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.

2 files changed, 65 insertions, 0 deletions

diff --git a/source/blender/io/wavefront_obj/importer/obj_import_file_reader.cc b/source/blender/io/wavefront_obj/importer/obj_import_file_reader.cc
index cc98dbdbf92..f92f9894f75 100644
--- a/source/blender/io/wavefront_obj/importer/obj_import_file_reader.cc
+++ b/source/blender/io/wavefront_obj/importer/obj_import_file_reader.cc
@@ -617,6 +617,15 @@ static MTLTexMapType mtl_line_start_to_texture_type(const char *&p, const char *
       parse_keyword(p, end, "map_bump")) {
     return MTLTexMapType::Normal;
   }
+  if (parse_keyword(p, end, "map_Pr")) {
+    return MTLTexMapType::Roughness;
+  }
+  if (parse_keyword(p, end, "map_Pm")) {
+    return MTLTexMapType::Metallic;
+  }
+  if (parse_keyword(p, end, "map_Ps")) {
+    return MTLTexMapType::Sheen;
+  }
   return MTLTexMapType::Count;
 }
 
@@ -806,6 +815,30 @@ void MTLParser::parse_and_store(Map<string, std::unique_ptr<MTLMaterial>> &r_mat
         parse_float(p, end, 1.0f, val);
         material->illum_mode = val;
       }
+      else if (parse_keyword(p, end, "Pr")) {
+        parse_float(p, end, 0.5f, material->roughness);
+      }
+      else if (parse_keyword(p, end, "Pm")) {
+        parse_float(p, end, 0.0f, material->metallic);
+      }
+      else if (parse_keyword(p, end, "Ps")) {
+        parse_float(p, end, 0.0f, material->sheen);
+      }
+      else if (parse_keyword(p, end, "Pc")) {
+        parse_float(p, end, 0.0f, material->cc_thickness);
+      }
+      else if (parse_keyword(p, end, "Pcr")) {
+        parse_float(p, end, 0.0f, material->cc_roughness);
+      }
+      else if (parse_keyword(p, end, "aniso")) {
+        parse_float(p, end, 0.0f, material->aniso);
+      }
+      else if (parse_keyword(p, end, "anisor")) {
+        parse_float(p, end, 0.0f, material->aniso_rot);
+      }
+      else if (parse_keyword(p, end, "Kt") || parse_keyword(p, end, "Tf")) {
+        parse_floats(p, end, 0.0f, material->transmit_color, 3);
+      }
       else {
         parse_texture_map(p, end, material, mtl_dir_path_);
       }
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 2819fe9efc8..c471b2002de 100644
--- a/source/blender/io/wavefront_obj/importer/obj_import_mtl.cc
+++ b/source/blender/io/wavefront_obj/importer/obj_import_mtl.cc
@@ -284,6 +284,14 @@ static void set_bsdf_socket_values(bNode *bsdf, Material *mat, const MTLMaterial
     alpha = 1.0f;
   }
 
+  /* PBR values, when present, override the ones calculated above. */
+  if (mtl_mat.roughness >= 0) {
+    roughness = mtl_mat.roughness;
+  }
+  if (mtl_mat.metallic >= 0) {
+    metallic = mtl_mat.metallic;
+  }
+
   float3 base_color = mtl_mat.color;
   if (base_color.x >= 0 && base_color.y >= 0 && base_color.z >= 0) {
     set_property_of_socket(SOCK_RGBA, "Base Color", {base_color, 3}, bsdf);
@@ -314,6 +322,30 @@ static void set_bsdf_socket_values(bNode *bsdf, Material *mat, const MTLMaterial
   if (do_tranparency || (alpha >= 0.0f && alpha < 1.0f)) {
     mat->blend_method = MA_BM_BLEND;
   }
+
+  if (mtl_mat.sheen >= 0) {
+    set_property_of_socket(SOCK_FLOAT, "Sheen", {mtl_mat.sheen}, bsdf);
+  }
+  if (mtl_mat.cc_thickness >= 0) {
+    set_property_of_socket(SOCK_FLOAT, "Clearcoat", {mtl_mat.cc_thickness}, bsdf);
+  }
+  if (mtl_mat.cc_roughness >= 0) {
+    set_property_of_socket(SOCK_FLOAT, "Clearcoat Roughness", {mtl_mat.cc_roughness}, bsdf);
+  }
+  if (mtl_mat.aniso >= 0) {
+    set_property_of_socket(SOCK_FLOAT, "Anisotropic", {mtl_mat.aniso}, bsdf);
+  }
+  if (mtl_mat.aniso_rot >= 0) {
+    set_property_of_socket(SOCK_FLOAT, "Anisotropic Rotation", {mtl_mat.aniso_rot}, bsdf);
+  }
+
+  /* Transmission: average of transmission color. */
+  float transmission = (mtl_mat.transmit_color[0] + mtl_mat.transmit_color[1] +
+                        mtl_mat.transmit_color[2]) /
+                       3;
+  if (transmission >= 0) {
+    set_property_of_socket(SOCK_FLOAT, "Transmission", {transmission}, bsdf);
+  }
 }
 
 static void add_image_textures(Main *bmain,