libservo: Add a WebView::take_screenshot() API and use it for reftests

Co-authored-by: Delan Azabani <dazabani@igalia.com>
Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/shared/compositing/lib.rs

@@ -12,6 +12,7 @@ use crossbeam_channel::Sender;
 use embedder_traits::{AnimationState, EventLoopWaker, TouchEventResult};
 use log::warn;
 use malloc_size_of_derive::MallocSizeOf;
+use rustc_hash::FxHashMap;
 use smallvec::SmallVec;
 use strum_macros::IntoStaticStr;
 use webrender_api::{DocumentId, FontVariation};
@@ -87,8 +88,6 @@ pub enum CompositorMsg {
     RemoveWebView(WebViewId),
     /// Script has handled a touch event, and either prevented or allowed default actions.
     TouchEventProcessed(WebViewId, TouchEventResult),
-    /// A reply to the compositor asking if the output image is stable.
-    IsReadyToSaveImageReply(bool),
     /// Set whether to use less resources by stopping animations.
     SetThrottled(WebViewId, PipelineId, bool),
     /// WebRender has produced a new frame. This message informs the compositor that
@@ -100,8 +99,6 @@ pub enum CompositorMsg {
     /// they have fully shut it down, to avoid recreating it due to any subsequent
     /// messages.
     PipelineExited(WebViewId, PipelineId, PipelineExitSource),
-    /// The load of a page has completed
-    LoadComplete(WebViewId),
     /// Inform WebRender of the existence of this pipeline.
     SendInitialTransaction(WebRenderPipelineId),
     /// Perform a scroll operation.
@@ -163,6 +160,9 @@ pub enum CompositorMsg {
     CollectMemoryReport(ReportsChan),
     /// A top-level frame has parsed a viewport metatag and is sending the new constraints.
     Viewport(WebViewId, ViewportDescription),
+    /// Let the compositor know that the given WebView is ready to have a screenshot taken
+    /// after the given pipeline's epochs have been rendered.
+    ScreenshotReadinessReponse(WebViewId, FxHashMap<PipelineId, Epoch>),
 }
 
 impl Debug for CompositorMsg {

components/shared/constellation/from_script_message.rs

@@ -501,6 +501,16 @@ pub enum KeyboardScroll {
     End,
 }
 
+#[derive(Debug, Deserialize, Serialize)]
+pub enum ScreenshotReadinessResponse {
+    /// The Pipeline associated with this response, is ready for a screenshot at the
+    /// provided [`Epoch`].
+    Ready(Epoch),
+    /// The Pipeline associated with this response is no longer active and should be
+    /// ignored for the purposes of the screenshot.
+    NoLongerActive,
+}
+
 /// Messages from the script to the constellation.
 #[derive(Deserialize, IntoStaticStr, Serialize)]
 pub enum ScriptToConstellationMessage {
@@ -641,8 +651,6 @@ pub enum ScriptToConstellationMessage {
     ActivateDocument,
     /// Set the document state for a pipeline (used by screenshot / reftests)
     SetDocumentState(DocumentState),
-    /// Update the layout epoch in the constellation (used by screenshot / reftests).
-    SetLayoutEpoch(Epoch, IpcSender<bool>),
     /// Update the pipeline Url, which can change after redirections.
     SetFinalUrl(ServoUrl),
     /// Script has handled a touch event, and either prevented or allowed default actions.
@@ -688,6 +696,8 @@ pub enum ScriptToConstellationMessage {
     WebDriverInputComplete(WebDriverMessageId),
     /// Forward a keyboard scroll operation from an `<iframe>` to a parent pipeline.
     ForwardKeyboardScroll(PipelineId, KeyboardScroll),
+    /// Notify the Constellation of the screenshot readiness of a given pipeline.
+    RespondToScreenshotReadinessRequest(ScreenshotReadinessResponse),
 }
 
 impl fmt::Debug for ScriptToConstellationMessage {

components/shared/constellation/lib.rs

@@ -15,7 +15,6 @@ use std::collections::VecDeque;
 use std::fmt;
 use std::time::Duration;
 
-use base::Epoch;
 use base::cross_process_instant::CrossProcessInstant;
 use base::id::{MessagePortId, PipelineId, WebViewId};
 use embedder_traits::{
@@ -41,8 +40,6 @@ use webrender_api::{ExternalScrollId, ImageKey};
 pub enum EmbedderToConstellationMessage {
     /// Exit the constellation.
     Exit,
-    /// Query the constellation to see if the current compositor output is stable
-    IsReadyToSaveImage(FxHashMap<PipelineId, Epoch>),
     /// Whether to allow script to navigate.
     AllowNavigationResponse(PipelineId, bool),
     /// Request to load a page.
@@ -109,6 +106,9 @@ pub enum EmbedderToConstellationMessage {
     SetWebDriverResponseSender(IpcSender<WebDriverCommandResponse>),
     /// A set of preferences were updated with the given new values.
     PreferencesUpdated(Vec<(&'static str, PrefValue)>),
+    /// Request preparation for a screenshot of the given WebView. The Constellation will
+    /// send a message to the Embedder when the screenshot is ready to be taken.
+    RequestScreenshotReadiness(WebViewId),
 }
 
 /// A description of a paint metric that is sent from the Servo renderer to the

components/shared/embedder/lib.rs

@@ -1063,6 +1063,15 @@ pub enum JavaScriptEvaluationError {
     SerializationError,
 }
 
+#[derive(Clone, Debug, Deserialize, PartialEq, Serialize)]
+pub enum ScreenshotCaptureError {
+    /// The screenshot request failed to read the screenshot image from the `WebView`'s
+    /// `RenderingContext`.
+    CouldNotReadImage,
+    /// The WebView that this screenshot request was made for no longer exists.
+    WebViewDoesNotExist,
+}
+
 #[derive(Clone, Copy, Debug, Deserialize, Serialize)]
 pub struct RgbColor {
     pub red: u8,

components/shared/script/lib.rs

@@ -267,6 +267,10 @@ pub enum ScriptThreadMessage {
     NoLongerWaitingOnAsychronousImageUpdates(PipelineId),
     /// Forward a keyboard scroll operation from an `<iframe>` to a parent pipeline.
     ForwardKeyboardScroll(PipelineId, KeyboardScroll),
+    /// Request readiness for a screenshot from the given pipeline. The pipeline will
+    /// respond when it is ready to take the screenshot or will not be able to take it
+    /// in the future.
+    RequestScreenshotReadiness(PipelineId),
 }
 
 impl fmt::Debug for ScriptThreadMessage {