[fuchsia] Composite PhysicalShapeLayers using Skia, except when they need to float above child views.

In that case, they will still need to be pulled
into separate Scenic nodes to be composited on top
of the child view[s].

Author: mikejurka

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) {

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/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)
   }
 }
 
@@ -78,37 +87,53 @@ void PhysicalShapeLayer::UpdateScene(SceneUpdateContext& context) {
   FML_DCHECK(needs_system_composite());
   TRACE_EVENT0("flutter", "PhysicalShapeLayer::UpdateScene");
 
-  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());
-
-    // Re-adjust the elevation.
-    retained_node->SetTranslation(0.f, 0.f, z_translation);
-
-    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());
 
-  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_float_round2int(context.alphaf() * 255),
-      "flutter::PhysicalShapeLayer", z_translation, this);
-  for (auto& layer : layers()) {
-    if (layer->needs_painting()) {
-      frame.AddPaintLayer(layer.get());
+    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());
+
+      // 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);
     }
   }
 }
@@ -128,7 +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

@@ -46,6 +46,8 @@ class PhysicalShapeLayer : public ContainerLayer {
  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_;

flow/scene_update_context.cc

@@ -4,6 +4,7 @@
 
 #include "flutter/flow/scene_update_context.h"
 
+#include <cfloat>
 #include "flutter/flow/layers/layer.h"
 #include "flutter/flow/matrix_decomposition.h"
 #include "flutter/fml/trace_event.h"
@@ -72,14 +73,13 @@ void SceneUpdateContext::CreateFrame(scenic::EntityNode entity_node,
   // and possibly for its texture.
   // TODO(SCN-137): Need to be able to express the radii as vectors.
   scenic::ShapeNode shape_node(session());
-  scenic::RoundedRectangle shape(
-      session_,                                      // session
-      rrect.width(),                                 // width
-      rrect.height(),                                // height
-      rrect.radii(SkRRect::kUpperLeft_Corner).x(),   // top_left_radius
-      rrect.radii(SkRRect::kUpperRight_Corner).x(),  // top_right_radius
-      rrect.radii(SkRRect::kLowerRight_Corner).x(),  // bottom_right_radius
-      rrect.radii(SkRRect::kLowerLeft_Corner).x()    // bottom_left_radius
+  scenic::RoundedRectangle shape(session_,        // session
+                                 rrect.width(),   // width
+                                 rrect.height(),  // height
+                                 0.f,             // top_left_radius
+                                 0.f,             // top_right_radius
+                                 0.f,             // bottom_right_radius
+                                 0.f              // bottom_left_radius
   );
   shape_node.SetShape(shape);
   shape_node.SetTranslation(shape_bounds.width() * 0.5f + shape_bounds.left(),
@@ -313,7 +313,11 @@ SceneUpdateContext::Frame::Frame(SceneUpdateContext& context,
   entity_node().SetLabel(label);
   entity_node().SetTranslation(0.f, 0.f, z_translation);
   entity_node().AddChild(opacity_node_);
-  opacity_node_.SetOpacity(opacity_ / 255.0f);
+  // Scenic currently lacks an API to enable rendering of alpha channel; this only happens
+  // if there is a OpacityNode higher in the tree with opacity != 1. For now,
+  // clamp to a infinitesimally smaller value than 1, which does not cause visual
+  // problems in practice.
+  opacity_node_.SetOpacity(std::min(1 - FLT_EPSILON, opacity_ / 255.0f));
 }
 
 SceneUpdateContext::Frame::~Frame() {