, BuiltDisplayListDescriptor, ExternalImage, ExternalImageData,
     ExternalImageHandler, ExternalImageId, ExternalImageSource, ExternalScrollId,
@@ -530,3 +531,12 @@ pub struct CompositorHitTestResult {
     /// The scroll tree node associated with this hit test item.
     pub scroll_tree_node: ScrollTreeNodeId,
 }
+
+/// The scroll state of a stacking context.
+#[derive(Clone, Copy, Debug, Deserialize, PartialEq, Serialize)]
+pub struct ScrollState {
+    /// The ID of the scroll root.
+    pub scroll_id: ExternalScrollId,
+    /// The scrolling offset of this stacking context.
+    pub scroll_offset: Vector2D<f32, LayoutPixel>,
+}