ViewLayer: Lazy sync of scene data.

When a change happens which invalidates view layers the syncing will be postponed until the first usage.
This will improve importing or adding many objects in a single operation/script.

`BKE_view_layer_need_resync_tag` is used to tag the view layer to be out of sync. Before accessing
`BKE_view_layer_active_base_get`, `BKE_view_layer_active_object_get`, `BKE_view_layer_active_collection`
or `BKE_view_layer_object_bases` the caller should call `BKE_view_layer_synced_ensure`.

Having two functions ensures that partial syncing could be added as smaller patches in the future. Tagging a
view layer out of sync could be replaced with a partial sync. Eventually the number of full resyncs could be
reduced. After all tagging has been replaced with partial syncs the ensure_sync could be phased out.

This patch has been added to discuss the details and consequences of the current approach. For clarity
the call to BKE_view_layer_ensure_sync is placed close to the getters.
In the future this could be placed in more strategical places to reduce the number of calls or improve
performance. Finding those strategical places isn't that clear. When multiple operations are grouped
in a single script you might want to always check for resync.

Some areas found that can be improved. This list isn't complete.
These areas aren't addressed by this patch as these changes would be hard to detect to the reviewer.
The idea is to add changes to these areas as a separate patch. It might be that the initial commit would reduce
performance compared to master, but will be fixed by the additional patches.

**Object duplication**
During object duplication the syncing is temporarily disabled. With this patch this isn't useful as when disabled
the view_layer is accessed to locate bases. This can be improved by first locating the source bases, then duplicate
and sync and locate the new bases. Will be solved in a separate patch for clarity reasons ({D15886}).

**Object add**
`BKE_object_add` not only adds a new object, but also selects and activates the new base. This requires the
view_layer to be resynced. Some callers reverse the selection and activation (See `get_new_constraint_target`).
We should make the selection and activation optional. This would make it possible to add multiple objects
without having to resync per object.

**Postpone Activate Base**
Setting the basact is done in many locations. They follow a rule as after an action find the base and set
the basact. Finding the base could require a resync. The idea is to store in the view_layer the object which
base will be set in the basact during the next sync, reducing the times resyncing needs to happen.

Reviewed By: mont29

Maniphest Tasks: T73411

Differential Revision: https://developer.blender.org/D15885

1 files changed, 72 insertions, 39 deletions

diff --git a/source/blender/blenkernel/intern/layer.c b/source/blender/blenkernel/intern/layer.c
index a388df7efc9..d779fc4f512 100644
--- a/source/blender/blenkernel/intern/layer.c
+++ b/source/blender/blenkernel/intern/layer.c
@@ -284,11 +284,10 @@ void BKE_view_layer_free_ex(ViewLayer *view_layer, const bool do_id_user)
   MEM_freeN(view_layer);
 }
 
-void BKE_view_layer_selected_objects_tag(const Scene *UNUSED(scene),
-                                         ViewLayer *view_layer,
-                                         const int tag)
+void BKE_view_layer_selected_objects_tag(const Scene *scene, ViewLayer *view_layer, const int tag)
 {
-  LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
     if ((base->flag & BASE_SELECTED) != 0) {
       base->object->flag |= tag;
     }
@@ -311,9 +310,10 @@ static bool find_scene_collection_in_scene_collections(ListBase *lb, const Layer
   return false;
 }
 
-Object *BKE_view_layer_camera_find(const Scene *UNUSED(scene), ViewLayer *view_layer)
+Object *BKE_view_layer_camera_find(const Scene *scene, ViewLayer *view_layer)
 {
-  LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
     if (base->object->type == OB_CAMERA) {
       return base->object;
     }
@@ -381,6 +381,8 @@ static void view_layer_bases_hash_create(ViewLayer *view_layer, const bool do_ba
 
 Base *BKE_view_layer_base_find(ViewLayer *view_layer, Object *ob)
 {
+  BLI_assert_msg((view_layer->flag & VIEW_LAYER_OUT_OF_SYNC) == 0,
+                 "View layer out of sync, invoke BKE_view_layer_synced_ensure.");
   if (!view_layer->object_bases_hash) {
     view_layer_bases_hash_create(view_layer, false);
   }
@@ -388,11 +390,10 @@ Base *BKE_view_layer_base_find(ViewLayer *view_layer, Object *ob)
   return BLI_ghash_lookup(view_layer->object_bases_hash, ob);
 }
 
-void BKE_view_layer_base_deselect_all(const Scene *UNUSED(scene), ViewLayer *view_layer)
+void BKE_view_layer_base_deselect_all(const Scene *scene, ViewLayer *view_layer)
 {
-  Base *base;
-
-  for (base = view_layer->object_bases.first; base; base = base->next) {
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
     base->flag &= ~BASE_SELECTED;
   }
 }
@@ -504,7 +505,9 @@ void BKE_view_layer_copy_data(Scene *scene_dst,
   /* Copy layer collections and object bases. */
   /* Inline 'BLI_duplicatelist' and update the active base. */
   BLI_listbase_clear(&view_layer_dst->object_bases);
-  LISTBASE_FOREACH (Base *, base_src, &view_layer_src->object_bases) {
+  BLI_assert_msg((view_layer_src->flag & VIEW_LAYER_OUT_OF_SYNC) == 0,
+                 "View Layer Object Base out of sync, invoke BKE_view_layer_synced_ensure.");
+  LISTBASE_FOREACH (const Base *, base_src, &view_layer_src->object_bases) {
     Base *base_dst = MEM_dupallocN(base_src);
     BLI_addtail(&view_layer_dst->object_bases, base_dst);
     if (view_layer_src->basact == base_src) {
@@ -959,6 +962,19 @@ static void layer_collection_resync_unused_layers_free(ViewLayer *view_layer,
   }
 }
 
+void BKE_view_layer_need_resync_tag(struct ViewLayer *view_layer)
+{
+  view_layer->flag |= VIEW_LAYER_OUT_OF_SYNC;
+}
+
+void BKE_view_layer_synced_ensure(const Scene *scene, struct ViewLayer *view_layer)
+{
+  if (view_layer->flag & VIEW_LAYER_OUT_OF_SYNC) {
+    BKE_layer_collection_sync(scene, view_layer);
+    view_layer->flag &= ~VIEW_LAYER_OUT_OF_SYNC;
+  }
+}
+
 static void layer_collection_objects_sync(ViewLayer *view_layer,
                                           LayerCollection *layer,
                                           ListBase *r_lb_new_object_bases,
@@ -1052,8 +1068,14 @@ static void layer_collection_sync(ViewLayer *view_layer,
 
   BLI_assert(layer_resync->is_used);
 
+  uint64_t skipped_children = 0;
   LISTBASE_FOREACH (CollectionChild *, child, &layer_resync->collection->children) {
     Collection *child_collection = child->collection;
+    /* Collection relations may not have rebuild yet. */
+    if (child_collection == NULL) {
+      skipped_children++;
+      continue;
+    }
     LayerCollectionResync *child_layer_resync = layer_collection_resync_find(layer_resync,
                                                                              child_collection);
 
@@ -1158,7 +1180,7 @@ static void layer_collection_sync(ViewLayer *view_layer,
 
   /* Replace layer collection list with new one. */
   layer_resync->layer->layer_collections = new_lb_layer;
-  BLI_assert(BLI_listbase_count(&layer_resync->collection->children) ==
+  BLI_assert(BLI_listbase_count(&layer_resync->collection->children) - skipped_children ==
              BLI_listbase_count(&new_lb_layer));
 
   /* Update bases etc. for objects. */
@@ -1344,7 +1366,7 @@ void BKE_scene_collection_sync(const Scene *scene)
   }
 
   LISTBASE_FOREACH (ViewLayer *, view_layer, &scene->view_layers) {
-    BKE_layer_collection_sync(scene, view_layer);
+    BKE_view_layer_need_resync_tag(view_layer);
   }
 }
 
@@ -1422,6 +1444,7 @@ bool BKE_layer_collection_objects_select(const Scene *scene,
   bool changed = false;
 
   if (!(lc->flag & LAYER_COLLECTION_EXCLUDE)) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
     LISTBASE_FOREACH (CollectionObject *, cob, &lc->collection->gobject) {
       Base *base = BKE_view_layer_base_find(view_layer, cob->ob);
 
@@ -1458,6 +1481,7 @@ bool BKE_layer_collection_has_selected_objects(const Scene *scene,
   }
 
   if (!(lc->flag & LAYER_COLLECTION_EXCLUDE)) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
     LISTBASE_FOREACH (CollectionObject *, cob, &lc->collection->gobject) {
       Base *base = BKE_view_layer_base_find(view_layer, cob->ob);
 
@@ -1502,7 +1526,8 @@ void BKE_base_set_visible(Scene *scene, ViewLayer *view_layer, Base *base, bool
 {
   if (!extend) {
     /* Make only one base visible. */
-    LISTBASE_FOREACH (Base *, other, &view_layer->object_bases) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
+    LISTBASE_FOREACH (Base *, other, BKE_view_layer_object_bases_get(view_layer)) {
       other->flag |= BASE_HIDDEN;
     }
 
@@ -1513,7 +1538,7 @@ void BKE_base_set_visible(Scene *scene, ViewLayer *view_layer, Base *base, bool
     base->flag ^= BASE_HIDDEN;
   }
 
-  BKE_layer_collection_sync(scene, view_layer);
+  BKE_view_layer_need_resync_tag(view_layer);
 }
 
 bool BKE_base_is_visible(const View3D *v3d, const Base *base)
@@ -1592,7 +1617,7 @@ static void layer_collection_flag_unset_recursive(LayerCollection *lc, const int
   }
 }
 
-void BKE_layer_collection_isolate_global(Scene *scene,
+void BKE_layer_collection_isolate_global(Scene *UNUSED(scene),
                                          ViewLayer *view_layer,
                                          LayerCollection *lc,
                                          bool extend)
@@ -1637,7 +1662,7 @@ void BKE_layer_collection_isolate_global(Scene *scene,
     BKE_layer_collection_activate(view_layer, lc);
   }
 
-  BKE_layer_collection_sync(scene, view_layer);
+  BKE_view_layer_need_resync_tag(view_layer);
 }
 
 static void layer_collection_local_visibility_set_recursive(LayerCollection *layer_collection,
@@ -1658,7 +1683,8 @@ static void layer_collection_local_visibility_unset_recursive(LayerCollection *l
   }
 }
 
-static void layer_collection_local_sync(ViewLayer *view_layer,
+static void layer_collection_local_sync(const Scene *scene,
+                                        ViewLayer *view_layer,
                                         LayerCollection *layer_collection,
                                         const unsigned short local_collections_uuid,
                                         bool visible)
@@ -1673,6 +1699,7 @@ static void layer_collection_local_sync(ViewLayer *view_layer,
         continue;
       }
 
+      BKE_view_layer_synced_ensure(scene, view_layer);
       Base *base = BKE_view_layer_base_find(view_layer, cob->ob);
       base->local_collections_bits |= local_collections_uuid;
     }
@@ -1680,14 +1707,12 @@ static void layer_collection_local_sync(ViewLayer *view_layer,
 
   LISTBASE_FOREACH (LayerCollection *, child, &layer_collection->layer_collections) {
     if ((child->flag & LAYER_COLLECTION_EXCLUDE) == 0) {
-      layer_collection_local_sync(view_layer, child, local_collections_uuid, visible);
+      layer_collection_local_sync(scene, view_layer, child, local_collections_uuid, visible);
     }
   }
 }
 
-void BKE_layer_collection_local_sync(const Scene *UNUSED(scene),
-                                     ViewLayer *view_layer,
-                                     const View3D *v3d)
+void BKE_layer_collection_local_sync(const Scene *scene, ViewLayer *view_layer, const View3D *v3d)
 {
   if (no_resync) {
     return;
@@ -1696,12 +1721,13 @@ void BKE_layer_collection_local_sync(const Scene *UNUSED(scene),
   const unsigned short local_collections_uuid = v3d->local_collections_uuid;
 
   /* Reset flags and set the bases visible by default. */
-  LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
     base->local_collections_bits &= ~local_collections_uuid;
   }
 
   LISTBASE_FOREACH (LayerCollection *, layer_collection, &view_layer->layer_collections) {
-    layer_collection_local_sync(view_layer, layer_collection, local_collections_uuid, true);
+    layer_collection_local_sync(scene, view_layer, layer_collection, local_collections_uuid, true);
   }
 }
 
@@ -1772,33 +1798,39 @@ void BKE_layer_collection_isolate_local(
   BKE_layer_collection_local_sync(scene, view_layer, v3d);
 }
 
-static void layer_collection_bases_show_recursive(ViewLayer *view_layer, LayerCollection *lc)
+static void layer_collection_bases_show_recursive(const Scene *scene,
+                                                  ViewLayer *view_layer,
+                                                  LayerCollection *lc)
 {
   if ((lc->flag & LAYER_COLLECTION_EXCLUDE) == 0) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
     LISTBASE_FOREACH (CollectionObject *, cob, &lc->collection->gobject) {
       Base *base = BKE_view_layer_base_find(view_layer, cob->ob);
       base->flag &= ~BASE_HIDDEN;
     }
   }
   LISTBASE_FOREACH (LayerCollection *, lc_iter, &lc->layer_collections) {
-    layer_collection_bases_show_recursive(view_layer, lc_iter);
+    layer_collection_bases_show_recursive(scene, view_layer, lc_iter);
   }
 }
 
-static void layer_collection_bases_hide_recursive(ViewLayer *view_layer, LayerCollection *lc)
+static void layer_collection_bases_hide_recursive(const Scene *scene,
+                                                  ViewLayer *view_layer,
+                                                  LayerCollection *lc)
 {
   if ((lc->flag & LAYER_COLLECTION_EXCLUDE) == 0) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
     LISTBASE_FOREACH (CollectionObject *, cob, &lc->collection->gobject) {
       Base *base = BKE_view_layer_base_find(view_layer, cob->ob);
       base->flag |= BASE_HIDDEN;
     }
   }
   LISTBASE_FOREACH (LayerCollection *, lc_iter, &lc->layer_collections) {
-    layer_collection_bases_hide_recursive(view_layer, lc_iter);
+    layer_collection_bases_hide_recursive(scene, view_layer, lc_iter);
   }
 }
 
-void BKE_layer_collection_set_visible(const Scene *UNUSED(scene),
+void BKE_layer_collection_set_visible(const Scene *scene,
                                       ViewLayer *view_layer,
                                       LayerCollection *lc,
                                       const bool visible,
@@ -1807,11 +1839,11 @@ void BKE_layer_collection_set_visible(const Scene *UNUSED(scene),
   if (hierarchy) {
     if (visible) {
       layer_collection_flag_unset_recursive(lc, LAYER_COLLECTION_HIDE);
-      layer_collection_bases_show_recursive(view_layer, lc);
+      layer_collection_bases_show_recursive(scene, view_layer, lc);
     }
     else {
       layer_collection_flag_set_recursive(lc, LAYER_COLLECTION_HIDE);
-      layer_collection_bases_hide_recursive(view_layer, lc);
+      layer_collection_bases_hide_recursive(scene, view_layer, lc);
     }
   }
   else {
@@ -1906,6 +1938,7 @@ bool BKE_view_layer_has_collection(const ViewLayer *view_layer, const Collection
 bool BKE_scene_has_object(Scene *scene, Object *ob)
 {
   LISTBASE_FOREACH (ViewLayer *, view_layer, &scene->view_layers) {
+    BKE_view_layer_synced_ensure(scene, view_layer);
     Base *base = BKE_view_layer_base_find(view_layer, ob);
     if (base) {
       return true;
@@ -1945,7 +1978,7 @@ static void object_bases_iterator_begin(BLI_Iterator *iter, void *data_in_v, con
   ObjectsVisibleIteratorData *data_in = data_in_v;
   ViewLayer *view_layer = data_in->view_layer;
   const View3D *v3d = data_in->v3d;
-  Base *base = view_layer->object_bases.first;
+  Base *base = BKE_view_layer_object_bases_get(view_layer)->first;
 
   /* when there are no objects */
   if (base == NULL) {
@@ -2244,18 +2277,19 @@ void BKE_base_eval_flags(Base *base)
 }
 
 static void layer_eval_view_layer(struct Depsgraph *depsgraph,
-                                  struct Scene *UNUSED(scene),
+                                  struct Scene *scene,
                                   ViewLayer *view_layer)
 {
   DEG_debug_print_eval(depsgraph, __func__, view_layer->name, view_layer);
 
   /* Create array of bases, for fast index-based lookup. */
-  const int num_object_bases = BLI_listbase_count(&view_layer->object_bases);
+  BKE_view_layer_synced_ensure(scene, view_layer);
+  const int num_object_bases = BLI_listbase_count(BKE_view_layer_object_bases_get(view_layer));
   MEM_SAFE_FREE(view_layer->object_bases_array);
   view_layer->object_bases_array = MEM_malloc_arrayN(
       num_object_bases, sizeof(Base *), "view_layer->object_bases_array");
   int base_index = 0;
-  LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+  LISTBASE_FOREACH (Base *, base, BKE_view_layer_object_bases_get(view_layer)) {
     view_layer->object_bases_array[base_index++] = base;
   }
 }
@@ -2285,12 +2319,11 @@ static void write_layer_collections(BlendWriter *writer, ListBase *lb)
   }
 }
 
-void BKE_view_layer_blend_write(BlendWriter *writer,
-                                const Scene *UNUSED(scene),
-                                ViewLayer *view_layer)
+void BKE_view_layer_blend_write(BlendWriter *writer, const Scene *scene, ViewLayer *view_layer)
 {
+  BKE_view_layer_synced_ensure(scene, view_layer);
   BLO_write_struct(writer, ViewLayer, view_layer);
-  BLO_write_struct_list(writer, Base, &view_layer->object_bases);
+  BLO_write_struct_list(writer, Base, BKE_view_layer_object_bases_get(view_layer));
 
   if (view_layer->id_properties) {
     IDP_BlendWrite(writer, view_layer->id_properties);