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>

components/compositing/compositor.rs

@@ -58,7 +58,7 @@ use webrender_api::{
 use crate::InitialCompositorState;
 use crate::webview::{UnknownWebView, WebView};
 use crate::webview_manager::WebViewManager;
-use crate::windowing::{self, WebRenderDebugOption, WindowMethods};
+use crate::windowing::{WebRenderDebugOption, WindowMethods};
 
 #[derive(Debug, PartialEq)]
 enum UnableToComposite {
@@ -258,22 +258,20 @@ impl PipelineDetails {
         self.animation_callbacks_running
     }
 
-    pub(crate) fn tick_animations(&self, compositor: &IOCompositor) -> bool {
-        let animation_callbacks_running = self.animation_callbacks_running;
-        let animations_running = self.animations_running;
-        if !animation_callbacks_running && !animations_running {
-            return false;
-        }
+    pub(crate) fn animating(&self) -> bool {
+        !self.throttled && (self.animation_callbacks_running || self.animations_running)
+    }
 
-        if self.throttled {
-            return false;
+    pub(crate) fn tick_animations(&self, compositor: &IOCompositor) {
+        if !self.animating() {
+            return;
         }
 
         let mut tick_type = AnimationTickType::empty();
-        if animations_running {
+        if self.animations_running {
             tick_type.insert(AnimationTickType::CSS_ANIMATIONS_AND_TRANSITIONS);
         }
-        if animation_callbacks_running {
+        if self.animation_callbacks_running {
             tick_type.insert(AnimationTickType::REQUEST_ANIMATION_FRAME);
         }
 
@@ -281,7 +279,6 @@ impl PipelineDetails {
         if let Err(e) = compositor.global.borrow().constellation_sender.send(msg) {
             warn!("Sending tick to constellation failed ({:?}).", e);
         }
-        true
     }
 }
 
@@ -490,6 +487,17 @@ impl IOCompositor {
         }
     }
 
+    pub fn webxr_running(&self) -> bool {
+        #[cfg(feature = "webxr")]
+        {
+            self.global.borrow().webxr_main_thread.running()
+        }
+        #[cfg(not(feature = "webxr"))]
+        {
+            false
+        }
+    }
+
     fn set_needs_repaint(&self, reason: RepaintReason) {
         let mut needs_repaint = self.needs_repaint.get();
         needs_repaint.insert(reason);
@@ -1313,23 +1321,9 @@ impl IOCompositor {
         }
         self.last_animation_tick = Instant::now();
 
-        #[cfg(feature = "webxr")]
-        let webxr_running = self.global.borrow().webxr_main_thread.running();
-        #[cfg(not(feature = "webxr"))]
-        let webxr_running = false;
-
-        let any_webviews_animating = !self
-            .webviews
-            .iter()
-            .all(|webview| !webview.tick_all_animations(self));
-
-        let animation_state = if !any_webviews_animating && !webxr_running {
-            windowing::AnimationState::Idle
-        } else {
-            windowing::AnimationState::Animating
-        };
-
-        self.window.set_animation_state(animation_state);
+        for webview in self.webviews.iter() {
+            webview.tick_all_animations(self);
+        }
     }
 
     pub(crate) fn device_pixels_per_page_pixel(&self) -> Scale<f32, CSSPixel, DevicePixel> {

components/compositing/webview.rs

@@ -217,37 +217,41 @@ impl WebView {
             })
     }
 
-    /// Sets or unsets the animations-running flag for the given pipeline, and schedules a
-    /// recomposite if necessary. Returns true if the pipeline is throttled.
+    /// Sets or unsets the animations-running flag for the given pipeline. Returns true if
+    /// the pipeline is throttled.
     pub(crate) fn change_running_animations_state(
         &mut self,
         pipeline_id: PipelineId,
         animation_state: AnimationState,
     ) -> bool {
-        let pipeline_details = self.ensure_pipeline_details(pipeline_id);
-        match animation_state {
-            AnimationState::AnimationsPresent => {
-                pipeline_details.animations_running = true;
-            },
-            AnimationState::AnimationCallbacksPresent => {
-                pipeline_details.animation_callbacks_running = true;
-            },
-            AnimationState::NoAnimationsPresent => {
-                pipeline_details.animations_running = false;
-            },
-            AnimationState::NoAnimationCallbacksPresent => {
-                pipeline_details.animation_callbacks_running = false;
-            },
-        }
-        pipeline_details.throttled
+        let throttled = {
+            let pipeline_details = self.ensure_pipeline_details(pipeline_id);
+            match animation_state {
+                AnimationState::AnimationsPresent => {
+                    pipeline_details.animations_running = true;
+                },
+                AnimationState::AnimationCallbacksPresent => {
+                    pipeline_details.animation_callbacks_running = true;
+                },
+                AnimationState::NoAnimationsPresent => {
+                    pipeline_details.animations_running = false;
+                },
+                AnimationState::NoAnimationCallbacksPresent => {
+                    pipeline_details.animation_callbacks_running = false;
+                },
+            }
+            pipeline_details.throttled
+        };
+
+        let animating = self.pipelines.values().any(PipelineDetails::animating);
+        self.renderer_webview.set_animating(animating);
+        throttled
     }
 
-    pub(crate) fn tick_all_animations(&self, compositor: &IOCompositor) -> bool {
-        let mut ticked_any = false;
+    pub(crate) fn tick_all_animations(&self, compositor: &IOCompositor) {
         for pipeline_details in self.pipelines.values() {
-            ticked_any = pipeline_details.tick_animations(compositor) || ticked_any;
+            pipeline_details.tick_animations(compositor)
         }
-        ticked_any
     }
 
     pub(crate) fn tick_animations_for_pipeline(

components/compositing/windowing.rs

@@ -4,8 +4,6 @@
 
 //! Abstract windowing methods. The concrete implementations of these can be found in `platform/`.
 
-use std::fmt::Debug;
-
 use embedder_traits::{EventLoopWaker, MouseButton};
 use euclid::Scale;
 use net::protocols::ProtocolRegistry;
@@ -27,12 +25,6 @@ pub enum WebRenderDebugOption {
     RenderTargetDebug,
 }
 
-#[derive(Clone, Copy, Debug, PartialEq)]
-pub enum AnimationState {
-    Idle,
-    Animating,
-}
-
 // TODO: this trait assumes that the window is responsible
 // for creating the GL context, making it current, buffer
 // swapping, etc. Really that should all be done by surfman.
@@ -40,12 +32,6 @@ pub trait WindowMethods {
     /// Get the HighDPI factor of the native window, the screen and the framebuffer.
     /// TODO(martin): Move this to `RendererWebView` when possible.
     fn hidpi_factor(&self) -> Scale<f32, DeviceIndependentPixel, DevicePixel>;
-    /// Set whether the application is currently animating.
-    /// Typically, when animations are active, the window
-    /// will want to avoid blocking on UI events, and just
-    /// run the event loop at the vsync interval.
-    /// TODO(martin): Move this to `RendererWebView` when possible.
-    fn set_animation_state(&self, _state: AnimationState);
 }
 
 pub trait EmbedderMethods {

components/servo/examples/winit_minimal.rs

@@ -1,11 +1,11 @@
 /* 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::{Cell, RefCell};
+use std::cell::RefCell;
 use std::error::Error;
 use std::rc::Rc;
 
-use compositing::windowing::{AnimationState, EmbedderMethods, WindowMethods};
+use compositing::windowing::{EmbedderMethods, WindowMethods};
 use euclid::{Point2D, Scale, Size2D};
 use servo::{RenderingContext, Servo, TouchEventType, WebView, WindowRenderingContext};
 use servo_geometry::DeviceIndependentPixel;
@@ -236,15 +236,11 @@ impl embedder_traits::EventLoopWaker for Waker {
 
 struct WindowDelegate {
     window: Window,
-    animation_state: Cell<AnimationState>,
 }
 
 impl WindowDelegate {
     fn new(window: Window) -> Self {
-        Self {
-            window,
-            animation_state: Cell::new(AnimationState::Idle),
-        }
+        Self { window }
     }
 }
 
@@ -252,10 +248,6 @@ impl WindowMethods for WindowDelegate {
     fn hidpi_factor(&self) -> Scale<f32, DeviceIndependentPixel, DevicePixel> {
         Scale::new(self.window.scale_factor() as f32)
     }
-
-    fn set_animation_state(&self, state: compositing::windowing::AnimationState) {
-        self.animation_state.set(state);
-    }
 }
 
 pub fn winit_size_to_euclid_size<T>(size: PhysicalSize<T>) -> Size2D<T, DevicePixel> {

components/servo/lib.rs

@@ -210,6 +210,8 @@ pub struct Servo {
     /// and deinitialization of the JS Engine. Multiprocess Servo instances have their
     /// own instance that exists in the content process instead.
     _js_engine_setup: Option<JSEngineSetup>,
+    /// Whether or not any WebView in this instance is animating or WebXR is enabled.
+    animating: Cell<bool>,
 }
 
 #[derive(Clone)]
@@ -507,6 +509,7 @@ impl Servo {
             webviews: Default::default(),
             servo_errors: ServoErrorChannel::default(),
             _js_engine_setup: js_engine_setup,
+            animating: Cell::new(false),
         }
     }
 
@@ -518,6 +521,15 @@ impl Servo {
         *self.delegate.borrow_mut() = delegate;
     }
 
+    /// Whether or not any [`WebView`] of this Servo instance has animating content, such as a CSS
+    /// animation or transition or is running `requestAnimationFrame` callbacks. In addition, this
+    /// returns true if WebXR content is running. This indicates that the embedding application
+    /// should be spinning the Servo event loop on regular intervals in order to trigger animation
+    /// updates.
+    pub fn animating(&self) -> bool {
+        self.animating.get()
+    }
+
     /// **EXPERIMENTAL:** Intialize GL accelerated media playback. This currently only works on a limited number
     /// of platforms. This should be run *before* calling [`Servo::new`] and creating the first [`WebView`].
     pub fn initialize_gl_accelerated_media(display: NativeDisplay, api: GlApi, context: GlContext) {
@@ -555,6 +567,7 @@ impl Servo {
 
         self.compositor.borrow_mut().perform_updates();
         self.send_new_frame_ready_messages();
+        self.send_animating_changed_messages();
         self.handle_delegate_errors();
         self.clean_up_destroyed_webview_handles();
 
@@ -580,6 +593,19 @@ impl Servo {
         }
     }
 
+    fn send_animating_changed_messages(&self) {
+        let animating = self.compositor.borrow().webxr_running() ||
+            self.webviews
+                .borrow()
+                .values()
+                .filter_map(WebView::from_weak_handle)
+                .any(|webview| webview.animating());
+        if animating != self.animating.get() {
+            self.animating.set(animating);
+            self.delegate().notify_animating_changed(animating);
+        }
+    }
+
     fn handle_delegate_errors(&self) {
         while let Some(error) = self.servo_errors.try_recv() {
             self.delegate().notify_error(self, error);

components/servo/servo_delegate.rs

@@ -28,6 +28,11 @@ pub trait ServoDelegate {
     /// Request a DevTools connection from a DevTools client. Typically an embedder application
     /// will show a permissions prompt when this happens to confirm a connection is allowed.
     fn request_devtools_connection(&self, _servo: &Servo, _request: AllowOrDenyRequest) {}
+    /// Any [`WebView`] in this Servo instance has either started to animate or WebXR is
+    /// running. When a [`WebView`] is animating, it is up to the embedding application
+    /// ensure that `Servo::spin_event_loop` is called at regular intervals in order to
+    /// update the painted contents of the [`WebView`].
+    fn notify_animating_changed(&self, _animating: bool) {}
     /// Triggered when Servo will load a web (HTTP/HTTPS) resource. The load may be
     /// intercepted and alternate contents can be loaded by the client by calling
     /// [`WebResourceLoad::intercept`]. If not handled, the load will continue as normal.

components/servo/webview.rs

@@ -81,6 +81,7 @@ pub(crate) struct WebViewInner {
     page_title: Option<String>,
     favicon_url: Option<Url>,
     focused: bool,
+    animating: bool,
     cursor: Cursor,
 }
 
@@ -110,6 +111,7 @@ impl WebView {
             page_title: None,
             favicon_url: None,
             focused: false,
+            animating: false,
             cursor: Cursor::Pointer,
         })));
 
@@ -265,6 +267,22 @@ impl WebView {
             .send(EmbedderToConstellationMessage::BlurWebView);
     }
 
+    /// Whether or not this [`WebView`] has animating content, such as a CSS animation or
+    /// transition or is running `requestAnimationFrame` callbacks. This indicates that the
+    /// embedding application should be spinning the Servo event loop on regular intervals
+    /// in order to trigger animation updates.
+    pub fn animating(self) -> bool {
+        self.inner().animating
+    }
+
+    pub(crate) fn set_animating(self, new_value: bool) {
+        if self.inner().animating == new_value {
+            return;
+        }
+        self.inner_mut().animating = new_value;
+        self.delegate().notify_animating_changed(self, new_value);
+    }
+
     pub fn rect(&self) -> DeviceRect {
         self.inner().rect
     }
@@ -475,12 +493,18 @@ struct ServoRendererWebView {
 }
 
 impl RendererWebView for ServoRendererWebView {
+    fn id(&self) -> WebViewId {
+        self.id
+    }
+
     fn screen_geometry(&self) -> Option<ScreenGeometry> {
         let webview = WebView::from_weak_handle(&self.weak_handle)?;
         webview.delegate().screen_geometry(webview)
     }
 
-    fn id(&self) -> WebViewId {
-        self.id
+    fn set_animating(&self, new_value: bool) {
+        if let Some(webview) = WebView::from_weak_handle(&self.weak_handle) {
+            webview.set_animating(new_value);
+        }
     }
 }

components/servo/webview_delegate.rs

@@ -375,6 +375,11 @@ pub trait WebViewDelegate {
     /// This [`WebView`] has either become focused or lost focus. Whether or not the
     /// [`WebView`] is focused can be accessed via [`WebView::focused`].
     fn notify_focus_changed(&self, _webview: WebView, _focused: bool) {}
+    /// This [`WebView`] has either started to animate or stopped animating. When a
+    /// [`WebView`] is animating, it is up to the embedding application ensure that
+    /// `Servo::spin_event_loop` is called at regular intervals in order to update the
+    /// painted contents of the [`WebView`].
+    fn notify_animating_changed(&self, _webview: WebView, _animating: bool) {}
     /// The `LoadStatus` of the currently loading or loaded page in this [`WebView`] has changed. The new
     /// status can accessed via [`WebView::load_status`].
     fn notify_load_status_changed(&self, _webview: WebView, _status: LoadStatus) {}

components/shared/compositing/lib.rs

@@ -590,4 +590,5 @@ impl From<SerializableImageData> for ImageData {
 pub trait RendererWebView {
     fn id(&self) -> WebViewId;
     fn screen_geometry(&self) -> Option<ScreenGeometry>;
+    fn set_animating(&self, new_value: bool);
 }