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, 6 insertions, 0 deletions

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 */