Depsgraph: Adds helpers to extract/restore despgraphs in a given Main.

Extract will steal all depsgraphs currently stored in given bmain, and
restore will put them back in place, using scene and viewlayers as keys.

Preliminary work for undo-speedup.

Part of T60695/D6580.

1 files changed, 23 insertions, 0 deletions

diff --git a/source/blender/depsgraph/intern/depsgraph.cc b/source/blender/depsgraph/intern/depsgraph.cc
index ce6797939b5..a19a2958f28 100644
--- a/source/blender/depsgraph/intern/depsgraph.cc
+++ b/source/blender/depsgraph/intern/depsgraph.cc
@@ -285,6 +285,29 @@ Depsgraph *DEG_graph_new(Main *bmain, Scene *scene, ViewLayer *view_layer, eEval
   return reinterpret_cast<Depsgraph *>(deg_depsgraph);
 }
 
+/* Replace the "owner" pointers (currently Main/Scene/ViewLayer) of this depsgraph.
+ * Used during undo steps when we do want to re-use the old depsgraph data as much as possible. */
+void DEG_graph_replace_owners(struct Depsgraph *depsgraph,
+                              Main *bmain,
+                              Scene *scene,
+                              ViewLayer *view_layer)
+{
+  DEG::Depsgraph *deg_graph = reinterpret_cast<DEG::Depsgraph *>(depsgraph);
+
+  const bool do_update_register = deg_graph->bmain != bmain;
+  if (do_update_register && deg_graph->bmain != NULL) {
+    DEG::unregister_graph(deg_graph);
+  }
+
+  deg_graph->bmain = bmain;
+  deg_graph->scene = scene;
+  deg_graph->view_layer = view_layer;
+
+  if (do_update_register) {
+    DEG::register_graph(deg_graph);
+  }
+}
+
 /* Free graph's contents and graph itself */
 void DEG_graph_free(Depsgraph *graph)
 {