USD import: temp fix for broken UDIMS.

Applying patch authored by Jesse Yurkovich to support
single file UDIMs, while this code is still under review,
to temporarily prevent a regression for those testing USD
features.  If the patch is rejected or rewritten, it might
be necessary to back out this commit or merge it with the
latest changes.

source/blender/blenkernel/BKE_image.h

@@ -378,6 +378,11 @@ typedef enum {
   UDIM_TILE_FORMAT_UVTILE = 2
 } eUDIM_TILE_FORMAT;
 
+/**
+ * Checks if the filename portion of the path contains a UDIM token.
+ */
+bool BKE_image_is_filename_tokenized(char *filepath);
+
 /**
  * Ensures that `filename` contains a UDIM token if we find a supported format pattern.
  * \note This must only be the name component (without slashes).

source/blender/blenkernel/intern/image.cc

@@ -2927,6 +2927,7 @@ void BKE_image_signal(Main *bmain, Image *ima, ImageUser *iuser, int signal)
           MEM_freeN(tile);
         }
         base_tile->next = nullptr;
+        base_tile->tile_number = 1001;
         ima->tiles.last = base_tile;
       }
 
@@ -3108,7 +3109,12 @@ bool BKE_image_get_tile_info(char *filepath, ListBase *tiles, int *r_tile_start,
   char filename[FILE_MAXFILE], dirname[FILE_MAXDIR];
   BLI_split_dirfile(filepath, dirname, filename, sizeof(dirname), sizeof(filename));
 
-  BKE_image_ensure_tile_token(filename);
+  /* If a tokenized path was provided, allow single-file sequences. Otherwise
+   * tokenize it here and attempt to find 2 or more files in the sequence. */
+  bool allow_single = BKE_image_is_filename_tokenized(filename);
+  if (!allow_single) {
+    BKE_image_ensure_tile_token(filename);
+  }
 
   eUDIM_TILE_FORMAT tile_format;
   char *udim_pattern = BKE_image_get_tile_strformat(filename, &tile_format);
@@ -3142,10 +3148,10 @@ bool BKE_image_get_tile_info(char *filepath, ListBase *tiles, int *r_tile_start,
   BLI_filelist_free(dirs, dirs_num);
   MEM_SAFE_FREE(udim_pattern);
 
-  /* Ensure that all discovered UDIMs are valid and that there's at least 2 files in total.
-   * Downstream code checks the range value to determine tiled-ness; it's important we match that
-   * expectation here too (T97366). */
-  if (all_valid_udim && min_udim <= IMA_UDIM_MAX && max_udim > min_udim) {
+  /* Ensure that all discovered UDIMs are valid and that there's at least 2 files in total if
+   * allow_single is false (T97366). */
+  bool valid_count = allow_single || max_udim > min_udim;
+  if (all_valid_udim && min_udim <= IMA_UDIM_MAX && valid_count) {
     BLI_join_dirfile(filepath, FILE_MAX, dirname, filename);
 
     *r_tile_start = min_udim;
@@ -3317,13 +3323,18 @@ bool BKE_image_fill_tile(struct Image *ima,
   return false;
 }
 
+bool BKE_image_is_filename_tokenized(char *filepath)
+{
+  const char *filename = BLI_path_basename(filepath);
+  return strstr(filename, "<UDIM>") != nullptr || strstr(filename, "<UVTILE>") != nullptr;
+}
+
 void BKE_image_ensure_tile_token(char *filename)
 {
   BLI_assert_msg(BLI_path_slash_find(filename) == nullptr,
                  "Only the file-name component should be used!");
 
-  /* Is there a '<' character in the filename? Assume tokens already present. */
-  if (strstr(filename, "<") != nullptr) {
+  if (BKE_image_is_filename_tokenized(filename)) {
     return;
   }
 

source/blender/editors/include/ED_image.h

@@ -173,6 +173,7 @@ typedef struct ImageFrameRange {
   int length;
   int offset;
   /* UDIM tiles. */
+  bool udims_detected;
   ListBase udim_tiles;
 
   /* Temporary data. */

source/blender/editors/space_image/image_ops.c

@@ -1274,8 +1274,8 @@ static Image *image_open_single(Main *bmain,
       BKE_image_free_views(ima);
     }
 
-    if ((range->length > 1) && (ima->source == IMA_SRC_FILE)) {
-      if (range->udim_tiles.first) {
+    if (ima->source == IMA_SRC_FILE) {
+      if (range->udims_detected && range->udim_tiles.first) {
         ima->source = IMA_SRC_TILED;
         ImageTile *first_tile = ima->tiles.first;
         first_tile->tile_number = range->offset;
@@ -1283,7 +1283,7 @@ static Image *image_open_single(Main *bmain,
           BKE_image_add_tile(ima, POINTER_AS_INT(node->data), NULL);
         }
       }
-      else {
+      else if (range->length > 1) {
         ima->source = IMA_SRC_SEQUENCE;
       }
     }

source/blender/editors/space_image/image_sequence.c

@@ -107,10 +107,10 @@ static void image_detect_frame_range(ImageFrameRange *range, const bool detect_u
   /* UDIM */
   if (detect_udim) {
     int udim_start, udim_range;
-    bool result = BKE_image_get_tile_info(
+    range->udims_detected = BKE_image_get_tile_info(
         range->filepath, &range->udim_tiles, &udim_start, &udim_range);
 
-    if (result) {
+    if (range->udims_detected) {
       range->offset = udim_start;
       range->length = udim_range;
       return;