Outliner: Port view layer elements to new tree-element code design

No user visible changes expected.

Part of #96713, continuation of work started in 249e4df110 and 2e221de4ce.
Refer to these for a motivation and design overview.

Adds a new class for view layer elements.

Pull Request: https://projects.blender.org/blender/blender/pulls/110920

source/blender/editors/space_outliner/outliner_intern.hh

@@ -315,6 +315,11 @@ struct ParticleSystemElementCreateData {
   ParticleSystem *psys;
 };
 
+struct ViewLayerElementCreateData {
+  Scene *scene;
+  ViewLayer *view_layer;
+};
+
 TreeTraversalAction outliner_collect_selected_collections(TreeElement *te, void *customdata);
 TreeTraversalAction outliner_collect_selected_objects(TreeElement *te, void *customdata);
 

source/blender/editors/space_outliner/outliner_tree.cc

@@ -258,6 +258,9 @@ TreeElement *outliner_add_element(SpaceOutliner *space_outliner,
   else if (type == TSE_LINKED_PSYS) {
     id = &static_cast<ParticleSystemElementCreateData *>(idv)->object->id;
   }
+  else if (type == TSE_R_LAYER) {
+    id = &static_cast<ViewLayerElementCreateData *>(idv)->scene->id;
+  }
 
   /* exceptions */
   if (ELEM(type, TSE_ID_BASE, TSE_GENERIC_LABEL)) {
@@ -325,7 +328,7 @@ TreeElement *outliner_add_element(SpaceOutliner *space_outliner,
   else if (type == TSE_LINKED_PSYS) {
     /* pass */
   }
-  else if (ELEM(type, TSE_R_LAYER_BASE)) {
+  else if (ELEM(type, TSE_R_LAYER, TSE_R_LAYER_BASE)) {
     /* pass */
   }
   else if (type == TSE_SOME_ID) {
@@ -383,6 +386,7 @@ TreeElement *outliner_add_element(SpaceOutliner *space_outliner,
                 TSE_DEFGROUP_BASE,
                 TSE_GPENCIL_EFFECT,
                 TSE_GPENCIL_EFFECT_BASE,
+                TSE_R_LAYER,
                 TSE_R_LAYER_BASE))
   {
     BLI_assert_msg(false, "Element type should already use new AbstractTreeElement design");

source/blender/editors/space_outliner/tree/tree_element.cc

@@ -80,6 +80,11 @@ std::unique_ptr<AbstractTreeElement> AbstractTreeElement::createFromType(const i
       return std::make_unique<TreeElementGPencilLayer>(legacy_te, *static_cast<bGPDlayer *>(idv));
     case TSE_R_LAYER_BASE:
       return std::make_unique<TreeElementViewLayerBase>(legacy_te, *static_cast<Scene *>(idv));
+    case TSE_R_LAYER: {
+      ViewLayerElementCreateData *view_layer_data = static_cast<ViewLayerElementCreateData *>(idv);
+      return std::make_unique<TreeElementViewLayer>(
+          legacy_te, *view_layer_data->scene, *view_layer_data->view_layer);
+    }
     case TSE_SCENE_COLLECTION_BASE:
       return std::make_unique<TreeElementCollectionBase>(legacy_te, *static_cast<Scene *>(idv));
     case TSE_SCENE_OBJECTS_BASE:

source/blender/editors/space_outliner/tree/tree_element_view_layer.cc

@@ -30,11 +30,21 @@ TreeElementViewLayerBase::TreeElementViewLayerBase(TreeElement &legacy_te, Scene
 void TreeElementViewLayerBase::expand(SpaceOutliner &space_outliner) const
 {
   for (auto *view_layer : ListBaseWrapper<ViewLayer>(scene_.view_layers)) {
-    TreeElement *tenlay = outliner_add_element(
+    ViewLayerElementCreateData view_layer_data = {&scene_, view_layer};
-        &space_outliner, &legacy_te_.subtree, &scene_, &legacy_te_, TSE_R_LAYER, 0);
+
-    tenlay->name = view_layer->name;
+    outliner_add_element(
-    tenlay->directdata = view_layer;
+        &space_outliner, &legacy_te_.subtree, &view_layer_data, &legacy_te_, TSE_R_LAYER, 0);
   }
 }
 
+TreeElementViewLayer::TreeElementViewLayer(TreeElement &legacy_te,
+                                           Scene & /* scene */,
+                                           ViewLayer &view_layer)
+    : AbstractTreeElement(legacy_te), /* scene_(scene), */ view_layer_(view_layer)
+{
+  BLI_assert(legacy_te.store_elem->type == TSE_R_LAYER);
+  legacy_te.name = view_layer_.name;
+  legacy_te.directdata = &view_layer_;
+}
+
 }  // namespace blender::ed::outliner

source/blender/editors/space_outliner/tree/tree_element_view_layer.hh

@@ -21,4 +21,13 @@ class TreeElementViewLayerBase final : public AbstractTreeElement {
   void expand(SpaceOutliner &) const override;
 };
 
+class TreeElementViewLayer final : public AbstractTreeElement {
+  /* Not needed right now, avoid unused member variable warning. */
+  // Scene &scene_;
+  ViewLayer &view_layer_;
+
+ public:
+  TreeElementViewLayer(TreeElement &legacy_te, Scene &scene, ViewLayer &view_layer);
+};
+
 }  // namespace blender::ed::outliner