Reland "Share engine layers with the framework" (#6412) (#6468)

This reverts commit 74662ab6.

This should land after https://github.com/flutter/engine/pull/6442

* Add pragma vm:entry-point

Otherwise, an object may be both null and an instance of EnginieLayer at
the same time in Dart.

ci/licenses_golden/licenses_flutter

@@ -561,6 +561,8 @@ TYPE: LicenseType.bsd
 FILE: ../../../flutter/flutter_kernel_transformers/lib/track_widget_constructor_locations.dart
 FILE: ../../../flutter/fml/paths_unittests.cc
 FILE: ../../../flutter/lib/ui/isolate_name_server.dart
+FILE: ../../../flutter/lib/ui/painting/engine_layer.cc
+FILE: ../../../flutter/lib/ui/painting/engine_layer.h
 FILE: ../../../flutter/lib/ui/painting/image_encoding.cc
 FILE: ../../../flutter/lib/ui/painting/image_encoding.h
 FILE: ../../../flutter/lib/ui/plugins.dart

flow/layers/container_layer.cc

@@ -10,7 +10,7 @@ ContainerLayer::ContainerLayer() {}
 
 ContainerLayer::~ContainerLayer() = default;
 
-void ContainerLayer::Add(std::unique_ptr<Layer> layer) {
+void ContainerLayer::Add(std::shared_ptr<Layer> layer) {
   layer->set_parent(this);
   layers_.push_back(std::move(layer));
 }

flow/layers/container_layer.h

@@ -15,7 +15,7 @@ class ContainerLayer : public Layer {
   ContainerLayer();
   ~ContainerLayer() override;
 
-  void Add(std::unique_ptr<Layer> layer);
+  void Add(std::shared_ptr<Layer> layer);
 
   void Preroll(PrerollContext* context, const SkMatrix& matrix) override;
 
@@ -23,7 +23,7 @@ class ContainerLayer : public Layer {
   void UpdateScene(SceneUpdateContext& context) override;
 #endif  // defined(OS_FUCHSIA)
 
-  const std::vector<std::unique_ptr<Layer>>& layers() const { return layers_; }
+  const std::vector<std::shared_ptr<Layer>>& layers() const { return layers_; }
 
  protected:
   void PrerollChildren(PrerollContext* context,
@@ -36,7 +36,7 @@ class ContainerLayer : public Layer {
 #endif  // defined(OS_FUCHSIA)
 
  private:
-  std::vector<std::unique_ptr<Layer>> layers_;
+  std::vector<std::shared_ptr<Layer>> layers_;
 
   FML_DISALLOW_COPY_AND_ASSIGN(ContainerLayer);
 };

flow/layers/layer_tree.h

@@ -39,7 +39,7 @@ class LayerTree {
 
   Layer* root_layer() const { return root_layer_.get(); }
 
-  void set_root_layer(std::unique_ptr<Layer> root_layer) {
+  void set_root_layer(std::shared_ptr<Layer> root_layer) {
     root_layer_ = std::move(root_layer);
   }
 
@@ -74,7 +74,7 @@ class LayerTree {
 
  private:
   SkISize frame_size_;  // Physical pixels.
-  std::unique_ptr<Layer> root_layer_;
+  std::shared_ptr<Layer> root_layer_;
   fml::TimeDelta construction_time_;
   uint32_t rasterizer_tracing_threshold_;
   bool checkerboard_raster_cache_images_;

lib/ui/BUILD.gn

@@ -23,6 +23,8 @@ source_set("ui") {
     "painting/canvas.h",
     "painting/codec.cc",
     "painting/codec.h",
+    "painting/engine_layer.h",
+    "painting/engine_layer.cc",
     "painting/frame_info.cc",
     "painting/frame_info.h",
     "painting/gradient.cc",

lib/ui/compositing.dart

@@ -69,7 +69,7 @@ class SceneBuilder extends NativeFieldWrapperClass2 {
   /// This is equivalent to [pushTransform] with a matrix with only translation.
   ///
   /// See [pop] for details about the operation stack.
-  void pushOffset(double dx, double dy) native 'SceneBuilder_pushOffset';
+  EngineLayer pushOffset(double dx, double dy) native 'SceneBuilder_pushOffset';
 
   /// Pushes a rectangular clip operation onto the operation stack.
   ///
@@ -177,10 +177,10 @@ class SceneBuilder extends NativeFieldWrapperClass2 {
   ///
   /// See [pop] for details about the operation stack, and [Clip] for different clip modes.
   // ignore: deprecated_member_use
-  void pushPhysicalShape({ Path path, double elevation, Color color, Color shadowColor, Clip clipBehavior = defaultClipBehavior}) {
-    _pushPhysicalShape(path, elevation, color.value, shadowColor?.value ?? 0xFF000000, clipBehavior.index);
+  EngineLayer pushPhysicalShape({ Path path, double elevation, Color color, Color shadowColor, Clip clipBehavior = defaultClipBehavior}) {
+    return _pushPhysicalShape(path, elevation, color.value, shadowColor?.value ?? 0xFF000000, clipBehavior.index);
   }
-  void _pushPhysicalShape(Path path, double elevation, int color, int shadowColor, int clipBehavior) native
+  EngineLayer _pushPhysicalShape(Path path, double elevation, int color, int shadowColor, int clipBehavior) native
     'SceneBuilder_pushPhysicalShape';
 
   /// Ends the effect of the most recently pushed operation.
@@ -191,6 +191,16 @@ class SceneBuilder extends NativeFieldWrapperClass2 {
   /// stack.
   void pop() native 'SceneBuilder_pop';
 
+  /// Add a retained engine layer subtree from previous frames.
+  ///
+  /// All the engine layers that are in the subtree of the retained layer will
+  /// be automatically appended to the current engine layer tree.
+  ///
+  /// Therefore, when implementing a subclas of the [Layer] concept defined in
+  /// the rendering layer of Flutter's framework, once this is called, there's
+  /// no need to call [addToScene] for its children layers.
+  EngineLayer addRetained(EngineLayer retainedLayer) native 'SceneBuilder_addRetained';
+
   /// Adds an object to the scene that displays performance statistics.
   ///
   /// Useful during development to assess the performance of the application.

lib/ui/compositing/scene.cc

@@ -26,7 +26,7 @@ IMPLEMENT_WRAPPERTYPEINFO(ui, Scene);
 
 DART_BIND_ALL(Scene, FOR_EACH_BINDING)
 
-fml::RefPtr<Scene> Scene::create(std::unique_ptr<flow::Layer> rootLayer,
+fml::RefPtr<Scene> Scene::create(std::shared_ptr<flow::Layer> rootLayer,
                                  uint32_t rasterizerTracingThreshold,
                                  bool checkerboardRasterCacheImages,
                                  bool checkerboardOffscreenLayers) {
@@ -35,7 +35,7 @@ fml::RefPtr<Scene> Scene::create(std::unique_ptr<flow::Layer> rootLayer,
       checkerboardRasterCacheImages, checkerboardOffscreenLayers);
 }
 
-Scene::Scene(std::unique_ptr<flow::Layer> rootLayer,
+Scene::Scene(std::shared_ptr<flow::Layer> rootLayer,
              uint32_t rasterizerTracingThreshold,
              bool checkerboardRasterCacheImages,
              bool checkerboardOffscreenLayers)

lib/ui/compositing/scene.h

@@ -24,7 +24,7 @@ class Scene : public RefCountedDartWrappable<Scene> {
 
  public:
   ~Scene() override;
-  static fml::RefPtr<Scene> create(std::unique_ptr<flow::Layer> rootLayer,
+  static fml::RefPtr<Scene> create(std::shared_ptr<flow::Layer> rootLayer,
                                    uint32_t rasterizerTracingThreshold,
                                    bool checkerboardRasterCacheImages,
                                    bool checkerboardOffscreenLayers);
@@ -40,7 +40,7 @@ class Scene : public RefCountedDartWrappable<Scene> {
   static void RegisterNatives(tonic::DartLibraryNatives* natives);
 
  private:
-  explicit Scene(std::unique_ptr<flow::Layer> rootLayer,
+  explicit Scene(std::shared_ptr<flow::Layer> rootLayer,
                  uint32_t rasterizerTracingThreshold,
                  bool checkerboardRasterCacheImages,
                  bool checkerboardOffscreenLayers);

lib/ui/compositing/scene_builder.cc

@@ -53,6 +53,7 @@ IMPLEMENT_WRAPPERTYPEINFO(ui, SceneBuilder);
   V(SceneBuilder, pushShaderMask)                   \
   V(SceneBuilder, pushPhysicalShape)                \
   V(SceneBuilder, pop)                              \
+  V(SceneBuilder, addRetained)                      \
   V(SceneBuilder, addPicture)                       \
   V(SceneBuilder, addTexture)                       \
   V(SceneBuilder, addChildScene)                    \
@@ -80,11 +81,12 @@ void SceneBuilder::pushTransform(const tonic::Float64List& matrix4) {
   PushLayer(std::move(layer));
 }
 
-void SceneBuilder::pushOffset(double dx, double dy) {
+fml::RefPtr<EngineLayer> SceneBuilder::pushOffset(double dx, double dy) {
   SkMatrix sk_matrix = SkMatrix::MakeTrans(dx, dy);
-  auto layer = std::make_unique<flow::TransformLayer>();
+  auto layer = std::make_shared<flow::TransformLayer>();
   layer->set_transform(sk_matrix);
-  PushLayer(std::move(layer));
+  PushLayer(layer);
+  return EngineLayer::MakeRetained(layer);
 }
 
 void SceneBuilder::pushClipRect(double left,
@@ -148,21 +150,29 @@ void SceneBuilder::pushShaderMask(Shader* shader,
   PushLayer(std::move(layer));
 }
 
-void SceneBuilder::pushPhysicalShape(const CanvasPath* path,
+fml::RefPtr<EngineLayer> SceneBuilder::pushPhysicalShape(const CanvasPath* path,
                                                          double elevation,
                                                          int color,
                                                          int shadow_color,
                                                          int clipBehavior) {
   const SkPath& sk_path = path->path();
   flow::Clip clip_behavior = static_cast<flow::Clip>(clipBehavior);
-  auto layer = std::make_unique<flow::PhysicalShapeLayer>(clip_behavior);
+  auto layer = std::make_shared<flow::PhysicalShapeLayer>(clip_behavior);
   layer->set_path(sk_path);
   layer->set_elevation(elevation);
   layer->set_color(static_cast<SkColor>(color));
   layer->set_shadow_color(static_cast<SkColor>(shadow_color));
   layer->set_device_pixel_ratio(
       UIDartState::Current()->window()->viewport_metrics().device_pixel_ratio);
-  PushLayer(std::move(layer));
+  PushLayer(layer);
+  return EngineLayer::MakeRetained(layer);
+}
+
+void SceneBuilder::addRetained(fml::RefPtr<EngineLayer> retainedLayer) {
+  if (!current_layer_) {
+    return;
+  }
+  current_layer_->Add(retainedLayer->Layer());
 }
 
 void SceneBuilder::pop() {
@@ -260,7 +270,7 @@ fml::RefPtr<Scene> SceneBuilder::build() {
   return scene;
 }
 
-void SceneBuilder::PushLayer(std::unique_ptr<flow::ContainerLayer> layer) {
+void SceneBuilder::PushLayer(std::shared_ptr<flow::ContainerLayer> layer) {
   FML_DCHECK(layer);
 
   if (!root_layer_) {

lib/ui/compositing/scene_builder.h

@@ -12,6 +12,7 @@
 #include "flutter/lib/ui/compositing/scene.h"
 #include "flutter/lib/ui/compositing/scene_host.h"
 #include "flutter/lib/ui/dart_wrapper.h"
+#include "flutter/lib/ui/painting/engine_layer.h"
 #include "flutter/lib/ui/painting/image_filter.h"
 #include "flutter/lib/ui/painting/path.h"
 #include "flutter/lib/ui/painting/picture.h"
@@ -33,7 +34,7 @@ class SceneBuilder : public RefCountedDartWrappable<SceneBuilder> {
   ~SceneBuilder() override;
 
   void pushTransform(const tonic::Float64List& matrix4);
-  void pushOffset(double dx, double dy);
+  fml::RefPtr<EngineLayer> pushOffset(double dx, double dy);
   void pushClipRect(double left,
                     double right,
                     double top,
@@ -50,12 +51,14 @@ class SceneBuilder : public RefCountedDartWrappable<SceneBuilder> {
                       double maskRectTop,
                       double maskRectBottom,
                       int blendMode);
-  void pushPhysicalShape(const CanvasPath* path,
+  fml::RefPtr<EngineLayer> pushPhysicalShape(const CanvasPath* path,
                                              double elevation,
                                              int color,
                                              int shadowColor,
                                              int clipBehavior);
 
+  void addRetained(fml::RefPtr<EngineLayer> retainedLayer);
+
   void pop();
 
   void addPerformanceOverlay(uint64_t enabledOptions,
@@ -92,14 +95,14 @@ class SceneBuilder : public RefCountedDartWrappable<SceneBuilder> {
  private:
   SceneBuilder();
 
-  std::unique_ptr<flow::ContainerLayer> root_layer_;
+  std::shared_ptr<flow::ContainerLayer> root_layer_;
   flow::ContainerLayer* current_layer_ = nullptr;
 
   int rasterizer_tracing_threshold_ = 0;
   bool checkerboard_raster_cache_images_ = false;
   bool checkerboard_offscreen_layers_ = false;
 
-  void PushLayer(std::unique_ptr<flow::ContainerLayer> layer);
+  void PushLayer(std::shared_ptr<flow::ContainerLayer> layer);
 
   FML_DISALLOW_COPY_AND_ASSIGN(SceneBuilder);
 };

lib/ui/dart_ui.cc

@@ -11,6 +11,7 @@
 #include "flutter/lib/ui/isolate_name_server/isolate_name_server_natives.h"
 #include "flutter/lib/ui/painting/canvas.h"
 #include "flutter/lib/ui/painting/codec.h"
+#include "flutter/lib/ui/painting/engine_layer.h"
 #include "flutter/lib/ui/painting/frame_info.h"
 #include "flutter/lib/ui/painting/gradient.h"
 #include "flutter/lib/ui/painting/image.h"
@@ -70,6 +71,7 @@ void DartUI::InitForGlobal() {
     CanvasPathMeasure::RegisterNatives(g_natives);
     Codec::RegisterNatives(g_natives);
     DartRuntimeHooks::RegisterNatives(g_natives);
+    EngineLayer::RegisterNatives(g_natives);
     FrameInfo::RegisterNatives(g_natives);
     ImageFilter::RegisterNatives(g_natives);
     ImageShader::RegisterNatives(g_natives);

lib/ui/painting.dart

@@ -1761,6 +1761,14 @@ enum PathOperation {
   reverseDifference,
 }
 
+/// A handle for the framework to hold and retain an engine layer across frames.
+class EngineLayer extends NativeFieldWrapperClass2 {
+  /// This class is created by the engine, and should not be instantiated
+  /// or extended directly.
+  @pragma('vm:entry-point')
+  EngineLayer._();
+}
+
 /// A complex, one-dimensional subset of a plane.
 ///
 /// A path consists of a number of subpaths, and a _current point_.

lib/ui/painting/engine_layer.cc

+// Copyright 2018 The Chromium 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/lib/ui/painting/engine_layer.h"
+
+#include "flutter/flow/layers/container_layer.h"
+
+#include "third_party/tonic/converter/dart_converter.h"
+#include "third_party/tonic/dart_args.h"
+#include "third_party/tonic/dart_binding_macros.h"
+#include "third_party/tonic/dart_library_natives.h"
+
+using tonic::ToDart;
+
+namespace blink {
+
+EngineLayer::~EngineLayer() = default;
+
+IMPLEMENT_WRAPPERTYPEINFO(ui, EngineLayer);
+
+#define FOR_EACH_BINDING(V)  // nothing to bind
+
+DART_BIND_ALL(EngineLayer, FOR_EACH_BINDING)
+
+}  // namespace blink

lib/ui/painting/engine_layer.h

+// Copyright 2018 The Chromium 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_LIB_UI_PAINTING_ENGINE_LAYER_H_
+#define FLUTTER_LIB_UI_PAINTING_ENGINE_LAYER_H_
+
+#include "flutter/lib/ui/dart_wrapper.h"
+
+#include "flutter/flow/layers/layer.h"
+
+namespace tonic {
+class DartLibraryNatives;
+}  // namespace tonic
+
+namespace blink {
+
+class EngineLayer;
+
+class EngineLayer : public RefCountedDartWrappable<EngineLayer> {
+  DEFINE_WRAPPERTYPEINFO();
+
+ public:
+  ~EngineLayer() override;
+  static fml::RefPtr<EngineLayer> MakeRetained(
+      std::shared_ptr<flow::ContainerLayer> layer) {
+    return fml::MakeRefCounted<EngineLayer>(layer);
+  }
+
+  static void RegisterNatives(tonic::DartLibraryNatives* natives);
+
+  std::shared_ptr<flow::ContainerLayer> Layer() const { return layer_; }
+
+ private:
+  explicit EngineLayer(std::shared_ptr<flow::ContainerLayer> layer)
+      : layer_(layer) {}
+  std::shared_ptr<flow::ContainerLayer> layer_;
+
+  FML_FRIEND_MAKE_REF_COUNTED(EngineLayer);
+};
+
+}  // namespace blink
+
+#endif  // FLUTTER_LIB_UI_PAINTING_ENGINE_LAYER_H_