Fix T97757: Some MTL import correctness issues in the new OBJ importer

Fix several correctness issues where the new OBJ/MTL importer was not
producing the same results as the old one, mostly because the code for
some reason had slightly different logic. Fixes T97757:

- When .obj file tries to use a material that does not exist, the code
  was continuing to use the previous material, instead of creating new
  default one, as the previous importer did.
- Previous importer was always searching/parsing "foo.mtl" for a
  "foo.obj" file, even if the file itself does not contain
  "mtllib foo.mtl" statement. One file from T97757 repros happens to
  depend on that, so resurrect that behavior.
- When IOR (Ni) or Alpha (d) are not specified in .mtl file, do not
  wrongly set -1 values to the blender material.
- When base (Kd) or emissive (Ke) colors are not specified in the .mtl
  file, do not set them on the blender material.
- Roughness and metallic values used by viewport shading were not set
  onto blender material.
- The logic for when metallic was set to zero was incorrect; it should
  be set to zero when "not using reflection", not when "mtl file does
  not contain metallic".
- Do not produce a warning when illum value is not spelled out in .mtl
  file, treat as default (1).
- Parse illum as a float just like python importer does, as to not
  reintroduce part of T60135.

Reviewed By: Howard Trickey
Differential Revision: https://developer.blender.org/D14822

1 files changed, 8 insertions, 9 deletions

diff --git a/source/blender/io/wavefront_obj/importer/obj_importer.cc b/source/blender/io/wavefront_obj/importer/obj_importer.cc
index c21d2d9583c..d9c033e1f77 100644
--- a/source/blender/io/wavefront_obj/importer/obj_importer.cc
+++ b/source/blender/io/wavefront_obj/importer/obj_importer.cc
@@ -29,15 +29,14 @@ namespace blender::io::obj {
 /**
  * Make Blender Mesh, Curve etc from Geometry and add them to the import collection.
  */
-static void geometry_to_blender_objects(
-    Main *bmain,
-    Scene *scene,
-    ViewLayer *view_layer,
-    const OBJImportParams &import_params,
-    Vector<std::unique_ptr<Geometry>> &all_geometries,
-    const GlobalVertices &global_vertices,
-    const Map<std::string, std::unique_ptr<MTLMaterial>> &materials,
-    Map<std::string, Material *> &created_materials)
+static void geometry_to_blender_objects(Main *bmain,
+                                        Scene *scene,
+                                        ViewLayer *view_layer,
+                                        const OBJImportParams &import_params,
+                                        Vector<std::unique_ptr<Geometry>> &all_geometries,
+                                        const GlobalVertices &global_vertices,
+                                        Map<std::string, std::unique_ptr<MTLMaterial>> &materials,
+                                        Map<std::string, Material *> &created_materials)
 {
   BKE_view_layer_base_deselect_all(view_layer);
   LayerCollection *lc = BKE_layer_collection_get_active(view_layer);