Mozart: Improve internal scene graph representation.

services/gfx/compositor/graph/scene_content.h

+// Copyright 2016 The Chromium 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 SERVICES_GFX_COMPOSITOR_GRAPH_SCENE_CONTENT_H_
+#define SERVICES_GFX_COMPOSITOR_GRAPH_SCENE_CONTENT_H_
+
+#include <iosfwd>
+#include <unordered_map>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "mojo/services/gfx/composition/interfaces/scenes.mojom.h"
+#include "services/gfx/compositor/graph/node_def.h"
+#include "services/gfx/compositor/graph/resource_def.h"
+#include "services/gfx/compositor/graph/scene_label.h"
+
+namespace compositor {
+
+class SceneContentBuilder;
+class SceneDef;
+
+// Represents the content of a particular published version of a scene.
+//
+// Holds a resource and node table which describes the content of a
+// scene as it was when a particular version was published.  Only the
+// internal state of the scene is described; links to other scenes are
+// not resolved at this level.
+//
+// Once fully constructed, instances of this class are immutable and
+// reference counted so they may be bound to scene references in other scenes.
+//
+// TODO(jeffbrown): To improve efficiency, we could replace the hash tables
+// with a vector of internally linked graph edges.  This is relatively easy
+// since the traversal order is well-known and we could even build some kind
+// of hierarchical iterator to walk the graph starting from the root.
+class SceneContent : public base::RefCounted<SceneContent> {
+ public:
+  // Gets the scene label.
+  const SceneLabel& label() const { return label_; }
+  std::string FormattedLabel() const {
+    return label_.FormattedLabelForVersion(version_);
+  }
+  std::string FormattedLabelForNode(uint32_t node_id) const {
+    return label_.FormattedLabelForNode(version_, node_id);
+  }
+
+  // Gets the version of the scene represented by this object.
+  uint32_t version() const { return version_; }
+
+  // Gets the requested resource, never null because it must be present.
+  const ResourceDef* GetResource(uint32_t resource_id,
+                                 ResourceDef::Type resource_type) const;
+
+  // Gets the requested node, never null because it must be present.
+  const NodeDef* GetNode(uint32_t node_id) const;
+
+  // Gets the root node if it exists, otherwise returns nullptr.
+  const NodeDef* GetRootNodeIfExists() const;
+
+ private:
+  friend class base::RefCounted<SceneContent>;
+  friend class SceneContentBuilder;
+  SceneContent(const SceneLabel& label,
+               uint32_t version,
+               size_t max_resources,
+               size_t max_nodes);
+  ~SceneContent();
+
+  const SceneLabel label_;
+  const uint32_t version_;
+  std::unordered_map<uint32_t, scoped_refptr<const ResourceDef>> resources_;
+  std::unordered_map<uint32_t, scoped_refptr<const NodeDef>> nodes_;
+
+  DISALLOW_COPY_AND_ASSIGN(SceneContent);
+};
+
+// Builds a table of all of the nodes and resources that make up the
+// content of a particular version of a scene.
+class SceneContentBuilder {
+ public:
+  SceneContentBuilder(const SceneDef* scene,
+                      uint32_t version,
+                      std::ostream& err,
+                      size_t max_resources,
+                      size_t max_nodes);
+  ~SceneContentBuilder();
+
+  // Stream for reporting validation error messages.
+  std::ostream& err() { return err_; }
+
+  // Ensures the requested resource is part of the retained scene graph and
+  // returns a reference to it, or nullptr if an error occurred.
+  const ResourceDef* RequireResource(uint32_t resource_id,
+                                     ResourceDef::Type resource_type,
+                                     uint32_t referrer_node_id);
+
+  // Ensures the requested node is part of the retained scene graph and
+  // returns a reference to it, or nullptr if an error occurred.
+  const NodeDef* RequireNode(uint32_t node_id, uint32_t referrer_node_id);
+
+  // Builds the content graph.
+  // Returns nullptr if an error occurred.
+  scoped_refptr<const SceneContent> Build();
+
+ private:
+  bool AddNode(const NodeDef* node);
+
+  scoped_refptr<SceneContent> content_;
+  const SceneDef* scene_;
+  std::ostream& err_;
+};
+
+}  // namespace compositor
+
+#endif  // SERVICES_GFX_COMPOSITOR_GRAPH_SCENE_CONTENT_H_