Cycles: introduce an ownership system to protect nodes from unwanted deletions.

Problem: the Blender synchronization process creates and tags nodes for usage. It does
this by directly adding and removing nodes from the scene data. If some node is not tagged
as used at the end of a synchronization, it then deletes the node from the scene. This poses
a problem when it comes to supporting procedural nodes who can create other nodes not known
by the Blender synchonization system, which will remove them.

Nodes now have a NodeOwner, which is set after creation. Those owners for now are the Scene
for scene level nodes and ShaderGraph for shader nodes. Instead of creating and deleting
nodes using `new` and `delete` explicitely, we now use `create_node` and `delete_node` methods
found on the owners. `delete_node` will assert that the owner is the right one.

Whenever a scene level node is created or deleted, the appropriate node manager is tagged for
an update, freeing this responsability from BlenderSync or other software exporters.

Concerning BlenderSync, the `id_maps` do not explicitely manipulate scene data anymore, they
only keep track of which nodes are used, employing the scene to create and delete them. To
achieve this, the ParticleSystem is now a Node, although it does not have any sockets.

This is part of T79131.

Reviewed By: #cycles, brecht

Maniphest Tasks: T79131

Differential Revision: https://developer.blender.org/D8540

1 files changed, 71 insertions, 1 deletions

diff --git a/intern/cycles/render/scene.h b/intern/cycles/render/scene.h
index 25b6b2ef0e4..0e32a70952b 100644
--- a/intern/cycles/render/scene.h
+++ b/intern/cycles/render/scene.h
@@ -59,6 +59,7 @@ class Progress;
 class BakeManager;
 class BakeData;
 class RenderStats;
+class Volume;
 
 /* Scene Device Data */
 
@@ -212,7 +213,7 @@ class SceneParams {
 
 /* Scene */
 
-class Scene {
+class Scene : public NodeOwner {
  public:
   /* Optional name. Is used for logging and reporting. */
   string name;
@@ -281,6 +282,40 @@ class Scene {
 
   bool update(Progress &progress, bool &kernel_switch_needed);
 
+  /* This function is used to create a node of a specified type instead of
+   * calling 'new', and sets the scene as the owner of the node.
+   * The function has overloads that will also add the created node to the right
+   * node array (e.g. Scene::geometry for Geometry nodes) and tag the appropriate
+   * manager for an update.
+   */
+  template<typename T, typename... Args> T *create_node(Args &&... args)
+  {
+    T *node = new T(args...);
+    node->set_owner(this);
+    return node;
+  }
+
+  /* This function is used to delete a node from the scene instead of calling 'delete'
+   * and manually removing the node from the data array. It also tags the
+   * appropriate manager for an update, if any, and checks that the scene is indeed
+   * the owner of the node. Calling this function on a node not owned by the scene
+   * will likely cause a crash which we want in order to detect such cases.
+   */
+  template<typename T> void delete_node(T *node)
+  {
+    assert(node->get_owner() == this);
+    delete_node_impl(node);
+  }
+
+  /* Same as above, but specify the actual owner.
+   */
+  template<typename T> void delete_node(T *node, const NodeOwner *owner)
+  {
+    assert(node->get_owner() == owner);
+    delete_node_impl(node);
+    (void)owner;
+  }
+
  protected:
   /* Check if some heavy data worth logging was updated.
    * Mainly used to suppress extra annoying logging.
@@ -303,8 +338,43 @@ class Scene {
 
   /* Get maximum number of closures to be used in kernel. */
   int get_max_closure_count();
+
+  template<typename T> void delete_node_impl(T *node)
+  {
+    delete node;
+  }
 };
 
+template<> Light *Scene::create_node<Light>();
+
+template<> Mesh *Scene::create_node<Mesh>();
+
+template<> Object *Scene::create_node<Object>();
+
+template<> Hair *Scene::create_node<Hair>();
+
+template<> Volume *Scene::create_node<Volume>();
+
+template<> ParticleSystem *Scene::create_node<ParticleSystem>();
+
+template<> Shader *Scene::create_node<Shader>();
+
+template<> void Scene::delete_node_impl(Light *node);
+
+template<> void Scene::delete_node_impl(Mesh *node);
+
+template<> void Scene::delete_node_impl(Volume *node);
+
+template<> void Scene::delete_node_impl(Hair *node);
+
+template<> void Scene::delete_node_impl(Geometry *node);
+
+template<> void Scene::delete_node_impl(Object *node);
+
+template<> void Scene::delete_node_impl(ParticleSystem *node);
+
+template<> void Scene::delete_node_impl(Shader *node);
+
 CCL_NAMESPACE_END
 
 #endif /*  __SCENE_H__ */