Fix T100075: OBJ import: images loaded multiple times instead of being reused

The new OBJ/MTL importer was creating a new image for any referenced
texture, even if another material (or another property of the same
material) already referenced the same texture. Make it use
BKE_image_load_exists function just like Collada or USD importers do.

Fixes T100075. Extended test coverage to count imported images;
without the fix import_cubes_with_textures_rel would have incorrectly
created 5 images instead of 4.

2 files changed, 47 insertions, 8 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 60e419728f3..f7685ba0b7b 100644
--- a/source/blender/io/wavefront_obj/importer/obj_import_mtl.cc
+++ b/source/blender/io/wavefront_obj/importer/obj_import_mtl.cc
@@ -65,7 +65,7 @@ static bool load_texture_image_at_path(Main *bmain,
                                        bNode *r_node,
                                        const std::string &path)
 {
-  Image *tex_image = BKE_image_load(bmain, path.c_str());
+  Image *tex_image = BKE_image_load_exists(bmain, path.c_str());
   if (!tex_image) {
     fprintf(stderr, "Cannot load image file: '%s'\n", path.c_str());
     return false;
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 183c543d7e3..ecf1243fa86 100644
--- a/source/blender/io/wavefront_obj/tests/obj_importer_tests.cc
+++ b/source/blender/io/wavefront_obj/tests/obj_importer_tests.cc
@@ -47,7 +47,8 @@ class obj_importer_test : public BlendfileLoadingBaseTest {
   void import_and_check(const char *path,
                         const Expectation *expect,
                         size_t expect_count,
-                        int expect_mat_count)
+                        int expect_mat_count,
+                        int expect_image_count = 0)
   {
     if (!blendfile_load("io_tests/blend_geometry/all_quads.blend")) {
       ADD_FAILURE();
@@ -132,12 +133,12 @@ class obj_importer_test : public BlendfileLoadingBaseTest {
     DEG_OBJECT_ITER_END;
     EXPECT_EQ(object_index, expect_count);
 
-    /* Count number of materials. */
-    int mat_count = 0;
-    LISTBASE_FOREACH (ID *, id, &bfile->main->materials) {
-      ++mat_count;
-    }
+    /* Check number of materials & textures. */
+    const int mat_count = BLI_listbase_count(&bfile->main->materials);
     EXPECT_EQ(mat_count, expect_mat_count);
+
+    const int ima_count = BLI_listbase_count(&bfile->main->images);
+    EXPECT_EQ(ima_count, expect_image_count);
   }
 };
 
@@ -306,7 +307,45 @@ 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);
+  import_and_check("materials.obj", expect, std::size(expect), 4, 1);
+}
+
+TEST_F(obj_importer_test, import_cubes_with_textures_rel)
+{
+  Expectation expect[] = {
+      {"OBCube", OB_MESH, 8, 12, 6, 24, float3(1, 1, -1), float3(-1, 1, 1)},
+      {"OBCube4Tex",
+       OB_MESH,
+       8,
+       12,
+       6,
+       24,
+       float3(1, 1, -1),
+       float3(-1, -1, 1),
+       float3(0, 1, 0),
+       float2(0.9935f, 0.0020f)},
+      {"OBCubeTiledTex",
+       OB_MESH,
+       8,
+       12,
+       6,
+       24,
+       float3(4, 1, -1),
+       float3(2, -1, 1),
+       float3(0, 1, 0),
+       float2(0.9935f, 0.0020f)},
+      {"OBCubeTiledTexFromAnotherFolder",
+       OB_MESH,
+       8,
+       12,
+       6,
+       24,
+       float3(7, 1, -1),
+       float3(5, -1, 1),
+       float3(0, 1, 0),
+       float2(0.9935f, 0.0020f)},
+  };
+  import_and_check("cubes_with_textures_rel.obj", expect, std::size(expect), 3, 4);
 }
 
 TEST_F(obj_importer_test, import_faces_invalid_or_with_holes)