tinyobjloader · syoyo · Jan 29, 2025 · Jan 27, 2025
diff --git a/models/issue-391.mtl b/models/issue-391.mtl
@@ -0,0 +1,4 @@
+newmtl has_kd
+Kd 1 0 0
+newmtl has_map
+map_Kd test.png
diff --git a/models/issue-391.obj b/models/issue-391.obj
@@ -0,0 +1,9 @@
+mtllib issue-391.mtl
+v 0 0 0
+v 1 0 0
+v 0 1 0
+vn 0 0 1
+usemtl has_map
+f 1//1 2//1 3//1
+usemtl has_kd
+f 1//1 2//1 3//1
diff --git a/tests/tester.cc b/tests/tester.cc
@@ -1433,6 +1433,41 @@ void test_comment_issue389() {
  TEST_CHECK(true == ret);
 }

+void test_default_kd_for_multiple_materials_issue391() {
+  tinyobj::attrib_t attrib;
+  std::vector<tinyobj::shape_t> shapes;
+  std::vector<tinyobj::material_t> materials;
+
+  std::string warn;
+  std::string err;
+  bool ret = tinyobj::LoadObj(&attrib, &shapes, &materials, &warn, &err,
+                              "../models/issue-391.obj", gMtlBasePath);
+  if (!warn.empty()) {
+    std::cout << "WARN: " << warn << std::endl;
+  }
+
+  if (!err.empty()) {
+    std::cerr << "ERR: " << err << std::endl;
+  }
+
+  const tinyobj::real_t kGrey[] = {0.6, 0.6, 0.6};
+  const tinyobj::real_t kRed[] = {1.0, 0.0, 0.0};
+
+  TEST_CHECK(true == ret);
+  TEST_CHECK(2 == materials.size());
+  for (size_t i = 0; i < materials.size(); ++i) {
+    const tinyobj::material_t& material = materials[i];
+    if (material.name == "has_map") {
+      for (int i = 0; i < 3; ++i) TEST_CHECK(material.diffuse[i] == kGrey[i]);
+    } else if (material.name == "has_kd") {
+      for (int i = 0; i < 3; ++i) TEST_CHECK(material.diffuse[i] == kRed[i]);
+    } else {
+      std::cerr << "Unexpected material found!" << std::endl;
+      TEST_CHECK(false);
+    }
+  }
+}
+
 // Fuzzer test.
 // Just check if it does not crash.
 // Disable by default since Windows filesystem can't create filename of afl
@@ -1542,4 +1577,6 @@ TEST_LIST = {
     test_invalid_relative_vertex_index},
    {"test_invalid_texture_vertex_index",
     test_invalid_texture_vertex_index},
+    {"default_kd_for_multiple_materials_issue391",
+     test_default_kd_for_multiple_materials_issue391},
    {NULL, NULL}};
diff --git a/tiny_obj_loader.h b/tiny_obj_loader.h
@@ -2134,6 +2134,7 @@ void LoadMtl(std::map<std::string, int> *material_map,

      has_d = false;
      has_tr = false;
+      has_kd = false;

      // set new mtl name
      token += 7;