Support loading PBR textures in OBJLoader (#216)

Extends the OBJLoader to support loading PBR textures. The Wavefront OBJ format has PBR extensions which our current version of the tiny_obj_loader is already able to parse and load. This updates the loader to load these new fields into the common::Material and common::Pbr data structures.

Signed-off-by: Ian Chen <[email protected]>

graphics/src/OBJLoader.cc

@@ -59,6 +59,21 @@ Mesh *OBJLoader::Load(const std::string &_filename)
   std::map<std::string, Material *> materialIds;
   std::string path = common::parentPath(_filename);
 
+  // check if obj is exported by blender
+  // blender shoves BR fields in standard textures
+  bool exportedByBlender = false;
+  std::ifstream infile(_filename);
+  if (infile.good())
+  {
+    std::string line;
+    std::getline(infile, line);
+    std::transform(line.begin(), line.end(), line.begin(),
+        [](unsigned char c){ return std::tolower(c); });
+    if (line.find("blender") != std::string::npos)
+      exportedByBlender = true;
+  }
+  infile.close();
+
   tinyobj::attrib_t attrib;
   std::vector<tinyobj::shape_t> shapes;
   std::vector<tinyobj::material_t> materials;
@@ -131,6 +146,50 @@ Mesh *OBJLoader::Load(const std::string &_filename)
             mat->SetTransparency(1.0 - m.dissolve);
             if (!m.diffuse_texname.empty())
               mat->SetTextureImage(m.diffuse_texname, path.c_str());
+
+            // load PBR textures
+            // Some obj exporters put PBR maps in the standard textures
+            // while others have proper support for obj PBR extension
+            Pbr pbrMat;
+            // PBR shoved into standard textures
+            if (!m.specular_texname.empty())
+              pbrMat.SetRoughnessMap(m.specular_texname);
+
+            // check if obj is exported by blender
+            // blender obj exporter puts roughness map in specular highlight
+            // field and metalness map in reflection map field!
+            // see summary in https://developer.blender.org/D8868
+            // detailing the existing exporter issues
+            // todo(anyone) add a check for blender version to avoid this hack
+            // when blender fixes their exporter issue
+            if (!m.specular_highlight_texname.empty() && exportedByBlender)
+            {
+              pbrMat.SetRoughnessMap(m.specular_highlight_texname);
+              if (!m.reflection_texname.empty())
+                pbrMat.SetMetalnessMap(m.reflection_texname);
+            }
+            else if (!m.reflection_texname.empty())
+            {
+              pbrMat.SetEnvironmentMap(m.reflection_texname);
+            }
+            if (!m.bump_texname.empty())
+              pbrMat.SetNormalMap(m.bump_texname);
+
+            // PBR extension - overrides standard materials
+            if (!m.roughness_texname.empty())
+              pbrMat.SetRoughnessMap(m.roughness_texname);
+            if (!m.metallic_texname.empty())
+              pbrMat.SetMetalnessMap(m.metallic_texname);
+            if (!m.normal_texname.empty())
+              pbrMat.SetNormalMap(m.normal_texname);
+            if (!m.emissive_texname.empty())
+              pbrMat.SetEmissiveMap(m.emissive_texname);
+
+            pbrMat.SetRoughness(m.roughness);
+            pbrMat.SetMetalness(m.metallic);
+
+            mat->SetPbrMaterial(pbrMat);
+
             materialIds[m.name] = mat;
           }
           int matIndex = mesh->IndexOfMaterial(mat);

graphics/src/OBJLoader_TEST.cc

@@ -69,9 +69,69 @@ TEST_F(OBJLoaderTest, InvalidMaterial)
     common::testing::TestFile("data", "invalid_material.obj");
 
   ignition::common::Mesh *mesh = objLoader.Load(meshFilename);
+
   EXPECT_TRUE(mesh != nullptr);
 }
 
+/////////////////////////////////////////////////
+// This tests opening an OBJ file that has PBR fields
+TEST_F(OBJLoaderTest, PBR)
+{
+  ignition::common::OBJLoader objLoader;
+
+  // load obj file exported by 3ds max that has pbr extension
+  {
+    std::string meshFilename =
+      common::testing::TestFile("data", "cube_pbr.obj");
+
+    ignition::common::Mesh *mesh = objLoader.Load(meshFilename);
+    EXPECT_NE(nullptr, mesh);
+
+    const common::MaterialPtr mat = mesh->MaterialByIndex(0u);
+    ASSERT_TRUE(mat.get());
+
+    EXPECT_EQ(math::Color(0.0f, 0.0f, 0.0f, 1.0f), mat->Ambient());
+    EXPECT_EQ(math::Color(0.5f, 0.5f, 0.5f, 1.0f), mat->Diffuse());
+    EXPECT_EQ(math::Color(1.0f, 1.0f, 1.0f, 1.0f), mat->Specular());
+    EXPECT_DOUBLE_EQ(0.0, mat->Transparency());
+    EXPECT_NE(std::string::npos,
+        mat->TextureImage().find("LightDome_Albedo.png"));
+    const common::Pbr *pbr = mat->PbrMaterial();
+    EXPECT_DOUBLE_EQ(0, pbr->Roughness());
+    EXPECT_DOUBLE_EQ(0, pbr->Metalness());
+    EXPECT_EQ("LightDome_Metalness.png", pbr->MetalnessMap());
+    EXPECT_EQ("LightDome_Roughness.png", pbr->RoughnessMap());
+    EXPECT_EQ("LightDome_Normal.png", pbr->NormalMap());
+  }
+
+  // load obj file exported by blender - it shoves pbr maps into
+  // existing fields
+  {
+    std::string meshFilename =
+      common::testing::TestFile("data", "blender_pbr.obj");
+
+    ignition::common::Mesh *mesh = objLoader.Load(meshFilename);
+    EXPECT_NE(nullptr, mesh);
+
+    const common::MaterialPtr mat = mesh->MaterialByIndex(0u);
+    ASSERT_TRUE(mat.get());
+
+    EXPECT_EQ(math::Color(1.0f, 1.0f, 1.0f, 1.0f), mat->Ambient());
+    EXPECT_EQ(math::Color(0.8f, 0.8f, 0.8f, 1.0f), mat->Diffuse());
+    EXPECT_EQ(math::Color(0.5f, 0.5f, 0.5f, 1.0f), mat->Specular());
+    EXPECT_EQ(math::Color(0.0f, 0.0f, 0.0f, 1.0f), mat->Emissive());
+    EXPECT_DOUBLE_EQ(0.0, mat->Transparency());
+    EXPECT_NE(std::string::npos,
+        mat->TextureImage().find("mesh_Diffuse.png"));
+    const common::Pbr *pbr = mat->PbrMaterial();
+    EXPECT_DOUBLE_EQ(0, pbr->Roughness());
+    EXPECT_DOUBLE_EQ(0, pbr->Metalness());
+    EXPECT_EQ("mesh_Metal.png", pbr->MetalnessMap());
+    EXPECT_EQ("mesh_Rough.png", pbr->RoughnessMap());
+    EXPECT_EQ("mesh_Normal.png", pbr->NormalMap());
+  }
+}
+
 /////////////////////////////////////////////////
 int main(int argc, char **argv)
 {

test/data/blender_pbr.mtl

@@ -0,0 +1,16 @@
+# Blender MTL File: 'WheelchairLightmap.blend'
+# Material Count: 1
+
+newmtl WheelchairUnfolded
+Ns 225.000000
+Ka 1.000000 1.000000 1.000000
+Kd 0.800000 0.800000 0.800000
+Ks 0.500000 0.500000 0.500000
+Ke 0.000000 0.000000 0.000000
+Ni 1.450000
+d 1.000000
+illum 2
+map_Bump mesh_Normal.png
+map_Kd mesh_Diffuse.png
+map_Ns mesh_Rough.png
+refl mesh_Metal.png