[Android] Remove overlay when platform views are removed from screen. (flutter#162908)

When there are no more platform views, make sure the overlay layer is
hidden. When a platform view is added again, show the overlay. The
show/hide allows us to avoid continually recreating and destroying the
overlay surface + swapchain when a platform view slides in and out of
frame.

To further reduce memory usage, we could do a delayed de-allocation of
the overlay layer (say after 50 frames of no platform view, destroy it).
But I'm leaving this to a follow up.

Author: Jonah Williams

dev/integration_tests/android_engine_test/lib/hcpp/platform_view_main.dart

@@ -12,6 +12,7 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_driver/driver_extension.dart';
 
+import '../platform_view/_shared.dart';
 import '../src/allow_list_devices.dart';
 
 void main() async {
@@ -27,40 +28,18 @@ void main() async {
 
   // Run on full screen.
   await SystemChrome.setEnabledSystemUIMode(SystemUiMode.immersive);
-  runApp(const MainApp());
-}
-
-final class MainApp extends StatelessWidget {
-  const MainApp({super.key});
-
-  // This should appear as the yellow line over a blue box. The
-  // green box should not be visible unless the platform view has not loaded yet.
-  @override
-  Widget build(BuildContext context) {
-    return const MaterialApp(
-      debugShowCheckedModeBanner: false,
-      home: Stack(
-        alignment: AlignmentDirectional.center,
-        children: <Widget>[
-          SizedBox(width: 190, height: 190, child: ColoredBox(color: Colors.green)),
-          SizedBox(
-            width: 200,
-            height: 200,
-            child: _HybridCompositionAndroidPlatformView(viewType: 'box_platform_view'),
-          ),
-          SizedBox(width: 800, height: 25, child: ColoredBox(color: Colors.yellow)),
-        ],
-      ),
-    );
-  }
+  runApp(
+    const MainApp(
+      platformView: _HybridCompositionAndroidPlatformView(viewType: 'box_platform_view'),
+    ),
+  );
 }
 
 final class _HybridCompositionAndroidPlatformView extends StatelessWidget {
   const _HybridCompositionAndroidPlatformView({required this.viewType});
 
   final String viewType;
 
-  // TODO(jonahwilliams): swap this out with new platform view APIs.
   @override
   Widget build(BuildContext context) {
     return PlatformViewLink(

dev/integration_tests/android_engine_test/lib/platform_view/_shared.dart

@@ -4,18 +4,50 @@
 
 import 'package:flutter/material.dart';
 
-final class MainApp extends StatelessWidget {
+// This should appear as the yellow line over a blue box. The
+// green box should not be visible unless the platform view has not loaded yet.
+final class MainApp extends StatefulWidget {
   const MainApp({super.key, required this.platformView});
+
   final Widget platformView;
 
+  @override
+  State<MainApp> createState() => _MainAppState();
+}
+
+class _MainAppState extends State<MainApp> {
+  bool showPlatformView = true;
+
+  void _togglePlatformView() {
+    setState(() {
+      showPlatformView = !showPlatformView;
+    });
+  }
+
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
       debugShowCheckedModeBanner: false,
       home: Stack(
+        alignment: AlignmentDirectional.center,
         children: <Widget>[
-          platformView,
-          Center(child: Container(width: 100, height: 100, color: Colors.red)),
+          TextButton(
+            key: const ValueKey<String>('AddOverlay'),
+            onPressed: _togglePlatformView,
+            child: const SizedBox(width: 190, height: 190, child: ColoredBox(color: Colors.green)),
+          ),
+          if (showPlatformView) ...<Widget>[
+            SizedBox(width: 200, height: 200, child: widget.platformView),
+            TextButton(
+              key: const ValueKey<String>('RemoveOverlay'),
+              onPressed: _togglePlatformView,
+              child: const SizedBox(
+                width: 800,
+                height: 25,
+                child: ColoredBox(color: Colors.yellow),
+              ),
+            ),
+          ],
         ],
       ),
     );

dev/integration_tests/android_engine_test/test_driver/hcpp/platform_view_main_test.dart

@@ -41,6 +41,8 @@ void main() async {
   });
 
   tearDownAll(() async {
+    await flutterDriver.tap(find.byValueKey('AddOverlay'));
+
     await nativeDriver.close();
     await flutterDriver.close();
   });
@@ -72,4 +74,16 @@ void main() async {
       matchesGoldenFile('$goldenPrefix.platform_view_portait_rotated_back.png'),
     );
   }, timeout: Timeout.none);
+
+  // Note: this doesn't reset the app so if additional test cases are added
+  // make sure to press the button again.
+  test('should remove overlay when platform view is removed', () async {
+    await flutterDriver.tap(find.byValueKey('RemoveOverlay'));
+    await Future<void>.delayed(const Duration(seconds: 1));
+
+    await expectLater(
+      nativeDriver.screenshot(),
+      matchesGoldenFile('$goldenPrefix.removed_overlay.png'),
+    );
+  }, timeout: Timeout.none);
 }

dev/integration_tests/android_engine_test/test_driver/platform_view/texture_layer_hybrid_composition_platform_view_main_test.dart

@@ -45,6 +45,8 @@ void main() async {
   });
 
   tearDownAll(() async {
+    await flutterDriver.tap(find.byValueKey('AddOverlay'));
+
     await nativeDriver.close();
     await flutterDriver.close();
   });
@@ -69,4 +71,14 @@ void main() async {
       matchesGoldenFile('$goldenPrefix.blue_orange_gradient_portait_rotated_back.png'),
     );
   }, timeout: Timeout.none);
+
+  test('should hide overlay layer', () async {
+    await flutterDriver.tap(find.byValueKey('RemoveOverlay'));
+    await Future<void>.delayed(const Duration(seconds: 1));
+
+    await expectLater(
+      nativeDriver.screenshot(),
+      matchesGoldenFile('$goldenPrefix.hide_overlay.png'),
+    );
+  }, timeout: Timeout.none);
 }

dev/integration_tests/android_engine_test/test_driver/platform_view/virtual_display_platform_view_main_test.dart

@@ -56,6 +56,8 @@ void main() async {
   });
 
   tearDownAll(() async {
+    await flutterDriver.tap(find.byValueKey('AddOverlay'));
+
     await nativeDriver.close();
     await flutterDriver.close();
   });
@@ -86,4 +88,14 @@ void main() async {
       ),
     );
   }, timeout: Timeout.none);
+
+  test('should hide overlay layer', () async {
+    await flutterDriver.tap(find.byValueKey('RemoveOverlay'));
+    await Future<void>.delayed(const Duration(seconds: 1));
+
+    await expectLater(
+      nativeDriver.screenshot(),
+      matchesGoldenFile('$goldenPrefix.hide_overlay.png'),
+    );
+  }, timeout: Timeout.none);
 }

engine/src/flutter/shell/platform/android/android_shell_holder_unittests.cc

@@ -111,6 +111,8 @@ class MockPlatformViewAndroidJNI : public PlatformViewAndroidJNI {
                MutatorsStack mutators_stack),
               (override));
   MOCK_METHOD(void, onEndFrame2, (), (override));
+  MOCK_METHOD(void, showOverlaySurface2, (), (override));
+  MOCK_METHOD(void, hideOverlaySurface2, (), (override));
   MOCK_METHOD(std::unique_ptr<std::vector<std::string>>,
               FlutterViewComputePlatformResolvedLocale,
               (std::vector<std::string> supported_locales_data),

engine/src/flutter/shell/platform/android/external_view_embedder/external_view_embedder_2.cc

@@ -76,10 +76,15 @@ void AndroidExternalViewEmbedder2::SubmitFlutterView(
 
   if (!FrameHasPlatformLayers()) {
     frame->Submit();
+    // If the previous frame had platform views, hide the overlay surface.
+    if (previous_frame_view_count_ > 0) {
+      jni_facade_->hideOverlaySurface2();
+    }
     jni_facade_->applyTransaction();
     return;
   }
 
+  bool prev_frame_no_platform_views = previous_frame_view_count_ == 0;
   std::unordered_map<int64_t, SkRect> view_rects;
   for (auto platform_id : composition_order_) {
     view_rects[platform_id] = GetViewRect(platform_id, view_params_);
@@ -143,9 +148,13 @@ void AndroidExternalViewEmbedder2::SubmitFlutterView(
   task_runners_.GetPlatformTaskRunner()->PostTask(fml::MakeCopyable(
       [&, composition_order = composition_order_, view_params = view_params_,
        jni_facade = jni_facade_, device_pixel_ratio = device_pixel_ratio_,
-       slices = std::move(slices_)]() -> void {
+       slices = std::move(slices_), prev_frame_no_platform_views]() -> void {
         jni_facade->swapTransaction();
 
+        if (prev_frame_no_platform_views) {
+          jni_facade_->showOverlaySurface2();
+        }
+
         for (int64_t view_id : composition_order) {
           SkRect view_rect = GetViewRect(view_id, view_params);
           const EmbeddedViewParams& params = view_params.at(view_id);

engine/src/flutter/shell/platform/android/io/flutter/embedding/engine/FlutterJNI.java

@@ -1322,6 +1322,28 @@ public FlutterOverlaySurface createOverlaySurface2() {
     return platformViewsController2.createOverlaySurface();
   }
 
+  @SuppressWarnings("unused")
+  @SuppressLint("NewApi")
+  @UiThread
+  public void showOverlaySurface2() {
+    if (platformViewsController2 == null) {
+      throw new RuntimeException(
+          "platformViewsController must be set before attempting to destroy an overlay surface");
+    }
+    platformViewsController2.showOverlaySurface();
+  }
+
+  @SuppressWarnings("unused")
+  @SuppressLint("NewApi")
+  @UiThread
+  public void hideOverlaySurface2() {
+    if (platformViewsController2 == null) {
+      throw new RuntimeException(
+          "platformViewsController must be set before attempting to destroy an overlay surface");
+    }
+    platformViewsController2.hideOverlaySurface();
+  }
+
   @SuppressWarnings("unused")
   @SuppressLint("NewApi")
   @UiThread

engine/src/flutter/shell/platform/android/io/flutter/plugin/platform/PlatformViewRegistryImpl.java

@@ -7,7 +7,7 @@
 import java.util.HashMap;
 import java.util.Map;
 
-class PlatformViewRegistryImpl implements PlatformViewRegistry {
+public class PlatformViewRegistryImpl implements PlatformViewRegistry {
 
   PlatformViewRegistryImpl() {
     viewFactories = new HashMap<>();

engine/src/flutter/shell/platform/android/io/flutter/plugin/platform/PlatformViewsController2.java

@@ -65,6 +65,7 @@ public class PlatformViewsController2 implements PlatformViewsAccessibilityDeleg
   private final ArrayList<SurfaceControl.Transaction> pendingTransactions;
   private final ArrayList<SurfaceControl.Transaction> activeTransactions;
   private Surface overlayerSurface = null;
+  private SurfaceControl overlaySurfaceControl = null;
 
   public PlatformViewsController2() {
     accessibilityEventsDelegate = new AccessibilityEventsDelegate();
@@ -577,6 +578,7 @@ public FlutterOverlaySurface createOverlaySurface() {
       tx.setLayer(surfaceControl, 1000);
       tx.apply();
       overlayerSurface = new Surface(surfaceControl);
+      overlaySurfaceControl = surfaceControl;
     }
 
     return new FlutterOverlaySurface(0, overlayerSurface);
@@ -586,9 +588,32 @@ public void destroyOverlaySurface() {
     if (overlayerSurface != null) {
       overlayerSurface.release();
       overlayerSurface = null;
+      overlaySurfaceControl = null;
     }
   }
 
+  @TargetApi(API_LEVELS.API_34)
+  @RequiresApi(API_LEVELS.API_34)
+  public void showOverlaySurface() {
+    if (overlaySurfaceControl == null) {
+      return;
+    }
+    SurfaceControl.Transaction tx = new SurfaceControl.Transaction();
+    tx.setVisibility(overlaySurfaceControl, /*visible=*/ true);
+    tx.apply();
+  }
+
+  @TargetApi(API_LEVELS.API_34)
+  @RequiresApi(API_LEVELS.API_34)
+  public void hideOverlaySurface() {
+    if (overlaySurfaceControl == null) {
+      return;
+    }
+    SurfaceControl.Transaction tx = new SurfaceControl.Transaction();
+    tx.setVisibility(overlaySurfaceControl, /*visible=*/ false);
+    tx.apply();
+  }
+
   //// Message Handler ///////
 
   private final PlatformViewsChannel2.PlatformViewsHandler channelHandler =