source/blender/blenkernel/BKE_screen.h

@@ -409,7 +409,11 @@ typedef struct AssetShelfType {
   int space_type;
 
   /* Determine if the asset shelf should be visible or not. */
-  bool (*poll)(const struct bContext *C, struct AssetShelfType *shelf_type);
+  bool (*poll)(const struct bContext *C, const struct AssetShelfType *shelf_type);
+
+  /* Determine if an individual asset should be visible or not. May be a temporary design,
+   * visibility should be first and foremost controlled by asset traits. */
+  bool (*asset_poll)(const struct AssetShelfType *shelf_type, const struct AssetHandle *asset);
 
   /* RNA integration */
   ExtensionRNA rna_ext;

source/blender/editors/interface/interface_template_asset_shelf.cc

@@ -7,6 +7,7 @@
 #include "AS_asset_library.hh"
 
 #include "BKE_context.h"
+#include "BKE_screen.h"
 
 #include "DNA_screen_types.h"
 #include "DNA_space_types.h"
@@ -106,6 +107,29 @@ static std::optional<asset_system::AssetCatalogFilter> catalog_filter_from_shelf
   return library->catalog_service->create_catalog_filter(active_catalog->catalog_id);
 }
 
+/* TODO calling a (.py defined) callback for every asset isn't exactly great. Should be a temporary
+solution until there is proper filtering by asset traits. */
+/**
+ * Returns true if the asset should be visible. That is, if any of the visible asset shelves has no
+ * poll function (all assets should be displayed), or its #AssetShelfType.asset_poll function
+ * returns true.
+ */
+static bool asset_shelf_asset_poll(const SpaceType &space_type,
+                                   const bContext &C,
+                                   const AssetHandle &asset)
+{
+  LISTBASE_FOREACH (AssetShelfType *, shelf_type, &space_type.asset_shelf_types) {
+    if (!shelf_type->poll || !shelf_type->poll(&C, shelf_type)) {
+      continue;
+    }
+    if (!shelf_type->asset_poll || shelf_type->asset_poll(shelf_type, &asset)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
 void uiTemplateAssetShelf(uiLayout *layout,
                           const bContext *C,
                           const AssetFilterSettings *filter_settings)
@@ -116,6 +140,8 @@ void uiTemplateAssetShelf(uiLayout *layout,
   const AssetShelfSettings *shelf_settings = static_cast<AssetShelfSettings *>(
       shelf_settings_ptr.data);
 
+  Vector<decltype(AssetShelfType::asset_poll)> asset_polls;
+
   ED_assetlist_storage_fetch(library_ref, C);
   ED_assetlist_ensure_previews_job(library_ref, C);
 
@@ -139,8 +165,13 @@ void uiTemplateAssetShelf(uiLayout *layout,
 
   uiLayout *box = uiLayoutBox(layout);
   uiLayout *row = uiLayoutRow(box, false);
+  const SpaceLink *space_link = CTX_wm_space_data(C);
+  const SpaceType *space_type = BKE_spacetype_from_id(space_link->spacetype);
 
   ED_assetlist_iterate(*library_ref, [&](AssetHandle asset) {
+    if (!asset_shelf_asset_poll(*space_type, *C, asset)) {
+      return true;
+    }
     if (!ED_asset_filter_matches_asset(filter_settings, &asset)) {
       /* Don't do anything else, but return true to continue iterating. */
       return true;

source/blender/makesrna/intern/rna_ui.c

@@ -1022,7 +1022,30 @@ static StructRNA *rna_Menu_refine(PointerRNA *mtr)
 
 /* Asset Shelf */
 
-static bool asset_shelf_poll(const bContext *C, AssetShelfType *shelf_type)
+static bool asset_shelf_asset_poll(const AssetShelfType *shelf_type, const AssetHandle *asset)
+{
+  extern FunctionRNA rna_AssetShelf_asset_poll___func;
+
+  PointerRNA ptr;
+  RNA_pointer_create(NULL, shelf_type->rna_ext.srna, NULL, &ptr); /* dummy */
+  FunctionRNA *func = &rna_AssetShelf_asset_poll___func;
+
+  ParameterList list;
+  RNA_parameter_list_create(&list, &ptr, func);
+  RNA_parameter_set_lookup(&list, "asset_handle", &asset);
+  shelf_type->rna_ext.call(NULL, &ptr, func, &list);
+
+  void *ret;
+  RNA_parameter_get_lookup(&list, "visible", &ret);
+  /* Get the value before freeing. */
+  const bool is_visible = *(bool *)ret;
+
+  RNA_parameter_list_free(&list);
+
+  return is_visible;
+}
+
+static bool asset_shelf_poll(const bContext *C, const AssetShelfType *shelf_type)
 {
   extern FunctionRNA rna_AssetShelf_poll_func;
 
@@ -1083,7 +1106,7 @@ static StructRNA *rna_AssetShelf_register(Main *bmain,
   dummy_shelf.type = &dummy_shelf_type;
   RNA_pointer_create(NULL, &RNA_AssetShelf, &dummy_shelf, &dummy_shelf_type_ptr);
 
-  int have_function[1];
+  int have_function[2];
 
   /* validate the python class */
   if (validate(&dummy_shelf_type_ptr, data, have_function) != 0) {
@@ -1131,6 +1154,7 @@ static StructRNA *rna_AssetShelf_register(Main *bmain,
   RNA_struct_blender_type_set(shelf_type->rna_ext.srna, shelf_type);
 
   shelf_type->poll = have_function[0] ? asset_shelf_poll : NULL;
+  shelf_type->asset_poll = have_function[1] ? asset_shelf_asset_poll : NULL;
 
   BLI_addtail(&space_type->asset_shelf_types, shelf_type);
 
@@ -2000,6 +2024,17 @@ static void rna_def_asset_shelf(BlenderRNA *brna)
   RNA_def_function_return(func, RNA_def_boolean(func, "visible", 1, "", ""));
   parm = RNA_def_pointer(func, "context", "Context", "", "");
   RNA_def_parameter_flags(parm, 0, PARM_REQUIRED);
+
+  func = RNA_def_function(srna, "asset_poll__", NULL);
+  RNA_def_function_ui_description(
+      func,
+      "TEMPORARY DESIGN; Expect compatibility breakage. Determine if an asset should be visible "
+      "in the asset shelf. If this method returns a non-null output, then the asset shelf will be "
+      "visible");
+  RNA_def_function_flag(func, FUNC_NO_SELF | FUNC_REGISTER_OPTIONAL);
+  RNA_def_function_return(func, RNA_def_boolean(func, "visible", 1, "", ""));
+  parm = RNA_def_pointer(func, "asset_handle", "AssetHandle", "", "");
+  RNA_def_parameter_flags(parm, 0, PARM_REQUIRED);
 }
 
 static void rna_def_asset_shelf_settings(BlenderRNA *brna)

source/blender/makesrna/intern/rna_ui_api.c

@@ -714,15 +714,6 @@ static const EnumPropertyItem *rna_uiTemplateAssetView_filter_id_types_itemf(
   return items;
 }
 
-static void rna_uiTemplateAssetShelf(uiLayout *layout, bContext *C, int filter_id_types)
-{
-  AssetFilterSettings filter_settings = {
-      .id_types = filter_id_types ? filter_id_types : FILTER_ID_ALL,
-  };
-
-  uiTemplateAssetShelf(layout, C, &filter_settings);
-}
-
 static uiLayout *rna_uiLayoutRowWithHeading(
     uiLayout *layout, bool align, const char *heading, const char *heading_ctxt, bool translate)
 {
@@ -1967,16 +1958,6 @@ void RNA_api_ui_layout(StructRNA *srna)
       "Operator properties to fill in for the custom drag operator passed to the template");
   RNA_def_parameter_flags(parm, 0, PARM_RNAPTR);
   RNA_def_function_output(func, parm);
-
-  func = RNA_def_function(srna, "template_asset_shelf", "rna_uiTemplateAssetShelf");
-  RNA_def_function_ui_description(func,
-                                  "Item. A list of assets in a horizontally scrollable layout. "
-                                  "Meant to be placed in a 'ASSET_SHELF' region");
-  RNA_def_function_flag(func, FUNC_USE_CONTEXT);
-  parm = RNA_def_property(func, "filter_id_types", PROP_ENUM, PROP_NONE);
-  RNA_def_property_enum_items(parm, DummyRNA_NULL_items);
-  RNA_def_property_enum_funcs(parm, NULL, NULL, "rna_uiTemplateAssetView_filter_id_types_itemf");
-  RNA_def_property_flag(parm, PROP_ENUM_FLAG);
 }
 
 #endif