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

3 files changed, 16 insertions, 6 deletions

diff --git a/source/blender/draw/engines/overlay/overlay_extra.c b/source/blender/draw/engines/overlay/overlay_extra.c
index 8211b2f0490..5d80ab3d0ea 100644
--- a/source/blender/draw/engines/overlay/overlay_extra.c
+++ b/source/blender/draw/engines/overlay/overlay_extra.c
@@ -1485,10 +1485,11 @@ static void OVERLAY_volume_extra(OVERLAY_ExtraCallBuffers *cb,
 static void OVERLAY_object_center(OVERLAY_ExtraCallBuffers *cb,
                                   Object *ob,
                                   OVERLAY_PrivateData *pd,
+                                  const Scene *scene,
                                   ViewLayer *view_layer)
 {
   const bool is_library = ID_REAL_USERS(&ob->id) > 1 || ID_IS_LINKED(ob);
-
+  BKE_view_layer_synced_ensure(scene, view_layer);
   if (ob == BKE_view_layer_active_object_get(view_layer)) {
     DRW_buffer_add_entry(cb->center_active, ob->obmat[3]);
   }
@@ -1573,7 +1574,7 @@ void OVERLAY_extra_cache_populate(OVERLAY_Data *vedata, Object *ob)
   /* don't show object extras in set's */
   if (!from_dupli) {
     if (draw_obcenters) {
-      OVERLAY_object_center(cb, ob, pd, view_layer);
+      OVERLAY_object_center(cb, ob, pd, scene, view_layer);
     }
     if (draw_relations) {
       OVERLAY_relationship_lines(cb, draw_ctx->depsgraph, draw_ctx->scene, ob);
diff --git a/source/blender/draw/intern/draw_common.c b/source/blender/draw/intern/draw_common.c
index de56b34df78..c1b4c3c1f81 100644
--- a/source/blender/draw/intern/draw_common.c
+++ b/source/blender/draw/intern/draw_common.c
@@ -280,10 +280,11 @@ int DRW_object_wire_theme_get(Object *ob, ViewLayer *view_layer, float **r_color
 {
   const DRWContextState *draw_ctx = DRW_context_state_get();
   const bool is_edit = (draw_ctx->object_mode & OB_MODE_EDIT) && (ob->mode & OB_MODE_EDIT);
-  const bool active = view_layer->basact &&
-                      ((ob->base_flag & BASE_FROM_DUPLI) ?
-                           (DRW_object_get_dupli_parent(ob) == view_layer->basact->object) :
-                           (view_layer->basact->object == ob));
+  BKE_view_layer_synced_ensure(draw_ctx->scene, view_layer);
+  const Base *base = BKE_view_layer_active_base_get(view_layer);
+  const bool active = base && ((ob->base_flag & BASE_FROM_DUPLI) ?
+                                   (DRW_object_get_dupli_parent(ob) == base->object) :
+                                   (base->object == ob));
 
   /* confusing logic here, there are 2 methods of setting the color
    * 'colortab[colindex]' and 'theme_id', colindex overrides theme_id.
diff --git a/source/blender/draw/intern/draw_manager.c b/source/blender/draw/intern/draw_manager.c
index 493fa4d5744..9761aa8c789 100644
--- a/source/blender/draw/intern/draw_manager.c
+++ b/source/blender/draw/intern/draw_manager.c
@@ -1324,6 +1324,7 @@ void DRW_notify_view_update(const DRWUpdateContext *update_ctx)
   /* Reset before using it. */
   drw_state_prepare_clean_for_draw(&DST);
 
+  BKE_view_layer_synced_ensure(scene, view_layer);
   DST.draw_ctx = (DRWContextState){
       .region = region,
       .rv3d = rv3d,
@@ -1377,6 +1378,7 @@ static void drw_notify_view_update_offscreen(struct Depsgraph *depsgraph,
     /* Reset before using it. */
     drw_state_prepare_clean_for_draw(&DST);
 
+    BKE_view_layer_synced_ensure(scene, view_layer);
     DST.draw_ctx = (DRWContextState){
         .region = region,
         .rv3d = rv3d,
@@ -1629,6 +1631,7 @@ void DRW_draw_render_loop_ex(struct Depsgraph *depsgraph,
   ViewLayer *view_layer = DEG_get_evaluated_view_layer(depsgraph);
   RegionView3D *rv3d = region->regiondata;
 
+  BKE_view_layer_synced_ensure(scene, view_layer);
   DST.draw_ctx.evil_C = evil_C;
   DST.draw_ctx = (DRWContextState){
       .region = region,
@@ -2143,6 +2146,7 @@ void DRW_draw_render_loop_2d_ex(struct Depsgraph *depsgraph,
   Scene *scene = DEG_get_evaluated_scene(depsgraph);
   ViewLayer *view_layer = DEG_get_evaluated_view_layer(depsgraph);
 
+  BKE_view_layer_synced_ensure(scene, view_layer);
   DST.draw_ctx.evil_C = evil_C;
   DST.draw_ctx = (DRWContextState){
       .region = region,
@@ -2349,6 +2353,8 @@ void DRW_draw_select_loop(struct Depsgraph *depsgraph,
   Scene *scene = DEG_get_evaluated_scene(depsgraph);
   RenderEngineType *engine_type = ED_view3d_engine_type(scene, v3d->shading.type);
   ViewLayer *view_layer = DEG_get_evaluated_view_layer(depsgraph);
+
+  BKE_view_layer_synced_ensure(scene, view_layer);
   Object *obact = BKE_view_layer_active_object_get(view_layer);
   Object *obedit = use_obedit_skip ? NULL : OBEDIT_FROM_OBACT(obact);
 #ifndef USE_GPU_SELECT
@@ -2580,6 +2586,7 @@ static void drw_draw_depth_loop_impl(struct Depsgraph *depsgraph,
   DST.options.is_depth = true;
 
   /* Instead of 'DRW_context_state_init(C, &DST.draw_ctx)', assign from args */
+  BKE_view_layer_synced_ensure(scene, view_layer);
   DST.draw_ctx = (DRWContextState){
       .region = region,
       .rv3d = rv3d,
@@ -2713,6 +2720,7 @@ void DRW_draw_select_id(Depsgraph *depsgraph, ARegion *region, View3D *v3d, cons
   drw_state_prepare_clean_for_draw(&DST);
 
   /* Instead of 'DRW_context_state_init(C, &DST.draw_ctx)', assign from args */
+  BKE_view_layer_synced_ensure(scene, view_layer);
   DST.draw_ctx = (DRWContextState){
       .region = region,
       .rv3d = region->regiondata,