Teach SkyShell.apk to stop posting frames when not visible

This listens to both surface destruction as well as activity
pause/unpause.

R=abarth@chromium.org, abarth@google.com

Review URL: https://codereview.chromium.org/1230073002 .

engine/src/flutter/shell/android/org/domokit/sky/shell/PlatformViewAndroid.java

@@ -97,6 +97,10 @@ public class PlatformViewAndroid extends SurfaceView
         KeyboardServiceImpl.setActiveView(this);
     }
 
+    SkyEngine getEngine() {
+        return mSkyEngine;
+    }
+
     @Override
     protected void onDetachedFromWindow() {
         getHolder().removeCallback(mSurfaceCallback);
@@ -199,24 +203,6 @@ public class PlatformViewAndroid extends SurfaceView
         mSkyEngine.onInputEvent(event);
     }
 
-    public void onBackPressed() {
-        InputEvent event = new InputEvent();
-        event.type = EventType.BACK;
-        mSkyEngine.onInputEvent(event);
-    }
-
-    public void loadSnapshot(String path) {
-        mSkyEngine.runFromSnapshot(path);
-    }
-
-    public void loadBundle(String path) {
-        mSkyEngine.runFromBundle(path);
-    }
-
-    public void loadUrl(String url) {
-        mSkyEngine.runFromNetwork(url);
-    }
-
     private void attach() {
         Core core = CoreImpl.getInstance();
         Pair<SkyEngine.Proxy, InterfaceRequest<SkyEngine>> result =

engine/src/flutter/shell/android/org/domokit/sky/shell/SkyActivity.java

@@ -11,6 +11,8 @@ import android.view.View;
 import android.view.WindowManager;
 
 import org.chromium.base.PathUtils;
+import org.chromium.mojom.sky.EventType;
+import org.chromium.mojom.sky.InputEvent;
 
 import org.domokit.activity.ActivityImpl;
 
@@ -64,14 +66,30 @@ public class SkyActivity extends Activity {
     @Override
     public void onBackPressed() {
         if (mView != null) {
-            mView.onBackPressed();
-            // TODO(abarth): We should have some way to trigger the default
-            // back behavior.
+            InputEvent event = new InputEvent();
+            event.type = EventType.BACK;
+            mView.getEngine().onInputEvent(event);
             return;
         }
         super.onBackPressed();
     }
 
+    @Override
+    protected void onPause() {
+        super.onPause();
+        if (mView != null) {
+            mView.getEngine().onActivityPaused();
+        }
+    }
+
+    @Override
+    protected void onPostResume() {
+        super.onPostResume();
+        if (mView != null) {
+            mView.getEngine().onActivityResumed();
+        }
+    }
+
     /**
       * Override this function to customize startup behavior.
       */
@@ -79,18 +97,18 @@ public class SkyActivity extends Activity {
         File dataDir = new File(PathUtils.getDataDirectory(this));
         File snapshot = new File(dataDir, SkyApplication.SNAPSHOT);
         if (snapshot.exists()) {
-            mView.loadSnapshot(snapshot.getPath());
+            mView.getEngine().runFromSnapshot(snapshot.getPath());
             return;
         }
         File appBundle = new File(dataDir, SkyApplication.APP_BUNDLE);
         if (appBundle.exists()) {
-            mView.loadBundle(appBundle.getPath());
+            mView.getEngine().runFromBundle(appBundle.getPath());
             return;
         }
     }
 
     public void loadUrl(String url) {
-        mView.loadUrl(url);
+        mView.getEngine().runFromNetwork(url);
     }
 
     public boolean loadBundleByName(String name) {
@@ -99,7 +117,7 @@ public class SkyActivity extends Activity {
         if (!bundle.exists()) {
             return false;
         }
-        mView.loadBundle(bundle.getPath());
+        mView.getEngine().runFromBundle(bundle.getPath());
         return true;
     }
 }

engine/src/flutter/shell/ui/animator.cc

@@ -16,6 +16,7 @@ Animator::Animator(const Engine::Config& config, Engine* engine)
       engine_(engine),
       engine_requested_frame_(false),
       frame_in_progress_(false),
+      paused_(false),
       weak_factory_(this) {
 }
 
@@ -37,10 +38,16 @@ void Animator::RequestFrame() {
   }
 }
 
-void Animator::CancelFrameRequest() {
+void Animator::Stop() {
+  paused_ = true;
   engine_requested_frame_ = false;
 }
 
+void Animator::Start() {
+  paused_ = false;
+  RequestFrame();
+}
+
 void Animator::BeginFrame() {
   DCHECK(frame_in_progress_);
   // There could be a request in the message loop at time of cancel.
@@ -62,6 +69,9 @@ void Animator::BeginFrame() {
 void Animator::OnFrameComplete() {
   DCHECK(frame_in_progress_);
   frame_in_progress_ = false;
+  if (paused_)
+    return;
+
   if (engine_requested_frame_) {
     frame_in_progress_ = true;
     BeginFrame();

engine/src/flutter/shell/ui/animator.h

@@ -17,7 +17,9 @@ class Animator {
   ~Animator();
 
   void RequestFrame();
-  void CancelFrameRequest();
+
+  void Start();
+  void Stop();
 
  private:
   void BeginFrame();
@@ -27,6 +29,7 @@ class Animator {
   Engine* engine_;
   bool engine_requested_frame_;
   bool frame_in_progress_;
+  bool paused_;
 
   base::WeakPtrFactory<Animator> weak_factory_;
 

engine/src/flutter/shell/ui/engine.cc

@@ -59,6 +59,8 @@ Engine::Engine(const Config& config)
     : config_(config),
       animator_(new Animator(config, this)),
       binding_(this),
+      activity_running_(false),
+      have_surface_(false),
       weak_factory_(this) {
 }
 
@@ -118,11 +120,15 @@ void Engine::OnAcceleratedWidgetAvailable(gfx::AcceleratedWidget widget) {
   config_.gpu_task_runner->PostTask(
       FROM_HERE, base::Bind(&GPUDelegate::OnAcceleratedWidgetAvailable,
                             config_.gpu_delegate, widget));
+  have_surface_ = true;
+  StartAnimatorIfPossible();
   if (sky_view_)
     ScheduleFrame();
 }
 
 void Engine::OnOutputSurfaceDestroyed() {
+  have_surface_ = false;
+  StopAnimator();
   config_.gpu_task_runner->PostTask(
       FROM_HERE,
       base::Bind(&GPUDelegate::OnOutputSurfaceDestroyed, config_.gpu_delegate));
@@ -195,12 +201,31 @@ void Engine::RunFromBundle(const mojo::String& path) {
                                        weak_factory_.GetWeakPtr(), path_str));
 }
 
+void Engine::OnActivityPaused() {
+  activity_running_ = false;
+  StopAnimator();
+}
+
+void Engine::OnActivityResumed() {
+  activity_running_ = true;
+  StartAnimatorIfPossible();
+}
+
 void Engine::DidCreateIsolate(Dart_Isolate isolate) {
   Internals::Create(isolate,
                     CreateServiceProvider(config_.service_provider_context),
                     root_bundle_.Pass());
 }
 
+void Engine::StopAnimator() {
+  animator_->Stop();
+}
+
+void Engine::StartAnimatorIfPossible() {
+  if (activity_running_ && have_surface_)
+    animator_->Start();
+}
+
 void Engine::ScheduleFrame() {
   animator_->RequestFrame();
 }

engine/src/flutter/shell/ui/engine.h

@@ -71,6 +71,9 @@ class Engine : public UIDelegate,
   void RunFromSnapshot(const mojo::String& path) override;
   void RunFromBundle(const mojo::String& path) override;
 
+  void OnActivityPaused() override;
+  void OnActivityResumed() override;
+
   // SkyViewClient methods:
   void ScheduleFrame() override;
   void DidCreateIsolate(Dart_Isolate isolate) override;
@@ -88,6 +91,9 @@ class Engine : public UIDelegate,
   void RunFromSnapshotStream(const std::string& name,
                              mojo::ScopedDataPipeConsumerHandle snapshot);
 
+  void StopAnimator();
+  void StartAnimatorIfPossible();
+
   Config config_;
   scoped_ptr<Animator> animator_;
 
@@ -99,6 +105,10 @@ class Engine : public UIDelegate,
   blink::SkyDisplayMetrics display_metrics_;
   mojo::Binding<SkyEngine> binding_;
 
+  // TODO(eseidel): This should move into an AnimatorStateMachine.
+  bool activity_running_;
+  bool have_surface_;
+
   base::WeakPtrFactory<Engine> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Engine);