[scene_host] Expose Opacity and remove ExportNode (#9297)

SCN-947 #comment
SCN-1291 #comment

ci/licenses_golden/licenses_flutter

@@ -30,8 +30,6 @@ FILE: ../../../flutter/flow/debug_print.cc
 FILE: ../../../flutter/flow/debug_print.h
 FILE: ../../../flutter/flow/embedded_views.cc
 FILE: ../../../flutter/flow/embedded_views.h
-FILE: ../../../flutter/flow/export_node.cc
-FILE: ../../../flutter/flow/export_node.h
 FILE: ../../../flutter/flow/instrumentation.cc
 FILE: ../../../flutter/flow/instrumentation.h
 FILE: ../../../flutter/flow/layers/backdrop_filter_layer.cc

flow/BUILD.gn

@@ -76,8 +76,6 @@ source_set("flow") {
 
   if (is_fuchsia) {
     sources += [
-      "export_node.cc",
-      "export_node.h",
       "layers/child_scene_layer.cc",
       "layers/child_scene_layer.h",
       "scene_update_context.cc",

flow/export_node.cc

-// Copyright 2013 The Flutter Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "flutter/flow/export_node.h"
-
-#include "flutter/fml/thread_local.h"
-
-namespace {
-
-using ExportNodeBindings =
-    std::unordered_map<zx_koid_t, std::unique_ptr<flutter::ExportNode>>;
-
-FML_THREAD_LOCAL fml::ThreadLocalUniquePtr<ExportNodeBindings>
-    tls_export_node_bindings;
-
-}  // namespace
-
-namespace flutter {
-
-ExportNode::ExportNode(zx::eventpair export_token)
-    : pending_export_token_(std::move(export_token)) {
-  FML_DCHECK(pending_export_token_);
-}
-
-void ExportNode::Create(zx_koid_t id, zx::eventpair export_token) {
-  // This GPU thread contains at least 1 ViewHolder.  Initialize the per-thread
-  // bindings.
-  if (tls_export_node_bindings.get() == nullptr) {
-    tls_export_node_bindings.reset(new ExportNodeBindings());
-  }
-
-  auto* bindings = tls_export_node_bindings.get();
-  FML_DCHECK(bindings);
-  FML_DCHECK(bindings->find(id) == bindings->end());
-
-  auto export_node =
-      std::unique_ptr<ExportNode>(new ExportNode(std::move(export_token)));
-  bindings->emplace(id, std::move(export_node));
-}
-
-void ExportNode::Destroy(zx_koid_t id) {
-  auto* bindings = tls_export_node_bindings.get();
-  FML_DCHECK(bindings);
-
-  bindings->erase(id);
-}
-
-ExportNode* ExportNode::FromId(zx_koid_t id) {
-  auto* bindings = tls_export_node_bindings.get();
-  if (!bindings) {
-    return nullptr;
-  }
-
-  auto binding = bindings->find(id);
-  if (binding == bindings->end()) {
-    return nullptr;
-  }
-
-  return binding->second.get();
-}
-
-void ExportNode::UpdateScene(SceneUpdateContext& context,
-                             const SkPoint& offset,
-                             const SkSize& size,
-                             bool hit_testable) {
-  if (pending_export_token_) {
-    export_node_ = std::make_unique<scenic::EntityNode>(context.session());
-    export_node_->Export(std::move(pending_export_token_));
-  }
-  FML_DCHECK(export_node_);
-
-  context.top_entity()->entity_node().AddChild(*export_node_);
-  export_node_->SetTranslation(offset.x(), offset.y(), -0.1f);
-  export_node_->SetHitTestBehavior(
-      hit_testable ? fuchsia::ui::gfx::HitTestBehavior::kDefault
-                   : fuchsia::ui::gfx::HitTestBehavior::kSuppress);
-}
-
-}  // namespace flutter

flow/export_node.h

-// Copyright 2013 The Flutter Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef FLUTTER_FLOW_EXPORT_NODE_H_
-#define FLUTTER_FLOW_EXPORT_NODE_H_
-
-#include <lib/ui/scenic/cpp/resources.h>
-#include <lib/zx/eventpair.h>
-#include <third_party/skia/include/core/SkMatrix.h>
-#include <third_party/skia/include/core/SkPoint.h>
-#include <third_party/skia/include/core/SkSize.h>
-#include <zircon/types.h>
-
-#include <memory>
-
-#include "flutter/flow/scene_update_context.h"
-#include "flutter/fml/macros.h"
-
-namespace flutter {
-
-// Represents a Scenic |ExportNode| resource that exports an |EntityNode| to
-// another session.
-//
-// This object is created and destroyed on the |Rasterizer|'s' thread.
-class ExportNode {
- public:
-  static void Create(zx_koid_t id, zx::eventpair export_token);
-  static void Destroy(zx_koid_t id);
-  static ExportNode* FromId(zx_koid_t id);
-
-  // Creates or updates the contained EntityNode resource using the specified
-  // |SceneUpdateContext|.
-  void UpdateScene(SceneUpdateContext& context,
-                   const SkPoint& offset,
-                   const SkSize& size,
-                   bool hit_testable);
-
- private:
-  ExportNode(zx::eventpair export_token);
-
-  zx::eventpair pending_export_token_;
-  std::unique_ptr<scenic::EntityNode> export_node_;
-
-  FML_DISALLOW_COPY_AND_ASSIGN(ExportNode);
-};
-
-}  // namespace flutter
-
-#endif  // FLUTTER_FLOW_EXPORT_NODE_H_

flow/layers/child_scene_layer.cc

@@ -4,21 +4,18 @@
 
 #include "flutter/flow/layers/child_scene_layer.h"
 
-#include "flutter/flow/export_node.h"
 #include "flutter/flow/view_holder.h"
 
 namespace flutter {
 
 ChildSceneLayer::ChildSceneLayer(zx_koid_t layer_id,
-                                 bool use_view_holder,
                                  const SkPoint& offset,
                                  const SkSize& size,
                                  bool hit_testable)
     : layer_id_(layer_id),
       offset_(offset),
       size_(size),
-      hit_testable_(hit_testable),
-      use_view_holder_(use_view_holder) {}
+      hit_testable_(hit_testable) {}
 
 void ChildSceneLayer::Preroll(PrerollContext* context, const SkMatrix& matrix) {
   set_needs_system_composite(true);
@@ -31,17 +28,10 @@ void ChildSceneLayer::Paint(PaintContext& context) const {
 void ChildSceneLayer::UpdateScene(SceneUpdateContext& context) {
   FML_DCHECK(needs_system_composite());
 
-  if (use_view_holder_) {
-    auto* view_holder = ViewHolder::FromId(layer_id_);
-    FML_DCHECK(view_holder);
+  auto* view_holder = ViewHolder::FromId(layer_id_);
+  FML_DCHECK(view_holder);
 
-    view_holder->UpdateScene(context, offset_, size_, hit_testable_);
-  } else {
-    auto* export_node = ExportNode::FromId(layer_id_);
-    FML_DCHECK(export_node);
-
-    export_node->UpdateScene(context, offset_, size_, hit_testable_);
-  }
+  view_holder->UpdateScene(context, offset_, size_, hit_testable_);
 }
 
 }  // namespace flutter

flow/layers/child_scene_layer.h

@@ -18,7 +18,6 @@ namespace flutter {
 class ChildSceneLayer : public Layer {
  public:
   ChildSceneLayer(zx_koid_t layer_id,
-                  bool use_view_holder,
                   const SkPoint& offset,
                   const SkSize& size,
                   bool hit_testable);
@@ -35,7 +34,6 @@ class ChildSceneLayer : public Layer {
   SkPoint offset_;
   SkSize size_;
   bool hit_testable_ = true;
-  bool use_view_holder_ = true;
 
   FML_DISALLOW_COPY_AND_ASSIGN(ChildSceneLayer);
 };

flow/view_holder.cc

@@ -48,16 +48,6 @@ fuchsia::ui::gfx::ViewProperties ToViewProperties(float width,
 
 namespace flutter {
 
-ViewHolder::ViewHolder(fml::RefPtr<fml::TaskRunner> ui_task_runner,
-                       fuchsia::ui::views::ViewHolderToken view_holder_token,
-                       BindCallback on_bind_callback)
-    : pending_view_holder_token_(std::move(view_holder_token)),
-      ui_task_runner_(std::move(ui_task_runner)),
-      pending_bind_callback_(std::move(on_bind_callback)) {
-  FML_DCHECK(pending_view_holder_token_.value);
-  FML_DCHECK(ui_task_runner_);
-}
-
 void ViewHolder::Create(zx_koid_t id,
                         fml::RefPtr<fml::TaskRunner> ui_task_runner,
                         fuchsia::ui::views::ViewHolderToken view_holder_token,
@@ -72,9 +62,9 @@ void ViewHolder::Create(zx_koid_t id,
   FML_DCHECK(bindings);
   FML_DCHECK(bindings->find(id) == bindings->end());
 
-  auto view_holder = std::unique_ptr<ViewHolder>(
-      new ViewHolder(std::move(ui_task_runner), std::move(view_holder_token),
-                     std::move(on_bind_callback)));
+  auto view_holder = std::make_unique<ViewHolder>(std::move(ui_task_runner),
+                                                  std::move(view_holder_token),
+                                                  std::move(on_bind_callback));
   bindings->emplace(id, std::move(view_holder));
 }
 
@@ -99,16 +89,29 @@ ViewHolder* ViewHolder::FromId(zx_koid_t id) {
   return binding->second.get();
 }
 
+ViewHolder::ViewHolder(fml::RefPtr<fml::TaskRunner> ui_task_runner,
+                       fuchsia::ui::views::ViewHolderToken view_holder_token,
+                       BindCallback on_bind_callback)
+    : ui_task_runner_(std::move(ui_task_runner)),
+      pending_view_holder_token_(std::move(view_holder_token)),
+      pending_bind_callback_(std::move(on_bind_callback)) {
+  FML_DCHECK(ui_task_runner_);
+  FML_DCHECK(pending_view_holder_token_.value);
+}
+
 void ViewHolder::UpdateScene(SceneUpdateContext& context,
                              const SkPoint& offset,
                              const SkSize& size,
                              bool hit_testable) {
   if (pending_view_holder_token_.value) {
+    opacity_node_ =
+        std::make_unique<scenic::OpacityNodeHACK>(context.session());
     entity_node_ = std::make_unique<scenic::EntityNode>(context.session());
     view_holder_ = std::make_unique<scenic::ViewHolder>(
         context.session(), std::move(pending_view_holder_token_),
         "Flutter SceneHost");
 
+    opacity_node_->AddChild(*entity_node_);
     entity_node_->Attach(*view_holder_);
     ui_task_runner_->PostTask(
         [bind_callback = std::move(pending_bind_callback_),
@@ -116,14 +119,19 @@ void ViewHolder::UpdateScene(SceneUpdateContext& context,
           bind_callback(view_holder_id);
         });
   }
-  FML_DCHECK(entity_node_);
+  FML_DCHECK(opacity_node_);
   FML_DCHECK(view_holder_);
 
-  context.top_entity()->entity_node().AddChild(*entity_node_);
+  context.top_entity()->entity_node().AddChild(*opacity_node_);
   entity_node_->SetTranslation(offset.x(), offset.y(), -0.1f);
   entity_node_->SetHitTestBehavior(
       hit_testable ? fuchsia::ui::gfx::HitTestBehavior::kDefault
                    : fuchsia::ui::gfx::HitTestBehavior::kSuppress);
+  if (has_pending_opacity_) {
+    opacity_node_->SetOpacity(pending_opacity_);
+
+    has_pending_opacity_ = false;
+  }
   if (has_pending_properties_) {
     view_holder_->SetViewProperties(std::move(pending_properties_));
 
@@ -143,4 +151,9 @@ void ViewHolder::SetProperties(double width,
   has_pending_properties_ = true;
 }
 
+void ViewHolder::SetOpacity(double opacity) {
+  pending_opacity_ = std::clamp(opacity, 0.0, 1.0);
+  has_pending_opacity_ = true;
+}
+
 }  // namespace flutter

flow/view_holder.h

@@ -38,7 +38,12 @@ class ViewHolder {
   static void Destroy(zx_koid_t id);
   static ViewHolder* FromId(zx_koid_t id);
 
-  // Sets the properties of the child view by issuing a Scenic command.
+  ViewHolder(fml::RefPtr<fml::TaskRunner> ui_task_runner,
+             fuchsia::ui::views::ViewHolderToken view_holder_token,
+             BindCallback on_bind_callback);
+  ~ViewHolder() = default;
+
+  // Sets the properties/opacity of the child view by issuing a Scenic command.
   void SetProperties(double width,
                      double height,
                      double insetTop,
@@ -46,6 +51,7 @@ class ViewHolder {
                      double insetBottom,
                      double insetLeft,
                      bool focusable);
+  void SetOpacity(double opacity);
 
   // Creates or updates the contained ViewHolder resource using the specified
   // |SceneUpdateContext|.
@@ -55,17 +61,19 @@ class ViewHolder {
                    bool hit_testable);
 
  private:
-  ViewHolder(fml::RefPtr<fml::TaskRunner> ui_task_runner,
-             fuchsia::ui::views::ViewHolderToken view_holder_token,
-             BindCallback on_bind_callback);
-
-  fuchsia::ui::gfx::ViewProperties pending_properties_;
-  fuchsia::ui::views::ViewHolderToken pending_view_holder_token_;
   fml::RefPtr<fml::TaskRunner> ui_task_runner_;
+
+  std::unique_ptr<scenic::OpacityNodeHACK> opacity_node_;
   std::unique_ptr<scenic::EntityNode> entity_node_;
   std::unique_ptr<scenic::ViewHolder> view_holder_;
+
+  fuchsia::ui::views::ViewHolderToken pending_view_holder_token_;
   BindCallback pending_bind_callback_;
+
+  fuchsia::ui::gfx::ViewProperties pending_properties_;
+  double pending_opacity_;
   bool has_pending_properties_ = false;
+  bool has_pending_opacity_ = false;
 
   FML_DISALLOW_COPY_AND_ASSIGN(ViewHolder);
 };

lib/stub_ui/lib/src/ui/compositing.dart

@@ -481,26 +481,33 @@ class EngineLayer {}
 
 /// (Fuchsia-only) Hosts content provided by another application.
 class SceneHost {
-  /// Creates a host for a child scene.
+  /// Creates a host for a child scene's content.
   ///
-  /// The export token is bound to a scene graph node which acts as a container
-  /// for the child's content.  The creator of the scene host is responsible for
-  /// sending the corresponding import token (the other endpoint of the event
-  /// pair) to the child.
+  /// The ViewHolder token is bound to a ViewHolder scene graph node which acts
+  /// as a container for the child's content.  The creator of the SceneHost is
+  /// responsible for sending the corresponding ViewToken to the child.
   ///
-  /// The export token is a dart:zircon Handle, but that type isn't
+  /// The ViewHolder token is a dart:zircon Handle, but that type isn't
   /// available here. This is called by ChildViewConnection in
-  /// //topaz/public/lib/ui/flutter/.
+  /// //topaz/public/dart/fuchsia_scenic_flutter/.
   ///
-  /// The scene host takes ownership of the provided export token handle.
-  SceneHost(dynamic exportTokenHandle);
+  /// The SceneHost takes ownership of the provided ViewHolder token.
+  SceneHost(dynamic viewHolderToken,
+    void Function() viewConnectedCallback,
+    void Function() viewDisconnectedCallback,
+    void Function(bool) viewStateChangedCallback);
 
   SceneHost.fromViewHolderToken(
-    dynamic viewHolderTokenHandle,
+    dynamic viewHolderToken,
     void Function() viewConnectedCallback,
     void Function() viewDisconnectedCallback,
     void Function(bool) viewStateChangedCallback);
 
+  /// Releases the resources associated with the SceneHost.
+  ///
+  /// After calling this function, the SceneHost cannot be used further.
+  void dispose() {}
+
   /// Set properties on the linked scene.  These properties include its bounds,
   /// as well as whether it can be the target of focus events or not.
   void setProperties(
@@ -514,8 +521,9 @@ class SceneHost {
       throw UnimplementedError();
     }
 
-  /// Releases the resources associated with the child scene host.
-  ///
-  /// After calling this function, the child scene host cannot be used further.
-  void dispose() {}
+  /// Set the opacity of the linked scene.  This opacity value is applied only
+  /// once, when the child scene is composited into our own.
+  void setOpacity(double opacity) {
+    throw UnimplementedError();
+  }
 }

lib/ui/compositing.dart

@@ -358,42 +358,38 @@ class SceneBuilder extends NativeFieldWrapperClass2 {
 
 /// (Fuchsia-only) Hosts content provided by another application.
 class SceneHost extends NativeFieldWrapperClass2 {
-  /// Creates a host for a child scene.
+  /// Creates a host for a child scene's content.
   ///
-  /// The export token is bound to a scene graph node which acts as a container
-  /// for the child's content.  The creator of the scene host is responsible for
-  /// sending the corresponding import token (the other endpoint of the event pair)
-  /// to the child.
+  /// The ViewHolder token is bound to a ViewHolder scene graph node which acts
+  /// as a container for the child's content.  The creator of the SceneHost is
+  /// responsible for sending the corresponding ViewToken to the child.
   ///
-  /// The export token is a dart:zircon Handle, but that type isn't
+  /// The ViewHolder token is a dart:zircon Handle, but that type isn't
   /// available here. This is called by ChildViewConnection in
   /// //topaz/public/dart/fuchsia_scenic_flutter/.
   ///
-  /// The scene host takes ownership of the provided export token handle.
-  SceneHost(dynamic exportTokenHandle) {
-    _constructor(exportTokenHandle);
+  /// The SceneHost takes ownership of the provided ViewHolder token.
+  SceneHost(
+      dynamic viewHolderToken,
+      void Function() viewConnectedCallback,
+      void Function() viewDisconnectedCallback,
+      void Function(bool) viewStateChangedCallback) {
+    _constructor(viewHolderToken, viewConnectedCallback, viewDisconnectedCallback, viewStateChangedCallback);
   }
   SceneHost.fromViewHolderToken(
-      dynamic viewHolderTokenHandle,
+      dynamic viewHolderToken,
       void Function() viewConnectedCallback,
       void Function() viewDisconnectedCallback,
       void Function(bool) viewStateChangedCallback) {
-    _constructorViewHolderToken(viewHolderTokenHandle, viewConnectedCallback,
-        viewDisconnectedCallback, viewStateChangedCallback);
+    _constructor(viewHolderToken, viewConnectedCallback, viewDisconnectedCallback, viewStateChangedCallback);
   }
 
-  void _constructor(dynamic exportTokenHandle) native 'SceneHost_constructor';
-  void
-      _constructorViewHolderToken(
-          dynamic viewHolderTokenHandle,
-          void Function() viewConnectedCallback,
-          void Function() viewDisconnectedCallback,
-          void Function(bool) viewStateChangedCallback)
-      native 'SceneHost_constructorViewHolderToken';
+  void _constructor(dynamic viewHolderToken, void Function() viewConnectedCallback, void Function() viewDisconnectedCallback, void Function(bool) viewStateChangedCallback)
+      native 'SceneHost_constructor';
 
-  /// Releases the resources associated with the child scene host.
+  /// Releases the resources associated with the SceneHost.
   ///
-  /// After calling this function, the child scene host cannot be used further.
+  /// After calling this function, the SceneHost cannot be used further.
   void dispose() native 'SceneHost_dispose';
 
   /// Set properties on the linked scene.  These properties include its bounds,
@@ -406,4 +402,8 @@ class SceneHost extends NativeFieldWrapperClass2 {
       double insetBottom,
       double insetLeft,
       bool focusable) native 'SceneHost_setProperties';
+
+  /// Set the opacity of the linked scene.  This opacity value is applied only
+  /// once, when the child scene is composited into our own.
+  void setOpacity(double opacity) native 'SceneHost_setOpacity';
 }

lib/ui/compositing/scene_builder.cc

@@ -256,8 +256,8 @@ void SceneBuilder::addChildScene(double dx,
     return;
   }
   auto layer = std::make_unique<flutter::ChildSceneLayer>(
-      sceneHost->id(), sceneHost->use_view_holder(), SkPoint::Make(dx, dy),
-      SkSize::Make(width, height), hitTestable);
+      sceneHost->id(), SkPoint::Make(dx, dy), SkSize::Make(width, height),
+      hitTestable);
   current_layer_->Add(std::move(layer));
 }
 #endif  // defined(OS_FUCHSIA)

lib/ui/compositing/scene_host.cc

@@ -10,7 +10,6 @@
 #include <third_party/tonic/dart_binding_macros.h>
 #include <third_party/tonic/logging/dart_invoke.h>
 
-#include "flutter/flow/export_node.h"
 #include "flutter/flow/view_holder.h"
 #include "flutter/fml/thread_local.h"
 #include "flutter/lib/ui/ui_dart_state.h"
@@ -23,17 +22,13 @@ FML_THREAD_LOCAL fml::ThreadLocalUniquePtr<SceneHostBindings>
     tls_scene_host_bindings;
 
 void SceneHost_constructor(Dart_NativeArguments args) {
-  tonic::DartCallConstructor(&flutter::SceneHost::Create, args);
-}
-
-void SceneHost_constructorViewHolderToken(Dart_NativeArguments args) {
   // This UI thread / Isolate contains at least 1 SceneHost.  Initialize the
   // per-Isolate bindings.
   if (tls_scene_host_bindings.get() == nullptr) {
     tls_scene_host_bindings.reset(new SceneHostBindings());
   }
 
-  tonic::DartCallConstructor(&flutter::SceneHost::CreateViewHolder, args);
+  tonic::DartCallConstructor(&flutter::SceneHost::Create, args);
 }
 
 flutter::SceneHost* GetSceneHost(scenic::ResourceId id) {
@@ -90,56 +85,59 @@ namespace flutter {
 
 IMPLEMENT_WRAPPERTYPEINFO(ui, SceneHost);
 
-#define FOR_EACH_BINDING(V) \
-  V(SceneHost, dispose)     \
-  V(SceneHost, setProperties)
+#define FOR_EACH_BINDING(V)   \
+  V(SceneHost, dispose)       \
+  V(SceneHost, setProperties) \
+  V(SceneHost, setOpacity)
 
 FOR_EACH_BINDING(DART_NATIVE_CALLBACK)
 
 void SceneHost::RegisterNatives(tonic::DartLibraryNatives* natives) {
-  natives->Register({{"SceneHost_constructor", SceneHost_constructor, 2, true},
-                     FOR_EACH_BINDING(DART_REGISTER_NATIVE)});
-  natives->Register({{"SceneHost_constructorViewHolderToken",
-                      SceneHost_constructorViewHolderToken, 5, true},
+  natives->Register({{"SceneHost_constructor", SceneHost_constructor, 5, true},
                      FOR_EACH_BINDING(DART_REGISTER_NATIVE)});
 }
 
 fml::RefPtr<SceneHost> SceneHost::Create(
-    fml::RefPtr<zircon::dart::Handle> exportTokenHandle) {
-  return fml::MakeRefCounted<SceneHost>(exportTokenHandle);
-}
-
-fml::RefPtr<SceneHost> SceneHost::CreateViewHolder(
-    fml::RefPtr<zircon::dart::Handle> viewHolderTokenHandle,
+    fml::RefPtr<zircon::dart::Handle> viewHolderToken,
     Dart_Handle viewConnectedCallback,
     Dart_Handle viewDisconnectedCallback,
     Dart_Handle viewStateChangedCallback) {
-  return fml::MakeRefCounted<SceneHost>(
-      viewHolderTokenHandle, viewConnectedCallback, viewDisconnectedCallback,
-      viewStateChangedCallback);
+  return fml::MakeRefCounted<SceneHost>(viewHolderToken, viewConnectedCallback,
+                                        viewDisconnectedCallback,
+                                        viewStateChangedCallback);
 }
 
-SceneHost::SceneHost(fml::RefPtr<zircon::dart::Handle> exportTokenHandle)
-    : gpu_task_runner_(
-          UIDartState::Current()->GetTaskRunners().GetGPUTaskRunner()),
-      koid_(GetKoid(exportTokenHandle->handle())),
-      use_view_holder_(false) {
-  // Pass the raw handle to the GPU thead; destroying a |zircon::dart::Handle|
-  // on that thread can cause a race condition.
-  gpu_task_runner_->PostTask(
-      [id = koid_, raw_handle = exportTokenHandle->ReleaseHandle()]() {
-        flutter::ExportNode::Create(id, zx::eventpair(raw_handle));
-      });
+void SceneHost::OnViewConnected(scenic::ResourceId id) {
+  auto* scene_host = GetSceneHost(id);
+
+  if (scene_host && !scene_host->view_connected_callback_.is_empty()) {
+    InvokeDartClosure(scene_host->view_connected_callback_);
+  }
+}
+
+void SceneHost::OnViewDisconnected(scenic::ResourceId id) {
+  auto* scene_host = GetSceneHost(id);
+
+  if (scene_host && !scene_host->view_disconnected_callback_.is_empty()) {
+    InvokeDartClosure(scene_host->view_disconnected_callback_);
+  }
 }
 
-SceneHost::SceneHost(fml::RefPtr<zircon::dart::Handle> viewHolderTokenHandle,
+void SceneHost::OnViewStateChanged(scenic::ResourceId id, bool state) {
+  auto* scene_host = GetSceneHost(id);
+
+  if (scene_host && !scene_host->view_state_changed_callback_.is_empty()) {
+    InvokeDartFunction(scene_host->view_state_changed_callback_, state);
+  }
+}
+
+SceneHost::SceneHost(fml::RefPtr<zircon::dart::Handle> viewHolderToken,
                      Dart_Handle viewConnectedCallback,
                      Dart_Handle viewDisconnectedCallback,
                      Dart_Handle viewStateChangedCallback)
     : gpu_task_runner_(
           UIDartState::Current()->GetTaskRunners().GetGPUTaskRunner()),
-      koid_(GetKoid(viewHolderTokenHandle->handle())),
-      use_view_holder_(true) {
+      koid_(GetKoid(viewHolderToken->handle())) {
   auto dart_state = UIDartState::Current();
 
   // Initialize callbacks it they are non-null in Dart.
@@ -169,7 +167,7 @@ SceneHost::SceneHost(fml::RefPtr<zircon::dart::Handle> viewHolderTokenHandle,
       [id = koid_,
        ui_task_runner =
            UIDartState::Current()->GetTaskRunners().GetUITaskRunner(),
-       raw_handle = viewHolderTokenHandle->ReleaseHandle(), bind_callback]() {
+       raw_handle = viewHolderToken->ReleaseHandle(), bind_callback]() {
         flutter::ViewHolder::Create(
             id, std::move(ui_task_runner),
             scenic::ToViewHolderToken(zx::eventpair(raw_handle)),
@@ -178,41 +176,16 @@ SceneHost::SceneHost(fml::RefPtr<zircon::dart::Handle> viewHolderTokenHandle,
 }
 
 SceneHost::~SceneHost() {
-  if (use_view_holder_) {
-    auto* bindings = tls_scene_host_bindings.get();
-    FML_DCHECK(bindings);
-    bindings->erase(koid_);
-
-    gpu_task_runner_->PostTask(
-        [id = koid_]() { flutter::ViewHolder::Destroy(id); });
-  } else {
-    gpu_task_runner_->PostTask(
-        [id = koid_]() { flutter::ExportNode::Destroy(id); });
-  }
-}
-
-void SceneHost::OnViewConnected(scenic::ResourceId id) {
-  auto* scene_host = GetSceneHost(id);
-
-  if (scene_host && !scene_host->view_connected_callback_.is_empty()) {
-    InvokeDartClosure(scene_host->view_connected_callback_);
-  }
-}
-
-void SceneHost::OnViewDisconnected(scenic::ResourceId id) {
-  auto* scene_host = GetSceneHost(id);
+  auto* bindings = tls_scene_host_bindings.get();
+  FML_DCHECK(bindings);
+  bindings->erase(koid_);
 
-  if (scene_host && !scene_host->view_disconnected_callback_.is_empty()) {
-    InvokeDartClosure(scene_host->view_disconnected_callback_);
-  }
+  gpu_task_runner_->PostTask(
+      [id = koid_]() { flutter::ViewHolder::Destroy(id); });
 }
 
-void SceneHost::OnViewStateChanged(scenic::ResourceId id, bool state) {
-  auto* scene_host = GetSceneHost(id);
-
-  if (scene_host && !scene_host->view_state_changed_callback_.is_empty()) {
-    InvokeDartFunction(scene_host->view_state_changed_callback_, state);
-  }
+void SceneHost::dispose() {
+  ClearDartWrapper();
 }
 
 void SceneHost::setProperties(double width,
@@ -222,8 +195,6 @@ void SceneHost::setProperties(double width,
                               double insetBottom,
                               double insetLeft,
                               bool focusable) {
-  FML_DCHECK(use_view_holder_);
-
   gpu_task_runner_->PostTask([id = koid_, width, height, insetTop, insetRight,
                               insetBottom, insetLeft, focusable]() {
     auto* view_holder = flutter::ViewHolder::FromId(id);
@@ -234,8 +205,13 @@ void SceneHost::setProperties(double width,
   });
 }
 
-void SceneHost::dispose() {
-  ClearDartWrapper();
+void SceneHost::setOpacity(double opacity) {
+  gpu_task_runner_->PostTask([id = koid_, opacity]() {
+    auto* view_holder = flutter::ViewHolder::FromId(id);
+    FML_DCHECK(view_holder);
+
+    view_holder->SetOpacity(opacity);
+  });
 }
 
 }  // namespace flutter

lib/ui/compositing/scene_host.h

@@ -23,13 +23,9 @@ class SceneHost : public RefCountedDartWrappable<SceneHost> {
   FML_FRIEND_MAKE_REF_COUNTED(SceneHost);
 
  public:
-  ~SceneHost() override;
-
   static void RegisterNatives(tonic::DartLibraryNatives* natives);
   static fml::RefPtr<SceneHost> Create(
-      fml::RefPtr<zircon::dart::Handle> exportTokenHandle);
-  static fml::RefPtr<SceneHost> CreateViewHolder(
-      fml::RefPtr<zircon::dart::Handle> viewHolderTokenHandle,
+      fml::RefPtr<zircon::dart::Handle> viewHolderToken,
       Dart_Handle viewConnectedCallback,
       Dart_Handle viewDisconnectedCallback,
       Dart_Handle viewStateChangedCallback);
@@ -37,9 +33,15 @@ class SceneHost : public RefCountedDartWrappable<SceneHost> {
   static void OnViewDisconnected(scenic::ResourceId id);
   static void OnViewStateChanged(scenic::ResourceId id, bool state);
 
+  SceneHost(fml::RefPtr<zircon::dart::Handle> viewHolderToken,
+            Dart_Handle viewConnectedCallback,
+            Dart_Handle viewDisconnectedCallback,
+            Dart_Handle viewStateChangedCallback);
+  ~SceneHost() override;
+
   zx_koid_t id() const { return koid_; }
-  bool use_view_holder() const { return use_view_holder_; }
 
+  void dispose();
   void setProperties(double width,
                      double height,
                      double insetTop,
@@ -47,21 +49,14 @@ class SceneHost : public RefCountedDartWrappable<SceneHost> {
                      double insetBottom,
                      double insetLeft,
                      bool focusable);
-  void dispose();
+  void setOpacity(double opacity);
 
  private:
-  explicit SceneHost(fml::RefPtr<zircon::dart::Handle> exportTokenHandle);
-  SceneHost(fml::RefPtr<zircon::dart::Handle> viewHolderTokenHandle,
-            Dart_Handle viewConnectedCallback,
-            Dart_Handle viewDisconnectedCallback,
-            Dart_Handle viewStateChangedCallback);
-
   fml::RefPtr<fml::TaskRunner> gpu_task_runner_;
   tonic::DartPersistentValue view_connected_callback_;
   tonic::DartPersistentValue view_disconnected_callback_;
   tonic::DartPersistentValue view_state_changed_callback_;
   zx_koid_t koid_ = ZX_KOID_INVALID;
-  bool use_view_holder_ = false;
 };
 
 }  // namespace flutter