Depsgraph: Support changing scene's render engine

source/blender/depsgraph/intern/eval/deg_eval_copy_on_write.cc

@@ -547,9 +547,11 @@ void update_copy_on_write_scene(const Depsgraph *depsgraph,
 	else {
 		scene_cow->obedit = NULL;
 	}
-	// TODO(sergey): Things which are still missing here:
-	// - Active render engine.
-	// - Something else?
+	/* Synchronize active render engine. */
+	BLI_strncpy_utf8(scene_cow->r.engine,
+	                 scene_orig->r.engine,
+	                 sizeof(scene_cow->r.engine));
+	/* TODO(sergey): What else do we need here? */
 }
 
 /* Update copy-on-write version of armature object from original scene. */

source/blender/makesrna/intern/rna_scene.c

@@ -1569,9 +1569,12 @@ static void rna_RenderSettings_engine_set(PointerRNA *ptr, int value)
 {
 	RenderData *rd = (RenderData *)ptr->data;
 	RenderEngineType *type = BLI_findlink(&R_engines, value);
+	Scene *scene = (Scene *)ptr->id.data;
 
 	if (type)
 		BLI_strncpy_utf8(rd->engine, type->idname, sizeof(rd->engine));
+
+	DEG_id_tag_update(&scene->id, DEG_TAG_COPY_ON_WRITE);
 }
 
 static EnumPropertyItem *rna_RenderSettings_engine_itemf(