Make updating window metrics multi-view (flutter/engine#43366)

This PR adds multi-view support to various methods that updates the window metrics by adding a `view_id` parameter.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

engine/src/flutter/lib/ui/window/platform_configuration.cc

@@ -308,6 +308,15 @@ void PlatformConfiguration::ReportTimings(std::vector<int64_t> timings) {
                                                }));
 }
 
+Window* PlatformConfiguration::get_window(int window_id) {
+  auto found = windows_.find(window_id);
+  if (found != windows_.end()) {
+    return found->second.get();
+  } else {
+    return nullptr;
+  }
+}
+
 void PlatformConfiguration::CompletePlatformMessageEmptyResponse(
     int response_id) {
   if (!response_id) {

engine/src/flutter/lib/ui/window/platform_configuration.h

@@ -413,9 +413,10 @@ class PlatformConfiguration final {
   ///
   /// @param[in] window_id The id of the window to find and return.
   ///
-  /// @return     a pointer to the Window.
+  /// @return     a pointer to the Window. Returns nullptr if the ID is not
+  ///             found.
   ///
-  Window* get_window(int window_id) { return windows_[window_id].get(); }
+  Window* get_window(int window_id);
 
   //----------------------------------------------------------------------------
   /// @brief      Responds to a previous platform message to the engine from the

engine/src/flutter/lib/ui/window/platform_configuration_unittests.cc

@@ -19,7 +19,9 @@
 namespace flutter {
 namespace testing {
 
-TEST_F(ShellTest, PlatformConfigurationInitialization) {
+class PlatformConfigurationTest : public ShellTest {};
+
+TEST_F(PlatformConfigurationTest, Initialization) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
 
   auto nativeValidateConfiguration = [message_latch](
@@ -63,7 +65,7 @@ TEST_F(ShellTest, PlatformConfigurationInitialization) {
   DestroyShell(std::move(shell), task_runners);
 }
 
-TEST_F(ShellTest, PlatformConfigurationWindowMetricsUpdate) {
+TEST_F(PlatformConfigurationTest, WindowMetricsUpdate) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
 
   auto nativeValidateConfiguration = [message_latch](
@@ -113,7 +115,46 @@ TEST_F(ShellTest, PlatformConfigurationWindowMetricsUpdate) {
   DestroyShell(std::move(shell), task_runners);
 }
 
-TEST_F(ShellTest, PlatformConfigurationOnErrorHandlesError) {
+TEST_F(PlatformConfigurationTest, GetWindowReturnsNullForNonexistentId) {
+  auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
+
+  auto nativeValidateConfiguration =
+      [message_latch](Dart_NativeArguments args) {
+        PlatformConfiguration* configuration =
+            UIDartState::Current()->platform_configuration();
+
+        ASSERT_EQ(configuration->get_window(1), nullptr);
+        ASSERT_EQ(configuration->get_window(2), nullptr);
+
+        message_latch->Signal();
+      };
+
+  Settings settings = CreateSettingsForFixture();
+  TaskRunners task_runners("test",                  // label
+                           GetCurrentTaskRunner(),  // platform
+                           CreateNewThread(),       // raster
+                           CreateNewThread(),       // ui
+                           CreateNewThread()        // io
+  );
+
+  AddNativeCallback("ValidateConfiguration",
+                    CREATE_NATIVE_ENTRY(nativeValidateConfiguration));
+
+  std::unique_ptr<Shell> shell = CreateShell(settings, task_runners);
+
+  ASSERT_TRUE(shell->IsSetup());
+  auto run_configuration = RunConfiguration::InferFromSettings(settings);
+  run_configuration.SetEntrypoint("validateConfiguration");
+
+  shell->RunEngine(std::move(run_configuration), [&](auto result) {
+    ASSERT_EQ(result, Engine::RunStatus::Success);
+  });
+
+  message_latch->Wait();
+  DestroyShell(std::move(shell), task_runners);
+}
+
+TEST_F(PlatformConfigurationTest, OnErrorHandlesError) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
   bool did_throw = false;
 
@@ -159,7 +200,7 @@ TEST_F(ShellTest, PlatformConfigurationOnErrorHandlesError) {
   DestroyShell(std::move(shell), task_runners);
 }
 
-TEST_F(ShellTest, PlatformConfigurationOnErrorDoesNotHandleError) {
+TEST_F(PlatformConfigurationTest, OnErrorDoesNotHandleError) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
   std::string ex;
   std::string st;
@@ -211,7 +252,7 @@ TEST_F(ShellTest, PlatformConfigurationOnErrorDoesNotHandleError) {
   DestroyShell(std::move(shell), task_runners);
 }
 
-TEST_F(ShellTest, PlatformConfigurationOnErrorThrows) {
+TEST_F(PlatformConfigurationTest, OnErrorThrows) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
   std::vector<std::string> errors;
   size_t throw_count = 0;
@@ -266,7 +307,7 @@ TEST_F(ShellTest, PlatformConfigurationOnErrorThrows) {
   DestroyShell(std::move(shell), task_runners);
 }
 
-TEST_F(ShellTest, PlatformConfigurationSetDartPerformanceMode) {
+TEST_F(PlatformConfigurationTest, SetDartPerformanceMode) {
   auto message_latch = std::make_shared<fml::AutoResetWaitableEvent>();
   auto finish = [message_latch](Dart_NativeArguments args) {
     // call needs to happen on the UI thread.

engine/src/flutter/runtime/runtime_controller.cc

@@ -20,7 +20,7 @@
 
 namespace flutter {
 
-const uint64_t kFlutterImplicitViewId = 0llu;
+constexpr uint64_t kFlutterImplicitViewId = 0ll;
 
 RuntimeController::RuntimeController(RuntimeDelegate& p_client,
                                      const TaskRunners& task_runners)
@@ -115,7 +115,10 @@ std::unique_ptr<RuntimeController> RuntimeController::Clone() const {
 }
 
 bool RuntimeController::FlushRuntimeStateToIsolate() {
-  return SetViewportMetrics(platform_data_.viewport_metrics) &&
+  // TODO(dkwingsmt): Needs a view ID here (or platform_data should probably
+  // have multiple view metrics).
+  return SetViewportMetrics(kFlutterImplicitViewId,
+                            platform_data_.viewport_metrics) &&
          SetLocales(platform_data_.locale_data) &&
          SetSemanticsEnabled(platform_data_.semantics_enabled) &&
          SetAccessibilityFeatures(
@@ -125,13 +128,19 @@ bool RuntimeController::FlushRuntimeStateToIsolate() {
          SetDisplays(platform_data_.displays);
 }
 
-bool RuntimeController::SetViewportMetrics(const ViewportMetrics& metrics) {
+bool RuntimeController::SetViewportMetrics(int64_t view_id,
+                                           const ViewportMetrics& metrics) {
   TRACE_EVENT0("flutter", "SetViewportMetrics");
   platform_data_.viewport_metrics = metrics;
 
   if (auto* platform_configuration = GetPlatformConfigurationIfAvailable()) {
-    platform_configuration->get_window(0)->UpdateWindowMetrics(metrics);
+    Window* window = platform_configuration->get_window(view_id);
-    return true;
+    if (window) {
+      window->UpdateWindowMetrics(metrics);
+      return true;
+    } else {
+      FML_LOG(WARNING) << "View ID " << view_id << " does not exist.";
+    }
   }
 
   return false;

engine/src/flutter/runtime/runtime_controller.h

@@ -168,11 +168,12 @@ class RuntimeController : public PlatformConfigurationClient {
   ///             If the isolate is not running, these metrics will be saved and
   ///             flushed to the isolate when it starts.
   ///
+  /// @param[in]  view_id  The ID for the view that `metrics` describes.
   /// @param[in]  metrics  The window's viewport metrics.
   ///
   /// @return     If the window metrics were forwarded to the running isolate.
   ///
-  bool SetViewportMetrics(const ViewportMetrics& metrics);
+  bool SetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics);
 
   //----------------------------------------------------------------------------
   /// @brief      Forward the specified display metrics to the running isolate.

engine/src/flutter/shell/common/engine.cc

@@ -292,8 +292,9 @@ tonic::DartErrorHandleType Engine::GetUIIsolateLastError() {
   return runtime_controller_->GetLastError();
 }
 
-void Engine::SetViewportMetrics(const ViewportMetrics& metrics) {
+void Engine::SetViewportMetrics(int64_t view_id,
-  runtime_controller_->SetViewportMetrics(metrics);
+                                const ViewportMetrics& metrics) {
+  runtime_controller_->SetViewportMetrics(view_id, metrics);
   ScheduleFrame();
 }
 

engine/src/flutter/shell/common/engine.h

@@ -677,16 +677,16 @@ class Engine final : public RuntimeDelegate, PointerDataDispatcher::Delegate {
   std::optional<uint32_t> GetUIIsolateReturnCode();
 
   //----------------------------------------------------------------------------
-  /// @brief      Updates the viewport metrics for the currently running Flutter
+  /// @brief      Updates the viewport metrics for a view. The viewport metrics
-  ///             application. The viewport metrics detail the size of the
+  ///             detail the size of the rendering viewport in texels as well as
-  ///             rendering viewport in texels as well as edge insets if
+  ///             edge insets if present.
-  ///             present.
   ///
   /// @see        `ViewportMetrics`
   ///
-  /// @param[in]  metrics  The metrics
+  /// @param[in]  view_id  The ID for the view that `metrics` describes.
+  /// @param[in]  metrics  The metrics.
   ///
-  void SetViewportMetrics(const ViewportMetrics& metrics);
+  void SetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics);
 
   //----------------------------------------------------------------------------
   /// @brief      Updates the display metrics for the currently running Flutter

engine/src/flutter/shell/common/engine_unittests.cc

@@ -21,6 +21,8 @@
 namespace flutter {
 
 namespace {
+constexpr int64_t kImplicitViewId = 0ll;
+
 class MockDelegate : public Engine::Delegate {
  public:
   MOCK_METHOD2(OnEngineUpdateSemantics,
@@ -330,7 +332,8 @@ TEST_F(EngineTest, SpawnResetsViewportMetrics) {
     const double kViewHeight = 1024;
     old_viewport_metrics.physical_width = kViewWidth;
     old_viewport_metrics.physical_height = kViewHeight;
-    mock_runtime_controller->SetViewportMetrics(old_viewport_metrics);
+    mock_runtime_controller->SetViewportMetrics(kImplicitViewId,
+                                                old_viewport_metrics);
     auto engine = std::make_unique<Engine>(
         /*delegate=*/delegate_,
         /*dispatcher_maker=*/dispatcher_maker_,

engine/src/flutter/shell/common/platform_view.cc

@@ -51,8 +51,9 @@ void PlatformView::SetAccessibilityFeatures(int32_t flags) {
   delegate_.OnPlatformViewSetAccessibilityFeatures(flags);
 }
 
-void PlatformView::SetViewportMetrics(const ViewportMetrics& metrics) {
+void PlatformView::SetViewportMetrics(int64_t view_id,
-  delegate_.OnPlatformViewSetViewportMetrics(metrics);
+                                      const ViewportMetrics& metrics) {
+  delegate_.OnPlatformViewSetViewportMetrics(view_id, metrics);
 }
 
 void PlatformView::NotifyCreated() {

engine/src/flutter/shell/common/platform_view.h

@@ -104,14 +104,15 @@ class PlatformView {
         const fml::closure& closure) = 0;
 
     //--------------------------------------------------------------------------
-    /// @brief      Notifies the delegate the viewport metrics of the platform
+    /// @brief      Notifies the delegate the viewport metrics of a view have
-    ///             view have been updated. The rasterizer will need to be
+    ///             been updated. The rasterizer will need to be reconfigured to
-    ///             reconfigured to render the frame in the updated viewport
+    ///             render the frame in the updated viewport metrics.
-    ///             metrics.
     ///
+    /// @param[in]  view_id  The ID for the view that `metrics` describes.
     /// @param[in]  metrics  The updated viewport metrics.
     ///
     virtual void OnPlatformViewSetViewportMetrics(
+        int64_t view_id,
         const ViewportMetrics& metrics) = 0;
 
     //--------------------------------------------------------------------------
@@ -465,16 +466,17 @@ class PlatformView {
                                CustomAccessibilityActionUpdates actions);
 
   //----------------------------------------------------------------------------
-  /// @brief      Used by embedders to specify the updated viewport metrics. In
+  /// @brief      Used by embedders to specify the updated viewport metrics for
-  ///             response to this call, on the raster thread, the rasterizer
+  ///             a view. In response to this call, on the raster thread, the
-  ///             may need to be reconfigured to the updated viewport
+  ///             rasterizer may need to be reconfigured to the updated viewport
   ///             dimensions. On the UI thread, the framework may need to start
   ///             generating a new frame for the updated viewport metrics as
   ///             well.
   ///
+  /// @param[in]  view_id  The ID for the view that `metrics` describes.
   /// @param[in]  metrics  The updated viewport metrics.
   ///
-  void SetViewportMetrics(const ViewportMetrics& metrics);
+  void SetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics);
 
   //----------------------------------------------------------------------------
   /// @brief      Used by embedders to notify the shell that a platform view

engine/src/flutter/shell/common/shell.cc

@@ -954,7 +954,8 @@ void Shell::OnPlatformViewScheduleFrame() {
 }
 
 // |PlatformView::Delegate|
-void Shell::OnPlatformViewSetViewportMetrics(const ViewportMetrics& metrics) {
+void Shell::OnPlatformViewSetViewportMetrics(int64_t view_id,
+                                             const ViewportMetrics& metrics) {
   FML_DCHECK(is_setup_);
   FML_DCHECK(task_runners_.GetPlatformTaskRunner()->RunsTasksOnCurrentThread());
 
@@ -978,9 +979,9 @@ void Shell::OnPlatformViewSetViewportMetrics(const ViewportMetrics& metrics) {
       });
 
   task_runners_.GetUITaskRunner()->PostTask(
-      [engine = engine_->GetWeakPtr(), metrics]() {
+      [engine = engine_->GetWeakPtr(), view_id, metrics]() {
         if (engine) {
-          engine->SetViewportMetrics(metrics);
+          engine->SetViewportMetrics(view_id, metrics);
         }
       });
 

engine/src/flutter/shell/common/shell.h

@@ -544,6 +544,7 @@ class Shell final : public PlatformView::Delegate,
 
   // |PlatformView::Delegate|
   void OnPlatformViewSetViewportMetrics(
+      int64_t view_id,
       const ViewportMetrics& metrics) override;
 
   // |PlatformView::Delegate|

engine/src/flutter/shell/common/shell_test.cc

@@ -20,6 +20,8 @@
 namespace flutter {
 namespace testing {
 
+constexpr int64_t kImplicitViewId = 0;
+
 ShellTest::ShellTest()
     : thread_host_("io.flutter.test." + GetCurrentTestName() + ".",
                    ThreadHost::Type::Platform | ThreadHost::Type::IO |
@@ -144,7 +146,7 @@ void ShellTest::SetViewportMetrics(Shell* shell, double width, double height) {
   shell->GetTaskRunners().GetUITaskRunner()->PostTask(
       [&latch, engine = shell->weak_engine_, viewport_metrics]() {
         if (engine) {
-          engine->SetViewportMetrics(viewport_metrics);
+          engine->SetViewportMetrics(kImplicitViewId, viewport_metrics);
           const auto frame_begin_time = fml::TimePoint::Now();
           const auto frame_end_time =
               frame_begin_time + fml::TimeDelta::FromSecondsF(1.0 / 60.0);
@@ -186,7 +188,7 @@ void ShellTest::PumpOneFrame(Shell* shell,
   fml::AutoResetWaitableEvent latch;
   shell->GetTaskRunners().GetUITaskRunner()->PostTask(
       [&latch, engine = shell->weak_engine_, viewport_metrics]() {
-        engine->SetViewportMetrics(viewport_metrics);
+        engine->SetViewportMetrics(kImplicitViewId, viewport_metrics);
         const auto frame_begin_time = fml::TimePoint::Now();
         const auto frame_end_time =
             frame_begin_time + fml::TimeDelta::FromSecondsF(1.0 / 60.0);

engine/src/flutter/shell/common/shell_unittests.cc

@@ -60,6 +60,8 @@
 namespace flutter {
 namespace testing {
 
+constexpr int64_t kImplicitViewId = 0ll;
+
 using ::testing::_;
 using ::testing::Return;
 
@@ -74,8 +76,8 @@ class MockPlatformViewDelegate : public PlatformView::Delegate {
   MOCK_METHOD1(OnPlatformViewSetNextFrameCallback,
                void(const fml::closure& closure));
 
-  MOCK_METHOD1(OnPlatformViewSetViewportMetrics,
+  MOCK_METHOD2(OnPlatformViewSetViewportMetrics,
-               void(const ViewportMetrics& metrics));
+               void(int64_t view_id, const ViewportMetrics& metrics));
 
   MOCK_METHOD1(OnPlatformViewDispatchPlatformMessage,
                void(std::unique_ptr<PlatformMessage> message));
@@ -1637,7 +1639,8 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
 
   RunEngine(shell.get(), std::move(configuration));
   PostSync(shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-    shell->GetPlatformView()->SetViewportMetrics({1.0, 100, 100, 22, 0});
+    shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
+                                                 {1.0, 100, 100, 22, 0});
   });
 
   // first cache bytes
@@ -1666,7 +1669,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(second_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&second_shell]() {
              second_shell->GetPlatformView()->SetViewportMetrics(
-                 {1.0, 100, 100, 22, 0});
+                 kImplicitViewId, {1.0, 100, 100, 22, 0});
            });
   // first cache bytes + second cache bytes
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1675,7 +1678,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(second_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&second_shell]() {
              second_shell->GetPlatformView()->SetViewportMetrics(
-                 {1.0, 100, 300, 22, 0});
+                 kImplicitViewId, {1.0, 100, 300, 22, 0});
            });
   // first cache bytes + second cache bytes
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1686,7 +1689,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(third_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&third_shell]() {
              third_shell->GetPlatformView()->SetViewportMetrics(
-                 {1.0, 400, 100, 22, 0});
+                 kImplicitViewId, {1.0, 400, 100, 22, 0});
            });
   // first cache bytes + second cache bytes + third cache bytes
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1695,7 +1698,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(third_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&third_shell]() {
              third_shell->GetPlatformView()->SetViewportMetrics(
-                 {1.0, 800, 100, 22, 0});
+                 kImplicitViewId, {1.0, 800, 100, 22, 0});
            });
   // max bytes threshold
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1708,7 +1711,7 @@ TEST_F(ShellTest, MultipleFluttersSetResourceCacheBytes) {
   PostSync(second_shell->GetTaskRunners().GetPlatformTaskRunner(),
            [&second_shell]() {
              second_shell->GetPlatformView()->SetViewportMetrics(
-                 {1.0, 100, 100, 22, 0});
+                 kImplicitViewId, {1.0, 100, 100, 22, 0});
            });
   // first cache bytes + second cache bytes
   EXPECT_EQ(GetRasterizerResourceCacheBytesSync(*shell),
@@ -1752,7 +1755,8 @@ TEST_F(ShellTest, SetResourceCacheSize) {
 
   fml::TaskRunner::RunNowOrPostTask(
       shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-        shell->GetPlatformView()->SetViewportMetrics({1.0, 400, 200, 22, 0});
+        shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
+                                                     {1.0, 400, 200, 22, 0});
       });
   PumpOneFrame(shell.get());
 
@@ -1772,7 +1776,8 @@ TEST_F(ShellTest, SetResourceCacheSize) {
 
   fml::TaskRunner::RunNowOrPostTask(
       shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-        shell->GetPlatformView()->SetViewportMetrics({1.0, 800, 400, 22, 0});
+        shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
+                                                     {1.0, 800, 400, 22, 0});
       });
   PumpOneFrame(shell.get());
 
@@ -1789,7 +1794,8 @@ TEST_F(ShellTest, SetResourceCacheSizeEarly) {
 
   fml::TaskRunner::RunNowOrPostTask(
       shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-        shell->GetPlatformView()->SetViewportMetrics({1.0, 400, 200, 22, 0});
+        shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
+                                                     {1.0, 400, 200, 22, 0});
       });
   PumpOneFrame(shell.get());
 
@@ -1816,7 +1822,8 @@ TEST_F(ShellTest, SetResourceCacheSizeNotifiesDart) {
 
   fml::TaskRunner::RunNowOrPostTask(
       shell->GetTaskRunners().GetPlatformTaskRunner(), [&shell]() {
-        shell->GetPlatformView()->SetViewportMetrics({1.0, 400, 200, 22, 0});
+        shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
+                                                     {1.0, 400, 200, 22, 0});
       });
   PumpOneFrame(shell.get());
 
@@ -2683,6 +2690,7 @@ TEST_F(ShellTest, DISABLED_DiscardLayerTreeOnResize) {
       shell->GetTaskRunners().GetPlatformTaskRunner(),
       [&shell, &expected_size]() {
         shell->GetPlatformView()->SetViewportMetrics(
+            kImplicitViewId,
             {1.0, static_cast<double>(expected_size.width()),
              static_cast<double>(expected_size.height()), 22, 0});
       });
@@ -2760,6 +2768,7 @@ TEST_F(ShellTest, DISABLED_DiscardResubmittedLayerTreeOnResize) {
       shell->GetTaskRunners().GetPlatformTaskRunner(),
       [&shell, &origin_size]() {
         shell->GetPlatformView()->SetViewportMetrics(
+            kImplicitViewId,
             {1.0, static_cast<double>(origin_size.width()),
              static_cast<double>(origin_size.height()), 22, 0});
       });
@@ -2779,8 +2788,8 @@ TEST_F(ShellTest, DISABLED_DiscardResubmittedLayerTreeOnResize) {
       shell->GetTaskRunners().GetPlatformTaskRunner(),
       [&shell, &new_size, &resize_latch]() {
         shell->GetPlatformView()->SetViewportMetrics(
-            {1.0, static_cast<double>(new_size.width()),
+            kImplicitViewId, {1.0, static_cast<double>(new_size.width()),
-             static_cast<double>(new_size.height()), 22, 0});
+                              static_cast<double>(new_size.height()), 22, 0});
         resize_latch.Signal();
       });
 
@@ -2843,14 +2852,21 @@ TEST_F(ShellTest, IgnoresInvalidMetrics) {
   RunEngine(shell.get(), std::move(configuration));
 
   task_runner->PostTask([&]() {
-    shell->GetPlatformView()->SetViewportMetrics({0.0, 400, 200, 22, 0});
+    // This one is invalid for having 0 pixel ratio.
+    shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
+                                                 {0.0, 400, 200, 22, 0});
     task_runner->PostTask([&]() {
-      shell->GetPlatformView()->SetViewportMetrics({0.8, 0.0, 200, 22, 0});
+      // This one is invalid for having 0 width.
+      shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
+                                                   {0.8, 0.0, 200, 22, 0});
       task_runner->PostTask([&]() {
-        shell->GetPlatformView()->SetViewportMetrics({0.8, 400, 0.0, 22, 0});
+        // This one is invalid for having 0 height.
+        shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
+                                                     {0.8, 400, 0.0, 22, 0});
         task_runner->PostTask([&]() {
+          // This one makes it through.
           shell->GetPlatformView()->SetViewportMetrics(
-              {0.8, 400, 200.0, 22, 0});
+              kImplicitViewId, {0.8, 400, 200.0, 22, 0});
         });
       });
     });
@@ -2862,7 +2878,8 @@ TEST_F(ShellTest, IgnoresInvalidMetrics) {
   latch.Reset();
 
   task_runner->PostTask([&]() {
-    shell->GetPlatformView()->SetViewportMetrics({1.2, 600, 300, 22, 0});
+    shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
+                                                 {1.2, 600, 300, 22, 0});
   });
   latch.Wait();
   ASSERT_EQ(last_device_pixel_ratio, 1.2);
@@ -2872,6 +2889,52 @@ TEST_F(ShellTest, IgnoresInvalidMetrics) {
   DestroyShell(std::move(shell), task_runners);
 }
 
+TEST_F(ShellTest, IgnoresMetricsUpdateToInvalidView) {
+  fml::AutoResetWaitableEvent latch;
+  double last_device_pixel_ratio;
+  // This callback will be called whenever any view's metrics change.
+  auto native_report_device_pixel_ratio = [&](Dart_NativeArguments args) {
+    // The correct call will have a DPR of 3.
+    auto dpr_handle = Dart_GetNativeArgument(args, 0);
+    ASSERT_TRUE(Dart_IsDouble(dpr_handle));
+    Dart_DoubleValue(dpr_handle, &last_device_pixel_ratio);
+    ASSERT_TRUE(last_device_pixel_ratio > 2.5);
+
+    latch.Signal();
+  };
+
+  Settings settings = CreateSettingsForFixture();
+  auto task_runner = CreateNewThread();
+  TaskRunners task_runners("test", task_runner, task_runner, task_runner,
+                           task_runner);
+
+  AddNativeCallback("ReportMetrics",
+                    CREATE_NATIVE_ENTRY(native_report_device_pixel_ratio));
+
+  std::unique_ptr<Shell> shell = CreateShell(settings, task_runners);
+
+  auto configuration = RunConfiguration::InferFromSettings(settings);
+  configuration.SetEntrypoint("reportMetrics");
+
+  RunEngine(shell.get(), std::move(configuration));
+
+  task_runner->PostTask([&]() {
+    // This one is invalid for having an nonexistent view ID.
+    // Also, it has a DPR of 2.0 for detection.
+    shell->GetPlatformView()->SetViewportMetrics(2, {2.0, 400, 200, 22, 0});
+    task_runner->PostTask([&]() {
+      // This one is valid with DPR 3.0.
+      shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId,
+                                                   {3.0, 400, 200, 22, 0});
+    });
+  });
+  latch.Wait();
+  ASSERT_EQ(last_device_pixel_ratio, 3.0);
+  latch.Reset();
+
+  DestroyShell(std::move(shell), task_runners);
+}
+
 TEST_F(ShellTest, OnServiceProtocolSetAssetBundlePathWorks) {
   Settings settings = CreateSettingsForFixture();
   std::unique_ptr<Shell> shell = CreateShell(settings);

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

@@ -37,6 +37,8 @@
 
 namespace flutter {
 
+static constexpr int64_t kFlutterImplicitViewId = 0ll;
+
 static fml::jni::ScopedJavaGlobalRef<jclass>* g_flutter_callback_info_class =
     nullptr;
 
@@ -338,7 +340,8 @@ static void SetViewportMetrics(JNIEnv* env,
       0,  // Display ID
   };
 
-  ANDROID_SHELL_HOLDER->GetPlatformView()->SetViewportMetrics(metrics);
+  ANDROID_SHELL_HOLDER->GetPlatformView()->SetViewportMetrics(
+      kFlutterImplicitViewId, metrics);
 }
 
 static void UpdateDisplayMetrics(JNIEnv* env,

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterEngine.mm

@@ -38,6 +38,8 @@
 #import "flutter/shell/platform/darwin/ios/rendering_api_selection.h"
 #include "flutter/shell/profiling/sampling_profiler.h"
 
+static constexpr int64_t kFlutterImplicitViewId = 0ll;
+
 /// Inheriting ThreadConfigurer and use iOS platform thread API to configure the thread priorities
 /// Using iOS platform thread API to configure thread priority
 static void IOSPlatformThreadConfigSetter(const fml::Thread::ThreadConfig& config) {
@@ -308,7 +310,7 @@ static constexpr int kNumProfilerSamplesPerSec = 5;
   if (!self.platformView) {
     return;
   }
-  self.platformView->SetViewportMetrics(viewportMetrics);
+  self.platformView->SetViewportMetrics(kFlutterImplicitViewId, viewportMetrics);
 }
 
 - (void)dispatchPointerDataPacket:(std::unique_ptr<flutter::PointerDataPacket>)packet {

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterEnginePlatformViewTest.mm

@@ -24,7 +24,7 @@ class FakeDelegate : public PlatformView::Delegate {
   void OnPlatformViewDestroyed() override {}
   void OnPlatformViewScheduleFrame() override {}
   void OnPlatformViewSetNextFrameCallback(const fml::closure& closure) override {}
-  void OnPlatformViewSetViewportMetrics(const ViewportMetrics& metrics) override {}
+  void OnPlatformViewSetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics) override {}
   const flutter::Settings& OnPlatformViewGetSettings() const override { return settings_; }
   void OnPlatformViewDispatchPlatformMessage(std::unique_ptr<PlatformMessage> message) override {}
   void OnPlatformViewDispatchPointerDataPacket(std::unique_ptr<PointerDataPacket> packet) override {

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterPlatformViewsTest.mm

@@ -93,7 +93,7 @@ class FlutterPlatformViewsTestMockPlatformViewDelegate : public PlatformView::De
   void OnPlatformViewDestroyed() override {}
   void OnPlatformViewScheduleFrame() override {}
   void OnPlatformViewSetNextFrameCallback(const fml::closure& closure) override {}
-  void OnPlatformViewSetViewportMetrics(const ViewportMetrics& metrics) override {}
+  void OnPlatformViewSetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics) override {}
   const flutter::Settings& OnPlatformViewGetSettings() const override { return settings_; }
   void OnPlatformViewDispatchPlatformMessage(std::unique_ptr<PlatformMessage> message) override {}
   void OnPlatformViewDispatchPointerDataPacket(std::unique_ptr<PointerDataPacket> packet) override {

engine/src/flutter/shell/platform/darwin/ios/framework/Source/accessibility_bridge_test.mm

@@ -77,7 +77,7 @@ class MockDelegate : public PlatformView::Delegate {
   void OnPlatformViewDestroyed() override {}
   void OnPlatformViewScheduleFrame() override {}
   void OnPlatformViewSetNextFrameCallback(const fml::closure& closure) override {}
-  void OnPlatformViewSetViewportMetrics(const ViewportMetrics& metrics) override {}
+  void OnPlatformViewSetViewportMetrics(int64_t view_id, const ViewportMetrics& metrics) override {}
   const flutter::Settings& OnPlatformViewGetSettings() const override { return settings_; }
   void OnPlatformViewDispatchPlatformMessage(std::unique_ptr<PlatformMessage> message) override {}
   void OnPlatformViewDispatchPointerDataPacket(std::unique_ptr<PointerDataPacket> packet) override {

engine/src/flutter/shell/platform/embedder/embedder.cc

@@ -83,6 +83,8 @@ extern const intptr_t kPlatformStrongDillSize;
 const int32_t kFlutterSemanticsNodeIdBatchEnd = -1;
 const int32_t kFlutterSemanticsCustomActionIdBatchEnd = -1;
 
+static constexpr int64_t kFlutterImplicitViewId = 0;
+
 // A message channel to send platform-independent FlutterKeyData to the
 // framework.
 //
@@ -2186,6 +2188,8 @@ FlutterEngineResult FlutterEngineSendWindowMetricsEvent(
   if (engine == nullptr || flutter_metrics == nullptr) {
     return LOG_EMBEDDER_ERROR(kInvalidArguments, "Engine handle was invalid.");
   }
+  // TODO(dkwingsmt): Use a real view ID when multiview is supported.
+  int64_t view_id = kFlutterImplicitViewId;
 
   flutter::ViewportMetrics metrics;
 
@@ -2227,7 +2231,7 @@ FlutterEngineResult FlutterEngineSendWindowMetricsEvent(
   }
 
   return reinterpret_cast<flutter::EmbedderEngine*>(engine)->SetViewportMetrics(
-             metrics)
+             view_id, metrics)
              ? kSuccess
              : LOG_EMBEDDER_ERROR(kInvalidArguments,
                                   "Viewport metrics were invalid.");

engine/src/flutter/shell/platform/embedder/embedder_engine.cc

@@ -100,6 +100,7 @@ bool EmbedderEngine::NotifyDestroyed() {
 }
 
 bool EmbedderEngine::SetViewportMetrics(
+    int64_t view_id,
     const flutter::ViewportMetrics& metrics) {
   if (!IsValid()) {
     return false;
@@ -109,7 +110,7 @@ bool EmbedderEngine::SetViewportMetrics(
   if (!platform_view) {
     return false;
   }
-  platform_view->SetViewportMetrics(metrics);
+  platform_view->SetViewportMetrics(view_id, metrics);
   return true;
 }
 

engine/src/flutter/shell/platform/embedder/embedder_engine.h

@@ -48,7 +48,8 @@ class EmbedderEngine {
 
   bool IsValid() const;
 
-  bool SetViewportMetrics(const flutter::ViewportMetrics& metrics);
+  bool SetViewportMetrics(int64_t view_id,
+                          const flutter::ViewportMetrics& metrics);
 
   bool DispatchPointerDataPacket(
       std::unique_ptr<flutter::PointerDataPacket> packet);

engine/src/flutter/shell/platform/embedder/platform_view_embedder_unittests.cc

@@ -21,8 +21,8 @@ class MockDelegate : public PlatformView::Delegate {
   MOCK_METHOD0(OnPlatformViewScheduleFrame, void());
   MOCK_METHOD1(OnPlatformViewSetNextFrameCallback,
                void(const fml::closure& closure));
-  MOCK_METHOD1(OnPlatformViewSetViewportMetrics,
+  MOCK_METHOD2(OnPlatformViewSetViewportMetrics,
-               void(const ViewportMetrics& metrics));
+               void(int64_t view_id, const ViewportMetrics& metrics));
   MOCK_METHOD1(OnPlatformViewDispatchPlatformMessage,
                void(std::unique_ptr<PlatformMessage> message));
   MOCK_METHOD1(OnPlatformViewDispatchPointerDataPacket,

engine/src/flutter/shell/platform/fuchsia/flutter/flatland_platform_view.cc

@@ -8,6 +8,8 @@
 
 namespace flutter_runner {
 
+static constexpr int64_t kFlutterImplicitViewId = 0ll;
+
 FlatlandPlatformView::FlatlandPlatformView(
     flutter::PlatformView::Delegate& delegate,
     flutter::TaskRunners task_runners,
@@ -84,8 +86,7 @@ void FlatlandPlatformView::OnGetLayout(
   }
 
   float pixel_ratio = view_pixel_ratio_ ? *view_pixel_ratio_ : 1.0f;
-
+  flutter::ViewportMetrics metrics{
-  SetViewportMetrics({
       pixel_ratio,  // device_pixel_ratio
       std::round(view_logical_size_.value()[0] *
                  pixel_ratio),  // physical_width
@@ -108,7 +109,8 @@ void FlatlandPlatformView::OnGetLayout(
       {},                       // p_physical_display_features_type
       {},                       // p_physical_display_features_state
       0,                        // p_display_id
-  });
+  };
+  SetViewportMetrics(kFlutterImplicitViewId, metrics);
 
   parent_viewport_watcher_->GetLayout(
       fit::bind_member(this, &FlatlandPlatformView::OnGetLayout));

engine/src/flutter/shell/platform/fuchsia/flutter/gfx_platform_view.cc

@@ -8,6 +8,8 @@
 
 namespace flutter_runner {
 
+static constexpr int64_t kFlutterImplicitViewId = 0ll;
+
 GfxPlatformView::GfxPlatformView(
     flutter::PlatformView::Delegate& delegate,
     flutter::TaskRunners task_runners,
@@ -213,7 +215,7 @@ void GfxPlatformView::OnScenicEvent(
       metrics_changed) {
     const float pixel_ratio = *view_pixel_ratio_;
     const std::array<float, 2> logical_size = *view_logical_size_;
-    SetViewportMetrics({
+    flutter::ViewportMetrics metrics{
         pixel_ratio,                                // device_pixel_ratio
         std::round(logical_size[0] * pixel_ratio),  // physical_width
         std::round(logical_size[1] * pixel_ratio),  // physical_height
@@ -234,7 +236,8 @@ void GfxPlatformView::OnScenicEvent(
         {},    // p_physical_display_features_type
         {},    // p_physical_display_features_state
         0,     // pdisplay_id
-    });
+    };
+    SetViewportMetrics(kFlutterImplicitViewId, metrics);
   }
 }
 

engine/src/flutter/shell/platform/fuchsia/flutter/platform_view_unittest.cc

@@ -90,6 +90,7 @@ class MockPlatformViewDelegate : public flutter::PlatformView::Delegate {
   void OnPlatformViewSetNextFrameCallback(const fml::closure& closure) {}
   // |flutter::PlatformView::Delegate|
   void OnPlatformViewSetViewportMetrics(
+      int64_t view_id,
       const flutter::ViewportMetrics& metrics) {
     metrics_ = metrics;
   }

engine/src/flutter/shell/platform/fuchsia/flutter/tests/flatland_platform_view_unittest.cc

@@ -89,6 +89,7 @@ class MockPlatformViewDelegate : public flutter::PlatformView::Delegate {
   void OnPlatformViewSetNextFrameCallback(const fml::closure& closure) {}
   // |flutter::PlatformView::Delegate|
   void OnPlatformViewSetViewportMetrics(
+      int64_t view_id,
       const flutter::ViewportMetrics& metrics) {
     metrics_ = metrics;
   }

engine/src/flutter/shell/testing/tester_main.cc

@@ -39,6 +39,8 @@
 
 namespace flutter {
 
+static constexpr int64_t kImplicitViewId = 0ll;
+
 class TesterExternalViewEmbedder : public ExternalViewEmbedder {
   // |ExternalViewEmbedder|
   DlCanvas* GetRootCanvas() override { return nullptr; }
@@ -353,7 +355,7 @@ int RunTester(const flutter::Settings& settings,
   metrics.physical_width = physical_width;
   metrics.physical_height = physical_height;
   metrics.display_id = 0;
-  shell->GetPlatformView()->SetViewportMetrics(metrics);
+  shell->GetPlatformView()->SetViewportMetrics(kImplicitViewId, metrics);
 
   // Run the message loop and wait for the script to do its thing.
   fml::MessageLoop::GetCurrent().Run();