obj: implement support for PBR .mtl extensions

Implement import & export support for "PBR extensions" in .mtl files
(T101029, also fixes T86736).

Newly supported parameters:
- Roughness (Pr, map_Pr)
- Metallic (Pm, map_Pm)
- Sheen (Ps, map_Ps)
- Clearcoat thickness (Pc) and roughness (Pcr)
- Anisotropy (aniso) and rotation (anisor)
- Transmittance (Tf / Kt)

Exporter has an option to enable these additional PBR parameters
export; defaults to off since not all software understands that.

Exporter UI tweaked and all material-related options were put into
their own separate box.

Added/extended test files in Subversion repository for test coverage.

1 files changed, 3 insertions, 6 deletions

diff --git a/source/blender/io/wavefront_obj/IO_wavefront_obj.h b/source/blender/io/wavefront_obj/IO_wavefront_obj.h
index 544630c9cc0..0a92bbca477 100644
--- a/source/blender/io/wavefront_obj/IO_wavefront_obj.h
+++ b/source/blender/io/wavefront_obj/IO_wavefront_obj.h
@@ -48,18 +48,15 @@ struct OBJExportParams {
   bool export_triangulated_mesh;
   bool export_curves_as_nurbs;
   ePathReferenceMode path_mode;
+  bool export_pbr_extensions;
 
   /* Grouping options. */
   bool export_object_groups;
   bool export_material_groups;
   bool export_vertex_groups;
-  /**
-   * Calculate smooth groups from sharp edges.
-   */
+  /* Calculate smooth groups from sharp edges. */
   bool export_smooth_groups;
-  /**
-   * Create bitflags instead of the default "0"/"1" group IDs.
-   */
+  /* Create bitflags instead of the default "0"/"1" group IDs. */
   bool smooth_groups_bitflags;
 };