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diff --git a/source/blender/editors/space_outliner/tree/tree_display.hh b/source/blender/editors/space_outliner/tree/tree_display.hh
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+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup spoutliner
+ *
+ * \brief Establish and manage Outliner trees for different display modes.
+ *
+ * Each Outliner display mode (e.g View Layer, Scenes, Blender File) is implemented as a
+ * tree-display class with the #AbstractTreeDisplay interface.
+ *
+ * Their main responsibility is building the Outliner tree for a display mode. For that, they
+ * implement the #buildTree() function, which based on Blender data (#TreeSourceData), builds a
+ * custom tree of whatever data it wants to visualize.
+ * Further, they can implement display mode dependent queries and general operations using the
+ * #AbstractTreeDisplay abstraction as common interface.
+ *
+ * Outliners keep the current tree-display object alive until the next full tree rebuild to keep
+ * access to it.
+ */
+
+#pragma once
+
+#include "tree_display.h"
+
+struct ListBase;
+struct Main;
+struct SpaceOutliner;
+struct TreeElement;
+struct TreeSourceData;
+
+namespace blender::ed::outliner {
+
+/* -------------------------------------------------------------------- */
+/* Tree-Display Interface */
+
+/**
+ * \brief Base Class For Tree-Displays
+ *
+ * Abstract base class defining the interface for tree-display variants.
+ */
+class AbstractTreeDisplay {
+ public:
+  AbstractTreeDisplay(SpaceOutliner &space_outliner) : space_outliner_(space_outliner)
+  {
+  }
+  virtual ~AbstractTreeDisplay() = default;
+
+  /**
+   * Build a tree for this display mode with the Blender context data given in \a source_data and
+   * the view settings in \a space_outliner.
+   */
+  virtual ListBase buildTree(const TreeSourceData &source_data) = 0;
+
+ protected:
+  /** All derived classes will need a handle to this, so storing it in the base for convenience. */
+  SpaceOutliner &space_outliner_;
+};
+
+/* -------------------------------------------------------------------- */
+/* View Layer Tree-Display */
+
+/**
+ * \brief Tree-Display for the View Layer display mode.
+ */
+class TreeDisplayViewLayer final : public AbstractTreeDisplay {
+  ViewLayer *view_layer_ = nullptr;
+  bool show_objects_ = true;
+
+ public:
+  TreeDisplayViewLayer(SpaceOutliner &space_outliner);
+
+  ListBase buildTree(const TreeSourceData &source_data) override;
+
+ private:
+  void add_view_layer(ListBase &, TreeElement &);
+  void add_layer_collections_recursive(ListBase &, ListBase &, TreeElement &);
+  void add_layer_collection_objects(ListBase &, LayerCollection &, TreeElement &);
+  void add_layer_collection_objects_children(TreeElement &);
+};
+
+/* -------------------------------------------------------------------- */
+/* Library Tree-Display */
+
+/**
+ * \brief Tree-Display for the Libraries display mode.
+ */
+class TreeDisplayLibraries final : public AbstractTreeDisplay {
+ public:
+  TreeDisplayLibraries(SpaceOutliner &space_outliner);
+
+  ListBase buildTree(const TreeSourceData &source_data) override;
+
+ private:
+  TreeElement *add_library_contents(Main &, ListBase &, Library *) const;
+  bool library_id_filter_poll(Library *lib, ID *id) const;
+  short id_filter_get() const;
+};
+
+}  // namespace blender::ed::outliner