IDTypeInfo: add .blend file io callbacks

This is part of T76372.
It adds the `blend_write`, `blend_read_data`, `blend_read_lib`
and `blend_read_expand` which correspond to the various
steps when reading and writing .blend files.
Having these callbacks allows us to decentralize the blenloader
code a lot more. This has the affect that code related to any
specific ID type is less scattered.

Reviewers: mont29

Differential Revision: https://developer.blender.org/D8670

2 files changed, 18 insertions, 0 deletions

diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index 304ba87402c..b35ad3d34c6 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -8240,6 +8240,9 @@ static bool direct_link_id(FileData *fd, Main *main, const int tag, ID *id, ID *
   }
 
   const IDTypeInfo *id_type = BKE_idtype_get_info_from_id(id);
+  if (id_type->blend_read_data != NULL) {
+    id_type->blend_read_data(&reader, id);
+  }
 
   /* XXX Very weakly handled currently, see comment in read_libblock() before trying to
    * use it for anything new. */
@@ -8959,6 +8962,11 @@ static void lib_link_all(FileData *fd, Main *bmain)
 
     lib_link_id(&reader, id);
 
+    const IDTypeInfo *id_type = BKE_idtype_get_info_from_id(id);
+    if (id_type->blend_read_lib != NULL) {
+      id_type->blend_read_lib(&reader, id);
+    }
+
     /* Note: ID types are processed in reverse order as defined by INDEX_ID_XXX enums in DNA_ID.h.
      * This ensures handling of most dependencies in proper order, as elsewhere in code.
      * Please keep order of entries in that switch matching that order, it's easier to quickly see
@@ -10372,6 +10380,11 @@ void BLO_expand_main(void *fdhandle, Main *mainvar)
         if (id->tag & LIB_TAG_NEED_EXPAND) {
           expand_id(&expander, id);
 
+          const IDTypeInfo *id_type = BKE_idtype_get_info_from_id(id);
+          if (id_type->blend_read_expand != NULL) {
+            id_type->blend_read_expand(&expander, id);
+          }
+
           switch (GS(id->name)) {
             case ID_OB:
               expand_object(&expander, (Object *)id);
diff --git a/source/blender/blenloader/intern/writefile.c b/source/blender/blenloader/intern/writefile.c
index a9f9685bf75..6ce822a09c1 100644
--- a/source/blender/blenloader/intern/writefile.c
+++ b/source/blender/blenloader/intern/writefile.c
@@ -3865,6 +3865,11 @@ static bool write_file_handle(Main *mainvar,
         ((ID *)id_buffer)->prev = NULL;
         ((ID *)id_buffer)->next = NULL;
 
+        const IDTypeInfo *id_type = BKE_idtype_get_info_from_id(id);
+        if (id_type->blend_write != NULL) {
+          id_type->blend_write(&writer, (ID *)id_buffer, id);
+        }
+
         switch ((ID_Type)GS(id->name)) {
           case ID_WM:
             write_windowmanager(&writer, (wmWindowManager *)id_buffer, id);