libservo: Move animation tracking from WindowMethods to delegates (#36400)

This changes removes animation tracking from the `WindowMethods` trait
and moves it to `ServoDelegate` and `WebViewDelegate`.

- Animation changes per-`WebView` are now triggered in the compositor
  only when the value is updated there, rather than right after ticking
  animations.
- Both `WebView` and `Servo` now expose an `animation()` method, so
  tracking animation state actually becomes unecessary in many cases,
  such as that of desktop servoshell, which can just read the value
  when the event loop spins.

Testing: No tests necessary as the API layer is still untested. Later,
tests will be added for the `WebView` API and this can be tested then.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>

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

ports/servoshell/desktop/app.rs

@@ -13,7 +13,7 @@ use std::{env, fs};
 
 use euclid::Scale;
 use log::{info, trace, warn};
-use servo::compositing::windowing::{AnimationState, WindowMethods};
+use servo::compositing::windowing::WindowMethods;
 use servo::config::opts::Opts;
 use servo::config::prefs::Preferences;
 use servo::servo_config::pref;
@@ -146,9 +146,6 @@ impl App {
             fn hidpi_factor(&self) -> Scale<f32, DeviceIndependentPixel, DevicePixel> {
                 self.0.hidpi_factor()
             }
-            fn set_animation_state(&self, state: AnimationState) {
-                self.0.set_animation_state(state);
-            }
         }
 
         let mut user_content_manager = UserContentManager::new();
@@ -183,8 +180,12 @@ impl App {
         self.state = AppState::Running(running_state);
     }
 
-    pub fn is_animating(&self) -> bool {
-        self.windows.iter().any(|(_, window)| window.is_animating())
+    pub(crate) fn animating(&self) -> bool {
+        match self.state {
+            AppState::Initializing => false,
+            AppState::Running(ref running_app_state) => running_app_state.servo().animating(),
+            AppState::ShuttingDown => false,
+        }
     }
 
     /// Handle events with winit contexts
@@ -401,10 +402,8 @@ impl ApplicationHandler<WakerEvent> for App {
             window.handle_winit_event(state.clone(), event);
         }
 
-        let animating = self.is_animating();
-
         // Block until the window gets an event
-        if !animating || self.suspended.get() {
+        if !self.animating() || self.suspended.get() {
             event_loop.set_control_flow(ControlFlow::Wait);
         } else {
             event_loop.set_control_flow(ControlFlow::Poll);
@@ -427,7 +426,7 @@ impl ApplicationHandler<WakerEvent> for App {
         );
         self.t = now;
 
-        if !matches!(self.state, AppState::Running(_)) {
+        if !matches!(self.state, AppState::Running(..)) {
             return;
         };
         let Some(window) = self.windows.values().next() else {
@@ -435,10 +434,8 @@ impl ApplicationHandler<WakerEvent> for App {
         };
         let window = window.clone();
 
-        let animating = self.is_animating();
-
         // Block until the window gets an event
-        if !animating || self.suspended.get() {
+        if !self.animating() || self.suspended.get() {
             event_loop.set_control_flow(ControlFlow::Wait);
         } else {
             event_loop.set_control_flow(ControlFlow::Poll);

ports/servoshell/desktop/events_loop.rs

@@ -96,7 +96,7 @@ impl EventsLoop {
                     if !app.handle_events_with_headless() {
                         break;
                     }
-                    if !app.is_animating() {
+                    if !app.animating() {
                         *flag.lock().unwrap() = false;
                     }
                 }

ports/servoshell/desktop/headed_window.rs

@@ -14,7 +14,7 @@ use euclid::{Angle, Length, Point2D, Rotation3D, Scale, Size2D, UnknownUnit, Vec
 use keyboard_types::{Modifiers, ShortcutMatcher};
 use log::{debug, info};
 use raw_window_handle::{HasDisplayHandle, HasWindowHandle, RawWindowHandle};
-use servo::compositing::windowing::{AnimationState, WebRenderDebugOption, WindowMethods};
+use servo::compositing::windowing::{WebRenderDebugOption, WindowMethods};
 use servo::servo_config::pref;
 use servo::servo_geometry::DeviceIndependentPixel;
 use servo::webrender_api::ScrollLocation;
@@ -62,7 +62,6 @@ pub struct Window {
     /// A map of winit's key codes to key values that are interpreted from
     /// winit's ReceivedChar events.
     keys_down: RefCell<HashMap<LogicalKey, Key>>,
-    animation_state: Cell<AnimationState>,
     fullscreen: Cell<bool>,
     device_pixel_ratio_override: Option<f32>,
     xr_window_poses: RefCell<Vec<Rc<XRWindowPose>>>,
@@ -151,7 +150,6 @@ impl Window {
             webview_relative_mouse_point: Cell::new(Point2D::zero()),
             last_pressed: Cell::new(None),
             keys_down: RefCell::new(HashMap::new()),
-            animation_state: Cell::new(AnimationState::Idle),
             fullscreen: Cell::new(false),
             inner_size: Cell::new(inner_size),
             monitor,
@@ -570,10 +568,6 @@ impl WindowPortsMethods for Window {
         self.winit_window.set_cursor_visible(true);
     }
 
-    fn is_animating(&self) -> bool {
-        self.animation_state.get() == AnimationState::Animating
-    }
-
     fn id(&self) -> winit::window::WindowId {
         self.winit_window.id()
     }
@@ -772,10 +766,6 @@ impl WindowMethods for Window {
         self.device_pixel_ratio_override()
             .unwrap_or_else(|| self.device_hidpi_factor())
     }
-
-    fn set_animation_state(&self, state: AnimationState) {
-        self.animation_state.set(state);
-    }
 }
 
 fn winit_phase_to_touch_event_type(phase: TouchPhase) -> TouchEventType {

ports/servoshell/desktop/headless_window.rs

@@ -9,7 +9,7 @@ use std::rc::Rc;
 
 use euclid::num::Zero;
 use euclid::{Length, Scale, Size2D};
-use servo::compositing::windowing::{AnimationState, WindowMethods};
+use servo::compositing::windowing::WindowMethods;
 use servo::servo_geometry::DeviceIndependentPixel;
 use servo::webrender_api::units::{DeviceIntSize, DevicePixel};
 use servo::{RenderingContext, ScreenGeometry, SoftwareRenderingContext};
@@ -20,7 +20,6 @@ use crate::desktop::window_trait::WindowPortsMethods;
 use crate::prefs::ServoShellPreferences;
 
 pub struct Window {
-    animation_state: Cell<AnimationState>,
     fullscreen: Cell<bool>,
     device_pixel_ratio_override: Option<Scale<f32, DeviceIndependentPixel, DevicePixel>>,
     inner_size: Cell<DeviceIntSize>,
@@ -50,7 +49,6 @@ impl Window {
             });
 
         let window = Window {
-            animation_state: Cell::new(AnimationState::Idle),
             fullscreen: Cell::new(false),
             device_pixel_ratio_override,
             inner_size: Cell::new(inner_size),
@@ -120,10 +118,6 @@ impl WindowPortsMethods for Window {
         self.fullscreen.get()
     }
 
-    fn is_animating(&self) -> bool {
-        self.animation_state.get() == AnimationState::Animating
-    }
-
     fn handle_winit_event(&self, _: Rc<RunningAppState>, _: winit::event::WindowEvent) {
         // Not expecting any winit events.
     }
@@ -157,8 +151,4 @@ impl WindowMethods for Window {
         self.device_pixel_ratio_override()
             .unwrap_or_else(|| self.device_hidpi_factor())
     }
-
-    fn set_animation_state(&self, state: AnimationState) {
-        self.animation_state.set(state);
-    }
 }

ports/servoshell/desktop/window_trait.rs

@@ -28,7 +28,6 @@ pub trait WindowPortsMethods: WindowMethods {
     fn page_height(&self) -> f32;
     fn get_fullscreen(&self) -> bool;
     fn handle_winit_event(&self, state: Rc<RunningAppState>, event: winit::event::WindowEvent);
-    fn is_animating(&self) -> bool;
     fn set_title(&self, _title: &str) {}
     /// Request a new inner size for the window, not including external decorations.
     fn request_resize(&self, webview: &WebView, inner_size: DeviceIntSize)

ports/servoshell/egl/app_state.rs

@@ -1,7 +1,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
-use std::cell::{Ref, RefCell, RefMut};
+use std::cell::{Cell, Ref, RefCell, RefMut};
 use std::collections::HashMap;
 use std::rc::Rc;
 
@@ -11,7 +11,7 @@ use keyboard_types::{CompositionEvent, CompositionState};
 use log::{debug, error, info, warn};
 use raw_window_handle::{RawWindowHandle, WindowHandle};
 use servo::base::id::WebViewId;
-use servo::compositing::windowing::{AnimationState, EmbedderMethods, WindowMethods};
+use servo::compositing::windowing::{EmbedderMethods, WindowMethods};
 use servo::euclid::{Point2D, Rect, Scale, Size2D, Vector2D};
 use servo::servo_geometry::DeviceIndependentPixel;
 use servo::webrender_api::ScrollLocation;
@@ -86,9 +86,16 @@ struct RunningAppStateInner {
     focused_webview_id: Option<WebViewId>,
 
     context_menu_sender: Option<IpcSender<ContextMenuResult>>,
+
+    /// Whether or not the animation state has changed. This is used to trigger
+    /// host callbacks indicating that animation state has changed.
+    animating_state_changed: Rc<Cell<bool>>,
+}
+
+struct ServoShellServoDelegate {
+    animating_state_changed: Rc<Cell<bool>>,
 }
 
-struct ServoShellServoDelegate;
 impl ServoDelegate for ServoShellServoDelegate {
     fn notify_devtools_server_started(&self, _servo: &Servo, port: u16, _token: String) {
         info!("Devtools Server running on port {port}");
@@ -101,6 +108,10 @@ impl ServoDelegate for ServoShellServoDelegate {
     fn notify_error(&self, _servo: &Servo, error: ServoError) {
         error!("Saw Servo error: {error:?}!");
     }
+
+    fn notify_animating_changed(&self, _animating: bool) {
+        self.animating_state_changed.set(true);
+    }
 }
 
 impl WebViewDelegate for RunningAppState {
@@ -263,7 +274,10 @@ impl RunningAppState {
             .or_else(|| Url::parse("about:blank").ok())
             .unwrap();
 
-        servo.set_delegate(Rc::new(ServoShellServoDelegate));
+        let animating_state_changed = Rc::new(Cell::new(false));
+        servo.set_delegate(Rc::new(ServoShellServoDelegate {
+            animating_state_changed: animating_state_changed.clone(),
+        }));
 
         let app_state = Rc::new(Self {
             rendering_context,
@@ -276,6 +290,7 @@ impl RunningAppState {
                 webviews: Default::default(),
                 creation_order: vec![],
                 focused_webview_id: None,
+                animating_state_changed,
             }),
         });
 
@@ -345,6 +360,12 @@ impl RunningAppState {
         if !should_continue {
             self.callbacks.host_callbacks.on_shutdown_complete();
         }
+        if self.inner().animating_state_changed.get() {
+            self.inner().animating_state_changed.set(false);
+            self.callbacks
+                .host_callbacks
+                .on_animating_changed(self.servo.animating());
+        }
     }
 
     /// Load an URL.
@@ -684,10 +705,4 @@ impl WindowMethods for ServoWindowCallbacks {
     fn hidpi_factor(&self) -> Scale<f32, DeviceIndependentPixel, DevicePixel> {
         self.hidpi_factor
     }
-
-    fn set_animation_state(&self, state: AnimationState) {
-        debug!("WindowMethods::set_animation_state: {:?}", state);
-        self.host_callbacks
-            .on_animating_changed(state == AnimationState::Animating);
-    }
 }