UI: Support persistent view state, write tree-view height to files

Adds support for saving some view state persistently and uses this to keep the
height of a tree-view, even as the region containing it is hidden, or the file
re-loaded.

Fixes #129058.

Basically the design is to have state stored in the region, so it can be saved
to files. Views types (tree-view, grid-view, etc) can decide themselves if they
have state to be preserved, and what state that is. If a view wants to preserve
state, it's stored in a list inside the region, identified by the view's idname.

Limitation is that multiple instances of the same view would share these bits of
state, in practice I don't think that's ever an issue.

More state can be added to be preserved as needed. Since different kinds of
views may require different state, I was thinking we could add ID properties to
`uiViewState` even, making it much more dynamic.

Pull Request: https://projects.blender.org/blender/blender/pulls/130292

source/blender/blenkernel/intern/screen.cc

@@ -369,6 +369,8 @@ ARegion *BKE_area_region_copy(const SpaceType *st, const ARegion *region)
 
   BLI_listbase_clear(&newar->ui_previews);
   BLI_duplicatelist(&newar->ui_previews, &region->ui_previews);
+  BLI_listbase_clear(&newar->view_states);
+  BLI_duplicatelist(&newar->view_states, &region->view_states);
 
   return newar;
 }
@@ -610,6 +612,7 @@ void BKE_area_region_free(SpaceType *st, ARegion *region)
   BLI_freelistN(&region->ui_previews);
   BLI_freelistN(&region->panels_category);
   BLI_freelistN(&region->panels_category_active);
+  BLI_freelistN(&region->view_states);
 }
 
 void BKE_screen_area_free(ScrArea *area)
@@ -1143,6 +1146,10 @@ static void write_area(BlendWriter *writer, ScrArea *area)
     LISTBASE_FOREACH (uiPreview *, ui_preview, &region->ui_previews) {
       BLO_write_struct(writer, uiPreview, ui_preview);
     }
+
+    LISTBASE_FOREACH (uiViewStateLink *, view_state, &region->view_states) {
+      BLO_write_struct(writer, uiViewStateLink, view_state);
+    }
   }
 
   LISTBASE_FOREACH (SpaceLink *, sl, &area->spacedata) {
@@ -1199,6 +1206,7 @@ static void direct_link_region(BlendDataReader *reader, ARegion *region, int spa
   BLO_read_struct_list(reader, PanelCategoryStack, &region->panels_category_active);
 
   BLO_read_struct_list(reader, uiList, &region->ui_lists);
+  BLO_read_struct_list(reader, uiViewStateLink, &region->view_states);
 
   /* The area's search filter is runtime only, so we need to clear the active flag on read. */
   /* Clear runtime flags (e.g. search filter is runtime only). */

source/blender/editors/asset/intern/asset_shelf.cc

@@ -527,8 +527,7 @@ void region_layout(const bContext *C, ARegion *region)
                                      0,
                                      style);
 
-  build_asset_view(
-      *layout, active_shelf->settings.asset_library_reference, *active_shelf, *C, *region);
+  build_asset_view(*layout, active_shelf->settings.asset_library_reference, *active_shelf, *C);
 
   int layout_height;
   UI_block_layout_resolve(block, nullptr, &layout_height);

source/blender/editors/asset/intern/asset_shelf.hh

@@ -31,8 +31,7 @@ namespace blender::ed::asset::shelf {
 void build_asset_view(uiLayout &layout,
                       const AssetLibraryReference &library_ref,
                       const AssetShelf &shelf,
-                      const bContext &C,
-                      const ARegion &region);
+                      const bContext &C);
 
 void catalog_selector_panel_register(ARegionType *region_type);
 void popover_panel_register(ARegionType *region_type);

source/blender/editors/asset/intern/asset_shelf_asset_view.cc

@@ -345,8 +345,7 @@ static std::string filter_string_get(const AssetShelf &shelf)
 void build_asset_view(uiLayout &layout,
                       const AssetLibraryReference &library_ref,
                       const AssetShelf &shelf,
-                      const bContext &C,
-                      const ARegion &region)
+                      const bContext &C)
 {
   list::storage_fetch(&library_ref, &C);
   list::previews_fetch(&library_ref, &C);
@@ -371,7 +370,7 @@ void build_asset_view(uiLayout &layout,
   grid_view->set_context_menu_title("Asset Shelf");
 
   ui::GridViewBuilder builder(*block);
-  builder.build_grid_view(C, *grid_view, region.v2d, layout, filter_string_get(shelf));
+  builder.build_grid_view(C, *grid_view, layout, filter_string_get(shelf));
 }
 
 /* ---------------------------------------------------------------------- */

source/blender/editors/asset/intern/asset_shelf_catalog_selector.cc

@@ -215,7 +215,7 @@ static void catalog_selector_panel_draw(const bContext *C, Panel *panel)
       "asset catalog tree view",
       std::make_unique<AssetCatalogSelectorTree>(*library, *shelf));
   tree_view->set_context_menu_title("Catalog");
-  ui::TreeViewBuilder::build_tree_view(*tree_view, *layout);
+  ui::TreeViewBuilder::build_tree_view(*C, *tree_view, *layout);
 }
 
 void catalog_selector_panel_register(ARegionType *region_type)

source/blender/editors/asset/intern/asset_shelf_popover.cc

@@ -155,7 +155,7 @@ class AssetCatalogTreeView : public ui::AbstractTreeView {
   }
 };
 
-static void catalog_tree_draw(uiLayout &layout, AssetShelf &shelf)
+static void catalog_tree_draw(const bContext &C, uiLayout &layout, AssetShelf &shelf)
 {
   const asset_system::AssetLibrary *library = list::library_get_once_available(
       shelf.settings.asset_library_reference);
@@ -169,7 +169,7 @@ static void catalog_tree_draw(uiLayout &layout, AssetShelf &shelf)
       "asset shelf catalog tree view",
       std::make_unique<AssetCatalogTreeView>(*library, shelf));
 
-  ui::TreeViewBuilder::build_tree_view(*tree_view, layout);
+  ui::TreeViewBuilder::build_tree_view(C, *tree_view, layout);
 }
 
 static AssetShelfType *lookup_type_from_idname_in_context(const bContext *C)
@@ -201,8 +201,6 @@ static void popover_panel_draw(const bContext *C, Panel *panel)
   AssetShelfType *shelf_type = lookup_type_from_idname_in_context(C);
   BLI_assert_msg(shelf_type != nullptr, "couldn't find asset shelf type from context");
 
-  const ARegion *region = CTX_wm_region_popup(C) ? CTX_wm_region_popup(C) : CTX_wm_region(C);
-
   uiLayout *layout = panel->layout;
   uiLayoutSetUnitsX(layout, layout_width_units);
 
@@ -222,7 +220,7 @@ static void popover_panel_draw(const bContext *C, Panel *panel)
   uiLayoutSetUnitsX(catalogs_col, LEFT_COL_WIDTH_UNITS);
   uiLayoutSetFixedSize(catalogs_col, true);
   library_selector_draw(C, catalogs_col, *shelf);
-  catalog_tree_draw(*catalogs_col, *shelf);
+  catalog_tree_draw(*C, *catalogs_col, *shelf);
 
   uiLayout *right_col = uiLayoutColumn(row, false);
   uiLayout *sub = uiLayoutRow(right_col, false);
@@ -241,7 +239,7 @@ static void popover_panel_draw(const bContext *C, Panel *panel)
   uiLayoutSetUnitsX(asset_view_col, layout_width_units - LEFT_COL_WIDTH_UNITS);
   uiLayoutSetFixedSize(asset_view_col, true);
 
-  build_asset_view(*asset_view_col, shelf->settings.asset_library_reference, *shelf, *C, *region);
+  build_asset_view(*asset_view_col, shelf->settings.asset_library_reference, *shelf, *C);
 }
 
 static bool popover_panel_poll(const bContext *C, PanelType * /*panel_type*/)

source/blender/editors/include/UI_abstract_view.hh

@@ -104,6 +104,20 @@ class AbstractView {
   virtual bool supports_scrolling() const;
   virtual void scroll(ViewScrollDirection direction);
 
+  /**
+   * From the current view state, return certain state that will be written to files (stored in
+   * #ARegion.view_states) to preserve it over UI changes and file loading. The state can be
+   * restored using #persistent_state_apply().
+   *
+   * Return an empty value if there's no state to preserve (default implementation).
+   */
+  virtual std::optional<uiViewState> persistent_state() const;
+  /**
+   * Restore a view state given in \a state, which was created by #persistent_state() for saving in
+   * files, and potentially loaded from a file.
+   */
+  virtual void persistent_state_apply(const uiViewState &state);
+
   /**
    * Makes \a item valid for display in this view. Behavior is undefined for items not registered
    * with this.

source/blender/editors/include/UI_grid_view.hh

@@ -172,7 +172,6 @@ class GridViewBuilder {
 
   void build_grid_view(const bContext &C,
                        AbstractGridView &grid_view,
-                       const View2D &v2d,
                        uiLayout &layout,
                        std::optional<StringRef> search_string = {});
 };

source/blender/editors/include/UI_interface.hh

@@ -273,6 +273,8 @@ void UI_list_filter_and_sort_items(uiList *ui_list,
 
 /**
  * Override this for all available view types.
+ * \param idname: Used for restoring persistent state of this view, potentially written to files.
+ * Must not be longer than #BKE_ST_MAXNAME (including 0 terminator).
  */
 blender::ui::AbstractGridView *UI_block_add_view(
     uiBlock &block,

source/blender/editors/include/UI_interface_c.hh

@@ -2857,6 +2857,7 @@ void template_asset_shelf_popover(uiLayout &layout,
 }
 
 void uiTemplateLightLinkingCollection(uiLayout *layout,
+                                      bContext *C,
                                       uiLayout *context_layout,
                                       PointerRNA *ptr,
                                       const char *propname);
@@ -2864,7 +2865,7 @@ void uiTemplateLightLinkingCollection(uiLayout *layout,
 void uiTemplateBoneCollectionTree(uiLayout *layout, bContext *C);
 void uiTemplateGreasePencilLayerTree(uiLayout *layout, bContext *C);
 
-void uiTemplateNodeTreeInterface(uiLayout *layout, PointerRNA *ptr);
+void uiTemplateNodeTreeInterface(uiLayout *layout, bContext *C, PointerRNA *ptr);
 /**
  * Draw all node buttons and socket default values with the same panel structure used by the node.
  */

source/blender/editors/include/UI_tree_view.hh

@@ -146,6 +146,9 @@ class AbstractTreeView : public AbstractView, public TreeViewItemContainer {
  protected:
   virtual void build_tree() = 0;
 
+  std::optional<uiViewState> persistent_state() const override;
+  void persistent_state_apply(const uiViewState &state) override;
+
  private:
   void foreach_view_item(FunctionRef<void(AbstractViewItem &)> iter_fn) const final;
   void update_children_from_old(const AbstractView &old_view) override;
@@ -404,7 +407,8 @@ class TreeViewItemDropTarget : public DropTargetInterface {
 
 class TreeViewBuilder {
  public:
-  static void build_tree_view(AbstractTreeView &tree_view,
+  static void build_tree_view(const bContext &C,
+                              AbstractTreeView &tree_view,
                               uiLayout &layout,
                               std::optional<StringRef> search_string = {},
                               bool add_box = true);

source/blender/editors/interface/interface.cc

@@ -2013,7 +2013,7 @@ void UI_block_end_ex(const bContext *C,
   /* Update bounds of all views in this block. If this block is a panel, this will be done later in
    * #UI_panels_end(), because buttons are offset there. */
   if (!block->panel) {
-    ui_block_views_bounds_calc(block);
+    ui_block_views_end(region, block);
   }
 
   if (block->rect.xmin == 0.0f && block->rect.xmax == 0.0f) {

source/blender/editors/interface/interface_intern.hh

@@ -1609,7 +1609,10 @@ void ui_interface_tag_script_reload_queries();
 /* interface_view.cc */
 
 void ui_block_free_views(uiBlock *block);
-void ui_block_views_bounds_calc(const uiBlock *block);
+void ui_block_views_end(ARegion *region, const uiBlock *block);
+void ui_block_view_persistent_state_restore(const ARegion &region,
+                                            const uiBlock &block,
+                                            blender::ui::AbstractView &view);
 void ui_block_views_listen(const uiBlock *block, const wmRegionListenerParams *listener_params);
 void ui_block_views_draw_overlays(const ARegion *region, const uiBlock *block);
 blender::ui::AbstractView *ui_block_view_find_matching_in_old_block(

source/blender/editors/interface/interface_panel.cc

@@ -1944,7 +1944,7 @@ void UI_panels_end(const bContext *C, ARegion *region, int *r_x, int *r_y)
 
       /* Update bounds for all "views" in this block. Usually this is done in #UI_block_end(), but
        * that wouldn't work because of the offset applied above. */
-      ui_block_views_bounds_calc(block);
+      ui_block_views_end(region, block);
     }
   }
 

source/blender/editors/interface/templates/interface_template_bone_collection_tree.cc

@@ -476,5 +476,5 @@ void uiTemplateBoneCollectionTree(uiLayout *layout, bContext *C)
   tree_view->set_context_menu_title("Bone Collection");
   tree_view->set_default_rows(3);
 
-  ui::TreeViewBuilder::build_tree_view(*tree_view, *layout);
+  ui::TreeViewBuilder::build_tree_view(*C, *tree_view, *layout);
 }

source/blender/editors/interface/templates/interface_template_grease_pencil_layer_tree.cc

@@ -513,5 +513,5 @@ void uiTemplateGreasePencilLayerTree(uiLayout *layout, bContext *C)
   tree_view->set_context_menu_title("Grease Pencil Layer");
   tree_view->set_default_rows(6);
 
-  ui::TreeViewBuilder::build_tree_view(*tree_view, *layout);
+  ui::TreeViewBuilder::build_tree_view(*C, *tree_view, *layout);
 }

source/blender/editors/interface/templates/interface_template_light_linking.cc

@@ -355,10 +355,8 @@ class CollectionView : public AbstractTreeView {
 
 }  // namespace blender::ui::light_linking
 
-void uiTemplateLightLinkingCollection(uiLayout *layout,
-                                      uiLayout *context_layout,
-                                      PointerRNA *ptr,
-                                      const char *propname)
+void uiTemplateLightLinkingCollection(
+    uiLayout *layout, bContext *C, uiLayout *context_layout, PointerRNA *ptr, const char *propname)
 {
   if (!ptr->data) {
     return;
@@ -402,5 +400,5 @@ void uiTemplateLightLinkingCollection(uiLayout *layout,
   tree_view->set_context_menu_title("Light Linking");
   tree_view->set_default_rows(3);
 
-  blender::ui::TreeViewBuilder::build_tree_view(*tree_view, *layout);
+  blender::ui::TreeViewBuilder::build_tree_view(*C, *tree_view, *layout);
 }

source/blender/editors/interface/templates/interface_template_node_tree_interface.cc

@@ -501,7 +501,7 @@ wmDragNodeTreeInterface *NodePanelDropTarget::get_drag_node_tree_declaration(
 
 }  // namespace blender::ui::nodes
 
-void uiTemplateNodeTreeInterface(uiLayout *layout, PointerRNA *ptr)
+void uiTemplateNodeTreeInterface(uiLayout *layout, bContext *C, PointerRNA *ptr)
 {
   if (!ptr->data) {
     return;
@@ -521,5 +521,5 @@ void uiTemplateNodeTreeInterface(uiLayout *layout, PointerRNA *ptr)
   tree_view->set_context_menu_title("Node Tree Interface");
   tree_view->set_default_rows(3);
 
-  blender::ui::TreeViewBuilder::build_tree_view(*tree_view, *layout);
+  blender::ui::TreeViewBuilder::build_tree_view(*C, *tree_view, *layout);
 }

source/blender/editors/interface/views/abstract_view.cc

@@ -136,6 +136,13 @@ void AbstractView::scroll(ViewScrollDirection /*direction*/)
   BLI_assert_msg(false, "Unsupported for this view type");
 }
 
+std::optional<uiViewState> AbstractView::persistent_state() const
+{
+  return {};
+}
+
+void AbstractView::persistent_state_apply(const uiViewState & /*state*/) {}
+
 /** \} */
 
 /* ---------------------------------------------------------------------- */

source/blender/editors/interface/views/grid_view.cc

@@ -12,6 +12,7 @@
 #include <optional>
 #include <stdexcept>
 
+#include "BKE_context.hh"
 #include "BKE_icons.h"
 
 #include "BLI_index_range.hh"
@@ -242,7 +243,7 @@ BuildOnlyVisibleButtonsHelper::BuildOnlyVisibleButtonsHelper(
     const AbstractGridViewItem *force_visible_item)
     : grid_view_(grid_view), style_(grid_view.get_style()), cols_per_row_(cols_per_row)
 {
-  if ((v2d.flag & V2D_IS_INIT) && grid_view.get_item_count_filtered()) {
+  if (v2d.flag & V2D_IS_INIT && grid_view.get_item_count_filtered()) {
     visible_items_range_ = this->get_visible_range(v2d, force_visible_item);
   }
 }
@@ -452,12 +453,14 @@ GridViewBuilder::GridViewBuilder(uiBlock & /*block*/) {}
 
 void GridViewBuilder::build_grid_view(const bContext &C,
                                       AbstractGridView &grid_view,
-                                      const View2D &v2d,
                                       uiLayout &layout,
                                       std::optional<StringRef> search_string)
 {
   uiBlock &block = *uiLayoutGetBlock(&layout);
 
+  const ARegion *region = CTX_wm_region_popup(&C) ? CTX_wm_region_popup(&C) : CTX_wm_region(&C);
+  ui_block_view_persistent_state_restore(*region, block, grid_view);
+
   grid_view.build_items();
   grid_view.update_from_old(block);
   grid_view.change_state_delayed();
@@ -467,7 +470,7 @@ void GridViewBuilder::build_grid_view(const bContext &C,
   UI_block_layout_set_current(&block, &layout);
 
   GridViewLayoutBuilder builder(layout);
-  builder.build_from_view(C, grid_view, v2d);
+  builder.build_from_view(C, grid_view, region->v2d);
 }
 
 /* ---------------------------------------------------------------------- */

source/blender/editors/interface/views/interface_view.cc

@@ -27,6 +27,7 @@
 
 #include "BLI_listbase.h"
 #include "BLI_map.hh"
+#include "BLI_string.h"
 
 #include "ED_screen.hh"
 
@@ -56,6 +57,8 @@ static T *ui_block_add_view_impl(uiBlock &block,
                                  StringRef idname,
                                  std::unique_ptr<AbstractView> view)
 {
+  BLI_assert(idname.size() < int64_t(sizeof(uiViewStateLink::idname)));
+
   ViewLink *view_link = MEM_new<ViewLink>(__func__);
   BLI_addtail(&block.views, view_link);
 
@@ -126,9 +129,58 @@ void ViewLink::views_bounds_calc(const uiBlock &block)
   }
 }
 
-void ui_block_views_bounds_calc(const uiBlock *block)
+void ui_block_view_persistent_state_restore(const ARegion &region,
+                                            const uiBlock &block,
+                                            ui::AbstractView &view)
+{
+  StringRef idname = [&]() -> StringRef {
+    LISTBASE_FOREACH (ViewLink *, link, &block.views) {
+      if (link->view.get() == &view) {
+        return link->idname;
+      }
+    }
+    return "";
+  }();
+
+  if (idname.is_empty()) {
+    BLI_assert_unreachable();
+    return;
+  }
+
+  LISTBASE_FOREACH (uiViewStateLink *, stored_state, &region.view_states) {
+    if (stored_state->idname == idname) {
+      view.persistent_state_apply(stored_state->state);
+    }
+  }
+}
+
+static uiViewStateLink *ensure_view_state(ARegion &region, const ViewLink &link)
+{
+  LISTBASE_FOREACH (uiViewStateLink *, stored_state, &region.view_states) {
+    if (link.idname == stored_state->idname) {
+      return stored_state;
+    }
+  }
+
+  uiViewStateLink *new_state = MEM_cnew<uiViewStateLink>(__func__);
+  link.idname.copy(new_state->idname, sizeof(new_state->idname));
+  BLI_addhead(&region.view_states, new_state);
+  return new_state;
+}
+
+void ui_block_views_end(ARegion *region, const uiBlock *block)
 {
   ViewLink::views_bounds_calc(*block);
+
+  if (region && region->regiontype != RGN_TYPE_TEMPORARY) {
+    LISTBASE_FOREACH (const ViewLink *, link, &block->views) {
+      /* Ensure persistent view state storage for writing to files if needed. */
+      if (std::optional<uiViewState> temp_state = link->view->persistent_state()) {
+        uiViewStateLink *state_link = ensure_view_state(*region, *link);
+        state_link->state = *temp_state;
+      }
+    }
+  }
 }
 
 void ui_block_views_listen(const uiBlock *block, const wmRegionListenerParams *listener_params)

source/blender/editors/interface/views/tree_view.cc

@@ -131,6 +131,28 @@ void AbstractTreeView::set_default_rows(int default_rows)
   custom_height_ = std::make_unique<int>(default_rows * padded_item_height());
 }
 
+std::optional<uiViewState> AbstractTreeView::persistent_state() const
+{
+  if (!custom_height_) {
+    return {};
+  }
+
+  uiViewState state{0};
+
+  if (custom_height_) {
+    state.custom_height = *custom_height_ * UI_INV_SCALE_FAC;
+  }
+
+  return state;
+}
+
+void AbstractTreeView::persistent_state_apply(const uiViewState &state)
+{
+  if (state.custom_height) {
+    set_default_rows(round_fl_to_int(state.custom_height * UI_SCALE_FAC) / padded_item_height());
+  }
+}
+
 int AbstractTreeView::count_visible_descendants(const AbstractTreeViewItem &parent) const
 {
   if (parent.is_collapsed()) {
@@ -915,13 +937,19 @@ void TreeViewBuilder::ensure_min_rows_items(AbstractTreeView &tree_view)
   }
 }
 
-void TreeViewBuilder::build_tree_view(AbstractTreeView &tree_view,
+void TreeViewBuilder::build_tree_view(const bContext &C,
+                                      AbstractTreeView &tree_view,
                                       uiLayout &layout,
                                       std::optional<StringRef> search_string,
                                       const bool add_box)
 {
   uiBlock &block = *uiLayoutGetBlock(&layout);
 
+  const ARegion *region = CTX_wm_region_popup(&C) ? CTX_wm_region_popup(&C) : CTX_wm_region(&C);
+  if (region) {
+    ui_block_view_persistent_state_restore(*region, block, tree_view);
+  }
+
   tree_view.build_tree();
   tree_view.update_from_old(block);
   tree_view.change_state_delayed();

source/blender/editors/space_file/asset_catalog_tree_view.cc

@@ -754,7 +754,8 @@ bool file_is_asset_visible_in_catalog_filter_settings(
 
 /* ---------------------------------------------------------------------- */
 
-void file_create_asset_catalog_tree_view_in_layout(asset_system::AssetLibrary *asset_library,
+void file_create_asset_catalog_tree_view_in_layout(const bContext *C,
+                                                   asset_system::AssetLibrary *asset_library,
                                                    uiLayout *layout,
                                                    SpaceFile *space_file,
                                                    FileAssetSelectParams *params)
@@ -769,7 +770,7 @@ void file_create_asset_catalog_tree_view_in_layout(asset_system::AssetLibrary *a
       std::make_unique<ed::asset_browser::AssetCatalogTreeView>(
           asset_library, params, *space_file));
   tree_view->set_context_menu_title("Catalog");
-  ui::TreeViewBuilder::build_tree_view(*tree_view, *layout);
+  ui::TreeViewBuilder::build_tree_view(*C, *tree_view, *layout);
 }
 
 }  // namespace blender::ed::asset_browser

source/blender/editors/space_file/file_intern.hh

@@ -232,7 +232,8 @@ void file_path_to_ui_path(const char *path, char *r_path, int r_path_maxncpy);
 
 namespace blender::ed::asset_browser {
 
-void file_create_asset_catalog_tree_view_in_layout(asset_system::AssetLibrary *asset_library,
+void file_create_asset_catalog_tree_view_in_layout(const bContext *C,
+                                                   asset_system::AssetLibrary *asset_library,
                                                    uiLayout *layout,
                                                    SpaceFile *space_file,
                                                    FileAssetSelectParams *params);

source/blender/editors/space_file/file_panels.cc

@@ -255,7 +255,7 @@ static void file_panel_asset_catalog_buttons_draw(const bContext *C, Panel *pane
   uiItemS(col);
 
   blender::ed::asset_browser::file_create_asset_catalog_tree_view_in_layout(
-      asset_library, col, sfile, params);
+      C, asset_library, col, sfile, params);
 }
 
 void file_tools_region_panels_register(ARegionType *art)

source/blender/editors/space_spreadsheet/spreadsheet_dataset_draw.cc

@@ -728,7 +728,7 @@ void spreadsheet_data_set_panel_draw(const bContext *C, Panel *panel)
         "Instances Tree View",
         std::make_unique<GeometryInstancesTreeView>(root_geometry, *C));
     tree_view->set_context_menu_title("Instance");
-    ui::TreeViewBuilder::build_tree_view(*tree_view, *panel, {}, false);
+    ui::TreeViewBuilder::build_tree_view(*C, *tree_view, *panel, {}, false);
   }
   if (uiLayout *panel = uiLayoutPanel(
           C, layout, "geometry_domain_tree_view", false, IFACE_("Domain")))
@@ -740,7 +740,7 @@ void spreadsheet_data_set_panel_draw(const bContext *C, Panel *panel)
         "Data Set Tree View",
         std::make_unique<GeometryDataSetTreeView>(std::move(instance_geometry), *C));
     tree_view->set_context_menu_title("Domain");
-    ui::TreeViewBuilder::build_tree_view(*tree_view, *panel, {}, false);
+    ui::TreeViewBuilder::build_tree_view(*C, *tree_view, *panel, {}, false);
   }
 }
 

source/blender/makesdna/DNA_screen_types.h

@@ -322,6 +322,31 @@ typedef struct uiList { /* some list UI data need to be saved in file */
   uiListDyn *dyn_data;
 } uiList;
 
+/** See #uiViewStateLink. */
+typedef struct uiViewState {
+  /**
+   * User set height of the view in unscaled pixels. A value of 0 means no custom height was set
+   * and the default should be used.
+   */
+  int custom_height;
+  char _pad[4];
+} uiViewState;
+
+/**
+ * Persistent storage for some state of views (#ui::AbstractView), for storage in a region. The
+ * view state is matched to the view using the view's idname.
+ *
+ * The actual state is stored in #uiViewState, so views can manage this conveniently without having
+ * to care about the idname and listbase pointers themselves.
+ */
+typedef struct uiViewStateLink {
+  struct uiViewStateLink *next, *prev;
+
+  char idname[64]; /* #BKE_ST_MAXNAME */
+
+  uiViewState state;
+} uiViewStateLink;
+
 typedef struct TransformOrientation {
   struct TransformOrientation *next, *prev;
   /** MAX_NAME. */
@@ -512,6 +537,11 @@ typedef struct ARegion {
   ListBase handlers;
   /** Panel categories runtime. */
   ListBase panels_category;
+  /**
+   * Permanent state storage of #ui::AbstractView instances, so hiding regions with views or
+   * loading files remembers the view state.
+   */
+  ListBase view_states; /* #uiViewStateLink */
 
   /** Gizmo-map of this region. */
   struct wmGizmoMap *gizmo_map;

source/blender/makesrna/intern/rna_ui_api.cc

@@ -2387,6 +2387,7 @@ void RNA_api_ui_layout(StructRNA *srna)
       srna, "template_light_linking_collection", "uiTemplateLightLinkingCollection");
   RNA_def_function_ui_description(func,
                                   "Visualization of a content of a light linking collection");
+  RNA_def_function_flag(func, FUNC_USE_CONTEXT);
   parm = RNA_def_pointer(func,
                          "context_layout",
                          "UILayout",
@@ -2406,6 +2407,7 @@ void RNA_api_ui_layout(StructRNA *srna)
 
   func = RNA_def_function(srna, "template_node_tree_interface", "uiTemplateNodeTreeInterface");
   RNA_def_function_ui_description(func, "Show a node tree interface");
+  RNA_def_function_flag(func, FUNC_USE_CONTEXT);
   parm = RNA_def_pointer(func,
                          "interface",
                          "NodeTreeInterface",