[fuchsia] Avoid creating separate system layers for PhysicalShapeLayers.

flow/layers/child_scene_layer.cc

@@ -20,6 +20,7 @@ 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);
+  context->child_scene_layer_exists_below = true;
 
   // An alpha "hole punch" is required if the frame behind us is not opaque.
   if (!context->is_opaque) {
@@ -49,7 +50,9 @@ void ChildSceneLayer::UpdateScene(SceneUpdateContext& context) {
   auto* view_holder = ViewHolder::FromId(layer_id_);
   FML_DCHECK(view_holder);
 
-  view_holder->UpdateScene(context, offset_, size_, hit_testable_);
+  view_holder->UpdateScene(context, offset_, size_,
+                           sk_float_round2int(context.alphaf() * 255),
+                           hit_testable_);
 }
 
 }  // namespace flutter

flow/layers/layer.h

@@ -66,6 +66,11 @@ struct PrerollContext {
   float total_elevation = 0.0f;
   bool has_platform_view = false;
   bool is_opaque = true;
+#if defined(OS_FUCHSIA)
+  // True if, during the traversal so far, we have seen a child_scene_layer.
+  // Informs whether a layer needs to be system composited.
+  bool child_scene_layer_exists_below = false;
+#endif  // defined(OS_FUCHSIA)
 };
 
 // Represents a single composited layer. Created on the UI thread but then

flow/layers/layer_tree.cc

@@ -83,7 +83,7 @@ void LayerTree::UpdateScene(SceneUpdateContext& context,
       context,
       SkRRect::MakeRect(
           SkRect::MakeWH(frame_size_.width(), frame_size_.height())),
-      SK_ColorTRANSPARENT, SK_AlphaOPAQUE);
+      SK_ColorTRANSPARENT, SK_AlphaOPAQUE, "flutter::LayerTree");
   if (root_layer_->needs_system_composite()) {
     root_layer_->UpdateScene(context);
   }

flow/layers/opacity_layer.cc

@@ -9,11 +9,6 @@
 
 namespace flutter {
 
-// The OpacityLayer has no real "elevation", but we want to avoid Z-fighting
-// when using the system compositor.  Choose a small but non-zero value for
-// this.
-constexpr float kOpacityElevationWhenUsingSystemCompositor = 0.01f;
-
 OpacityLayer::OpacityLayer(SkAlpha alpha, const SkPoint& offset)
     : alpha_(alpha), offset_(offset) {
   // Ensure OpacityLayer has only one direct child.
@@ -40,8 +35,6 @@ void OpacityLayer::Preroll(PrerollContext* context, const SkMatrix& matrix) {
   SkMatrix child_matrix = matrix;
   child_matrix.postTranslate(offset_.fX, offset_.fY);
 
-  total_elevation_ = context->total_elevation;
-  context->total_elevation += kOpacityElevationWhenUsingSystemCompositor;
   context->is_opaque = parent_is_opaque && (alpha_ == SK_AlphaOPAQUE);
   context->mutators_stack.PushTransform(
       SkMatrix::MakeTrans(offset_.fX, offset_.fY));
@@ -52,17 +45,7 @@ void OpacityLayer::Preroll(PrerollContext* context, const SkMatrix& matrix) {
   context->mutators_stack.Pop();
   context->mutators_stack.Pop();
   context->is_opaque = parent_is_opaque;
-  context->total_elevation = total_elevation_;
 
-#if defined(OS_FUCHSIA)
-  if (needs_system_composite()) {
-    // When using the system compositor, do not include the offset since we
-    // are rendering as a separate piece of geometry and the offset will be
-    // baked into that geometry's transform.
-    frameRRect_ = SkRRect::MakeRect(paint_bounds());
-    set_paint_bounds(SkRect::MakeEmpty());
-  } else
-#endif
   {
     set_paint_bounds(paint_bounds().makeOffset(offset_.fX, offset_.fY));
     if (!context->has_platform_view && context->raster_cache &&
@@ -123,36 +106,10 @@ void OpacityLayer::Paint(PaintContext& context) const {
 #if defined(OS_FUCHSIA)
 
 void OpacityLayer::UpdateScene(SceneUpdateContext& context) {
-  FML_DCHECK(needs_system_composite());
-  TRACE_EVENT0("flutter", "OpacityLayer::UpdateScene");
-
-  ContainerLayer* container = GetChildContainer();
-  FML_DCHECK(!container->layers().empty());  // OpacityLayer can't be a leaf.
-
-  SceneUpdateContext::Transform transform(
-      context, SkMatrix::MakeTrans(offset_.fX, offset_.fY));
-
-  // 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 PhysicalShapeLayer::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", "cache miss, creating");
-  // If we can't find an existing retained surface, create one.
-  SceneUpdateContext::Frame frame(
-      context, frameRRect_, SK_ColorTRANSPARENT, alpha_,
-      kOpacityElevationWhenUsingSystemCompositor, total_elevation_, this);
-  frame.AddPaintLayer(container);
-
-  UpdateSceneChildren(context);
+  float saved_alpha = context.alphaf();
+  context.set_alphaf(context.alphaf() * (alpha_ / 255.f));
+  ContainerLayer::UpdateScene(context);
+  context.set_alphaf(saved_alpha);
 }
 
 #endif  // defined(OS_FUCHSIA)

flow/layers/opacity_layer.h

@@ -43,7 +43,6 @@ class OpacityLayer : public ContainerLayer {
   SkAlpha alpha_;
   SkPoint offset_;
   SkRRect frameRRect_;
-  float total_elevation_ = 0.0f;
 
   FML_DISALLOW_COPY_AND_ASSIGN(OpacityLayer);
 };

flow/layers/physical_shape_layer.cc

@@ -52,23 +52,32 @@ void PhysicalShapeLayer::Preroll(PrerollContext* context,
 
   context->total_elevation += elevation_;
   total_elevation_ = context->total_elevation;
+#if defined(OS_FUCHSIA)
+  child_layer_exists_below_ = context->child_scene_layer_exists_below;
+  context->child_scene_layer_exists_below = false;
+ #endif
+
   SkRect child_paint_bounds;
   PrerollChildren(context, matrix, &child_paint_bounds);
+
+#if defined(OS_FUCHSIA)
+  children_need_system_compositing_ = needs_system_composite();
+  if (child_layer_exists_below_) {
+    set_needs_system_composite(true);
+  }
+  context->child_scene_layer_exists_below =
+      context->child_scene_layer_exists_below || child_layer_exists_below_;
+#endif
   context->total_elevation -= elevation_;
 
   if (elevation_ == 0) {
     set_paint_bounds(path_.getBounds());
   } else {
-#if defined(OS_FUCHSIA)
-    // Let the system compositor draw all shadows for us.
-    set_needs_system_composite(true);
-#else
     // We will draw the shadow in Paint(), so add some margin to the paint
     // bounds to leave space for the shadow. We fill this whole region and clip
     // children to it so we don't need to join the child paint bounds.
     set_paint_bounds(ComputeShadowBounds(path_.getBounds(), elevation_,
                                          context->frame_device_pixel_ratio));
-#endif  // defined(OS_FUCHSIA)
   }
 }
 
@@ -78,30 +87,64 @@ void PhysicalShapeLayer::UpdateScene(SceneUpdateContext& context) {
   FML_DCHECK(needs_system_composite());
   TRACE_EVENT0("flutter", "PhysicalShapeLayer::UpdateScene");
 
-  // 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 PhysicalShapeLayer::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()->entity_node().AddChild(retained_node);
-    return;
-  }
+  // If there is embedded Fuchsia content in the scene (a ChildSceneLayer),
+  // PhysicalShapeLayers that appear above the embedded content will be turned
+  // into their own Scenic layers.
+  if (child_layer_exists_below_) {
+    // Reset paint bounds, because shadows are not rendered in this case
+    // (see comment in Paint()).
+    set_paint_bounds(path_.getBounds());
+
+    float global_scenic_elevation = context.GetGlobalElevationForNextScenicLayer();
+    float local_scenic_elevation_ =
+        global_scenic_elevation - context.scenic_elevation();
+    float z_translation = -local_scenic_elevation_;
+
+    // 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 PhysicalShapeLayer::Paint.
+    LayerRasterCacheKey key(unique_id(), context.Matrix());
+    if (context.HasRetainedNode(key)) {
+      TRACE_EVENT_INSTANT0("flutter", "retained layer cache hit");
+      scenic::EntityNode* retained_node = context.GetRetainedNode(key);
+      FML_DCHECK(context.top_entity());
+      FML_DCHECK(retained_node->session() == context.session());
 
-  TRACE_EVENT_INSTANT0("flutter", "cache miss, creating");
-  // If we can't find an existing retained surface, create one.
-  SceneUpdateContext::Frame frame(context, frameRRect_, color_, SK_AlphaOPAQUE,
-                                  elevation_, total_elevation_, this);
-  for (auto& layer : layers()) {
-    if (layer->needs_painting()) {
-      frame.AddPaintLayer(layer.get());
+      // Re-adjust the elevation.
+      retained_node->SetTranslation(0.f, 0.f, z_translation);
+
+      context.top_entity()->entity_node().AddChild(*retained_node);
+      return;
+    }
+
+    TRACE_EVENT_INSTANT0("flutter", "cache miss, creating");
+    // If we can't find an existing retained surface, create one.
+    SceneUpdateContext::Frame frame(context, frameRRect_, SK_ColorTRANSPARENT,
+                                    sk_float_round2int(context.alphaf() * 255),
+                                    "flutter::PhysicalShapeLayer",
+                                    z_translation, this);
+
+    frame.AddPaintLayer(this);
+
+    // Node: UpdateSceneChildren needs to be called here so that |frame| is still
+    // in scope (and therefore alive) while UpdateSceneChildren is being called.
+    if (children_need_system_compositing_) {
+      UpdateSceneChildren(context);
+    }
+  } else {
+    if (children_need_system_compositing_) {
+      UpdateSceneChildren(context);
     }
   }
+}
+
+void PhysicalShapeLayer::UpdateSceneChildren(SceneUpdateContext& context) {
+  float scenic_elevation = context.scenic_elevation();
+  context.set_scenic_elevation(scenic_elevation + local_scenic_elevation_);
+
+  ContainerLayer::UpdateSceneChildren(context);
 
-  UpdateSceneChildren(context);
+  context.set_scenic_elevation(scenic_elevation);
 }
 
 #endif  // defined(OS_FUCHSIA)
@@ -110,7 +153,19 @@ void PhysicalShapeLayer::Paint(PaintContext& context) const {
   TRACE_EVENT0("flutter", "PhysicalShapeLayer::Paint");
   FML_DCHECK(needs_painting());
 
+
+#if defined(OS_FUCHSIA)
+  // TODO: Re-enable shadow drawing here.
+  // Shadows are not rendered for PhysicalShapeLayers that exist as separate
+  // system services; this is to maintain compatibility with the previous
+  // implementation and has the added benefit of requiring smaller textures, since
+  // extra space is not needed for the shadows.
+  // This behavior might change  after clients adjust their usage of PhysicalShaperLayer
+  // to make elevation correlate to desired shadow size.
+  if (false && !child_layer_exists_below_ && elevation_ != 0) {
+#else
   if (elevation_ != 0) {
+#endif
     DrawShadow(context.leaf_nodes_canvas, path_, shadow_color_, elevation_,
                SkColorGetA(color_) != 0xff, context.frame_device_pixel_ratio);
   }

flow/layers/physical_shape_layer.h

@@ -37,11 +37,18 @@ class PhysicalShapeLayer : public ContainerLayer {
 
 #if defined(OS_FUCHSIA)
   void UpdateScene(SceneUpdateContext& context) override;
+
+  void UpdateSceneChildren(SceneUpdateContext& context);
 #endif  // defined(OS_FUCHSIA)
 
   float total_elevation() const { return total_elevation_; }
 
  private:
+#if defined(OS_FUCHSIA)
+  float local_scenic_elevation_ = 0.0f;
+  bool child_layer_exists_below_ = false;
+  bool children_need_system_compositing_ = false;
+#endif
   SkColor color_;
   SkColor shadow_color_;
   float elevation_ = 0.0f;

flow/layers/transform_layer.cc

@@ -56,8 +56,12 @@ void TransformLayer::UpdateScene(SceneUpdateContext& context) {
   TRACE_EVENT0("flutter", "TransformLayer::UpdateScene");
   FML_DCHECK(needs_system_composite());
 
-  SceneUpdateContext::Transform transform(context, transform_);
-  UpdateSceneChildren(context);
+  if (!transform_.isIdentity()) {
+    SceneUpdateContext::Transform transform(context, transform_);
+    UpdateSceneChildren(context);
+  } else {
+    UpdateSceneChildren(context);
+  }
 }
 
 #endif  // defined(OS_FUCHSIA)