Extend AssimpLoader to parse material transmission factor

graphics/src/AssimpLoader.cc

@@ -357,8 +357,26 @@ MaterialPtr AssimpLoader::Implementation::CreateMaterial(
   }
   float opacity = 1.0;
   ret = assimpMat->Get(AI_MATKEY_OPACITY, opacity);
-  mat->SetTransparency(1.0 - opacity);
-  mat->SetBlendFactors(opacity, 1.0 - opacity);
+  if (ret == AI_SUCCESS)
+  {
+    mat->SetTransparency(1.0 - opacity);
+    mat->SetBlendFactors(opacity, 1.0 - opacity);
+  }
+
+#ifndef GZ_ASSIMP_PRE_5_1_0
+  // basic support for transmission - currently just overrides opacity
+  // \todo(iche033) The transmission factor can be used with volume
+  // material extension to simulate effects like refraction
+  // so consider also extending support for other properties like
+  // AI_MATKEY_VOLUME_THICKNESS_FACTOR
+  float transmission = 0.0;
+  ret = assimpMat->Get(AI_MATKEY_TRANSMISSION_FACTOR, transmission);
+  if (ret == AI_SUCCESS)
+  {
+    mat->SetTransparency(transmission);
+  }
+#endif
+
   // TODO(luca) more than one texture, Gazebo assumes UV index 0
   Pbr pbr;
   aiString texturePath(_path.c_str());
@@ -593,6 +611,7 @@ std::string AssimpLoader::Implementation::GenerateTextureName(
     "_" + _type;
 }
 
+//////////////////////////////////////////////////
 SubMesh AssimpLoader::Implementation::CreateSubMesh(
     const aiMesh* _assimpMesh, const math::Matrix4d& _transform) const
 {

graphics/src/AssimpLoader_TEST.cc

@@ -665,6 +665,30 @@ TEST_F(AssimpLoader, LoadGlTF2BoxExternalTexture)
   delete mesh;
 }
 
+/////////////////////////////////////////////////
+// Open a gltf mesh with transmission extension
+TEST_F(AssimpLoader, LoadGlTF2BoxTransmission)
+{
+#ifndef GZ_ASSIMP_PRE_5_1_0
+  common::AssimpLoader loader;
+  common::Mesh *mesh = loader.Load(
+      common::testing::TestFile("data", "box_transmission.glb"));
+
+  EXPECT_STREQ("unknown", mesh->Name().c_str());
+
+  // Make sure we can read the submesh name
+  EXPECT_STREQ("Cube", mesh->SubMeshByIndex(0).lock()->Name().c_str());
+
+  EXPECT_EQ(mesh->MaterialCount(), 1u);
+
+  const common::MaterialPtr mat = mesh->MaterialByIndex(0u);
+  ASSERT_TRUE(mat.get());
+  // transmission currently modeled as transparency
+  EXPECT_FLOAT_EQ(0.1, mat->Transparency());
+  delete mesh;
+#endif
+}
+
 /////////////////////////////////////////////////
 // This test loads a box glb mesh with embedded compressed jpeg texture
 TEST_F(AssimpLoader, LoadGlTF2BoxWithJPEGTexture)

graphics/src/CMakeLists.txt

@@ -29,16 +29,22 @@ gz_build_tests(
 )
 
 # Assimp doesn't offer preprocessor version, use cmake to set a compatibility
-# mode for versions below 5.2.0
+# mode for versions below 5.2.0 and 5.1.0
 if(${GzAssimp_VERSION} STRLESS "5.2.0")
   message("Warning, assimp below 5.2.0 detected, setting compatibility mode")
   target_compile_definitions(${graphics_target} PRIVATE GZ_ASSIMP_PRE_5_2_0)
   if(TARGET UNIT_AssimpLoader_TEST)
     target_compile_definitions(UNIT_AssimpLoader_TEST PRIVATE GZ_ASSIMP_PRE_5_2_0)
   endif()
+  if(${GzAssimp_VERSION} STRLESS "5.1.0")
+    message("Warning, assimp below 5.1.0 detected, setting compatibility mode")
+    target_compile_definitions(${graphics_target} PRIVATE GZ_ASSIMP_PRE_5_1_0)
+    if(TARGET UNIT_AssimpLoader_TEST)
+      target_compile_definitions(UNIT_AssimpLoader_TEST PRIVATE GZ_ASSIMP_PRE_5_1_0)
+    endif()
+  endif()
 endif()
 
-
 if(USE_EXTERNAL_TINYXML2)
 
   # If we are using an external copy of tinyxml2, add its imported target