[platform_view]fix regression for addSubview when re-ordering

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm

@@ -750,17 +750,34 @@ static bool ClipRRectContainsPlatformViewBoundingRect(const SkRRect& clip_rrect,
   UIView* flutter_view = flutter_view_.get();
   // Clear the `active_composition_order_`, which will be populated down below.
   active_composition_order_.clear();
+  NSMutableArray* desired_platform_subviews = [NSMutableArray array];
   for (size_t i = 0; i < composition_order_.size(); i++) {
     int64_t platform_view_id = composition_order_[i];
     std::vector<std::shared_ptr<FlutterPlatformViewLayer>> layers = layer_map[platform_view_id];
     UIView* platform_view_root = root_views_[platform_view_id].get();
-    // `addSubview` will automatically reorder subview if it is already added.
-    [flutter_view addSubview:platform_view_root];
+    [desired_platform_subviews addObject:platform_view_root];
     for (const std::shared_ptr<FlutterPlatformViewLayer>& layer : layers) {
-      [flutter_view addSubview:layer->overlay_view_wrapper];
+      [desired_platform_subviews addObject:layer->overlay_view_wrapper];
     }
     active_composition_order_.push_back(platform_view_id);
   }
+
+  NSSet* desired_platform_subviews_set = [NSSet setWithArray:desired_platform_subviews];
+  NSArray* existing_platform_subviews = [flutter_view.subviews
+      filteredArrayUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(id object,
+                                                                        NSDictionary* bindings) {
+        return [desired_platform_subviews_set containsObject:object];
+      }]];
+  // Manipulate view hierarchy only if needed, to address a performance issue where
+  // `BringLayersIntoView` is called even when view hierarchy stays the same.
+  // See: https://github.com/flutter/flutter/issues/121833
+  // TODO(hellohuanlin): investigate if it is possible to skip unnecessary BringLayersIntoView.
+  if (![desired_platform_subviews isEqualToArray:existing_platform_subviews]) {
+    for (UIView* subview in desired_platform_subviews) {
+      // `addSubview` will automatically reorder subview if it is already added.
+      [flutter_view addSubview:subview];
+    }
+  }
 }
 
 std::shared_ptr<FlutterPlatformViewLayer> FlutterPlatformViewsController::GetLayer(

shell/platform/darwin/ios/framework/Source/FlutterPlatformViewsTest.mm

@@ -2342,7 +2342,8 @@ - (void)testFlutterPlatformViewControllerBeginFrameShouldResetCompisitionOrder {
   XCTAssertEqual(flutterPlatformViewsController->EmbeddedViewCount(), 1UL);
 }
 
-- (void)testFlutterPlatformViewControllerSubmitFrameShouldOrderSubviewsCorrectly {
+- (void)
+    testFlutterPlatformViewControllerSubmitFrameShouldOrderSubviewsCorrectlyWithDifferentViewHierarchy {
   flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
   auto thread_task_runner = CreateNewThread("FlutterPlatformViewsTest");
   flutter::TaskRunners runners(/*label=*/self.name.UTF8String,
@@ -2437,6 +2438,102 @@ - (void)testFlutterPlatformViewControllerSubmitFrameShouldOrderSubviewsCorrectly
                 @"The first clipping view should be added after the second clipping view.");
 }
 
+- (void)
+    testFlutterPlatformViewControllerSubmitFrameShouldOrderSubviewsCorrectlyWithSameViewHierarchy {
+  flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
+  auto thread_task_runner = CreateNewThread("FlutterPlatformViewsTest");
+  flutter::TaskRunners runners(/*label=*/self.name.UTF8String,
+                               /*platform=*/thread_task_runner,
+                               /*raster=*/thread_task_runner,
+                               /*ui=*/thread_task_runner,
+                               /*io=*/thread_task_runner);
+  auto flutterPlatformViewsController = std::make_shared<flutter::FlutterPlatformViewsController>();
+  auto platform_view = std::make_unique<flutter::PlatformViewIOS>(
+      /*delegate=*/mock_delegate,
+      /*rendering_api=*/flutter::IOSRenderingAPI::kSoftware,
+      /*platform_views_controller=*/flutterPlatformViewsController,
+      /*task_runners=*/runners);
+
+  UIView* mockFlutterView = [[[UIView alloc] initWithFrame:CGRectMake(0, 0, 500, 500)] autorelease];
+  flutterPlatformViewsController->SetFlutterView(mockFlutterView);
+
+  FlutterPlatformViewsTestMockFlutterPlatformFactory* factory =
+      [[FlutterPlatformViewsTestMockFlutterPlatformFactory new] autorelease];
+  flutterPlatformViewsController->RegisterViewFactory(
+      factory, @"MockFlutterPlatformView",
+      FlutterPlatformViewGestureRecognizersBlockingPolicyEager);
+  FlutterResult result = ^(id result) {
+  };
+  flutterPlatformViewsController->OnMethodCall(
+      [FlutterMethodCall
+          methodCallWithMethodName:@"create"
+                         arguments:@{@"id" : @0, @"viewType" : @"MockFlutterPlatformView"}],
+      result);
+  UIView* view1 = gMockPlatformView;
+
+  // This overwrites `gMockPlatformView` to another view.
+  flutterPlatformViewsController->OnMethodCall(
+      [FlutterMethodCall
+          methodCallWithMethodName:@"create"
+                         arguments:@{@"id" : @1, @"viewType" : @"MockFlutterPlatformView"}],
+      result);
+  UIView* view2 = gMockPlatformView;
+
+  flutterPlatformViewsController->BeginFrame(SkISize::Make(300, 300));
+  flutter::MutatorsStack stack;
+  SkMatrix finalMatrix;
+  auto embeddedViewParams1 =
+      std::make_unique<flutter::EmbeddedViewParams>(finalMatrix, SkSize::Make(300, 300), stack);
+  flutterPlatformViewsController->PrerollCompositeEmbeddedView(0, std::move(embeddedViewParams1));
+  flutterPlatformViewsController->CompositeEmbeddedView(0);
+  auto embeddedViewParams2 =
+      std::make_unique<flutter::EmbeddedViewParams>(finalMatrix, SkSize::Make(500, 500), stack);
+  flutterPlatformViewsController->PrerollCompositeEmbeddedView(1, std::move(embeddedViewParams2));
+  flutterPlatformViewsController->CompositeEmbeddedView(1);
+
+  // SKSurface is required if the root FlutterView is present.
+  const SkImageInfo image_info = SkImageInfo::MakeN32Premul(1000, 1000);
+  sk_sp<SkSurface> mock_sk_surface = SkSurface::MakeRaster(image_info);
+  flutter::SurfaceFrame::FramebufferInfo framebuffer_info;
+  auto mock_surface = std::make_unique<flutter::SurfaceFrame>(
+      std::move(mock_sk_surface), framebuffer_info,
+      [](const flutter::SurfaceFrame& surface_frame, flutter::DlCanvas* canvas) { return true; },
+      /*frame_size=*/SkISize::Make(800, 600));
+
+  XCTAssertTrue(
+      flutterPlatformViewsController->SubmitFrame(nullptr, nullptr, std::move(mock_surface)));
+  // platform view is wrapped by touch interceptor, which itself is wrapped by clipping view.
+  UIView* clippingView1 = view1.superview.superview;
+  UIView* clippingView2 = view2.superview.superview;
+  UIView* flutterView = clippingView1.superview;
+  XCTAssertTrue([flutterView.subviews indexOfObject:clippingView1] <
+                    [flutterView.subviews indexOfObject:clippingView2],
+                @"The first clipping view should be added before the second clipping view.");
+
+  // Need to recreate these params since they are `std::move`ed.
+  flutterPlatformViewsController->BeginFrame(SkISize::Make(300, 300));
+  // Process the second frame in the same order.
+  embeddedViewParams1 =
+      std::make_unique<flutter::EmbeddedViewParams>(finalMatrix, SkSize::Make(300, 300), stack);
+  flutterPlatformViewsController->PrerollCompositeEmbeddedView(0, std::move(embeddedViewParams1));
+  flutterPlatformViewsController->CompositeEmbeddedView(0);
+  embeddedViewParams2 =
+      std::make_unique<flutter::EmbeddedViewParams>(finalMatrix, SkSize::Make(500, 500), stack);
+  flutterPlatformViewsController->PrerollCompositeEmbeddedView(1, std::move(embeddedViewParams2));
+  flutterPlatformViewsController->CompositeEmbeddedView(1);
+
+  mock_sk_surface = SkSurface::MakeRaster(image_info);
+  mock_surface = std::make_unique<flutter::SurfaceFrame>(
+      std::move(mock_sk_surface), framebuffer_info,
+      [](const flutter::SurfaceFrame& surface_frame, flutter::DlCanvas* canvas) { return true; },
+      /*frame_size=*/SkISize::Make(800, 600));
+  XCTAssertTrue(
+      flutterPlatformViewsController->SubmitFrame(nullptr, nullptr, std::move(mock_surface)));
+  XCTAssertTrue([flutterView.subviews indexOfObject:clippingView1] <
+                    [flutterView.subviews indexOfObject:clippingView2],
+                @"The first clipping view should be added before the second clipping view.");
+}
+
 - (void)testThreadMergeAtEndFrame {
   flutter::FlutterPlatformViewsTestMockPlatformViewDelegate mock_delegate;
   auto thread_task_runner_platform = CreateNewThread("FlutterPlatformViewsTest1");