Mozart: Improve internal scene graph representation.

services/gfx/compositor/graph/snapshot.cc

Index: services/gfx/compositor/graph/snapshot.cc
diff --git a/services/gfx/compositor/graph/snapshot.cc b/services/gfx/compositor/graph/snapshot.cc
index 935fa2055b790c2a5b402736cb9be84e08e02344..ab4a4478ed2d2302cc30cce06bdf70ab306621fb 100644
--- a/services/gfx/compositor/graph/snapshot.cc
+++ b/services/gfx/compositor/graph/snapshot.cc
@@ -5,9 +5,10 @@
 #include "services/gfx/compositor/graph/snapshot.h"
 
 #include "base/logging.h"
+#include "services/gfx/compositor/graph/scene_content.h"
 #include "services/gfx/compositor/graph/scene_def.h"
 #include "services/gfx/compositor/render/render_frame.h"
-#include "services/gfx/compositor/render/render_layer.h"
+#include "third_party/skia/include/core/SkPictureRecorder.h"
 #include "third_party/skia/include/core/SkRect.h"
 
 namespace compositor {
@@ -20,19 +21,42 @@ bool Snapshot::Invalidate() {
   if (valid_) {
     valid_ = false;
     dependencies_.clear();
-    frame_.reset();
+    ClearContent();
     return true;
   }
   return false;
 }
 
-bool Snapshot::InvalidateScene(SceneDef* scene_def) {
+bool Snapshot::InvalidateScene(const SceneDef* scene_def) {
   DCHECK(scene_def);
+  return valid_ &&
+         dependencies_.find(scene_def->label().token()) !=
+             dependencies_.end() &&
+         Invalidate();
+}
 
-  if (valid_ && dependencies_.find(scene_def) != dependencies_.end()) {
-    return Invalidate();
-  }
-  return false;
+void Snapshot::ClearContent() {
+  root_scene_content_ = nullptr;
+  resolved_scene_contents_.clear();
+  node_dispositions_.clear();
+  frame_.reset();
+}
+
+bool Snapshot::IsBlocked(const NodeDef* node) const {
+  DCHECK(valid_);
+  auto it = node_dispositions_.find(node);
+  DCHECK(it != node_dispositions_.end());
+  DCHECK(it->second == Disposition::kSuccess ||
+         it->second == Disposition::kBlocked);
+  return it->second == Disposition::kBlocked;
+}
+
+const SceneContent* Snapshot::GetResolvedSceneContent(
+    const SceneNodeDef* scene_node) const {
+  DCHECK(valid_);
+  auto it = resolved_scene_contents_.find(scene_node);
+  DCHECK(it != resolved_scene_contents_.end());
+  return it->second.get();
 }
 
 SnapshotBuilder::SnapshotBuilder(std::ostream* block_log)
@@ -40,26 +64,164 @@ SnapshotBuilder::SnapshotBuilder(std::ostream* block_log)
 
 SnapshotBuilder::~SnapshotBuilder() {}
 
-void SnapshotBuilder::AddSceneDependency(SceneDef* scene) {
+Snapshot::Disposition SnapshotBuilder::SnapshotNode(
+    const NodeDef* node,
+    const SceneContent* content) {
+  DCHECK(snapshot_);
+  DCHECK(node);
+  DCHECK(content);
+  DCHECK(node != content->GetRootNodeIfExists());
+
+  auto it = snapshot_->node_dispositions_.find(node);
+  if (it != snapshot_->node_dispositions_.end())
+    return it->second;
+
+  Snapshot::Disposition disposition = node->RecordSnapshot(content, this);
+  snapshot_->node_dispositions_[node] = disposition;
+  return disposition;
+}
+
+Snapshot::Disposition SnapshotBuilder::SnapshotRootAndDetectCycles(
+    const NodeDef* node,
+    const SceneContent* content) {
   DCHECK(snapshot_);
-  snapshot_->dependencies_.insert(scene);
+  DCHECK(node);
+  DCHECK(content);
+  DCHECK(node == content->GetRootNodeIfExists());
+
+  auto storage = snapshot_->node_dispositions_.emplace(
+      node, Snapshot::Disposition::kCycle);
+  if (!storage.second) {
+    if (storage.first->second == Snapshot::Disposition::kCycle)
+      cycle_ = content;  // start unwinding, remember where to stop
+    return storage.first->second;
+  }
+
+  Snapshot::Disposition disposition = node->RecordSnapshot(content, this);
+  if (disposition == Snapshot::Disposition::kSuccess) {
+    snapshot_->node_dispositions_[node] = disposition;
+    return disposition;
+  }
+
+  // We cannot reuse the iterator in |storage.first| because it may have
+  // been invalidated by the call to |RecordSnapshot| due to rehashing so
+  // we must look up the node again just in case.
+  snapshot_->node_dispositions_[node] = Snapshot::Disposition::kBlocked;
+
+  if (disposition == Snapshot::Disposition::kCycle) {
+    DCHECK(cycle_);
+    if (block_log_) {
+      *block_log_ << "Scene blocked because it is part of a cycle: "
+                  << content->FormattedLabel() << std::endl;
+    }
+    if (cycle_ == content) {
+      cycle_ = nullptr;  // found the ouroboros tail, stop unwinding
+      disposition = Snapshot::Disposition::kBlocked;
+    }
+  }
+  return disposition;
+}
+Snapshot::Disposition SnapshotBuilder::SnapshotScene(
+    const SceneDef* scene,
+    uint32_t version,
+    const SceneNodeDef* referrer_node,
+    const SceneContent* referrer_content) {
+  DCHECK(snapshot_);
+  DCHECK(scene);
+  DCHECK(referrer_node);
+  DCHECK(referrer_content);
+
+  // This function should only ever be called once when snapshotting the
+  // referring |SceneNodeDef| at which point the result will be memoized
+  // by |SnapshotNode| as usual so reentrance should not occur.
+  DCHECK(snapshot_->resolved_scene_contents_.find(referrer_node) ==
+         snapshot_->resolved_scene_contents_.end());
+
+  snapshot_->dependencies_.insert(scene->label().token());
+
+  const SceneContent* content = scene->FindContent(version);
+  if (!content) {
+    if (block_log_) {
+      *block_log_ << "Scene node blocked because its referenced scene is not "
+                     "available with the requested version: "
+                  << referrer_node->FormattedLabel(referrer_content)
+                  << ", scene " << scene->label().FormattedLabel()
+                  << ", requested version " << version << ", current version "
+                  << scene->version() << std::endl;
+    }
+    return Snapshot::Disposition::kBlocked;
+  }
+
+  const NodeDef* root = content->GetRootNodeIfExists();
+  if (!root) {
+    if (block_log_) {
+      *block_log_ << "Scene node blocked because its referenced scene has no "
+                     "root node: "
+                  << referrer_node->FormattedLabel(referrer_content)
+                  << ", scene " << content->FormattedLabel() << std::endl;
+    }
+    return Snapshot::Disposition::kBlocked;
+  }
+
+  snapshot_->resolved_scene_contents_[referrer_node] = content;
+  return SnapshotRootAndDetectCycles(root, content);
+}
+
+Snapshot::Disposition SnapshotBuilder::SnapshotRenderer(const SceneDef* scene) {
+  DCHECK(!snapshot_->root_scene_content_);
+
+  snapshot_->dependencies_.insert(scene->label().token());
+
+  const SceneContent* content =
+      scene->FindContent(mojo::gfx::composition::kSceneVersionNone);
+  if (!content) {
+    if (block_log_) {
+      *block_log_ << "Rendering blocked because the root scene has no content: "
+                  << scene->label().FormattedLabel() << std::endl;
+    }
+    return Snapshot::Disposition::kBlocked;
+  }
+
+  const NodeDef* root = content->GetRootNodeIfExists();
+  if (!root) {
+    if (block_log_) {
+      *block_log_ << "Rendering blocked the root scene has no root node: "
+                  << content->FormattedLabel() << std::endl;
+    }
+    return Snapshot::Disposition::kBlocked;
+  }
+
+  snapshot_->root_scene_content_ = content;
+  return SnapshotRootAndDetectCycles(root, content);
 }
 
 std::unique_ptr<Snapshot> SnapshotBuilder::Build(
-    SceneDef* root_scene,
+    const SceneDef* root_scene,
     const mojo::Rect& viewport,
     const mojo::gfx::composition::FrameInfo& frame_info) {
   DCHECK(snapshot_);
   DCHECK(root_scene);
 
-  SkRect sk_viewport =
-      SkRect::MakeXYWH(viewport.x, viewport.y, viewport.width, viewport.height);
-  RenderLayerBuilder layer_builder(&sk_viewport);
-  if (root_scene->Snapshot(this, &layer_builder)) {
+  Snapshot::Disposition disposition = SnapshotRenderer(root_scene);
+  DCHECK(!cycle_);  // must have properly unwound any cycles by now
+
+  if (disposition == Snapshot::Disposition::kSuccess) {
+    SkRect sk_viewport = SkRect::MakeXYWH(viewport.x, viewport.y,
+                                          viewport.width, viewport.height);
+    SkPictureRecorder recorder;
+    recorder.beginRecording(sk_viewport);
+
+    const NodeDef* root_node =
+        snapshot_->root_scene_content_->GetRootNodeIfExists();
+    DCHECK(root_node);  // otherwise would have failed to snapshot
+    root_node->RecordPicture(snapshot_->root_scene_content_.get(),
+                             snapshot_.get(), recorder.getRecordingCanvas());
+
     snapshot_->frame_ =
-        RenderFrame::Create(layer_builder.Build(), sk_viewport, frame_info);
+        RenderFrame::Create(skia::AdoptRef(recorder.endRecordingAsPicture()),
+                            sk_viewport, frame_info);
   } else {
-    snapshot_->valid_ = false;
+    snapshot_->ClearContent();
   }
   return std::move(snapshot_);
 }