Asset System: Data-block asset metadata storage, reading and API

Asset metadata is what turns a regular data-block into an asset. It is a small
data-structure, but a key part of the technical design of the asset system.

The design foresees that asset data-blocks store an `ID.asset_data` pointer of
type `AssetMetaData`. This data **must not** have dependencies on other
data-blocks or data-block data, it must be an independent unit. That way we can
read asset-metadata from .blends without reading anything else from the file.
The Asset Browser will use this metadata (together with the data-block name,
preview and file path) to represent assets in the file list.

Includes:
* New `ID.asset_data` for asset metadata.
* Asset tags, description and custom properties.
* BKE code to manage asset meta-data and asset tags.
* Code to read asset data from files, without reading IDs.
* RNA for asset metadata (including tags)

Part of the first Asset Browser milestone. Check the #asset_browser_milestone_1
project milestone on developer.blender.org.

Differential Revision: https://developer.blender.org/D9716

Reviewed by: Bastien Montagne, Brecht Van Lommel

1 files changed, 40 insertions, 1 deletions

diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index fd10eac4302..8dff1aa1ed0 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -44,6 +44,7 @@
 #define DNA_DEPRECATED_ALLOW
 
 #include "DNA_anim_types.h"
+#include "DNA_asset_types.h"
 #include "DNA_cachefile_types.h"
 #include "DNA_collection_types.h"
 #include "DNA_fileglobal_types.h"
@@ -73,6 +74,7 @@
 
 #include "BKE_anim_data.h"
 #include "BKE_animsys.h"
+#include "BKE_asset.h"
 #include "BKE_collection.h"
 #include "BKE_global.h" /* for G */
 #include "BKE_idprop.h"
@@ -957,12 +959,21 @@ static BHead *blo_bhead_read_full(FileData *fd, BHead *thisblock)
 }
 #endif /* USE_BHEAD_READ_ON_DEMAND */
 
-/* Warning! Caller's responsibility to ensure given bhead **is** and ID one! */
+/* Warning! Caller's responsibility to ensure given bhead **is** an ID one! */
 const char *blo_bhead_id_name(const FileData *fd, const BHead *bhead)
 {
   return (const char *)POINTER_OFFSET(bhead, sizeof(*bhead) + fd->id_name_offs);
 }
 
+/* Warning! Caller's responsibility to ensure given bhead **is** an ID one! */
+AssetMetaData *blo_bhead_id_asset_data_address(const FileData *fd, const BHead *bhead)
+{
+  BLI_assert(BKE_idtype_idcode_is_valid(bhead->code));
+  return (fd->id_asset_data_offs >= 0) ?
+             *(AssetMetaData **)POINTER_OFFSET(bhead, sizeof(*bhead) + fd->id_asset_data_offs) :
+             NULL;
+}
+
 static void decode_blender_header(FileData *fd)
 {
   char header[SIZEOFBLENDERHEADER], num[4];
@@ -1040,6 +1051,8 @@ static bool read_file_dna(FileData *fd, const char **r_error_message)
         /* used to retrieve ID names from (bhead+1) */
         fd->id_name_offs = DNA_elem_offset(fd->filesdna, "ID", "char", "name[]");
         BLI_assert(fd->id_name_offs != -1);
+        fd->id_asset_data_offs = DNA_elem_offset(
+            fd->filesdna, "ID", "AssetMetaData", "*asset_data");
 
         return true;
       }
@@ -2360,6 +2373,11 @@ static void direct_link_id_common(
     return;
   }
 
+  if (id->asset_data) {
+    BLO_read_data_address(reader, &id->asset_data);
+    BKE_asset_metadata_read(reader, id->asset_data);
+  }
+
   /*link direct data of ID properties*/
   if (id->properties) {
     BLO_read_data_address(reader, &id->properties);
@@ -3608,6 +3626,27 @@ static BHead *read_libblock(FileData *fd,
 /** \} */
 
 /* -------------------------------------------------------------------- */
+/** \name Read Asset Data
+ * \{ */
+
+BHead *blo_read_asset_data_block(FileData *fd, BHead *bhead, AssetMetaData **r_asset_data)
+{
+  BLI_assert(BKE_idtype_idcode_is_valid(bhead->code));
+
+  bhead = read_data_into_datamap(fd, bhead, "asset-data read");
+
+  BlendDataReader reader = {fd};
+  BLO_read_data_address(&reader, r_asset_data);
+  BKE_asset_metadata_read(&reader, *r_asset_data);
+
+  oldnewmap_clear(fd->datamap);
+
+  return bhead;
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
 /** \name Read Global Data
  * \{ */