Assets: Sanitize threaded preview creation with undo

Basically, this fixes disappearing previews when editing asset metadata
or performing undo/redo actions.

The preview generation in a background job will eventually modify ID
data, but the undo push was done prior to that. So obviously, an undo
then would mean the preview is lost.

This patch makes it so undo/redo will regenerate the preview, if the preview
rendering was invoked but not finished in the undone/redone state.

The preview flag PRV_UNFINISHED wasn't entirely what we needed. So I had to
change it to a slightly different flag, with different semantics.

3 files changed, 8 insertions, 0 deletions

diff --git a/source/blender/windowmanager/intern/wm_event_system.c b/source/blender/windowmanager/intern/wm_event_system.c
index 474d900a53d..0b28b6b4b57 100644
--- a/source/blender/windowmanager/intern/wm_event_system.c
+++ b/source/blender/windowmanager/intern/wm_event_system.c
@@ -64,6 +64,7 @@
 #include "ED_asset.h"
 #include "ED_fileselect.h"
 #include "ED_info.h"
+#include "ED_render.h"
 #include "ED_screen.h"
 #include "ED_undo.h"
 #include "ED_util.h"
@@ -457,6 +458,9 @@ void wm_event_do_notifiers(bContext *C)
         else if (note->data == ND_DATACHANGED) {
           wm_window_title(wm, win);
         }
+        else if (note->data == ND_UNDO) {
+          ED_preview_restart_queue_work(C);
+        }
       }
       if (note->window == win) {
         if (note->category == NC_SCREEN) {
diff --git a/source/blender/windowmanager/intern/wm_files.c b/source/blender/windowmanager/intern/wm_files.c
index a301b17227d..e95ce98352a 100644
--- a/source/blender/windowmanager/intern/wm_files.c
+++ b/source/blender/windowmanager/intern/wm_files.c
@@ -111,6 +111,7 @@
 #include "ED_fileselect.h"
 #include "ED_image.h"
 #include "ED_outliner.h"
+#include "ED_render.h"
 #include "ED_screen.h"
 #include "ED_undo.h"
 #include "ED_util.h"
@@ -620,6 +621,8 @@ static void wm_file_read_pre(bContext *C, bool use_data, bool UNUSED(use_userdef
   /* Always do this as both startup and preferences may have loaded in many font's
    * at a different zoom level to the file being loaded. */
   UI_view2d_zoom_cache_reset();
+
+  ED_preview_restart_queue_free();
 }
 
 /**
diff --git a/source/blender/windowmanager/intern/wm_init_exit.c b/source/blender/windowmanager/intern/wm_init_exit.c
index c382af03c4a..1a45e535a4a 100644
--- a/source/blender/windowmanager/intern/wm_init_exit.c
+++ b/source/blender/windowmanager/intern/wm_init_exit.c
@@ -547,6 +547,7 @@ void WM_exit_ex(bContext *C, const bool do_python)
   RE_engines_exit();
 
   ED_preview_free_dbase(); /* frees a Main dbase, before BKE_blender_free! */
+  ED_preview_restart_queue_free();
   ED_assetlist_storage_exit();
 
   if (wm) {