Fix T99502: OBJ/MTL import: behavior changed for missing texture files

Python based OBJ importer, as well as glTF2 importer, are creating
"placeholder" images for texture images that can't be found. These
are empty textures (displayed as magenta), but with their file paths
set so that File > External Data > Report Missing Files can report
them as missing.

Make the new C++ OBJ importer do the same as well. Fixes T99502.

2 files changed, 54 insertions, 35 deletions

diff --git a/source/blender/io/wavefront_obj/importer/obj_import_mtl.cc b/source/blender/io/wavefront_obj/importer/obj_import_mtl.cc
index 099929b0e67..0023d1159c5 100644
--- a/source/blender/io/wavefront_obj/importer/obj_import_mtl.cc
+++ b/source/blender/io/wavefront_obj/importer/obj_import_mtl.cc
@@ -62,65 +62,81 @@ static void set_property_of_socket(eNodeSocketDatatype property_type,
   }
 }
 
-static bool load_texture_image_at_path(Main *bmain,
-                                       const tex_map_XX &tex_map,
-                                       bNode *r_node,
-                                       const std::string &path,
-                                       bool relative_paths)
+static Image *load_image_at_path(Main *bmain, const std::string &path, bool relative_paths)
 {
-  Image *tex_image = BKE_image_load_exists(bmain, path.c_str());
-  if (!tex_image) {
+  Image *image = BKE_image_load_exists(bmain, path.c_str());
+  if (!image) {
     fprintf(stderr, "Cannot load image file: '%s'\n", path.c_str());
-    return false;
+    return nullptr;
   }
   fprintf(stderr, "Loaded image from: '%s'\n", path.c_str());
   if (relative_paths) {
-    BLI_path_rel(tex_image->filepath, BKE_main_blendfile_path(bmain));
+    BLI_path_rel(image->filepath, BKE_main_blendfile_path(bmain));
   }
-  r_node->id = reinterpret_cast<ID *>(tex_image);
-  NodeTexImage *image = static_cast<NodeTexImage *>(r_node->storage);
-  image->projection = tex_map.projection_type;
-  return true;
+  return image;
 }
 
-/**
- * Load image for Image Texture node and set the node properties.
- * Return success if Image can be loaded successfully.
- */
-static bool load_texture_image(Main *bmain,
-                               const tex_map_XX &tex_map,
-                               bNode *r_node,
-                               bool relative_paths)
+static Image *create_placeholder_image(Main *bmain, const std::string &path)
+{
+  const float color[4] = {0, 0, 0, 1};
+  Image *image = BKE_image_add_generated(bmain,
+                                         32,
+                                         32,
+                                         BLI_path_basename(path.c_str()),
+                                         24,
+                                         false,
+                                         IMA_GENTYPE_BLANK,
+                                         color,
+                                         false,
+                                         false,
+                                         false);
+  STRNCPY(image->filepath, path.c_str());
+  image->source = IMA_SRC_FILE;
+  return image;
+}
+
+static Image *load_texture_image(Main *bmain,
+                                 const tex_map_XX &tex_map,
+                                 bNode *r_node,
+                                 bool relative_paths)
 {
   BLI_assert(r_node && r_node->type == SH_NODE_TEX_IMAGE);
+  Image *image = nullptr;
 
   /* First try treating texture path as relative. */
   std::string tex_path{tex_map.mtl_dir_path + tex_map.image_path};
-  if (load_texture_image_at_path(bmain, tex_map, r_node, tex_path, relative_paths)) {
-    return true;
+  image = load_image_at_path(bmain, tex_path, relative_paths);
+  if (image != nullptr) {
+    return image;
   }
   /* Then try using it directly as absolute path. */
   std::string raw_path{tex_map.image_path};
-  if (load_texture_image_at_path(bmain, tex_map, r_node, raw_path, relative_paths)) {
-    return true;
+  image = load_image_at_path(bmain, raw_path, relative_paths);
+  if (image != nullptr) {
+    return image;
   }
   /* Try removing quotes. */
   std::string no_quote_path{tex_path};
   auto end_pos = std::remove(no_quote_path.begin(), no_quote_path.end(), '"');
   no_quote_path.erase(end_pos, no_quote_path.end());
-  if (no_quote_path != tex_path &&
-      load_texture_image_at_path(bmain, tex_map, r_node, no_quote_path, relative_paths)) {
-    return true;
+  if (no_quote_path != tex_path) {
+    image = load_image_at_path(bmain, no_quote_path, relative_paths);
+    if (image != nullptr) {
+      return image;
+    }
   }
   /* Try replacing underscores with spaces. */
   std::string no_underscore_path{no_quote_path};
   std::replace(no_underscore_path.begin(), no_underscore_path.end(), '_', ' ');
-  if (no_underscore_path != no_quote_path && no_underscore_path != tex_path &&
-      load_texture_image_at_path(bmain, tex_map, r_node, no_underscore_path, relative_paths)) {
-    return true;
+  if (no_underscore_path != no_quote_path && no_underscore_path != tex_path) {
+    image = load_image_at_path(bmain, no_underscore_path, relative_paths);
+    if (image != nullptr) {
+      return image;
+    }
   }
 
-  return false;
+  image = create_placeholder_image(bmain, tex_path);
+  return image;
 }
 
 ShaderNodetreeWrap::ShaderNodetreeWrap(Main *bmain,
@@ -347,10 +363,13 @@ void ShaderNodetreeWrap::add_image_textures(Main *bmain, Material *mat, bool rel
     }
 
     bNode *image_texture = add_node_to_tree(SH_NODE_TEX_IMAGE);
-    if (!load_texture_image(bmain, texture_map.value, image_texture, relative_paths)) {
-      /* Image could not be added, so don't add or link further nodes. */
+    Image *image = load_texture_image(bmain, texture_map.value, image_texture, relative_paths);
+    if (image == nullptr) {
       continue;
     }
+    image_texture->id = &image->id;
+    static_cast<NodeTexImage *>(image_texture->storage)->projection =
+        texture_map.value.projection_type;
 
     /* Add normal map node if needed. */
     bNode *normal_map = nullptr;
diff --git a/source/blender/io/wavefront_obj/tests/obj_importer_tests.cc b/source/blender/io/wavefront_obj/tests/obj_importer_tests.cc
index 2b446042f33..4055d892332 100644
--- a/source/blender/io/wavefront_obj/tests/obj_importer_tests.cc
+++ b/source/blender/io/wavefront_obj/tests/obj_importer_tests.cc
@@ -308,7 +308,7 @@ TEST_F(obj_importer_test, import_materials)
       {"OBCube", OB_MESH, 8, 12, 6, 24, float3(1, 1, -1), float3(-1, 1, 1)},
       {"OBmaterials", OB_MESH, 8, 12, 6, 24, float3(-1, -1, 1), float3(1, -1, -1)},
   };
-  import_and_check("materials.obj", expect, std::size(expect), 4, 1);
+  import_and_check("materials.obj", expect, std::size(expect), 4, 8);
 }
 
 TEST_F(obj_importer_test, import_cubes_with_textures_rel)