libservo: Start moving WindowMethods to WebViewDelegate (#36223)

`WindowMethods` is used by the embedding layer to get information from
the embedder. This change moves the functionality for getting screen
size and `WebView` offsets to `WebViewDelegate`.

This is important because `WebView`s might be on different screens or
have different offsets on the screen itself, so it makes sense for this
to be per-`WebView` and not global to the embedder. HiDPI and animation
state functionality will move to the embedder in subsequent changes.

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

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---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because they just modify the
`WebView` API surface a bit.

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is checked, so that we can help you if you get stuck somewhere along the
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will require additional verification as part of the review process. -->

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

components/compositing/compositor.rs

@@ -26,7 +26,8 @@ use constellation_traits::{
 use crossbeam_channel::Sender;
 use dpi::PhysicalSize;
 use embedder_traits::{
-    Cursor, InputEvent, MouseButtonEvent, MouseMoveEvent, ShutdownState, TouchEventType,
+    Cursor, InputEvent, MouseButtonEvent, MouseMoveEvent, ScreenGeometry, ShutdownState,
+    TouchEventType,
 };
 use euclid::{Box2D, Point2D, Rect, Scale, Size2D, Transform3D};
 use fnv::FnvHashMap;
@@ -54,11 +55,11 @@ use webrender_api::{
 };
 use webrender_traits::display_list::{HitTestInfo, ScrollTree};
 use webrender_traits::rendering_context::RenderingContext;
-use webrender_traits::{CrossProcessCompositorMessage, ImageUpdate};
+use webrender_traits::{CrossProcessCompositorMessage, ImageUpdate, RendererWebView};
 
 use crate::InitialCompositorState;
 use crate::webview::{UnknownWebView, WebView, WebViewManager};
-use crate::windowing::{self, EmbedderCoordinates, WebRenderDebugOption, WindowMethods};
+use crate::windowing::{self, WebRenderDebugOption, WindowMethods};
 
 #[derive(Debug, PartialEq)]
 enum UnableToComposite {
@@ -167,8 +168,9 @@ pub struct IOCompositor {
     /// The surfman instance that webrender targets
     rendering_context: Rc<dyn RenderingContext>,
 
-    /// The coordinates of the native window, its view and the screen.
-    embedder_coordinates: EmbedderCoordinates,
+    /// The HighDPI factor of the native window, its view and the screen.
+    /// TODO: Eventually this should be a property of the `WebView`.
+    hidpi_factor: Scale<f32, DeviceIndependentPixel, DevicePixel>,
 
     /// The number of frames pending to receive from WebRender.
     pending_frames: usize,
@@ -442,7 +444,7 @@ impl IOCompositor {
                 cursor_pos: DevicePoint::new(0.0, 0.0),
             })),
             webviews: WebViewManager::default(),
-            embedder_coordinates: window.get_coordinates(),
+            hidpi_factor: window.hidpi_factor(),
             window,
             needs_repaint: Cell::default(),
             page_zoom: Scale::new(1.0),
@@ -895,27 +897,46 @@ impl IOCompositor {
                     .collect();
                 let _ = result_sender.send((font_keys, font_instance_keys));
             },
-            CrossProcessCompositorMessage::GetClientWindowRect(req) => {
-                if let Err(e) = req.send(self.embedder_coordinates.window_rect) {
-                    warn!("Sending response to get client window failed ({:?}).", e);
+            CrossProcessCompositorMessage::GetClientWindowRect(webview_id, response_sender) => {
+                let screen_geometry = self.webview_screen_geometry(webview_id);
+                let rect = DeviceIntRect::from_origin_and_size(
+                    screen_geometry.offset,
+                    self.rendering_context.size2d().to_i32(),
+                )
+                .to_f32() /
+                    self.hidpi_factor;
+
+                if let Err(error) = response_sender.send(rect.to_i32()) {
+                    warn!("Sending response to get client window failed ({error:?}).");
                 }
             },
-            CrossProcessCompositorMessage::GetScreenSize(req) => {
-                if let Err(e) = req.send(self.embedder_coordinates.screen_size) {
-                    warn!("Sending response to get screen size failed ({:?}).", e);
+            CrossProcessCompositorMessage::GetScreenSize(webview_id, response_sender) => {
+                let screen_geometry = self.webview_screen_geometry(webview_id);
+                let screen_size = screen_geometry.size.to_f32() / self.hidpi_factor;
+
+                if let Err(error) = response_sender.send(screen_size.to_i32()) {
+                    warn!("Sending response to get screen size failed ({error:?}).");
                 }
             },
-            CrossProcessCompositorMessage::GetAvailableScreenSize(req) => {
-                if let Err(e) = req.send(self.embedder_coordinates.available_screen_size) {
-                    warn!(
-                        "Sending response to get screen avail size failed ({:?}).",
-                        e
-                    );
+            CrossProcessCompositorMessage::GetAvailableScreenSize(webview_id, response_sender) => {
+                let screen_geometry = self.webview_screen_geometry(webview_id);
+                let available_screen_size =
+                    screen_geometry.available_size.to_f32() / self.hidpi_factor;
+
+                if let Err(error) = response_sender.send(available_screen_size.to_i32()) {
+                    warn!("Sending response to get screen size failed ({error:?}).");
                 }
             },
         }
     }
 
+    fn webview_screen_geometry(&self, webview_id: WebViewId) -> ScreenGeometry {
+        self.webviews
+            .get(webview_id)
+            .and_then(|webview| webview.renderer_webview.screen_geometry())
+            .unwrap_or_default()
+    }
+
     /// Handle messages sent to the compositor during the shutdown process. In general,
     /// the things the compositor can do in this state are limited. It's very important to
     /// answer any synchronous messages though as other threads might be waiting on the
@@ -961,25 +982,27 @@ impl IOCompositor {
                 let _ = result_sender.send((font_keys, font_instance_keys));
             },
             CompositorMsg::CrossProcess(CrossProcessCompositorMessage::GetClientWindowRect(
-                req,
+                _,
+                response_sender,
             )) => {
-                if let Err(e) = req.send(self.embedder_coordinates.window_rect) {
-                    warn!("Sending response to get client window failed ({:?}).", e);
+                if let Err(error) = response_sender.send(Default::default()) {
+                    warn!("Sending response to get client window failed ({error:?}).");
                 }
             },
-            CompositorMsg::CrossProcess(CrossProcessCompositorMessage::GetScreenSize(req)) => {
-                if let Err(e) = req.send(self.embedder_coordinates.screen_size) {
-                    warn!("Sending response to get screen size failed ({:?}).", e);
+            CompositorMsg::CrossProcess(CrossProcessCompositorMessage::GetScreenSize(
+                _,
+                response_sender,
+            )) => {
+                if let Err(error) = response_sender.send(Default::default()) {
+                    warn!("Sending response to get client window failed ({error:?}).");
                 }
             },
             CompositorMsg::CrossProcess(CrossProcessCompositorMessage::GetAvailableScreenSize(
-                req,
+                _,
+                response_sender,
             )) => {
-                if let Err(e) = req.send(self.embedder_coordinates.available_screen_size) {
-                    warn!(
-                        "Sending response to get screen avail size failed ({:?}).",
-                        e
-                    );
+                if let Err(error) = response_sender.send(Default::default()) {
+                    warn!("Sending response to get client window failed ({error:?}).");
                 }
             },
             CompositorMsg::NewWebRenderFrameReady(..) => {
@@ -1102,10 +1125,10 @@ impl IOCompositor {
         }
     }
 
-    pub fn add_webview(&mut self, webview_id: WebViewId) {
+    pub fn add_webview(&mut self, webview: Box<dyn RendererWebView>) {
         let size = self.rendering_context.size2d().to_f32();
-        self.webviews.entry(webview_id).or_insert(WebView::new(
-            webview_id,
+        self.webviews.entry(webview.id()).or_insert(WebView::new(
+            webview,
             Box2D::from_origin_and_size(Point2D::origin(), size),
             self.global.clone(),
         ));
@@ -1239,20 +1262,14 @@ impl IOCompositor {
         }
     }
 
-    pub fn on_embedder_window_moved(&mut self) {
-        self.embedder_coordinates = self.window.get_coordinates();
-    }
-
     pub fn resize_rendering_context(&mut self, new_size: PhysicalSize<u32>) -> bool {
         if self.global.borrow().shutdown_state() != ShutdownState::NotShuttingDown {
             return false;
         }
 
-        let old_hidpi_factor = self.embedder_coordinates.hidpi_factor;
-        self.embedder_coordinates = self.window.get_coordinates();
-        if self.embedder_coordinates.hidpi_factor == old_hidpi_factor &&
-            self.rendering_context.size() == new_size
-        {
+        let old_hidpi_factor = self.hidpi_factor;
+        self.hidpi_factor = self.window.hidpi_factor();
+        if self.hidpi_factor == old_hidpi_factor && self.rendering_context.size() == new_size {
             return false;
         }
 
@@ -1303,10 +1320,6 @@ impl IOCompositor {
         self.window.set_animation_state(animation_state);
     }
 
-    fn hidpi_factor(&self) -> Scale<f32, DeviceIndependentPixel, DevicePixel> {
-        self.embedder_coordinates.hidpi_factor
-    }
-
     pub(crate) fn device_pixels_per_page_pixel(&self) -> Scale<f32, CSSPixel, DevicePixel> {
         self.device_pixels_per_page_pixel_not_including_page_zoom() * self.pinch_zoom_level()
     }
@@ -1314,7 +1327,7 @@ impl IOCompositor {
     fn device_pixels_per_page_pixel_not_including_page_zoom(
         &self,
     ) -> Scale<f32, CSSPixel, DevicePixel> {
-        self.page_zoom * self.hidpi_factor()
+        self.page_zoom * self.hidpi_factor
     }
 
     pub fn on_zoom_reset_window_event(&mut self) {

components/compositing/webview.rs

@@ -23,6 +23,7 @@ use webrender_api::units::{DeviceIntPoint, DevicePoint, DeviceRect, LayoutVector
 use webrender_api::{
     ExternalScrollId, HitTestFlags, RenderReasons, SampledScrollOffset, ScrollLocation,
 };
+use webrender_traits::RendererWebView;
 
 use crate::IOCompositor;
 use crate::compositor::{PipelineDetails, ServoRenderer};
@@ -50,6 +51,10 @@ enum ScrollZoomEvent {
 pub(crate) struct WebView {
     /// The [`WebViewId`] of the `WebView` associated with this [`WebViewDetails`].
     pub id: WebViewId,
+    /// The renderer's view of the embedding layer `WebView` as a trait implementation,
+    /// so that the renderer doesn't need to depend on the embedding layer. This avoids
+    /// a dependency cycle.
+    pub renderer_webview: Box<dyn RendererWebView>,
     /// The root [`PipelineId`] of the currently displayed page in this WebView.
     pub root_pipeline_id: Option<PipelineId>,
     pub rect: DeviceRect,
@@ -73,9 +78,14 @@ impl Drop for WebView {
 }
 
 impl WebView {
-    pub(crate) fn new(id: WebViewId, rect: DeviceRect, global: Rc<RefCell<ServoRenderer>>) -> Self {
+    pub(crate) fn new(
+        renderer_webview: Box<dyn RendererWebView>,
+        rect: DeviceRect,
+        global: Rc<RefCell<ServoRenderer>>,
+    ) -> Self {
         Self {
-            id,
+            id: renderer_webview.id(),
+            renderer_webview,
             root_pipeline_id: None,
             rect,
             pipelines: Default::default(),

components/compositing/windowing.rs

@@ -9,7 +9,7 @@ use std::fmt::Debug;
 use embedder_traits::{EventLoopWaker, MouseButton};
 use euclid::Scale;
 use net::protocols::ProtocolRegistry;
-use servo_geometry::{DeviceIndependentIntRect, DeviceIndependentIntSize, DeviceIndependentPixel};
+use servo_geometry::DeviceIndependentPixel;
 use webrender_api::units::{DevicePixel, DevicePoint};
 
 #[derive(Clone)]
@@ -37,12 +37,14 @@ pub enum AnimationState {
 // for creating the GL context, making it current, buffer
 // swapping, etc. Really that should all be done by surfman.
 pub trait WindowMethods {
-    /// Get the coordinates of the native window, the screen and the framebuffer.
-    fn get_coordinates(&self) -> EmbedderCoordinates;
+    /// 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);
 }
 
@@ -65,15 +67,3 @@ pub trait EmbedderMethods {
         ProtocolRegistry::default()
     }
 }
-
-#[derive(Clone, Copy, Debug)]
-pub struct EmbedderCoordinates {
-    /// The pixel density of the display.
-    pub hidpi_factor: Scale<f32, DeviceIndependentPixel, DevicePixel>,
-    /// Size of the screen.
-    pub screen_size: DeviceIndependentIntSize,
-    /// Size of the available screen space (screen without toolbars and docks).
-    pub available_screen_size: DeviceIndependentIntSize,
-    /// Position and size of the native window.
-    pub window_rect: DeviceIndependentIntRect,
-}

components/script/dom/screen.rs

@@ -35,28 +35,34 @@ impl Screen {
     }
 
     fn screen_size(&self) -> Size2D<u32, CSSPixel> {
-        let (send, recv) =
+        let (sender, receiver) =
             ipc::channel::<DeviceIndependentIntSize>(self.global().time_profiler_chan().clone())
                 .unwrap();
         self.window
             .compositor_api()
             .sender()
-            .send(CrossProcessCompositorMessage::GetScreenSize(send))
+            .send(CrossProcessCompositorMessage::GetScreenSize(
+                self.window.webview_id(),
+                sender,
+            ))
             .unwrap();
-        let size = recv.recv().unwrap_or(Size2D::zero()).to_u32();
+        let size = receiver.recv().unwrap_or(Size2D::zero()).to_u32();
         Size2D::new(size.width, size.height)
     }
 
     fn screen_avail_size(&self) -> Size2D<u32, CSSPixel> {
-        let (send, recv) =
+        let (sender, receiver) =
             ipc::channel::<DeviceIndependentIntSize>(self.global().time_profiler_chan().clone())
                 .unwrap();
         self.window
             .compositor_api()
             .sender()
-            .send(CrossProcessCompositorMessage::GetAvailableScreenSize(send))
+            .send(CrossProcessCompositorMessage::GetAvailableScreenSize(
+                self.window.webview_id(),
+                sender,
+            ))
             .unwrap();
-        let size = recv.recv().unwrap_or(Size2D::zero()).to_u32();
+        let size = receiver.recv().unwrap_or(Size2D::zero()).to_u32();
         Size2D::new(size.width, size.height)
     }
 }

components/script/dom/window.rs

@@ -1859,13 +1859,15 @@ impl Window {
 
     fn client_window(&self) -> (Size2D<u32, CSSPixel>, Point2D<i32, CSSPixel>) {
         let timer_profile_chan = self.global().time_profiler_chan().clone();
-        let (send, recv) =
+        let (sender, receiver) =
             ProfiledIpc::channel::<DeviceIndependentIntRect>(timer_profile_chan).unwrap();
-        let _ = self
-            .compositor_api
-            .sender()
-            .send(webrender_traits::CrossProcessCompositorMessage::GetClientWindowRect(send));
-        let rect = recv.recv().unwrap_or_default();
+        let _ = self.compositor_api.sender().send(
+            webrender_traits::CrossProcessCompositorMessage::GetClientWindowRect(
+                self.webview_id(),
+                sender,
+            ),
+        );
+        let rect = receiver.recv().unwrap_or_default();
         (
             Size2D::new(rect.size().width as u32, rect.size().height as u32),
             Point2D::new(rect.min.x, rect.min.y),

components/servo/examples/winit_minimal.rs

@@ -1,6 +1,5 @@
 /* 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/. */
+ * 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::error::Error;
@@ -13,7 +12,7 @@ use servo_geometry::DeviceIndependentPixel;
 use tracing::warn;
 use url::Url;
 use webrender_api::ScrollLocation;
-use webrender_api::units::{DeviceIntPoint, DeviceIntRect, DevicePixel, LayoutVector2D};
+use webrender_api::units::{DeviceIntPoint, DevicePixel, LayoutVector2D};
 use winit::application::ApplicationHandler;
 use winit::dpi::{PhysicalPosition, PhysicalSize};
 use winit::event::{MouseScrollDelta, WindowEvent};
@@ -250,26 +249,8 @@ impl WindowDelegate {
 }
 
 impl WindowMethods for WindowDelegate {
-    fn get_coordinates(&self) -> compositing::windowing::EmbedderCoordinates {
-        let monitor = self
-            .window
-            .current_monitor()
-            .or_else(|| self.window.available_monitors().nth(0))
-            .expect("Failed to get winit monitor");
-        let scale =
-            Scale::<f64, DeviceIndependentPixel, DevicePixel>::new(self.window.scale_factor());
-        let window_size = winit_size_to_euclid_size(self.window.outer_size()).to_i32();
-        let window_origin = self.window.outer_position().unwrap_or_default();
-        let window_origin = winit_position_to_euclid_point(window_origin).to_i32();
-        let window_rect = DeviceIntRect::from_origin_and_size(window_origin, window_size);
-
-        compositing::windowing::EmbedderCoordinates {
-            hidpi_factor: Scale::new(self.window.scale_factor() as f32),
-            screen_size: (winit_size_to_euclid_size(monitor.size()).to_f64() / scale).to_i32(),
-            available_screen_size: (winit_size_to_euclid_size(monitor.size()).to_f64() / scale)
-                .to_i32(),
-            window_rect: (window_rect.to_f64() / scale).to_i32(),
-        }
+    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) {

components/servo/lib.rs

@@ -321,8 +321,7 @@ impl Servo {
             None
         };
 
-        let coordinates: compositing::windowing::EmbedderCoordinates = window.get_coordinates();
-        let device_pixel_ratio = coordinates.hidpi_factor.get();
+        let device_pixel_ratio = window.hidpi_factor().get();
         let viewport_size = rendering_context.size2d();
 
         let (mut webrender, webrender_api_sender) = {

components/servo/webview.rs

@@ -13,11 +13,12 @@ use compositing::windowing::WebRenderDebugOption;
 use constellation_traits::{ConstellationMsg, TraversalDirection};
 use dpi::PhysicalSize;
 use embedder_traits::{
-    Cursor, InputEvent, LoadStatus, MediaSessionActionType, Theme, TouchEventType,
+    Cursor, InputEvent, LoadStatus, MediaSessionActionType, ScreenGeometry, Theme, TouchEventType,
 };
 use url::Url;
 use webrender_api::ScrollLocation;
 use webrender_api::units::{DeviceIntPoint, DeviceRect};
+use webrender_traits::RendererWebView;
 
 use crate::ConstellationProxy;
 use crate::clipboard_delegate::{ClipboardDelegate, DefaultClipboardDelegate};
@@ -96,11 +97,10 @@ impl WebView {
         compositor: Rc<RefCell<IOCompositor>>,
     ) -> Self {
         let id = WebViewId::new();
-        compositor.borrow_mut().add_webview(id);
-        Self(Rc::new(RefCell::new(WebViewInner {
+        let webview = Self(Rc::new(RefCell::new(WebViewInner {
             id,
             constellation_proxy: constellation_proxy.clone(),
-            compositor,
+            compositor: compositor.clone(),
             delegate: Rc::new(DefaultWebViewDelegate),
             clipboard_delegate: Rc::new(DefaultClipboardDelegate),
             rect: DeviceRect::zero(),
@@ -111,7 +111,16 @@ impl WebView {
             favicon_url: None,
             focused: false,
             cursor: Cursor::Pointer,
-        })))
+        })));
+
+        compositor
+            .borrow_mut()
+            .add_webview(Box::new(ServoRendererWebView {
+                weak_handle: webview.weak_handle(),
+                id,
+            }));
+
+        webview
     }
 
     fn inner(&self) -> Ref<'_, WebViewInner> {
@@ -382,13 +391,6 @@ impl WebView {
             .resize_rendering_context(new_size);
     }
 
-    pub fn notify_embedder_window_moved(&self) {
-        self.inner()
-            .compositor
-            .borrow_mut()
-            .on_embedder_window_moved();
-    }
-
     pub fn set_zoom(&self, new_zoom: f32) {
         self.inner()
             .compositor
@@ -452,3 +454,21 @@ impl WebView {
         self.inner().compositor.borrow_mut().render()
     }
 }
+
+/// A structure used to expose a view of the [`WebView`] to the Servo
+/// renderer, without having the Servo renderer depend on the embedding layer.
+struct ServoRendererWebView {
+    id: WebViewId,
+    weak_handle: Weak<RefCell<WebViewInner>>,
+}
+
+impl RendererWebView for ServoRendererWebView {
+    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
+    }
+}

components/servo/webview_delegate.rs

@@ -9,7 +9,7 @@ use constellation_traits::ConstellationMsg;
 use embedder_traits::{
     AllowOrDeny, AuthenticationResponse, ContextMenuResult, Cursor, FilterPattern,
     GamepadHapticEffectType, InputMethodType, LoadStatus, MediaSessionEvent, Notification,
-    PermissionFeature, SimpleDialog, WebResourceRequest, WebResourceResponse,
+    PermissionFeature, ScreenGeometry, SimpleDialog, WebResourceRequest, WebResourceResponse,
     WebResourceResponseMsg,
 };
 use ipc_channel::ipc::IpcSender;
@@ -297,6 +297,12 @@ impl Drop for InterceptedWebResourceLoad {
 }
 
 pub trait WebViewDelegate {
+    /// Get the [`ScreenGeometry`] for this [`WebView`]. If this is unimplemented or returns `None`
+    /// the screen will have the size of the [`WebView`]'s `RenderingContext` and `WebView` will be
+    /// considered to be positioned at the screen's origin.
+    fn screen_geometry(&self, _webview: WebView) -> Option<ScreenGeometry> {
+        None
+    }
     /// The URL of the currently loaded page in this [`WebView`] has changed. The new
     /// URL can accessed via [`WebView::url`].
     fn notify_url_changed(&self, _webview: WebView, _url: Url) {}

components/shared/embedder/lib.rs

@@ -636,3 +636,22 @@ pub struct NotificationAction {
     /// Icon's raw image data and metadata.
     pub icon_resource: Option<Arc<Image>>,
 }
+
+/// Information about a `WebView`'s screen geometry and offset. This is used
+/// for the [Screen](https://drafts.csswg.org/cssom-view/#the-screen-interface)
+/// CSSOM APIs and `window.screenLeft` / `window.screenTop`.
+#[derive(Clone, Copy, Debug, Default)]
+pub struct ScreenGeometry {
+    /// The size of the screen in device pixels. This will be converted to
+    /// CSS pixels based on the pixel scaling of the `WebView`.
+    pub size: DeviceIntSize,
+    /// The available size of the screen in device pixels. This size is the size
+    /// available for web content on the screen, and should be `size` minus any system
+    /// toolbars, docks, and interface elements of the browser. This will be converted to
+    /// CSS pixels based on the pixel scaling of the `WebView`.
+    pub available_size: DeviceIntSize,
+    /// The offset of the `WebView` in device pixels for the purposes of the `window.screenLeft`
+    /// and `window.screenTop` APIs. This will be converted to CSS pixels based on the pixel scaling
+    /// of the `WebView`.
+    pub offset: DeviceIntPoint,
+}

components/shared/webrender/lib.rs

@@ -14,6 +14,7 @@ use std::sync::{Arc, Mutex};
 use base::id::WebViewId;
 use constellation_traits::CompositorHitTestResult;
 use display_list::CompositorDisplayListInfo;
+use embedder_traits::ScreenGeometry;
 use euclid::default::Size2D as UntypedSize2D;
 use ipc_channel::ipc::{self, IpcSender, IpcSharedMemory};
 use log::warn;
@@ -82,12 +83,12 @@ pub enum CrossProcessCompositorMessage {
     RemoveFonts(Vec<FontKey>, Vec<FontInstanceKey>),
 
     /// Get the client window size and position.
-    GetClientWindowRect(IpcSender<DeviceIndependentIntRect>),
+    GetClientWindowRect(WebViewId, IpcSender<DeviceIndependentIntRect>),
     /// Get the size of the screen that the client window inhabits.
-    GetScreenSize(IpcSender<DeviceIndependentIntSize>),
+    GetScreenSize(WebViewId, IpcSender<DeviceIndependentIntSize>),
     /// Get the available screen size (without toolbars and docks) for the screen
     /// the client window inhabits.
-    GetAvailableScreenSize(IpcSender<DeviceIndependentIntSize>),
+    GetAvailableScreenSize(WebViewId, IpcSender<DeviceIndependentIntSize>),
 }
 
 impl fmt::Debug for CrossProcessCompositorMessage {
@@ -478,3 +479,11 @@ impl From<SerializableImageData> for ImageData {
         }
     }
 }
+
+/// A trait that exposes the embedding layer's `WebView` to the Servo renderer.
+/// This is to prevent a dependency cycle between the renderer and the embedding
+/// layer.
+pub trait RendererWebView {
+    fn id(&self) -> WebViewId;
+    fn screen_geometry(&self) -> Option<ScreenGeometry>;
+}