File Browser: Fix slowdown with non-existing ID previews in big files

When the File (or Asset) Browser would display data-blocks without
previews in a heavy .blend file, there would be a drastic slowdown.

See patch for details and comparison videos.

Differential Revision: https://developer.blender.org/D16273

Reviewed by: Bastien Montagne

2 files changed, 20 insertions, 0 deletions

diff --git a/source/blender/blenloader/BLO_readfile.h b/source/blender/blenloader/BLO_readfile.h
index 93040fa01ee..75a1956ce12 100644
--- a/source/blender/blenloader/BLO_readfile.h
+++ b/source/blender/blenloader/BLO_readfile.h
@@ -182,6 +182,11 @@ void BLO_blendfiledata_free(BlendFileData *bfd);
 typedef struct BLODataBlockInfo {
   char name[64]; /* MAX_NAME */
   struct AssetMetaData *asset_data;
+  /* Optimization: Tag data-blocks for which we know there is no preview.
+   * Knowing this can be used to skip the (potentially expensive) preview loading process. If this
+   * is set to true it means we looked for a preview and couldn't find one. False may mean that
+   * either no preview was found, or that it wasn't looked for in the first place. */
+  bool no_preview_found;
 } BLODataBlockInfo;
 
 /**
diff --git a/source/blender/blenloader/intern/readblenentry.cc b/source/blender/blenloader/intern/readblenentry.cc
index 55ac2d31277..ead796c0e28 100644
--- a/source/blender/blenloader/intern/readblenentry.cc
+++ b/source/blender/blenloader/intern/readblenentry.cc
@@ -138,11 +138,15 @@ LinkNode *BLO_blendhandle_get_datablock_info(BlendHandle *bh,
   BHead *bhead;
   int tot = 0;
 
+  const int sdna_nr_preview_image = DNA_struct_find_nr(fd->filesdna, "PreviewImage");
+
   for (bhead = blo_bhead_first(fd); bhead; bhead = blo_bhead_next(fd, bhead)) {
     if (bhead->code == ENDB) {
       break;
     }
     if (bhead->code == ofblocktype) {
+      BHead *id_bhead = bhead;
+
       const char *name = blo_bhead_id_name(fd, bhead) + 2;
       AssetMetaData *asset_meta_data = blo_bhead_id_asset_data_address(fd, bhead);
 
@@ -165,6 +169,17 @@ LinkNode *BLO_blendhandle_get_datablock_info(BlendHandle *bh,
       STRNCPY(info->name, name);
       info->asset_data = asset_meta_data;
 
+      bool has_preview = false;
+      /* See if we can find a preview in the data of this ID. */
+      for (BHead *data_bhead = blo_bhead_next(fd, id_bhead); data_bhead->code == DATA;
+           data_bhead = blo_bhead_next(fd, data_bhead)) {
+        if (data_bhead->SDNAnr == sdna_nr_preview_image) {
+          has_preview = true;
+          break;
+        }
+      }
+      info->no_preview_found = !has_preview;
+
       BLI_linklist_prepend(&infos, info);
       tot++;
     }