From 0bff9574d462ca376365bf73515a0ebeaf4e66dc Mon Sep 17 00:00:00 2001
From: Loic Sharma <sharma.loic@gmail.com>
Date: Tue, 5 Mar 2024 15:06:28 -0800
Subject: [PATCH 1/2] [Embedder API] Add multi-view present callback

---
 shell/platform/embedder/embedder.cc           | 43 +++++++--
 shell/platform/embedder/embedder.h            | 46 ++++++++-
 .../embedder_external_view_embedder.cc        |  5 +-
 .../embedder_external_view_embedder.h         |  3 +-
 shell/platform/embedder/embedder_layers.cc    |  3 +-
 shell/platform/embedder/embedder_layers.h     |  6 +-
 shell/platform/embedder/fixtures/main.dart    | 20 ++++
 .../embedder/tests/embedder_config_builder.cc | 33 ++++---
 .../embedder/tests/embedder_config_builder.h  |  3 +-
 .../embedder/tests/embedder_gl_unittests.cc   | 96 ++++++++++++++-----
 .../tests/embedder_metal_unittests.mm         |  4 +-
 .../tests/embedder_test_compositor.cc         |  5 +-
 .../embedder/tests/embedder_test_compositor.h |  9 +-
 .../embedder/tests/embedder_unittests.cc      | 81 +++++++++++++++-
 14 files changed, 292 insertions(+), 65 deletions(-)

diff --git a/shell/platform/embedder/embedder.cc b/shell/platform/embedder/embedder.cc
index 4633fcad552d2..4603b20104cd3 100644
--- a/shell/platform/embedder/embedder.cc
+++ b/shell/platform/embedder/embedder.cc
@@ -1290,14 +1290,23 @@ InferExternalViewEmbedderFromArgs(const FlutterCompositor* compositor,
       SAFE_ACCESS(compositor, collect_backing_store_callback, nullptr);
   auto c_present_callback =
       SAFE_ACCESS(compositor, present_layers_callback, nullptr);
+  auto c_present_view_callback =
+      SAFE_ACCESS(compositor, present_view_callback, nullptr);
   bool avoid_backing_store_cache =
       SAFE_ACCESS(compositor, avoid_backing_store_cache, false);
 
   // Make sure the required callbacks are present
-  if (!c_create_callback || !c_collect_callback || !c_present_callback) {
+  if (!c_create_callback || !c_collect_callback) {
     FML_LOG(ERROR) << "Required compositor callbacks absent.";
     return {nullptr, true};
   }
+  // Either the present view or the present layers callback must be provided.
+  if ((!c_present_view_callback && !c_present_callback) ||
+      (c_present_view_callback && c_present_callback)) {
+    FML_LOG(ERROR) << "Either present_layers_callback or present_view_callback "
+                      "must be provided but not both.";
+    return {nullptr, true};
+  }
 
   FlutterCompositor captured_compositor = *compositor;
 
@@ -1312,15 +1321,33 @@ InferExternalViewEmbedderFromArgs(const FlutterCompositor* compositor,
                                               enable_impeller);
           };
 
-  flutter::EmbedderExternalViewEmbedder::PresentCallback present_callback =
-      [c_present_callback,
-       user_data = compositor->user_data](const auto& layers) {
-        TRACE_EVENT0("flutter", "FlutterCompositorPresentLayers");
-        return c_present_callback(
-            const_cast<const FlutterLayer**>(layers.data()), layers.size(),
-            user_data);
+  flutter::EmbedderExternalViewEmbedder::PresentCallback present_callback;
+  if (c_present_callback) {
+    present_callback = [c_present_callback, user_data = compositor->user_data](
+                           FlutterViewId view_id, const auto& layers) {
+      TRACE_EVENT0("flutter", "FlutterCompositorPresentLayers");
+      return c_present_callback(const_cast<const FlutterLayer**>(layers.data()),
+                                layers.size(), user_data);
+    };
+  } else {
+    FML_DCHECK(c_present_view_callback != nullptr);
+    present_callback = [c_present_view_callback,
+                        user_data = compositor->user_data](
+                           FlutterViewId view_id, const auto& layers) {
+      TRACE_EVENT0("flutter", "FlutterCompositorPresentLayers");
+
+      FlutterPresentViewInfo info = {
+          .struct_size = sizeof(FlutterPresentViewInfo),
+          .view_id = view_id,
+          .layers = const_cast<const FlutterLayer**>(layers.data()),
+          .layers_count = layers.size(),
+          .user_data = user_data,
       };
 
+      return c_present_view_callback(&info);
+    };
+  }
+
   return {std::make_unique<flutter::EmbedderExternalViewEmbedder>(
               avoid_backing_store_cache, create_render_target_callback,
               present_callback),
diff --git a/shell/platform/embedder/embedder.h b/shell/platform/embedder/embedder.h
index d8adf5e77834c..d2f26ac3eb505 100644
--- a/shell/platform/embedder/embedder.h
+++ b/shell/platform/embedder/embedder.h
@@ -1738,6 +1738,24 @@ typedef struct {
   FlutterBackingStorePresentInfo* backing_store_present_info;
 } FlutterLayer;
 
+typedef struct {
+  /// The size of this struct.
+  /// Must be sizeof(FlutterPresentViewInfo).
+  size_t struct_size;
+
+  /// The identifier of the target view.
+  FlutterViewId view_id;
+
+  /// The layers that should be composited onto the view.
+  const FlutterLayer** layers;
+
+  /// The count of layers.
+  size_t layers_count;
+
+  /// The |FlutterCompositor.user_data|.
+  void* user_data;
+} FlutterPresentViewInfo;
+
 typedef bool (*FlutterBackingStoreCreateCallback)(
     const FlutterBackingStoreConfig* config,
     FlutterBackingStore* backing_store_out,
@@ -1751,13 +1769,22 @@ typedef bool (*FlutterLayersPresentCallback)(const FlutterLayer** layers,
                                              size_t layers_count,
                                              void* user_data);
 
+/// The callback invoked when the embedder should present
+/// to a view.
+///
+/// The |FlutterPresentViewInfo| will be deallocated
+/// once the callback returns.
+typedef bool (*FlutterPresentViewCallback)(
+    const FlutterPresentViewInfo* /* present info */);
+
 typedef struct {
   /// This size of this struct. Must be sizeof(FlutterCompositor).
   size_t struct_size;
   /// A baton that in not interpreted by the engine in any way. If it passed
   /// back to the embedder in `FlutterCompositor.create_backing_store_callback`,
-  /// `FlutterCompositor.collect_backing_store_callback` and
-  /// `FlutterCompositor.present_layers_callback`
+  /// `FlutterCompositor.collect_backing_store_callback`,
+  /// `FlutterCompositor.present_layers_callback`, and
+  /// `FlutterCompositor.present_view_callback`.
   void* user_data;
   /// A callback invoked by the engine to obtain a backing store for a specific
   /// `FlutterLayer`.
@@ -1771,10 +1798,23 @@ typedef struct {
   /// embedder may collect any resources associated with the backing store.
   FlutterBackingStoreCollectCallback collect_backing_store_callback;
   /// Callback invoked by the engine to composite the contents of each layer
-  /// onto the screen.
+  /// onto the implicit view.
+  ///
+  /// DEPRECATED: Use |present_view_callback| to support multiple views.
+  ///
+  /// Only one of `present_layers_callback` and `present_view_callback` may be
+  /// provided. Providing both is an error and engine initialization will
+  /// terminate.
   FlutterLayersPresentCallback present_layers_callback;
   /// Avoid caching backing stores provided by this compositor.
   bool avoid_backing_store_cache;
+  /// Callback invoked by the engine to composite the contents of each layer
+  /// onto the specified view.
+  ///
+  /// Only one of `present_layers_callback` and `present_view_callback` may be
+  /// provided. Providing both is an error and engine initialization will
+  /// terminate.
+  FlutterPresentViewCallback present_view_callback;
 } FlutterCompositor;
 
 typedef struct {
diff --git a/shell/platform/embedder/embedder_external_view_embedder.cc b/shell/platform/embedder/embedder_external_view_embedder.cc
index aaf78f6e75c27..87656a37a598a 100644
--- a/shell/platform/embedder/embedder_external_view_embedder.cc
+++ b/shell/platform/embedder/embedder_external_view_embedder.cc
@@ -488,7 +488,10 @@ void EmbedderExternalViewEmbedder::SubmitFlutterView(
 
     builder.PushLayers(presented_layers);
 
-    presented_layers.InvokePresentCallback(present_callback_);
+    // TODO(loic-sharma): Currently only supports a single view.
+    // See https://github.com/flutter/flutter/issues/135530.
+    presented_layers.InvokePresentCallback(kFlutterImplicitViewId,
+                                           present_callback_);
   }
 
   // See why this is necessary in the comment where this collection in
diff --git a/shell/platform/embedder/embedder_external_view_embedder.h b/shell/platform/embedder/embedder_external_view_embedder.h
index ae7cd4fecd318..d850fa85e8443 100644
--- a/shell/platform/embedder/embedder_external_view_embedder.h
+++ b/shell/platform/embedder/embedder_external_view_embedder.h
@@ -35,7 +35,8 @@ class EmbedderExternalViewEmbedder final : public ExternalViewEmbedder {
           const std::shared_ptr<impeller::AiksContext>& aiks_context,
           const FlutterBackingStoreConfig& config)>;
   using PresentCallback =
-      std::function<bool(const std::vector<const FlutterLayer*>& layers)>;
+      std::function<bool(FlutterViewId view_id,
+                         const std::vector<const FlutterLayer*>& layers)>;
   using SurfaceTransformationCallback = std::function<SkMatrix(void)>;
 
   //----------------------------------------------------------------------------
diff --git a/shell/platform/embedder/embedder_layers.cc b/shell/platform/embedder/embedder_layers.cc
index 2b1035908550c..d07b614bf95bf 100644
--- a/shell/platform/embedder/embedder_layers.cc
+++ b/shell/platform/embedder/embedder_layers.cc
@@ -229,13 +229,14 @@ void EmbedderLayers::PushPlatformViewLayer(
 }
 
 void EmbedderLayers::InvokePresentCallback(
+    FlutterViewId view_id,
     const PresentCallback& callback) const {
   std::vector<const FlutterLayer*> presented_layers_pointers;
   presented_layers_pointers.reserve(presented_layers_.size());
   for (const auto& layer : presented_layers_) {
     presented_layers_pointers.push_back(&layer);
   }
-  callback(presented_layers_pointers);
+  callback(view_id, presented_layers_pointers);
 }
 
 }  // namespace flutter
diff --git a/shell/platform/embedder/embedder_layers.h b/shell/platform/embedder/embedder_layers.h
index e821cb09a7e85..98bcffc7886a8 100644
--- a/shell/platform/embedder/embedder_layers.h
+++ b/shell/platform/embedder/embedder_layers.h
@@ -31,8 +31,10 @@ class EmbedderLayers {
                              const EmbeddedViewParams& params);
 
   using PresentCallback =
-      std::function<bool(const std::vector<const FlutterLayer*>& layers)>;
-  void InvokePresentCallback(const PresentCallback& callback) const;
+      std::function<bool(FlutterViewId view_id,
+                         const std::vector<const FlutterLayer*>& layers)>;
+  void InvokePresentCallback(FlutterViewId view_id,
+                             const PresentCallback& callback) const;
 
  private:
   const SkISize frame_size_;
diff --git a/shell/platform/embedder/fixtures/main.dart b/shell/platform/embedder/fixtures/main.dart
index dffa430fbb520..d26bface876d1 100644
--- a/shell/platform/embedder/fixtures/main.dart
+++ b/shell/platform/embedder/fixtures/main.dart
@@ -814,6 +814,26 @@ Future<void> key_data_late_echo() async {
   signalNativeTest();
 }
 
+@pragma('vm:entry-point')
+void render_implicit_view() {
+  PlatformDispatcher.instance.onBeginFrame = (Duration duration) {
+    final Size size = Size(800.0, 600.0);
+    final Color red = Color.fromARGB(127, 255, 0, 0);
+
+    final SceneBuilder builder = SceneBuilder();
+
+    builder.pushOffset(0.0, 0.0);
+
+    builder.addPicture(
+        Offset(0.0, 0.0), CreateColoredBox(red, size));
+
+    builder.pop();
+
+    PlatformDispatcher.instance.implicitView?.render(builder.build());
+  };
+  PlatformDispatcher.instance.scheduleFrame();
+}
+
 @pragma('vm:entry-point')
 void render_gradient() {
   PlatformDispatcher.instance.onBeginFrame = (Duration duration) {
diff --git a/shell/platform/embedder/tests/embedder_config_builder.cc b/shell/platform/embedder/tests/embedder_config_builder.cc
index 03844fffd3971..72e10f0ebbdc0 100644
--- a/shell/platform/embedder/tests/embedder_config_builder.cc
+++ b/shell/platform/embedder/tests/embedder_config_builder.cc
@@ -4,6 +4,7 @@
 
 #include "flutter/shell/platform/embedder/tests/embedder_config_builder.h"
 
+#include "flutter/common/constants.h"
 #include "flutter/runtime/dart_vm.h"
 #include "flutter/shell/platform/embedder/embedder.h"
 #include "tests/embedder_test_context.h"
@@ -354,7 +355,8 @@ void EmbedderConfigBuilder::SetPlatformMessageCallback(
   context_.SetPlatformMessageCallback(callback);
 }
 
-void EmbedderConfigBuilder::SetCompositor(bool avoid_backing_store_cache) {
+void EmbedderConfigBuilder::SetCompositor(bool avoid_backing_store_cache,
+                                          bool use_present_layers_callback) {
   context_.SetupCompositor();
   auto& compositor = context_.GetCompositor();
   compositor_.struct_size = sizeof(compositor_);
@@ -374,16 +376,25 @@ void EmbedderConfigBuilder::SetCompositor(bool avoid_backing_store_cache) {
         return reinterpret_cast<EmbedderTestCompositor*>(user_data)
             ->CollectBackingStore(backing_store);
       };
-  compositor_.present_layers_callback = [](const FlutterLayer** layers,  //
-                                           size_t layers_count,          //
-                                           void* user_data               //
-                                        ) {
-    return reinterpret_cast<EmbedderTestCompositor*>(user_data)->Present(
-        layers,       //
-        layers_count  //
-
-    );
-  };
+  if (use_present_layers_callback) {
+    compositor_.present_view_callback = [](const FlutterPresentViewInfo* info) {
+      auto compositor =
+          reinterpret_cast<EmbedderTestCompositor*>(info->user_data);
+
+      return compositor->Present(info->view_id, info->layers,
+                                 info->layers_count);
+    };
+  } else {
+    compositor_.present_layers_callback = [](const FlutterLayer** layers,
+                                             size_t layers_count,
+                                             void* user_data) {
+      auto compositor = reinterpret_cast<EmbedderTestCompositor*>(user_data);
+
+      // The present layers callback is incompatible with multiple views;
+      // it can only be used to render the implicit view.
+      return compositor->Present(kFlutterImplicitViewId, layers, layers_count);
+    };
+  }
   compositor_.avoid_backing_store_cache = avoid_backing_store_cache;
   project_args_.compositor = &compositor_;
 }
diff --git a/shell/platform/embedder/tests/embedder_config_builder.h b/shell/platform/embedder/tests/embedder_config_builder.h
index a79cedf812b2f..82498ac06b17b 100644
--- a/shell/platform/embedder/tests/embedder_config_builder.h
+++ b/shell/platform/embedder/tests/embedder_config_builder.h
@@ -105,7 +105,8 @@ class EmbedderConfigBuilder {
   void SetPlatformMessageCallback(
       const std::function<void(const FlutterPlatformMessage*)>& callback);
 
-  void SetCompositor(bool avoid_backing_store_cache = false);
+  void SetCompositor(bool avoid_backing_store_cache = false,
+                     bool use_present_layers_callback = false);
 
   FlutterCompositor& GetCompositor();
 
diff --git a/shell/platform/embedder/tests/embedder_gl_unittests.cc b/shell/platform/embedder/tests/embedder_gl_unittests.cc
index f62985df3592d..0720e54a458de 100644
--- a/shell/platform/embedder/tests/embedder_gl_unittests.cc
+++ b/shell/platform/embedder/tests/embedder_gl_unittests.cc
@@ -73,6 +73,27 @@ TEST_F(EmbedderTest,
   builder.GetCompositor().create_backing_store_callback = nullptr;
   builder.GetCompositor().collect_backing_store_callback = nullptr;
   builder.GetCompositor().present_layers_callback = nullptr;
+  builder.GetCompositor().present_view_callback = nullptr;
+  auto engine = builder.LaunchEngine();
+  ASSERT_FALSE(engine.is_valid());
+}
+
+//------------------------------------------------------------------------------
+/// Either present_layers_callback or present_view_callback must be provided,
+/// but not both, otherwise the engine must fail to launch instead of failing to
+/// render a frame at a later point in time.
+///
+TEST_F(EmbedderTest, LaunchFailsWhenMultiplePresentCallbacks) {
+  auto& context = GetEmbedderContext(EmbedderTestContextType::kSoftwareContext);
+  EmbedderConfigBuilder builder(context);
+  builder.SetOpenGLRendererConfig(SkISize::Make(1, 1));
+  builder.SetCompositor();
+  builder.GetCompositor().present_layers_callback =
+      [](const FlutterLayer** layers, size_t layers_count, void* user_data) {
+        return true;
+      };
+  builder.GetCompositor().present_view_callback =
+      [](const FlutterPresentViewInfo* info) { return true; };
   auto engine = builder.LaunchEngine();
   ASSERT_FALSE(engine.is_valid());
 }
@@ -94,7 +115,8 @@ TEST_F(EmbedderTest, CompositorMustBeAbleToRenderToOpenGLFramebuffer) {
 
   fml::CountDownLatch latch(3);
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 3u);
 
         {
@@ -215,7 +237,8 @@ TEST_F(EmbedderTest, RasterCacheDisabledWithPlatformViews) {
   fml::CountDownLatch verify(1);
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 3u);
 
         {
@@ -347,7 +370,8 @@ TEST_F(EmbedderTest, RasterCacheEnabled) {
   fml::CountDownLatch verify(1);
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 1u);
 
         {
@@ -430,7 +454,8 @@ TEST_F(EmbedderTest, CompositorMustBeAbleToRenderToOpenGLTexture) {
 
   fml::CountDownLatch latch(3);
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 3u);
 
         {
@@ -550,7 +575,8 @@ TEST_F(EmbedderTest, CompositorMustBeAbleToRenderToSoftwareBuffer) {
 
   fml::CountDownLatch latch(3);
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 3u);
 
         {
@@ -673,7 +699,8 @@ TEST_F(EmbedderTest, CompositorMustBeAbleToRenderKnownScene) {
   auto scene_image = context.GetNextSceneImage();
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 5u);
 
         // Layer Root
@@ -898,7 +925,8 @@ TEST_F(EmbedderTest, CustomCompositorMustWorkWithCustomTaskRunner) {
 
   fml::CountDownLatch latch(3);
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 3u);
 
         {
@@ -1054,7 +1082,8 @@ TEST_F(EmbedderTest, CompositorMustBeAbleToRenderWithRootLayerOnly) {
   auto scene_image = context.GetNextSceneImage();
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 1u);
 
         // Layer Root
@@ -1135,7 +1164,8 @@ TEST_F(EmbedderTest, CompositorMustBeAbleToRenderWithPlatformLayerOnBottom) {
   auto scene_image = context.GetNextSceneImage();
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 2u);
 
         // Layer Root
@@ -1269,7 +1299,8 @@ TEST_F(EmbedderTest,
   auto scene_image = context.GetNextSceneImage();
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 5u);
 
         // Layer Root
@@ -1659,7 +1690,8 @@ TEST_P(EmbedderTestMultiBackend,
   builder.SetRenderTargetType(GetRenderTargetFromBackend(backend, true));
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 3u);
 
         // Layer Root
@@ -1799,7 +1831,8 @@ TEST_F(EmbedderTest, CanRenderGradientWithCompositorOnNonRootLayerWithXform) {
       EmbedderTestBackingStoreProducer::RenderTargetType::kOpenGLFramebuffer);
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 3u);
 
         // Layer Root
@@ -1954,7 +1987,8 @@ TEST_F(EmbedderTest, VerifyB141980393) {
   fml::AutoResetWaitableEvent latch;
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 1u);
 
         // Layer Root
@@ -2171,7 +2205,8 @@ TEST_P(EmbedderTestMultiBackend,
   auto rendered_scene = context.GetNextSceneImage();
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 3u);
 
         // Layer 0 (Root)
@@ -2293,7 +2328,8 @@ TEST_F(
   fml::CountDownLatch latch(1);
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 3u);
 
         // Layer 0 (Root)
@@ -2491,7 +2527,8 @@ TEST_P(EmbedderTestMultiBackend, PlatformViewMutatorsAreValid) {
 
   fml::CountDownLatch latch(1);
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 2u);
 
         // Layer 0 (Root)
@@ -2600,7 +2637,8 @@ TEST_F(EmbedderTest, PlatformViewMutatorsAreValidWithPixelRatio) {
 
   fml::CountDownLatch latch(1);
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 2u);
 
         // Layer 0 (Root)
@@ -2716,7 +2754,8 @@ TEST_F(EmbedderTest,
 
   fml::CountDownLatch latch(1);
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 2u);
 
         // Layer 0 (Root)
@@ -2921,7 +2960,8 @@ TEST_F(EmbedderTest, ClipsAreCorrectlyCalculated) {
 
   fml::AutoResetWaitableEvent latch;
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 2u);
 
         {
@@ -3000,7 +3040,8 @@ TEST_F(EmbedderTest, ComplexClipsAreCorrectlyCalculated) {
 
   fml::AutoResetWaitableEvent latch;
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 2u);
 
         {
@@ -3279,7 +3320,8 @@ TEST_F(EmbedderTest, CompositorCanPostZeroLayersForPresentation) {
   fml::AutoResetWaitableEvent latch;
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 0u);
         latch.Signal();
       });
@@ -3312,7 +3354,8 @@ TEST_F(EmbedderTest, CompositorCanPostOnlyPlatformViews) {
   fml::AutoResetWaitableEvent latch;
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 2u);
 
         // Layer 0
@@ -3380,7 +3423,8 @@ TEST_F(EmbedderTest, CompositorRenderTargetsAreRecycled) {
                             }));
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 20u);
         latch.CountDown();
       });
@@ -3427,7 +3471,8 @@ TEST_F(EmbedderTest, CompositorRenderTargetsAreInStableOrder) {
   size_t frame_count = 0;
   std::vector<void*> first_frame_backing_store_user_data;
   context.GetCompositor().SetPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 20u);
 
         if (first_frame_backing_store_user_data.empty()) {
@@ -4236,7 +4281,8 @@ TEST_F(EmbedderTest, CompositorRenderTargetsNotRecycledWhenAvoidsCacheSet) {
                             }));
 
   context.GetCompositor().SetPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 20u);
         latch.CountDown();
       },
diff --git a/shell/platform/embedder/tests/embedder_metal_unittests.mm b/shell/platform/embedder/tests/embedder_metal_unittests.mm
index c23a6553a5360..13a9d49f552f0 100644
--- a/shell/platform/embedder/tests/embedder_metal_unittests.mm
+++ b/shell/platform/embedder/tests/embedder_metal_unittests.mm
@@ -138,7 +138,7 @@ GrBackendTexture backend_texture(texture_size.width(), texture_size.height(),
 
   fml::CountDownLatch latch(3);
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers, size_t layers_count) {
         ASSERT_EQ(layers_count, 3u);
 
         {
@@ -326,7 +326,7 @@ GrBackendTexture backend_texture(texture_size.width(), texture_size.height(),
   auto scene_image = context.GetNextSceneImage();
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers, size_t layers_count) {
         ASSERT_EQ(layers_count, 5u);
 
         // Layer Root
diff --git a/shell/platform/embedder/tests/embedder_test_compositor.cc b/shell/platform/embedder/tests/embedder_test_compositor.cc
index 4bbcf2ac83cac..66f6d55af0c7f 100644
--- a/shell/platform/embedder/tests/embedder_test_compositor.cc
+++ b/shell/platform/embedder/tests/embedder_test_compositor.cc
@@ -60,7 +60,8 @@ sk_sp<SkImage> EmbedderTestCompositor::GetLastComposition() {
   return last_composition_;
 }
 
-bool EmbedderTestCompositor::Present(const FlutterLayer** layers,
+bool EmbedderTestCompositor::Present(FlutterViewId view_id,
+                                     const FlutterLayer** layers,
                                      size_t layers_count) {
   if (!UpdateOffscrenComposition(layers, layers_count)) {
     FML_LOG(ERROR)
@@ -75,7 +76,7 @@ bool EmbedderTestCompositor::Present(const FlutterLayer** layers,
     if (present_callback_is_one_shot_) {
       present_callback_ = nullptr;
     }
-    callback(layers, layers_count);
+    callback(view_id, layers, layers_count);
   }
 
   InvokeAllCallbacks(on_present_callbacks_);
diff --git a/shell/platform/embedder/tests/embedder_test_compositor.h b/shell/platform/embedder/tests/embedder_test_compositor.h
index e9ad712034014..705579d76e08b 100644
--- a/shell/platform/embedder/tests/embedder_test_compositor.h
+++ b/shell/platform/embedder/tests/embedder_test_compositor.h
@@ -21,8 +21,9 @@ class EmbedderTestCompositor {
   using PlatformViewRendererCallback =
       std::function<sk_sp<SkImage>(const FlutterLayer& layer,
                                    GrDirectContext* context)>;
-  using PresentCallback =
-      std::function<void(const FlutterLayer** layers, size_t layers_count)>;
+  using PresentCallback = std::function<void(FlutterViewId view_id,
+                                             const FlutterLayer** layers,
+                                             size_t layers_count)>;
 
   EmbedderTestCompositor(SkISize surface_size, sk_sp<GrDirectContext> context);
 
@@ -36,7 +37,9 @@ class EmbedderTestCompositor {
 
   bool CollectBackingStore(const FlutterBackingStore* backing_store);
 
-  bool Present(const FlutterLayer** layers, size_t layers_count);
+  bool Present(FlutterViewId view_id,
+               const FlutterLayer** layers,
+               size_t layers_count);
 
   void SetPlatformViewRendererCallback(
       const PlatformViewRendererCallback& callback);
diff --git a/shell/platform/embedder/tests/embedder_unittests.cc b/shell/platform/embedder/tests/embedder_unittests.cc
index da76770763d34..40c5a91cee0b3 100644
--- a/shell/platform/embedder/tests/embedder_unittests.cc
+++ b/shell/platform/embedder/tests/embedder_unittests.cc
@@ -10,6 +10,7 @@
 
 #include "embedder.h"
 #include "embedder_engine.h"
+#include "flutter/common/constants.h"
 #include "flutter/flow/raster_cache.h"
 #include "flutter/fml/file.h"
 #include "flutter/fml/make_copyable.h"
@@ -640,6 +641,71 @@ TEST_F(EmbedderTest, VMAndIsolateSnapshotSizesAreRedundantInAOTMode) {
   ASSERT_TRUE(engine.is_valid());
 }
 
+TEST_F(EmbedderTest, CanRenderImplicitView) {
+  auto& context = GetEmbedderContext(EmbedderTestContextType::kSoftwareContext);
+
+  EmbedderConfigBuilder builder(context);
+  builder.SetSoftwareRendererConfig(SkISize::Make(800, 600));
+  builder.SetCompositor();
+  builder.SetDartEntrypoint("render_implicit_view");
+  builder.SetRenderTargetType(
+      EmbedderTestBackingStoreProducer::RenderTargetType::kSoftwareBuffer);
+
+  fml::AutoResetWaitableEvent latch;
+
+  context.GetCompositor().SetNextPresentCallback(
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
+        ASSERT_EQ(view_id, kFlutterImplicitViewId);
+        latch.Signal();
+      });
+
+  auto engine = builder.LaunchEngine();
+
+  FlutterWindowMetricsEvent event = {};
+  event.struct_size = sizeof(event);
+  event.width = 300;
+  event.height = 200;
+  event.pixel_ratio = 1.0;
+  ASSERT_EQ(FlutterEngineSendWindowMetricsEvent(engine.get(), &event),
+            kSuccess);
+  ASSERT_TRUE(engine.is_valid());
+  latch.Wait();
+}
+
+TEST_F(EmbedderTest, CanRenderImplicitViewUsingPresentLayersCallback) {
+  auto& context = GetEmbedderContext(EmbedderTestContextType::kSoftwareContext);
+
+  EmbedderConfigBuilder builder(context);
+  builder.SetSoftwareRendererConfig(SkISize::Make(800, 600));
+  builder.SetCompositor(/* avoid_backing_store_cache = */ false,
+                        /* use_present_layers_callback = */ true);
+  builder.SetDartEntrypoint("render_implicit_view");
+  builder.SetRenderTargetType(
+      EmbedderTestBackingStoreProducer::RenderTargetType::kSoftwareBuffer);
+
+  fml::AutoResetWaitableEvent latch;
+
+  context.GetCompositor().SetNextPresentCallback(
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
+        ASSERT_EQ(view_id, kFlutterImplicitViewId);
+        latch.Signal();
+      });
+
+  auto engine = builder.LaunchEngine();
+
+  FlutterWindowMetricsEvent event = {};
+  event.struct_size = sizeof(event);
+  event.width = 300;
+  event.height = 200;
+  event.pixel_ratio = 1.0;
+  ASSERT_EQ(FlutterEngineSendWindowMetricsEvent(engine.get(), &event),
+            kSuccess);
+  ASSERT_TRUE(engine.is_valid());
+  latch.Wait();
+}
+
 //------------------------------------------------------------------------------
 /// Test the layer structure and pixels rendered when using a custom software
 /// compositor.
@@ -668,7 +734,8 @@ TEST_F(EmbedderTest,
   auto scene_image = context.GetNextSceneImage();
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 5u);
 
         // Layer Root
@@ -886,7 +953,8 @@ TEST_F(EmbedderTest, NoLayerCreatedForTransparentOverlayOnTopOfPlatformLayer) {
   auto scene_image = context.GetNextSceneImage();
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 2u);
 
         // Layer Root
@@ -1022,7 +1090,8 @@ TEST_F(EmbedderTest, NoLayerCreatedForNoOverlayOnTopOfPlatformLayer) {
   auto scene_image = context.GetNextSceneImage();
 
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 2u);
 
         // Layer Root
@@ -1303,7 +1372,8 @@ TEST_F(EmbedderTest, VerifyB143464703WithSoftwareBackend) {
 
   fml::CountDownLatch latch(1);
   context.GetCompositor().SetNextPresentCallback(
-      [&](const FlutterLayer** layers, size_t layers_count) {
+      [&](FlutterViewId view_id, const FlutterLayer** layers,
+          size_t layers_count) {
         ASSERT_EQ(layers_count, 2u);
 
         // Layer 0 (Root)
@@ -1935,7 +2005,8 @@ static void expectSoftwareRenderingOutputMatches(
   ASSERT_TRUE(engine.is_valid());
 
   context.GetCompositor().SetNextPresentCallback(
-      [&matches, &bytes, &latch](const FlutterLayer** layers,
+      [&matches, &bytes, &latch](FlutterViewId view_id,
+                                 const FlutterLayer** layers,
                                  size_t layers_count) {
         ASSERT_EQ(layers[0]->type, kFlutterLayerContentTypeBackingStore);
         ASSERT_EQ(layers[0]->backing_store->type,

From e94fa08da9aeda501fb3e869861f8c5a91d11352 Mon Sep 17 00:00:00 2001
From: Loic Sharma <sharma.loic@gmail.com>
Date: Wed, 13 Mar 2024 16:31:52 -0700
Subject: [PATCH 2/2] Format

---
 shell/platform/embedder/embedder.h | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/shell/platform/embedder/embedder.h b/shell/platform/embedder/embedder.h
index d2f26ac3eb505..241d3dc58c5e2 100644
--- a/shell/platform/embedder/embedder.h
+++ b/shell/platform/embedder/embedder.h
@@ -1769,11 +1769,9 @@ typedef bool (*FlutterLayersPresentCallback)(const FlutterLayer** layers,
                                              size_t layers_count,
                                              void* user_data);
 
-/// The callback invoked when the embedder should present
-/// to a view.
+/// The callback invoked when the embedder should present to a view.
 ///
-/// The |FlutterPresentViewInfo| will be deallocated
-/// once the callback returns.
+/// The |FlutterPresentViewInfo| will be deallocated once the callback returns.
 typedef bool (*FlutterPresentViewCallback)(
     const FlutterPresentViewInfo* /* present info */);