Fix T87621: Win32 Do Not Create Preview Thumbnails for Offline Files

This patch turns off the creation of file thumbnails for files that are
offline and therefore not fully-present on the file system. These types
of files - typically cloud-based or stored on slower backup media -
only have their contents available when actually accessed, at which
point there will be a short delay. If we allow thumbnail creation in
this state then all offline files in a folder will be downloaded just
to view a listing, which can take a long time.

Files in this state will instead get a more generic thumbnail that
still indicates file type (icon in center) and that shows offline state
will a special icon at the bottom-left.

Although this currently only affects Windows users, most of this patch
is platform-agnostic. So other platforms inherit this behavior if they
only add FILE_ATTR_OFFLINE attribute to files in this state.

See D11101 for more information.

Differential Revision: https://developer.blender.org/D11101

Reviewed by Julian Eisel

2 files changed, 10 insertions, 4 deletions

diff --git a/source/blender/editors/space_file/file_draw.c b/source/blender/editors/space_file/file_draw.c
index c1dcf2e56d3..189b9b4c874 100644
--- a/source/blender/editors/space_file/file_draw.c
+++ b/source/blender/editors/space_file/file_draw.c
@@ -323,6 +323,7 @@ static void file_draw_preview(uiBlock *block,
   int ex, ey;
   bool show_outline = !is_icon &&
                       (file->typeflag & (FILE_TYPE_IMAGE | FILE_TYPE_MOVIE | FILE_TYPE_BLENDER));
+  const bool is_offline = (file->attributes & FILE_ATTR_OFFLINE);
 
   BLI_assert(imb != NULL);
 
@@ -419,14 +420,14 @@ static void file_draw_preview(uiBlock *block,
         icon_x, icon_y, icon, icon_aspect / U.dpi_fac, icon_opacity, 0.0f, icon_color, false);
   }
 
-  if (is_link) {
-    /* Arrow icon to indicate it is a shortcut, link, or alias. */
+  if (is_link || is_offline) {
+    /* Icon at bottom to indicate it is a shortcut, link, alias, or offline. */
     float icon_x, icon_y;
     icon_x = xco + (2.0f * UI_DPI_FAC);
     icon_y = yco + (2.0f * UI_DPI_FAC);
-    const int arrow = ICON_LOOP_FORWARDS;
+    const int arrow = is_link ? ICON_LOOP_FORWARDS : ICON_URL;
     if (!is_icon) {
-      /* Arrow at very bottom-left if preview style. */
+      /* At very bottom-left if preview style. */
       const uchar dark[4] = {0, 0, 0, 255};
       const uchar light[4] = {255, 255, 255, 255};
       UI_icon_draw_ex(icon_x + 1, icon_y - 1, arrow, 1.0f / U.dpi_fac, 0.2f, 0.0f, dark, false);
diff --git a/source/blender/editors/space_file/filelist.c b/source/blender/editors/space_file/filelist.c
index ca16563a7e2..37a32164cfc 100644
--- a/source/blender/editors/space_file/filelist.c
+++ b/source/blender/editors/space_file/filelist.c
@@ -1601,6 +1601,11 @@ static void filelist_cache_previews_push(FileList *filelist, FileDirEntry *entry
 
   BLI_assert(cache->flags & FLC_PREVIEWS_ACTIVE);
 
+  if (!entry->preview_icon_id && (entry->attributes & FILE_ATTR_OFFLINE)) {
+    entry->flags |= FILE_ENTRY_INVALID_PREVIEW;
+    return;
+  }
+
   if (entry->preview_icon_id) {
     return;
   }