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

4 files changed, 99 insertions, 1 deletions

diff --git a/source/blender/blenloader/BLO_readfile.h b/source/blender/blenloader/BLO_readfile.h
index 0ab9a5e9e14..1d7c5d8a1d3 100644
--- a/source/blender/blenloader/BLO_readfile.h
+++ b/source/blender/blenloader/BLO_readfile.h
@@ -119,12 +119,20 @@ void BLO_blendfiledata_free(BlendFileData *bfd);
 /** \name BLO Blend File Handle API
  * \{ */
 
+struct BLODataBlockInfo {
+  char name[64]; /* MAX_NAME */
+  struct AssetMetaData *asset_data;
+};
+
 BlendHandle *BLO_blendhandle_from_file(const char *filepath, struct ReportList *reports);
 BlendHandle *BLO_blendhandle_from_memory(const void *mem, int memsize);
 
 struct LinkNode *BLO_blendhandle_get_datablock_names(BlendHandle *bh,
                                                      int ofblocktype,
                                                      int *tot_names);
+struct LinkNode *BLO_blendhandle_get_datablock_info(BlendHandle *bh,
+                                                    int ofblocktype,
+                                                    int *tot_info_items);
 struct LinkNode *BLO_blendhandle_get_previews(BlendHandle *bh, int ofblocktype, int *tot_prev);
 struct LinkNode *BLO_blendhandle_get_linkable_groups(BlendHandle *bh);
 
diff --git a/source/blender/blenloader/intern/readblenentry.c b/source/blender/blenloader/intern/readblenentry.c
index 1aecba5ba90..3a1ccbeda01 100644
--- a/source/blender/blenloader/intern/readblenentry.c
+++ b/source/blender/blenloader/intern/readblenentry.c
@@ -160,6 +160,51 @@ LinkNode *BLO_blendhandle_get_datablock_names(BlendHandle *bh, int ofblocktype,
 }
 
 /**
+ * Gets the names and asset-data (if ID is an asset) of all the data-blocks in a file of a certain
+ * type (e.g. all the scene names in a file).
+ *
+ * \param bh: The blendhandle to access.
+ * \param ofblocktype: The type of names to get.
+ * \param tot_info_items: The length of the returned list.
+ * \return A BLI_linklist of BLODataBlockInfo *. The links and #BLODataBlockInfo.asset_data should
+ *         be freed with MEM_freeN.
+ */
+LinkNode *BLO_blendhandle_get_datablock_info(BlendHandle *bh, int ofblocktype, int *tot_info_items)
+{
+  FileData *fd = (FileData *)bh;
+  LinkNode *infos = NULL;
+  BHead *bhead;
+  int tot = 0;
+
+  for (bhead = blo_bhead_first(fd); bhead; bhead = blo_bhead_next(fd, bhead)) {
+    if (bhead->code == ofblocktype) {
+      struct BLODataBlockInfo *info = MEM_mallocN(sizeof(*info), __func__);
+      const char *name = blo_bhead_id_name(fd, bhead) + 2;
+
+      STRNCPY(info->name, name);
+
+      /* Lastly, read asset data from the following blocks. */
+      info->asset_data = blo_bhead_id_asset_data_address(fd, bhead);
+      if (info->asset_data) {
+        bhead = blo_read_asset_data_block(fd, bhead, &info->asset_data);
+        /* blo_read_asset_data_block() reads all DATA heads and already advances bhead to the next
+         * non-DATA one. Go back, so the loop doesn't skip the non-DATA head. */
+        bhead = blo_bhead_prev(fd, bhead);
+      }
+
+      BLI_linklist_prepend(&infos, info);
+      tot++;
+    }
+    else if (bhead->code == ENDB) {
+      break;
+    }
+  }
+
+  *tot_info_items = tot;
+  return infos;
+}
+
+/**
  * Gets the previews of all the data-blocks in a file of a certain type
  * (e.g. all the scene previews in a file).
  *
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
  * \{ */
 
diff --git a/source/blender/blenloader/intern/readfile.h b/source/blender/blenloader/intern/readfile.h
index fb950e37da8..3e7cdb30e1f 100644
--- a/source/blender/blenloader/intern/readfile.h
+++ b/source/blender/blenloader/intern/readfile.h
@@ -112,6 +112,9 @@ typedef struct FileData {
   int fileversion;
   /** Used to retrieve ID names from (bhead+1). */
   int id_name_offs;
+  /** Used to retrieve asset data from (bhead+1). NOTE: This may not be available in old files,
+   * will be -1 then! */
+  int id_asset_data_offs;
   /** For do_versions patching. */
   int globalf, fileflags;
 
@@ -159,6 +162,8 @@ void blo_end_packed_pointer_map(FileData *fd, struct Main *oldmain);
 void blo_add_library_pointer_map(ListBase *old_mainlist, FileData *fd);
 void blo_make_old_idmap_from_main(FileData *fd, struct Main *bmain);
 
+BHead *blo_read_asset_data_block(FileData *fd, BHead *bhead, struct AssetMetaData **r_asset_data);
+
 void blo_cache_storage_init(FileData *fd, struct Main *bmain);
 void blo_cache_storage_old_bmain_clear(FileData *fd, struct Main *bmain_old);
 void blo_cache_storage_end(FileData *fd);
@@ -170,6 +175,7 @@ BHead *blo_bhead_next(FileData *fd, BHead *thisblock);
 BHead *blo_bhead_prev(FileData *fd, BHead *thisblock);
 
 const char *blo_bhead_id_name(const FileData *fd, const BHead *bhead);
+struct AssetMetaData *blo_bhead_id_asset_data_address(const FileData *fd, const BHead *bhead);
 
 /* do versions stuff */