Wire up Opacity on Fuchsia, round 2 (flutter#14024)

* Remove erroneous ChildView opacity

* Wire frame metrics through contexts

* Maintain layer stack inside of SceneBuilder

* Remove EnsureSingleChild

* Centralize system-composite and elevation logic

* Wire up OpacityLayer to Scenic

Author: arbreng

ci/licenses_golden/licenses_flutter

@@ -48,6 +48,10 @@ FILE: ../../../flutter/flow/layers/color_filter_layer_unittests.cc
 FILE: ../../../flutter/flow/layers/container_layer.cc
 FILE: ../../../flutter/flow/layers/container_layer.h
 FILE: ../../../flutter/flow/layers/container_layer_unittests.cc
+FILE: ../../../flutter/flow/layers/elevated_container_layer.cc
+FILE: ../../../flutter/flow/layers/elevated_container_layer.h
+FILE: ../../../flutter/flow/layers/fuchsia_system_composited_layer.cc
+FILE: ../../../flutter/flow/layers/fuchsia_system_composited_layer.h
 FILE: ../../../flutter/flow/layers/layer.cc
 FILE: ../../../flutter/flow/layers/layer.h
 FILE: ../../../flutter/flow/layers/layer_tree.cc

flow/BUILD.gn

@@ -28,6 +28,8 @@ source_set("flow") {
     "layers/color_filter_layer.h",
     "layers/container_layer.cc",
     "layers/container_layer.h",
+    "layers/elevated_container_layer.cc",
+    "layers/elevated_container_layer.h",
     "layers/layer.cc",
     "layers/layer.h",
     "layers/layer_tree.cc",
@@ -76,6 +78,8 @@ source_set("flow") {
     sources += [
       "layers/child_scene_layer.cc",
       "layers/child_scene_layer.h",
+      "layers/fuchsia_system_composited_layer.cc",
+      "layers/fuchsia_system_composited_layer.h",
       "scene_update_context.cc",
       "scene_update_context.h",
       "view_holder.cc",

flow/layers/child_scene_layer.cc

@@ -20,10 +20,25 @@ ChildSceneLayer::ChildSceneLayer(zx_koid_t layer_id,
 void ChildSceneLayer::Preroll(PrerollContext* context, const SkMatrix& matrix) {
   TRACE_EVENT0("flutter", "ChildSceneLayer::Preroll");
   set_needs_system_composite(true);
+
+  // An alpha "hole punch" is required if the frame behind us is not opaque.
+  if (!context->is_opaque) {
+    set_paint_bounds(
+        SkRect::MakeXYWH(offset_.fX, offset_.fY, size_.fWidth, size_.fHeight));
+  }
 }
 
 void ChildSceneLayer::Paint(PaintContext& context) const {
-  FML_NOTREACHED() << "This layer never needs painting.";
+  TRACE_EVENT0("flutter", "ChildSceneLayer::Paint");
+  FML_DCHECK(needs_painting());
+
+  // If we are being rendered into our own frame using the system compositor,
+  // then it is neccesary to "punch a hole" in the canvas/frame behind us so
+  // that group opacity looks correct.
+  SkPaint paint;
+  paint.setColor(SK_ColorTRANSPARENT);
+  paint.setBlendMode(SkBlendMode::kSrc);
+  context.leaf_nodes_canvas->drawRect(paint_bounds(), paint);
 }
 
 void ChildSceneLayer::UpdateScene(SceneUpdateContext& context) {

flow/layers/container_layer.cc

@@ -9,8 +9,7 @@ namespace flutter {
 ContainerLayer::ContainerLayer() {}
 
 void ContainerLayer::Add(std::shared_ptr<Layer> layer) {
-  layer->set_parent(this);
-  layers_.push_back(std::move(layer));
+  layers_.emplace_back(std::move(layer));
 }
 
 void ContainerLayer::Preroll(PrerollContext* context, const SkMatrix& matrix) {

flow/layers/container_layer.h

@@ -14,7 +14,7 @@ class ContainerLayer : public Layer {
  public:
   ContainerLayer();
 
-  void Add(std::shared_ptr<Layer> layer);
+  virtual void Add(std::shared_ptr<Layer> layer);
 
   void Preroll(PrerollContext* context, const SkMatrix& matrix) override;
   void Paint(PaintContext& context) const override;

flow/layers/elevated_container_layer.cc

@@ -0,0 +1,49 @@
+// 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/layers/elevated_container_layer.h"
+
+namespace flutter {
+namespace {
+
+float ClampElevation(float elevation,
+                     float parent_elevation,
+                     float max_elevation) {
+  // TODO(mklim): Deal with bounds overflow more elegantly. We'd like to be
+  // able to have developers specify the behavior here to alternatives besides
+  // clamping, like normalization on some arbitrary curve.
+  float clamped_elevation = elevation;
+  if (max_elevation > -1 && (parent_elevation + elevation) > max_elevation) {
+    // Clamp the local z coordinate at our max bound. Take into account the
+    // parent z position here to fix clamping in cases where the child is
+    // overflowing because of its parents.
+    clamped_elevation = max_elevation - parent_elevation;
+  }
+
+  return clamped_elevation;
+}
+
+}  // namespace
+
+ElevatedContainerLayer::ElevatedContainerLayer(float elevation)
+    : elevation_(elevation), clamped_elevation_(elevation) {}
+
+void ElevatedContainerLayer::Preroll(PrerollContext* context,
+                                     const SkMatrix& matrix) {
+  TRACE_EVENT0("flutter", "ElevatedContainerLayer::Preroll");
+
+  // Track total elevation as we walk the tree, in order to deal with bounds
+  // overflow in z.
+  parent_elevation_ = context->total_elevation;
+  clamped_elevation_ = ClampElevation(elevation_, parent_elevation_,
+                                      context->frame_physical_depth);
+  context->total_elevation += clamped_elevation_;
+
+  ContainerLayer::Preroll(context, matrix);
+
+  // Restore the elevation for our parent.
+  context->total_elevation = parent_elevation_;
+}
+
+}  // namespace flutter

flow/layers/elevated_container_layer.h

@@ -0,0 +1,34 @@
+// 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_LAYERS_ELEVATED_CONTAINER_LAYER_H_
+#define FLUTTER_FLOW_LAYERS_ELEVATED_CONTAINER_LAYER_H_
+
+#include "flutter/flow/layers/container_layer.h"
+
+namespace flutter {
+
+class ElevatedContainerLayer : public ContainerLayer {
+ public:
+  ElevatedContainerLayer(float elevation);
+  ~ElevatedContainerLayer() override = default;
+
+  void Preroll(PrerollContext* context, const SkMatrix& matrix) override;
+
+  float elevation() const { return clamped_elevation_; }
+  float total_elevation() const {
+    return parent_elevation_ + clamped_elevation_;
+  }
+
+ private:
+  float parent_elevation_ = 0.0f;
+  float elevation_ = 0.0f;
+  float clamped_elevation_ = 0.0f;
+
+  FML_DISALLOW_COPY_AND_ASSIGN(ElevatedContainerLayer);
+};
+
+}  // namespace flutter
+
+#endif  // FLUTTER_FLOW_LAYERS_ELEVATED_CONTAINER_LAYER_H_

flow/layers/fuchsia_system_composited_layer.cc

@@ -0,0 +1,55 @@
+// 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/layers/fuchsia_system_composited_layer.h"
+
+namespace flutter {
+
+FuchsiaSystemCompositedLayer::FuchsiaSystemCompositedLayer(SkColor color,
+                                                           SkAlpha opacity,
+                                                           float elevation)
+    : ElevatedContainerLayer(elevation), color_(color), opacity_(opacity) {}
+
+void FuchsiaSystemCompositedLayer::Preroll(PrerollContext* context,
+                                           const SkMatrix& matrix) {
+  TRACE_EVENT0("flutter", "FuchsiaSystemCompositedLayer::Preroll");
+
+  const float parent_is_opaque = context->is_opaque;
+  context->mutators_stack.PushOpacity(opacity_);
+  context->is_opaque = parent_is_opaque && (opacity_ == SK_AlphaOPAQUE);
+  ElevatedContainerLayer::Preroll(context, matrix);
+  context->is_opaque = parent_is_opaque;
+  context->mutators_stack.Pop();
+}
+
+void FuchsiaSystemCompositedLayer::UpdateScene(SceneUpdateContext& context) {
+  FML_DCHECK(needs_system_composite());
+
+  // Retained rendering: speedup by reusing a retained entity node if
+  // possible. When an entity node is reused, no paint layer is added to the
+  // frame so we won't call Paint.
+  LayerRasterCacheKey key(unique_id(), context.Matrix());
+  if (context.HasRetainedNode(key)) {
+    TRACE_EVENT_INSTANT0("flutter", "retained layer cache hit");
+    const scenic::EntityNode& retained_node = context.GetRetainedNode(key);
+    FML_DCHECK(context.top_entity());
+    FML_DCHECK(retained_node.session() == context.session());
+    context.top_entity()->embedder_node().AddChild(retained_node);
+    return;
+  }
+
+  TRACE_EVENT_INSTANT0("flutter", "retained cache miss, creating");
+  // If we can't find an existing retained surface, create one.
+  SceneUpdateContext::Frame frame(context, rrect_, color_, opacity_ / 255.0f,
+                                  elevation(), this);
+  for (auto& layer : layers()) {
+    if (layer->needs_painting()) {
+      frame.AddPaintLayer(layer.get());
+    }
+  }
+
+  ElevatedContainerLayer::UpdateScene(context);
+}
+
+}  // namespace flutter

flow/layers/fuchsia_system_composited_layer.h

@@ -0,0 +1,37 @@
+// 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_LAYERS_FUCHSIA_SYSTEM_COMPOSITED_LAYER_H_
+#define FLUTTER_FLOW_LAYERS_FUCHSIA_SYSTEM_COMPOSITED_LAYER_H_
+
+#include "flutter/flow/layers/elevated_container_layer.h"
+#include "flutter/flow/scene_update_context.h"
+
+namespace flutter {
+
+class FuchsiaSystemCompositedLayer : public ElevatedContainerLayer {
+ public:
+  static bool can_system_composite() { return true; }
+
+  FuchsiaSystemCompositedLayer(SkColor color, SkAlpha opacity, float elevation);
+
+  void Preroll(PrerollContext* context, const SkMatrix& matrix) override;
+  void UpdateScene(SceneUpdateContext& context) override;
+
+  void set_dimensions(SkRRect rrect) { rrect_ = rrect; }
+
+  SkColor color() const { return color_; }
+  SkAlpha opacity() const { return opacity_; }
+
+ private:
+  SkRRect rrect_ = SkRRect::MakeEmpty();
+  SkColor color_ = SK_ColorTRANSPARENT;
+  SkAlpha opacity_ = SK_AlphaOPAQUE;
+
+  FML_DISALLOW_COPY_AND_ASSIGN(FuchsiaSystemCompositedLayer);
+};
+
+}  // namespace flutter
+
+#endif  // FLUTTER_FLOW_LAYERS_FUCHSIA_SYSTEM_COMPOSITED_LAYER_H_

flow/layers/layer.cc

@@ -10,10 +10,9 @@
 namespace flutter {
 
 Layer::Layer()
-    : parent_(nullptr),
-      needs_system_composite_(false),
-      paint_bounds_(SkRect::MakeEmpty()),
-      unique_id_(NextUniqueID()) {}
+    : paint_bounds_(SkRect::MakeEmpty()),
+      unique_id_(NextUniqueID()),
+      needs_system_composite_(false) {}
 
 Layer::~Layer() = default;