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

6 files changed, 117 insertions, 1 deletions

diff --git a/source/blender/makesdna/DNA_ID.h b/source/blender/makesdna/DNA_ID.h
index f2d860a2851..84757e313ed 100644
--- a/source/blender/makesdna/DNA_ID.h
+++ b/source/blender/makesdna/DNA_ID.h
@@ -264,7 +264,12 @@ typedef struct IDOverrideLibrary {
 typedef struct ID {
   void *next, *prev;
   struct ID *newid;
+
   struct Library *lib;
+
+  /** If the ID is an asset, this pointer is set. Owning pointer. */
+  struct AssetMetaData *asset_data;
+
   /** MAX_ID_NAME. */
   char name[66];
   /**
@@ -310,6 +315,7 @@ typedef struct ID {
   struct ID *orig_id;
 
   void *py_instance;
+  void *_pad1;
 } ID;
 
 /**
diff --git a/source/blender/makesdna/DNA_asset_defaults.h b/source/blender/makesdna/DNA_asset_defaults.h
new file mode 100644
index 00000000000..ff00ba79cf0
--- /dev/null
+++ b/source/blender/makesdna/DNA_asset_defaults.h
@@ -0,0 +1,37 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup DNA
+ */
+
+#pragma once
+
+/* Struct members on own line. */
+/* clang-format off */
+
+/* -------------------------------------------------------------------- */
+/** \name Asset Struct
+ * \{ */
+
+#define _DNA_DEFAULT_AssetMetaData \
+  { \
+    0 \
+  }
+
+/** \} */
+
+/* clang-format on */
diff --git a/source/blender/makesdna/DNA_asset_types.h b/source/blender/makesdna/DNA_asset_types.h
new file mode 100644
index 00000000000..671012e54ef
--- /dev/null
+++ b/source/blender/makesdna/DNA_asset_types.h
@@ -0,0 +1,62 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup DNA
+ */
+
+#ifndef __DNA_ASSET_TYPES_H__
+#define __DNA_ASSET_TYPES_H__
+
+#include "DNA_listBase.h"
+
+/**
+ * \brief User defined tag.
+ * Currently only used by assets, could be used more often at some point.
+ * Maybe add a custom icon and color to these in future?
+ */
+typedef struct AssetTag {
+  struct AssetTag *next, *prev;
+  char name[64]; /* MAX_NAME */
+} AssetTag;
+
+/**
+ * \brief The meta-data of an asset.
+ * By creating and giving this for a data-block (#ID.asset_data), the data-block becomes an asset.
+ *
+ * \note This struct must be readable without having to read anything but blocks from the ID it is
+ *       attached to! That way, asset information of a file can be read, without reading anything
+ *       more than that from the file. So pointers to other IDs or ID data are strictly forbidden.
+ */
+typedef struct AssetMetaData {
+  /** Custom asset meta-data. Cannot store pointers to IDs (#STRUCT_NO_DATABLOCK_IDPROPERTIES)! */
+  struct IDProperty *properties;
+
+  /** Optional description of this asset for display in the UI. Dynamic length. */
+  char *description;
+  /** User defined tags for this asset. The asset manager uses these for filtering, but how they
+   * function exactly (e.g. how they are registered to provide a list of searchable available tags)
+   * is up to the asset-engine. */
+  ListBase tags; /* AssetTag */
+  short active_tag;
+  /** Store the number of tags to avoid continuous counting. Could be turned into runtime data, we
+   * can always reliably reconstruct it from the list. */
+  short tot_tags;
+
+  char _pad[4];
+} AssetMetaData;
+
+#endif /* __DNA_ASSET_TYPES_H__ */
diff --git a/source/blender/makesdna/intern/CMakeLists.txt b/source/blender/makesdna/intern/CMakeLists.txt
index 2051335dd7e..a7adaa7e258 100644
--- a/source/blender/makesdna/intern/CMakeLists.txt
+++ b/source/blender/makesdna/intern/CMakeLists.txt
@@ -138,6 +138,7 @@ set(SRC
   ../../blenlib/intern/hash_mm2a.c
   ../../blenlib/intern/listbase.c
 
+  ../DNA_asset_defaults.h
   ../DNA_brush_defaults.h
   ../DNA_cachefile_defaults.h
   ../DNA_camera_defaults.h
diff --git a/source/blender/makesdna/intern/dna_defaults.c b/source/blender/makesdna/intern/dna_defaults.c
index 1a8bd25215f..3e4d5d87fb0 100644
--- a/source/blender/makesdna/intern/dna_defaults.c
+++ b/source/blender/makesdna/intern/dna_defaults.c
@@ -85,6 +85,7 @@
 #include "DNA_defaults.h"
 
 #include "DNA_armature_types.h"
+#include "DNA_asset_types.h"
 #include "DNA_brush_types.h"
 #include "DNA_cachefile_types.h"
 #include "DNA_camera_types.h"
@@ -117,6 +118,7 @@
 #include "DNA_world_types.h"
 
 #include "DNA_armature_defaults.h"
+#include "DNA_asset_defaults.h"
 #include "DNA_brush_defaults.h"
 #include "DNA_cachefile_defaults.h"
 #include "DNA_camera_defaults.h"
@@ -148,6 +150,9 @@
 #define SDNA_DEFAULT_DECL_STRUCT(struct_name) \
   static const struct_name DNA_DEFAULT_##struct_name = _DNA_DEFAULT_##struct_name
 
+/* DNA_asset_defaults.h */
+SDNA_DEFAULT_DECL_STRUCT(AssetMetaData);
+
 /* DNA_armature_defaults.h */
 SDNA_DEFAULT_DECL_STRUCT(bArmature);
 
@@ -338,7 +343,10 @@ extern const bTheme U_theme_default;
 /** Keep headers sorted. */
 const void *DNA_default_table[SDNA_TYPE_MAX] = {
 
-    /* DNA_arnature_defaults.h */
+    /* DNA_asset_defaults.h */
+    SDNA_DEFAULT_DECL(AssetMetaData),
+
+    /* DNA_armature_defaults.h */
     SDNA_DEFAULT_DECL(bArmature),
 
     /* DNA_brush_defaults.h */
diff --git a/source/blender/makesdna/intern/makesdna.c b/source/blender/makesdna/intern/makesdna.c
index 81a7da7b4d8..54d2bc88d16 100644
--- a/source/blender/makesdna/intern/makesdna.c
+++ b/source/blender/makesdna/intern/makesdna.c
@@ -139,6 +139,7 @@ static const char *includefiles[] = {
     "DNA_volume_types.h",
     "DNA_simulation_types.h",
     "DNA_pointcache_types.h",
+    "DNA_asset_types.h",
 
     /* see comment above before editing! */
 
@@ -1533,6 +1534,7 @@ int main(int argc, char **argv)
 #include "DNA_action_types.h"
 #include "DNA_anim_types.h"
 #include "DNA_armature_types.h"
+#include "DNA_asset_types.h"
 #include "DNA_boid_types.h"
 #include "DNA_brush_types.h"
 #include "DNA_cachefile_types.h"