Fix Mozart child views (#3232)

When we pipelined the drawing commands we caused UpdateScene to be called
before Preroll, which isn't allowed. Now we call Preroll, UpdateScene, and
Paint separately.

content_handler/rasterizer.cc

@@ -37,38 +37,52 @@ void Rasterizer::Draw(std::unique_ptr<flow::LayerTree> layer_tree,
   const SkISize& frame_size = layer_tree->frame_size();
   auto update = mozart::SceneUpdate::New();
 
-  sk_sp<SkSurface> surface;
-  if (!frame_size.isEmpty()) {
-    // Get a surface to draw the contents.
-    mozart::ImagePtr image;
-    surface = mozart::MakeSkSurface(frame_size, buffer_producer_.get(), &image);
-    FTL_CHECK(surface);
-
-    // Update the scene contents.
-    mozart::RectF bounds;
-    bounds.width = frame_size.width();
-    bounds.height = frame_size.height();
-
-    auto content_resource = mozart::Resource::New();
-    content_resource->set_image(mozart::ImageResource::New());
-    content_resource->get_image()->image = std::move(image);
-    update->resources.insert(kContentImageResourceId,
-                             std::move(content_resource));
-
-    auto root_node = mozart::Node::New();
-    root_node->hit_test_behavior = mozart::HitTestBehavior::New();
-    root_node->op = mozart::NodeOp::New();
-    root_node->op->set_image(mozart::ImageNodeOp::New());
-    root_node->op->get_image()->content_rect = bounds.Clone();
-    root_node->op->get_image()->image_resource_id = kContentImageResourceId;
-
-    layer_tree->UpdateScene(update.get(), root_node.get());
-
-    update->nodes.insert(kRootNodeId, std::move(root_node));
-  } else {
+  if (frame_size.isEmpty()) {
     update->nodes.insert(kRootNodeId, mozart::Node::New());
+    // Publish the updated scene contents.
+    // TODO(jeffbrown): We should set the metadata's presentation_time here too.
+    scene_->Update(std::move(update));
+    auto metadata = mozart::SceneMetadata::New();
+    metadata->version = layer_tree->scene_version();
+    scene_->Publish(std::move(metadata));
+    callback();
+    return;
   }
 
+  // Get a surface to draw the contents.
+  mozart::ImagePtr image;
+  sk_sp<SkSurface> surface =
+      mozart::MakeSkSurface(frame_size, buffer_producer_.get(), &image);
+
+  FTL_CHECK(surface);
+
+  flow::CompositorContext::ScopedFrame frame =
+      compositor_context_.AcquireFrame(nullptr, *surface->getCanvas());
+
+  layer_tree->Preroll(frame);
+
+  // Update the scene contents.
+  mozart::RectF bounds;
+  bounds.width = frame_size.width();
+  bounds.height = frame_size.height();
+
+  auto content_resource = mozart::Resource::New();
+  content_resource->set_image(mozart::ImageResource::New());
+  content_resource->get_image()->image = std::move(image);
+  update->resources.insert(kContentImageResourceId,
+                           std::move(content_resource));
+
+  auto root_node = mozart::Node::New();
+  root_node->hit_test_behavior = mozart::HitTestBehavior::New();
+  root_node->op = mozart::NodeOp::New();
+  root_node->op->set_image(mozart::ImageNodeOp::New());
+  root_node->op->get_image()->content_rect = bounds.Clone();
+  root_node->op->get_image()->image_resource_id = kContentImageResourceId;
+
+  layer_tree->UpdateScene(update.get(), root_node.get());
+
+  update->nodes.insert(kRootNodeId, std::move(root_node));
+
   // Publish the updated scene contents.
   // TODO(jeffbrown): We should set the metadata's presentation_time here too.
   scene_->Update(std::move(update));
@@ -80,14 +94,10 @@ void Rasterizer::Draw(std::unique_ptr<flow::LayerTree> layer_tree,
   // We do this after publishing to take advantage of pipelining.
   // The image buffer's fence is signalled automatically when the surface
   // goes out of scope.
-  if (surface) {
-    SkCanvas* canvas = surface->getCanvas();
-    flow::CompositorContext::ScopedFrame frame =
-        compositor_context_.AcquireFrame(nullptr, *canvas);
-    canvas->clear(SK_ColorBLACK);
-    layer_tree->Raster(frame);
-    canvas->flush();
-  }
+  SkCanvas* canvas = surface->getCanvas();
+  canvas->clear(SK_ColorBLACK);
+  layer_tree->Paint(frame);
+  canvas->flush();
 
   callback();
 }

flow/layers/layer_tree.cc

@@ -19,23 +19,20 @@ LayerTree::~LayerTree() {}
 
 void LayerTree::Raster(CompositorContext::ScopedFrame& frame,
                        bool ignore_raster_cache) {
-  {
-    TRACE_EVENT0("flutter", "LayerTree::Preroll");
-    frame.context().raster_cache().SetCheckboardCacheImages(
-        checkerboard_raster_cache_images_);
-    Layer::PrerollContext context = {
-        ignore_raster_cache ? nullptr : &frame.context().raster_cache(),
-        frame.gr_context(), SkRect::MakeEmpty(),
-    };
-    root_layer_->Preroll(&context, SkMatrix());
-  }
-
-  {
-    Layer::PaintContext context = {frame.canvas(), frame.context().frame_time(),
-                                   frame.context().engine_time()};
-    TRACE_EVENT0("flutter", "LayerTree::Paint");
-    root_layer_->Paint(context);
-  }
+  Preroll(frame, ignore_raster_cache);
+  Paint(frame);
+}
+
+void LayerTree::Preroll(CompositorContext::ScopedFrame& frame,
+                        bool ignore_raster_cache) {
+  TRACE_EVENT0("flutter", "LayerTree::Preroll");
+  frame.context().raster_cache().SetCheckboardCacheImages(
+      checkerboard_raster_cache_images_);
+  Layer::PrerollContext context = {
+      ignore_raster_cache ? nullptr : &frame.context().raster_cache(),
+      frame.gr_context(), SkRect::MakeEmpty(),
+  };
+  root_layer_->Preroll(&context, SkMatrix());
 }
 
 #if defined(OS_FUCHSIA)
@@ -46,4 +43,11 @@ void LayerTree::UpdateScene(mozart::SceneUpdate* update,
 }
 #endif
 
+void LayerTree::Paint(CompositorContext::ScopedFrame& frame) {
+  Layer::PaintContext context = {frame.canvas(), frame.context().frame_time(),
+                                 frame.context().engine_time()};
+  TRACE_EVENT0("flutter", "LayerTree::Paint");
+  root_layer_->Paint(context);
+}
+
 }  // namespace flow

flow/layers/layer_tree.h

@@ -23,9 +23,13 @@ class LayerTree {
 
   ~LayerTree();
 
+  // Raster includes both Preroll and Paint.
   void Raster(CompositorContext::ScopedFrame& frame,
               bool ignore_raster_cache = false);
 
+  void Preroll(CompositorContext::ScopedFrame& frame,
+               bool ignore_raster_cache = false);
+
 #if defined(OS_FUCHSIA)
   // TODO(abarth): Integrate scene updates with the rasterization pass so that
   // we can draw on top of child scenes (and so that we can apply clips and
@@ -33,6 +37,8 @@ class LayerTree {
   void UpdateScene(mozart::SceneUpdate* update, mozart::Node* container);
 #endif
 
+  void Paint(CompositorContext::ScopedFrame& frame);
+
   Layer* root_layer() const { return root_layer_.get(); }
 
   void set_root_layer(std::unique_ptr<Layer> root_layer) {