Add key structure and hashing utils for ID caches.

Part of D8183, refactoring how we preserve caches across undo steps in
readfile code.

1 files changed, 13 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_idtype.h b/source/blender/blenkernel/BKE_idtype.h
index b6dfadd3b2a..56e788ccfe8 100644
--- a/source/blender/blenkernel/BKE_idtype.h
+++ b/source/blender/blenkernel/BKE_idtype.h
@@ -46,6 +46,19 @@ enum {
   IDTYPE_FLAGS_NO_MAKELOCAL = 1 << 2,
 };
 
+typedef struct IDCacheKey {
+  /* The session uuid of the ID owning the cached data. */
+  unsigned int id_session_uuid;
+  /* Value uniquely indentifying the cache whithin its ID.
+   * Typically the offset of its member in the data-block struct, but can be anything. */
+  size_t offset_in_ID;
+  /* Actual address of the cached data to save and restore. */
+  void *cache_v;
+} IDCacheKey;
+
+uint BKE_idtype_cache_key_hash(const void *key_v);
+bool BKE_idtype_cache_key_cmp(const void *key_a_v, const void *key_b_v);
+
 /* ********** Prototypes for IDTypeInfo callbacks. ********** */
 
 typedef void (*IDTypeInitDataFunction)(struct ID *id);