Fix T100737: OBJ/USD import: imported object has no active material, material has 2 users

Fixes issues in importers written in C++ (T100737):

- Materials had one reference count too much. Affected Collada,
  Alembic, USD, OBJ importers, looks like "since forever".
- Active material index was not properly set on imported meshes.
  Regression since 3.3 (D15145). Affected Alembic, USD, OBJ. Note:
  now it sets the first material as the active one, whereas
  previously the last one was set as active. First one sounds more
  "intuitive" to me.

Reviewed By: Bastien Montagne
Differential Revision: https://developer.blender.org/D15831

2 files changed, 5 insertions, 0 deletions

diff --git a/source/blender/io/usd/intern/usd_reader_material.cc b/source/blender/io/usd/intern/usd_reader_material.cc
index 8feceee55ed..52addfeb418 100644
--- a/source/blender/io/usd/intern/usd_reader_material.cc
+++ b/source/blender/io/usd/intern/usd_reader_material.cc
@@ -4,6 +4,7 @@
 #include "usd_reader_material.h"
 
 #include "BKE_image.h"
+#include "BKE_lib_id.h"
 #include "BKE_main.h"
 #include "BKE_material.h"
 #include "BKE_node.h"
@@ -266,6 +267,7 @@ Material *USDMaterialReader::add_material(const pxr::UsdShadeMaterial &usd_mater
 
   /* Create the material. */
   Material *mtl = BKE_material_add(bmain_, mtl_name.c_str());
+  id_us_min(&mtl->id);
 
   /* Get the UsdPreviewSurface shader source for the material,
    * if there is one. */
diff --git a/source/blender/io/usd/intern/usd_reader_mesh.cc b/source/blender/io/usd/intern/usd_reader_mesh.cc
index 45657525527..de638b0a837 100644
--- a/source/blender/io/usd/intern/usd_reader_mesh.cc
+++ b/source/blender/io/usd/intern/usd_reader_mesh.cc
@@ -168,6 +168,9 @@ static void assign_materials(Main *bmain,
       std::cout << "WARNING: Couldn't assign material " << it->first << std::endl;
     }
   }
+  if (ob->totcol > 0) {
+    ob->actcol = 1;
+  }
 }
 
 }  // namespace utils