UI/Assets: Initial Asset View UI template

The asset view UI template is a mini-version of the Asset Browser that
can be placed in regular layouts, regions or popups. At this point it's
made specifically for placement in vertical layouts, it can be made more
flexible in the future.
Generally the way this is implemented will likely change a lot still as
the asset system evolves.

The Pose Library add-on will use the asset view to display pose
libraries in the 3D View sidebar.

References:
* https://developer.blender.org/T86139
* https://code.blender.org/2021/06/asset-browser-project-update/#what-are-we-building
* https://code.blender.org/2021/05/pose-library-v2-0/#use-from-3d-viewport

Notes:
* Important limitation: Due to the early & WIP implementation of the
  asset list, all asset views showing the same library will show the
  same assets. That is despite the ID type filter option the template
  provides. The first asset view created will determine what's visible.
  Of course this should be made to work eventually.
* The template supports passing an activate and a drag operator name.
  The former is called when an asset is clicked on (e.g. to apply the
  asset) the latter when dragging (e.g. to .blend a pose asset). If no
  drag operator is set, regular asset drag & drop will be executed.
* The template returns the properties for both operators (see example
  below).
* The argument list for using the template is quite long, but we can't
  avoid that currently. The UI list design requires that we pass a
  number of RNA or custom properties to work with, that for the Pose
  Libraries should be registered at the Pose Library add-on level, not
  in core Blender.
* Idea is that Python scripts or add-ons that want to use the asset view
  can register custom properties, to hold data like the list of assets,
  and the active asset index. Maybe that will change in future and we
  can manage these internally.

As an example, the pose library add-on uses it like this:
```
activate_op_props, drag_op_props = layout.template_asset_view(
    "pose_assets",
    workspace,
    "active_asset_library",
    wm,
    "pose_assets",
    workspace,
    "active_pose_asset_index",
    filter_id_types={"filter_action"},
    activate_operator="poselib.apply_pose_asset",
    drag_operator="poselib.blend_pose_asset",
)
drag_op_props.release_confirm = True
drag_op_props.flipped = wm.poselib_flipped
activate_op_props.flipped = wm.poselib_flipped
```

1 files changed, 140 insertions, 0 deletions

diff --git a/source/blender/makesrna/intern/rna_ui_api.c b/source/blender/makesrna/intern/rna_ui_api.c
index 4b8938053ba..e06cc39a88b 100644
--- a/source/blender/makesrna/intern/rna_ui_api.c
+++ b/source/blender/makesrna/intern/rna_ui_api.c
@@ -50,6 +50,8 @@ const EnumPropertyItem rna_enum_icon_items[] = {
 
 #ifdef RNA_RUNTIME
 
+#  include "DNA_asset_types.h"
+
 const char *rna_translate_ui_text(
     const char *text, const char *text_ctxt, StructRNA *type, PropertyRNA *prop, bool translate)
 {
@@ -610,6 +612,69 @@ static void rna_uiTemplateEventFromKeymapItem(
   uiTemplateEventFromKeymapItem(layout, name, kmi, true);
 }
 
+static void rna_uiTemplateAssetView(uiLayout *layout,
+                                    bContext *C,
+                                    const char *list_id,
+                                    PointerRNA *asset_library_dataptr,
+                                    const char *asset_library_propname,
+                                    PointerRNA *assets_dataptr,
+                                    const char *assets_propname,
+                                    PointerRNA *active_dataptr,
+                                    const char *active_propname,
+                                    int filter_id_types,
+                                    const char *activate_opname,
+                                    PointerRNA *r_activate_op_properties,
+                                    const char *drag_opname,
+                                    PointerRNA *r_drag_op_properties)
+{
+  AssetFilterSettings filter_settings = {
+      .id_types = filter_id_types ? filter_id_types : FILTER_ID_ALL,
+  };
+  uiTemplateAssetView(layout,
+                      C,
+                      list_id,
+                      asset_library_dataptr,
+                      asset_library_propname,
+                      assets_dataptr,
+                      assets_propname,
+                      active_dataptr,
+                      active_propname,
+                      &filter_settings,
+                      activate_opname,
+                      r_activate_op_properties,
+                      drag_opname,
+                      r_drag_op_properties);
+}
+
+/**
+ * XXX Remove filter items that require more than 32 bits for storage. RNA enums don't support
+ * that currently.
+ */
+static const EnumPropertyItem *rna_uiTemplateAssetView_filter_id_types_itemf(
+    bContext *UNUSED(C), PointerRNA *UNUSED(ptr), PropertyRNA *UNUSED(prop), bool *r_free)
+{
+  EnumPropertyItem *items = NULL;
+  int totitem = 0;
+
+  for (int i = 0; rna_enum_id_type_filter_items[i].identifier; i++) {
+    if (rna_enum_id_type_filter_items[i].flag > (1ULL << 31)) {
+      continue;
+    }
+
+    EnumPropertyItem tmp = {0, "", 0, "", ""};
+    tmp.value = rna_enum_id_type_filter_items[i].flag;
+    tmp.identifier = rna_enum_id_type_filter_items[i].identifier;
+    tmp.icon = rna_enum_id_type_filter_items[i].icon;
+    tmp.name = rna_enum_id_type_filter_items[i].name;
+    tmp.description = rna_enum_id_type_filter_items[i].description;
+    RNA_enum_item_add(&items, &totitem, &tmp);
+  }
+  RNA_enum_item_end(&items, &totitem);
+
+  *r_free = true;
+  return items;
+}
+
 static uiLayout *rna_uiLayoutRowWithHeading(
     uiLayout *layout, bool align, const char *heading, const char *heading_ctxt, bool translate)
 {
@@ -1729,6 +1794,81 @@ void RNA_api_ui_layout(StructRNA *srna)
   RNA_def_property_ui_text(parm, "Item", "");
   RNA_def_parameter_flags(parm, PROP_NEVER_NULL, PARM_REQUIRED);
   api_ui_item_common_text(func);
+
+  func = RNA_def_function(srna, "template_asset_view", "rna_uiTemplateAssetView");
+  RNA_def_function_ui_description(func, "Item. A scrollable list of assets in a grid view");
+  RNA_def_function_flag(func, FUNC_USE_CONTEXT);
+  parm = RNA_def_string(func,
+                        "list_id",
+                        NULL,
+                        0,
+                        "",
+                        "Identifier of this asset view. Necessary to tell apart different asset "
+                        "views and to idenify an asset view read from a .blend");
+  RNA_def_parameter_flags(parm, 0, PARM_REQUIRED);
+  parm = RNA_def_pointer(func,
+                         "asset_library_dataptr",
+                         "AnyType",
+                         "",
+                         "Data from which to take the active asset library property");
+  RNA_def_parameter_flags(parm, PROP_NEVER_NULL, PARM_REQUIRED | PARM_RNAPTR);
+  parm = RNA_def_string(
+      func, "asset_library_propname", NULL, 0, "", "Identifier of the asset library property");
+  RNA_def_parameter_flags(parm, 0, PARM_REQUIRED);
+  parm = RNA_def_pointer(
+      func, "assets_dataptr", "AnyType", "", "Data from which to take the asset list property");
+  RNA_def_parameter_flags(parm, PROP_NEVER_NULL, PARM_REQUIRED | PARM_RNAPTR);
+  parm = RNA_def_string(
+      func, "assets_propname", NULL, 0, "", "Identifier of the asset list property");
+  RNA_def_parameter_flags(parm, 0, PARM_REQUIRED);
+  parm = RNA_def_pointer(func,
+                         "active_dataptr",
+                         "AnyType",
+                         "",
+                         "Data from which to take the integer property, index of the active item");
+  RNA_def_parameter_flags(parm, PROP_NEVER_NULL, PARM_REQUIRED | PARM_RNAPTR);
+  parm = RNA_def_string(
+      func,
+      "active_propname",
+      NULL,
+      0,
+      "",
+      "Identifier of the integer property in active_data, index of the active item");
+  RNA_def_parameter_flags(parm, 0, PARM_REQUIRED);
+  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);
+  RNA_def_string(func,
+                 "activate_operator",
+                 NULL,
+                 0,
+                 "",
+                 "Name of a custom operator to invoke when activating an item");
+  parm = RNA_def_pointer(
+      func,
+      "activate_operator_properties",
+      "OperatorProperties",
+      "",
+      "Operator properties to fill in for the custom activate operator passed to the template");
+  RNA_def_parameter_flags(parm, 0, PARM_RNAPTR);
+  RNA_def_function_output(func, parm);
+  RNA_def_string(func,
+                 "drag_operator",
+                 NULL,
+                 0,
+                 "",
+                 "Name of a custom operator to invoke when starting to drag an item. Never "
+                 "invoked together with the `active_operator` (if set), it's either the drag or "
+                 "the activate one");
+  parm = RNA_def_pointer(
+      func,
+      "drag_operator_properties",
+      "OperatorProperties",
+      "",
+      "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);
 }
 
 #endif