// Copyright 2013 The Flutter Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. #ifndef SHELL_COMMON_ENGINE_H_ #define SHELL_COMMON_ENGINE_H_ #include #include #include "flutter/assets/asset_manager.h" #include "flutter/common/task_runners.h" #include "flutter/fml/macros.h" #include "flutter/fml/memory/weak_ptr.h" #include "flutter/lib/ui/painting/image_decoder.h" #include "flutter/lib/ui/semantics/custom_accessibility_action.h" #include "flutter/lib/ui/semantics/semantics_node.h" #include "flutter/lib/ui/text/font_collection.h" #include "flutter/lib/ui/window/platform_message.h" #include "flutter/lib/ui/window/viewport_metrics.h" #include "flutter/runtime/dart_vm.h" #include "flutter/runtime/runtime_controller.h" #include "flutter/runtime/runtime_delegate.h" #include "flutter/shell/common/animator.h" #include "flutter/shell/common/rasterizer.h" #include "flutter/shell/common/run_configuration.h" #include "flutter/shell/common/shell_io_manager.h" #include "third_party/skia/include/core/SkPicture.h" namespace flutter { //------------------------------------------------------------------------------ /// The engine is a component owned by the shell that resides on the UI task /// runner and is responsible for managing the needs of the root isolate and its /// runtime. The engine can only be created, accessed and collected on the UI /// task runner. Each shell owns exactly one instance of the engine. /// /// The root isolate of Flutter application gets "window" bindings. Using these /// bindings, the application can schedule frames, post layer-trees for /// rendering, ask to decompress images and upload them to the GPU, etc.. /// Non-root isolates of the VM do not get any of these capabilities and are run /// in a VM managed thread pool (so if they did have "window", the threading /// guarantees needed for engine operation would be violated). /// /// The engine is responsible for the entire life-cycle of the root isolate. /// When the engine is collected, its owner assumes that the root isolate has /// been shutdown and appropriate resources collected. While each engine /// instance can only manage a single instance of a root isolate, it may restart /// that isolate on request. This is how the cold-restart development scenario /// is supported. /// /// When the engine instance is initially created, the root isolate is created /// but it is not in the |DartIsolate::Phase::Running| phase yet. It only moves /// into that phase when a successful call to `Engine::Run` is made. /// /// @see `Shell` /// /// @note This name of this class is perhaps a bit unfortunate and has /// sometimes been the cause of confusion. For a class named "Engine" /// in the Flutter "Engine" repository, its responsibilities are /// decidedly unremarkable. But, it does happen to be the primary /// entry-point used by components higher up in the Flutter tech stack /// (usually in Dart code) to peer into the lower level functionality. /// Besides, the authors haven't been able to come up with a more apt /// name and it does happen to be one of the older classes in the /// repository. /// class Engine final : public RuntimeDelegate { public: //---------------------------------------------------------------------------- /// @brief Indicates the result of the call to `Engine::Run`. /// enum class RunStatus { //-------------------------------------------------------------------------- /// The call to |Engine::Run| was successful and the root isolate is in the /// `DartIsolate::Phase::Running` phase with its entry-point invocation /// already pending in the task queue. /// Success, //-------------------------------------------------------------------------- /// The engine can only manage a single instance of a root isolate. If a /// previous call to run the root isolate was successful, subsequent calls /// to run the isolate (even if the new run configuration is different) will /// be rejected. /// /// It is up to the caller to decide to re-purpose the running isolate, /// terminate it, or use another shell to host the new isolate. This is /// mostly used by embedders which have a fire-and-forget strategy to root /// isolate launch. For example, the application may try to "launch" and /// isolate when the embedders launches or resumes from a paused state. That /// the isolate is running is not necessarily a failure condition for them. /// But from the engine's perspective, the run configuration was rejected. /// FailureAlreadyRunning, //-------------------------------------------------------------------------- /// Used to indicate to the embedder that a root isolate was not already /// running but the run configuration was not valid and root isolate could /// not be moved into the `DartIsolate::Phase::Running` phase. /// /// The caller must attempt the run call again with a valid configuration. /// The set of all failure modes is massive and can originate from a variety /// of sub-components. The engine will attempt to log the same when /// possible. With the aid of logs, the common causes of failure are: /// /// * AOT assets give to JIT/DBC mode VM's and vice-versa. /// * The assets could not be found in the asset manager. Callers must make /// sure their run configuration asset managers have been correctly setup. /// * The assets themselves were corrupt or invalid. Callers must make sure /// their asset delivery mechanisms are sound. /// * The application entry-point or the root library of the entry-point /// specified in the run configuration was invalid. Callers must make sure /// that the entry-point is present in the application. If the name of the /// entrypoint is not "main" in the root library, callers must also ensure /// that the snapshotting process has not tree-shaken away this /// entrypoint. This requires the decoration of the entrypoint with the /// `@pragma('vm:entry-point')` directive. This problem will manifest in /// AOT mode operation of the Dart VM. /// Failure, }; //---------------------------------------------------------------------------- /// @brief While the engine operates entirely on the UI task runner, it /// needs the capabilities of the other components to fulfill the /// requirements of the root isolate. The shell is the only class /// that implements this interface as no other component has /// access to all components in a thread safe manner. The engine /// delegates these tasks to the shell via this interface. /// class Delegate { public: //-------------------------------------------------------------------------- /// @brief When the accessibility tree has been updated by the Flutter /// application, this new information needs to be conveyed to /// the underlying platform. The engine delegates this task to /// the shell via this call. The engine cannot access the /// underlying platform directly because of threading /// considerations. Most platform specific APIs to convey /// accessibility information are only safe to access on the /// platform task runner while the engine is running on the UI /// task runner. /// /// @see `SemanticsNode`, `SemticsNodeUpdates`, /// `CustomAccessibilityActionUpdates`, /// `PlatformView::UpdateSemantics` /// /// @param[in] updates A map with the stable semantics node identifier as /// key and the node properties as the value. /// @param[in] actions A map with the stable semantics node identifier as /// key and the custom node action as the value. /// virtual void OnEngineUpdateSemantics( SemanticsNodeUpdates updates, CustomAccessibilityActionUpdates actions) = 0; //-------------------------------------------------------------------------- /// @brief When the Flutter application has a message to send to the /// underlying platform, the message needs to be forwarded to /// the platform on the the appropriate thread (via the platform /// task runner). The engine delegates this task to the shell /// via this method. /// /// @see `PlatformView::HandlePlatformMessage` /// /// @param[in] message The message from the Flutter application to send to /// the underlying platform. /// virtual void OnEngineHandlePlatformMessage( fml::RefPtr message) = 0; //-------------------------------------------------------------------------- /// @brief Notifies the delegate that the root isolate of the /// application is about to be discarded and a new isolate with /// the same runtime started in its place. This should only /// happen in the Flutter "debug" runtime mode in the /// cold-restart scenario. The embedder may need to reset native /// resource in response to the restart. /// /// @see `PlatformView::OnPreEngineRestart` /// virtual void OnPreEngineRestart() = 0; //-------------------------------------------------------------------------- /// @brief Notifies the shell of the name of the root isolate and its /// port when that isolate is launched, restarted (in the /// cold-restart scenario) or the application itself updates the /// name of the root isolate (via `Window.setIsolateDebugName` /// in `window.dart`). The name of the isolate is meaningless to /// the engine but is used in instrumentation and tooling. /// Currently, this information is to update the service /// protocol list of available root isolates running in the VM /// and their names so that the appropriate isolate can be /// selected in the tools for debugging and instrumentation. /// /// @param[in] isolate_name The isolate name /// @param[in] isolate_port The isolate port /// virtual void UpdateIsolateDescription(const std::string isolate_name, int64_t isolate_port) = 0; //-------------------------------------------------------------------------- /// @brief Notifies the shell that the application has an opinion about /// whether its frame timings need to be reported backed to it. /// Due to the asynchronous nature of rendering in Flutter, it /// is not possible for the application to determine the total /// time it took to render a specific frame. While the /// layer-tree is constructed on the UI thread, it needs to be /// rendering on the GPU thread. Dart code cannot execute on /// this thread. So any instrumentation about the frame times /// gathered on this thread needs to be aggregated and sent back /// to the UI thread for processing in Dart. /// /// When the application indicates that frame times need to be /// reported, it collects this information till a specified /// number of data points are gathered. Then this information is /// sent back to Dart code via `Engine::ReportTimings`. /// /// This option is engine counterpart of the /// `Window._setNeedsReportTimings` in `window.dart`. /// /// @param[in] needs_reporting If reporting information should be /// collected and send back to Dart. /// virtual void SetNeedsReportTimings(bool needs_reporting) = 0; }; //---------------------------------------------------------------------------- /// @brief Creates an instance of the engine. This is done by the Shell /// on the the UI task runner. /// /// @param delegate The object used by the engine to perform /// tasks that require access to components /// that cannot be safely accessed by the /// engine. This is the shell. /// @param vm An instance of the running Dart VM. /// @param[in] isolate_snapshot The snapshot used to create the root /// isolate. Even though the isolate is not /// `DartIsolate::Phase::Running` phase, it is /// created when the engine is created. This /// requires access to the isolate snapshot /// upfront. /// @param[in] shared_snapshot The portion of the isolate snapshot shared /// among multiple isolates. // TODO(chinmaygarde): This is probably redundant now that the IO manager is // it's own object. /// @param[in] task_runners The task runners used by the shell that /// hosts this engine. /// @param[in] settings The settings used to initialize the shell /// and the engine. /// @param[in] animator The animator used to schedule frames. // TODO(chinmaygarde): Move this to `Engine::Delegate` /// @param[in] snapshot_delegate The delegate used to fulfill requests to /// snapshot a specified scene. The engine /// cannot snapshot a scene on the UI thread /// directly because the scene (described via /// an `SkPicture`) may reference resources on /// the GPU and there is no GPU context current /// on the UI thread. The delegate is a /// component that has access to all the /// requisite GPU resources. /// @param[in] io_manager The IO manager used by this root isolate to /// schedule tasks that manage resources on the /// GPU. /// Engine(Delegate& delegate, DartVM& vm, fml::RefPtr isolate_snapshot, fml::RefPtr shared_snapshot, TaskRunners task_runners, Settings settings, std::unique_ptr animator, fml::WeakPtr io_manager); //---------------------------------------------------------------------------- /// @brief Destroys the engine engine. Called by the shell on the UI task /// runner. The running root isolate is terminated and will no /// longer access the task runner after this call returns. This /// allows the embedder to tear down the thread immediately if /// needed. /// ~Engine() override; //---------------------------------------------------------------------------- /// @brief Gets the refresh rate in frames per second of the vsync waiter /// used by the animator managed by this engine. This information /// is purely advisory and is not used by any component. It is /// only used by the tooling to visualize frame performance. /// /// @attention The display refresh rate is useless for frame scheduling /// because it can vary and more accurate frame specific /// information is given to the engine by the vsync waiter /// already. However, this call is used by the tooling to ask very /// high level questions about display refresh rate. For example, /// "Is the display 60 or 120Hz?". This information is quite /// unreliable (not available immediately on launch on some /// platforms), variable and advisory. It must not be used by any /// component that claims to use it to perform accurate frame /// scheduling. /// /// @return The display refresh rate in frames per second. This may change /// from frame to frame, throughout the lifecycle of the /// application, and, may not be available immediately upon /// application launch. /// float GetDisplayRefreshRate() const; //---------------------------------------------------------------------------- /// @return The pointer to this instance of the engine. The engine may /// only be accessed safely on the UI task runner. /// fml::WeakPtr GetWeakPtr() const; //---------------------------------------------------------------------------- /// @brief Moves the root isolate to the `DartIsolate::Phase::Running` /// phase on a successful call to this method. /// /// The isolate itself is created when the engine is created, but /// it is not yet in the running phase. This is done to amortize /// initial time taken to launch the root isolate. The isolate /// snapshots used to run the isolate can be fetched on another /// thread while the engine itself is launched on the UI task /// runner. /// /// Repeated calls to this method after a successful run will be /// rejected even if the run configuration is valid (with the /// appropriate error returned). /// /// @param[in] configuration The configuration used to run the root isolate. /// The configuration must be valid. /// /// @return The result of the call to run the root isolate. /// FML_WARN_UNUSED_RESULT RunStatus Run(RunConfiguration configuration); //---------------------------------------------------------------------------- /// @brief Tears down an existing root isolate, reuses the components of /// that isolate and attempts to launch a new isolate using the /// given the run configuration. This is only used in the /// "debug" Flutter runtime mode in the cold-restart scenario. /// /// @attention This operation must be performed with care as even a /// non-successful restart will still tear down any existing root /// isolate. In such cases, the engine and its shell must be /// discarded. /// /// @param[in] configuration The configuration used to launch the new /// isolate. /// /// @return Whether the restart was successful. If not, the engine and its /// shell must be discarded. /// FML_WARN_UNUSED_RESULT bool Restart(RunConfiguration configuration); //---------------------------------------------------------------------------- /// @brief Updates the asset manager referenced by the root isolate of a /// Flutter application. This happens implicitly in the call to /// `Engine::Run` and `Engine::Restart` as the asset manager is /// referenced from the run configuration provided to those calls. /// In addition to the the `Engine::Run` and `Engine::Restart` /// calls, the tooling may need to update the assets available to /// the application as the user adds them to their project. For /// example, these assets may be referenced by code that is newly /// patched in after a hot-reload. Neither the shell or the /// isolate in relaunched in such cases. The tooling usually /// patches in the new assets in a temporary location and updates /// the asset manager to point to that location. /// /// @param[in] asset_manager The new asset manager to use for the running /// root isolate. /// /// @return If the asset manager was successfully replaced. This may fail /// if the new asset manager is invalid. /// bool UpdateAssetManager(std::shared_ptr asset_manager); //---------------------------------------------------------------------------- /// @brief Notifies the engine that it is time to begin working on a new /// frame previously scheduled via a call to /// `Engine::ScheduleFrame`. This call originates in the animator. /// /// The frame time given as the argument indicates the point at /// which the current frame interval began. It is very slightly /// (because of scheduling overhead) in the past. If a new layer /// tree is not produced and given to the GPU task runner within /// one frame interval from this point, the Flutter application /// will jank. /// /// If an root isolate is running, this method calls the /// `::_beginFrame` method in `hooks.dart`. If a root isolate is /// not running, this call does nothing. /// /// This method encapsulates the entire UI thread frame workload. /// The following (mis)behavior in the functioning of the method /// will cause the jank in the Flutter application: /// * The time taken by this method to create a layer-tree exceeds /// on frame interval (for example, 16.66 ms on a 60Hz display). /// * The time take by this method to generate a new layer-tree /// causes the current layer-tree pipeline depth to change. To /// illustrate this point, note that maximum pipeline depth used /// by layer tree in the engine is 2. If both the UI and GPU /// task runner tasks finish within one frame interval, the /// pipeline depth is one. If the UI thread happens to be /// working on a frame when the GPU thread is still not done /// with the previous frame, the pipeline depth is 2. When the /// pipeline depth changes from 1 to 2, animations and UI /// interactions that cause the generation of the new layer tree /// appropriate for (frame_time + one frame interval) will /// actually end up at (frame_time + two frame intervals). This /// is not what code running on the UI thread expected would /// happen. This causes perceptible jank. /// /// @param[in] frame_time The point at which the current frame interval /// began. May be used by animation interpolators, /// physics simulations, etc.. /// void BeginFrame(fml::TimePoint frame_time); //---------------------------------------------------------------------------- /// @brief Notifies the engine that the UI task runner is not expected to /// undertake a new frame workload till a specified timepoint. The /// timepoint is measured in microseconds against the system's /// monotonic clock. It is recommended that the clock be accessed /// via `Dart_TimelineGetMicros` from `dart_api.h` for /// consistency. In reality, the clocks used by Dart, FML and /// std::steady_clock are all the same and the timepoints can be /// converted from on clock type to another. /// /// The Dart VM uses this notification to schedule book-keeping /// tasks that may include a garbage collection. In this way, it /// is less likely for the VM to perform such (potentially long /// running) tasks in the middle of a frame workload. /// /// This notification is advisory. That is, not providing this /// notification does not mean garbage collection is postponed /// till this call is made. If this notification is not provided, /// garbage collection will happen based on the usual heuristics /// used by the Dart VM. /// /// Currently, this idle notification is delivered to the engine /// at two points. Once, the deadline is calculated based on how /// much time in the current frame interval is left on the UI task /// runner. Since the next frame workload cannot begin till at /// least the next callback from the vsync waiter, this period may /// be used to used as a "small" idle notification. On the other /// hand, if no more frames are scheduled, a large (but arbitrary) /// idle notification deadline is chosen for a "big" idle /// notification. Again, this notification does not guarantee /// collection, just gives the Dart VM more hints about opportune /// moments to perform collections. /// // TODO(chinmaygarde): This should just use fml::TimePoint instead of having // to remember that the unit is microseconds (which is no used anywhere else // in the engine). /// /// @param[in] deadline The deadline as a timepoint in microseconds measured /// against the system monotonic clock. Use /// `Dart_TimelineGetMicros()`, for consistency. /// void NotifyIdle(int64_t deadline); //---------------------------------------------------------------------------- /// @brief Dart code cannot fully measure the time it takes for a /// specific frame to be rendered. This is because Dart code only /// runs on the UI task runner. That is only a small part of the /// overall frame workload. The GPU task runner frame workload is /// executed on a thread where Dart code cannot run (and hence /// instrument). Besides, due to the pipelined nature of rendering /// in Flutter, there may be multiple frame workloads being /// processed at any given time. However, for non-Timeline based /// profiling, it is useful for trace collection and processing to /// happen in Dart. To do this, the GPU task runner frame /// workloads need to be instrumented separately. After a set /// number of these profiles have been gathered, they need to be /// reported back to Dart code. The shell reports this extra /// instrumentation information back to Dart code running on the /// engine by invoking this method at predefined intervals. /// /// @see `FrameTiming` /// // TODO(chinmaygarde): The use `int64_t` is added for ease of conversion to // Dart but hurts readability. The phases and the units of the timepoints are // not obvious without some sleuthing. The conversion can happen at the // native interface boundary instead. /// /// @param[in] timings Collection of `FrameTiming::kCount` * `n` timestamps /// for `n` frames whose timings have not been reported /// yet. A collection of integers is reported here for /// easier conversions to Dart objects. The timestamps /// are measured against the system monotonic clock /// measured in microseconds. /// void ReportTimings(std::vector timings); //---------------------------------------------------------------------------- /// @brief Gets the main port of the root isolate. Since the isolate is /// created immediately in the constructor of the engine, it is /// possible to get its main port immediately (even before a call /// to `Run` can be made). This is useful in registering the port /// in a race free manner with a port nameserver. /// /// @return The main port of the root isolate. /// Dart_Port GetUIIsolateMainPort(); //---------------------------------------------------------------------------- /// @brief Gets the debug name of the root isolate. But default, the /// debug name of the isolate is derived from its advisory script /// URI, advisory main entrypoint and its main port name. For /// example, "main.dart$main-1234" where the script URI is /// "main.dart", the entrypoint is "main" and the port name /// "1234". Once launched, the isolate may re-christen itself /// using a name it selects via `setIsolateDebugName` in /// `window.dart`. This name is purely advisory and only used by /// instrumentation and reporting purposes. /// /// @return The debug name of the root isolate. /// std::string GetUIIsolateName(); //---------------------------------------------------------------------------- /// @brief It is an unexpected challenge to determine when a Dart /// application is "done". The application cannot simply terminate /// the native process (and perhaps return an exit code) because /// it does not have that power. After all, Flutter applications /// reside within a host process that may have other /// responsibilities besides just running Flutter applications. /// Also, the `main` entry-points are run on an event loop and /// returning from "main" (unlike in C/C++ applications) does not /// mean termination of the process. Besides, the return value of /// the main entrypoint is discarded. /// /// One technique used by embedders to determine "liveness" is to /// count the outstanding live ports dedicated to the application. /// These ports may be live as a result of pending timers, /// scheduled tasks, pending IO on sockets, channels open with /// other isolates, etc.. At regular intervals (sometimes as often /// as after the UI task runner processes any task), embedders may /// check for the "liveness" of the application and perform /// teardown of the embedder when no more ports are live. /// /// @return Check if the root isolate has any live ports. /// bool UIIsolateHasLivePorts(); //---------------------------------------------------------------------------- /// @brief Errors that are unhandled on the Dart message loop are kept /// for further inspection till the next unhandled error comes /// along. This accessor returns the last unhandled error /// encountered by the root isolate. /// /// @return The ui isolate last error. /// tonic::DartErrorHandleType GetUIIsolateLastError(); //---------------------------------------------------------------------------- /// @brief As described in the discussion for `UIIsolateHasLivePorts`, /// the "done-ness" of a Dart application is tricky to ascertain /// and the return value from the main entrypoint is discarded /// (because the Dart isolate is still running after the main /// entrypoint returns). But, the concept of an exit code akin to /// those returned by native applications is still useful. Short /// lived Dart applications (usually tests), emulate this by /// setting a per isolate "return value" and then indicating their /// "done-ness" (usually via closing all live ports). This /// accessor returns that "return value" is present. /// /// @see `UIIsolateHasLivePorts` /// // TODO(chinmaygarde): Use std::optional instead of the pair now that it is // available. /// /// @return A pair containing a boolean value indicating if the isolate /// set a "return value" and that value if present. When the first /// item of the pair is false, second item is meaningless. /// std::pair GetUIIsolateReturnCode(); //---------------------------------------------------------------------------- /// @brief Indicates to the Flutter application that it has obtained a /// rendering surface. This is a good opportunity for the engine /// to start servicing any outstanding frame requests from the /// Flutter applications. Flutter application that have no /// rendering concerns may never get a rendering surface. In such /// cases, while their root isolate can perform as normal, any /// frame requests made by them will never be serviced and layer /// trees produced outside of frame workloads will be dropped. /// /// Very close to when this call is made, the application can /// expect the updated viewport metrics. Rendering only begins /// when the Flutter application gets an output surface and a /// valid set of viewport metrics. /// /// @see `OnOutputSurfaceDestroyed` /// void OnOutputSurfaceCreated(); //---------------------------------------------------------------------------- /// @brief Indicates to the Flutter application that a previously /// acquired rendering surface has been lost. Further frame /// requests will no longer be serviced and any layer tree /// submitted for rendering will be dropped. If/when a new surface /// is acquired, a new layer tree must be generated. /// /// @see `OnOutputSurfaceCreated` /// void OnOutputSurfaceDestroyed(); //---------------------------------------------------------------------------- /// @brief Updates the viewport metrics for the currently running Flutter /// application. The viewport metrics detail the size of the /// rendering viewport in texels as well as edge insets if /// present. /// /// @see `ViewportMetrics` /// /// @param[in] metrics The metrics /// void SetViewportMetrics(const ViewportMetrics& metrics); //---------------------------------------------------------------------------- /// @brief Notifies the engine that the embedder has sent it a message. /// This call originates in the platform view and has been /// forwarded to the engine on the UI task runner here. /// /// @param[in] message The message sent from the embedder to the Dart /// application. /// void DispatchPlatformMessage(fml::RefPtr message); //---------------------------------------------------------------------------- /// @brief Notifies the engine that the embedder has sent it a pointer /// data packet. A pointer data packet may contain multiple /// input events. This call originates in the platform view and /// the shell has forwarded the same to the engine on the UI task /// runner here. /// /// @param[in] packet The pointer data packet containing multiple /// input events. /// @param[in] trace_flow_id The trace flow identifier associated with the /// pointer data packet. The engine uses this trace /// identifier to connect trace flows in the /// timeline from the input event event to the /// frames generated due to those input events. /// These flows are tagged as "PointerEvent" in the /// timeline and allow grouping frames and input /// events into logical chunks. /// void DispatchPointerDataPacket(const PointerDataPacket& packet, uint64_t trace_flow_id); //---------------------------------------------------------------------------- /// @brief Notifies the engine that the embedder encountered an /// accessibility related action on the specified node. This call /// originates on the platform view and has been forwarded to the /// engine here on the UI task runner by the shell. /// /// @param[in] id The identifier of the accessibility node. /// @param[in] action The accessibility related action performed on the /// node of the specified ID. /// @param[in] args Optional data that applies to the specified action. /// void DispatchSemanticsAction(int id, SemanticsAction action, std::vector args); //---------------------------------------------------------------------------- /// @brief Notifies the engine that the embedder has expressed an opinion /// about where the accessibility tree should be generated or not. /// This call originates in the platform view and is forwarded to /// the engine here on the UI task runner by the shell. /// /// @param[in] enabled Whether the accessibility tree is enabled or /// disabled. /// void SetSemanticsEnabled(bool enabled); //---------------------------------------------------------------------------- /// @brief Notifies the engine that the embedder has expressed an opinion /// about where the flags to set on the accessibility tree. This /// flag originates in the platform view and is forwarded to the /// engine here on the UI task runner by the shell. /// /// The engine does not care about the accessibility feature flags /// as all it does is forward this information from the embedder /// to the framework. However, curious readers may refer to /// `AccessibilityFeatures` in `window.dart` for currently /// supported accessibility feature flags. /// /// @param[in] flags The features to enable in the accessibility tree. /// void SetAccessibilityFeatures(int32_t flags); // |RuntimeDelegate| void ScheduleFrame(bool regenerate_layer_tree = true) override; // |RuntimeDelegate| FontCollection& GetFontCollection() override; private: Engine::Delegate& delegate_; const Settings settings_; std::unique_ptr animator_; std::unique_ptr runtime_controller_; std::string initial_route_; ViewportMetrics viewport_metrics_; std::shared_ptr asset_manager_; bool activity_running_; bool have_surface_; FontCollection font_collection_; ImageDecoder image_decoder_; fml::WeakPtrFactory weak_factory_; // |RuntimeDelegate| std::string DefaultRouteName() override; // |RuntimeDelegate| void Render(std::unique_ptr layer_tree) override; // |RuntimeDelegate| void UpdateSemantics(SemanticsNodeUpdates update, CustomAccessibilityActionUpdates actions) override; // |RuntimeDelegate| void HandlePlatformMessage(fml::RefPtr message) override; // |RuntimeDelegate| void UpdateIsolateDescription(const std::string isolate_name, int64_t isolate_port) override; void SetNeedsReportTimings(bool value) override; void StopAnimator(); void StartAnimatorIfPossible(); bool HandleLifecyclePlatformMessage(PlatformMessage* message); bool HandleNavigationPlatformMessage(fml::RefPtr message); bool HandleLocalizationPlatformMessage(PlatformMessage* message); void HandleSettingsPlatformMessage(PlatformMessage* message); void HandleAssetPlatformMessage(fml::RefPtr message); bool GetAssetAsBuffer(const std::string& name, std::vector* data); RunStatus PrepareAndLaunchIsolate(RunConfiguration configuration); friend class testing::ShellTest; FML_DISALLOW_COPY_AND_ASSIGN(Engine); }; } // namespace flutter #endif // SHELL_COMMON_ENGINE_H_