Fix T96470 new obj exporter writing material groups

This is patch D14349 from Aras Pranckevicius.

The logic in the code was _completely different_ from the documentation
and what the python exporter in 3.0 did. The new code assumed that
"export material groups" meant "append material name to the object name",
and was only ever kicking in when the "export object groups" option was
also checked. But the proper behavior (as in 3.0 exporter & the online docs),
is to emit g objectname_materialname before each usemtl line. Which is something entirely else.

1 files changed, 13 insertions, 0 deletions

diff --git a/source/blender/io/wavefront_obj/tests/obj_exporter_tests.cc b/source/blender/io/wavefront_obj/tests/obj_exporter_tests.cc
index e96a7d28561..b8fecfb25f3 100644
--- a/source/blender/io/wavefront_obj/tests/obj_exporter_tests.cc
+++ b/source/blender/io/wavefront_obj/tests/obj_exporter_tests.cc
@@ -511,4 +511,17 @@ TEST_F(obj_exporter_regression_test, all_objects)
                                _export.params);
 }
 
+TEST_F(obj_exporter_regression_test, all_objects_mat_groups)
+{
+  OBJExportParamsDefault _export;
+  _export.params.forward_axis = OBJ_AXIS_Y_FORWARD;
+  _export.params.up_axis = OBJ_AXIS_Z_UP;
+  _export.params.export_smooth_groups = true;
+  _export.params.export_material_groups = true;
+  compare_obj_export_to_golden("io_tests/blend_scene/all_objects.blend",
+                               "io_tests/obj/all_objects_mat_groups.obj",
+                               "io_tests/obj/all_objects_mat_groups.mtl",
+                               _export.params);
+}
+
 }  // namespace blender::io::obj