Add regression test for issue 321

Also ensure `inverseBindMatrices` should not be -2 or other negative values.

README.md

@@ -170,6 +170,7 @@ if (!ret) {
 * `TINYGLTF_ANDROID_LOAD_FROM_ASSETS`: Load all files from packaged app assets instead of the regular file system. **Note:** You must pass a valid asset manager from your android app to `tinygltf::asset_manager` beforehand.
 * `TINYGLTF_ENABLE_DRACO`: Enable Draco compression. User must provide include path and link correspnding libraries in your project file.
 * `TINYGLTF_NO_INCLUDE_JSON `: Disable including `json.hpp` from within `tiny_gltf.h` because it has been already included before or you want to include it using custom path before including `tiny_gltf.h`.
+* `TINYGLTF_NO_INCLUDE_RAPIDJSON `: Disable including RapidJson's header files from within `tiny_gltf.h` because it has been already included before or you want to include it using custom path before including `tiny_gltf.h`.
 * `TINYGLTF_NO_INCLUDE_STB_IMAGE `: Disable including `stb_image.h` from within `tiny_gltf.h` because it has been already included before or you want to include it using custom path before including `tiny_gltf.h`.
 * `TINYGLTF_NO_INCLUDE_STB_IMAGE_WRITE `: Disable including `stb_image_write.h` from within `tiny_gltf.h` because it has been already included before or you want to include it using custom path before including `tiny_gltf.h`.
 * `TINYGLTF_USE_RAPIDJSON` : Use RapidJSON as a JSON parser/serializer. RapidJSON files are not included in TinyGLTF repo. Please set an include path to RapidJSON if you enable this featrure.

tests/tester.cc

@@ -436,6 +436,36 @@ TEST_CASE("serialize-empty-material", "[issue-294]") {
 
 }
 
+TEST_CASE("empty-skeleton-id", "[issue-321]") {
+
+  tinygltf::Model model;
+  tinygltf::TinyGLTF ctx;
+  std::string err;
+  std::string warn;
+
+  bool ret = ctx.LoadASCIIFromFile(&model, &err, &warn, "../models/regression/unassigned-skeleton.gltf");
+  if (!err.empty()) {
+    std::cerr << err << std::endl;
+  }
+  REQUIRE(true == ret);
+
+  REQUIRE(model.skins.size() == 1);
+  REQUIRE(model.skins[0].skeleton == -1); // unassigned
+
+  std::stringstream os;
+
+  ctx.WriteGltfSceneToStream(&model, os, false, false);
+
+  // use nlohmann json
+  nlohmann::json j = nlohmann::json::parse(os.str());
+
+  // Ensure `skeleton` property is not written to .gltf(was serialized as -1)
+  REQUIRE(1 == j["skins"].size());
+  REQUIRE(j["skins"][0].is_object());
+  REQUIRE(j["skins"][0].count("skeleton") == 0);
+
+}
+
 #ifndef TINYGLTF_NO_FS
 TEST_CASE("expandpath-utf-8", "[pr-226]") {
 

tiny_gltf.h

@@ -1538,6 +1538,7 @@ class TinyGLTF {
 #ifndef TINYGLTF_USE_RAPIDJSON
 #include "json.hpp"
 #else
+#ifndef TINYGLTF_NO_INCLUDE_RAPIDJSON
 #include "document.h"
 #include "prettywriter.h"
 #include "rapidjson.h"
@@ -1545,6 +1546,7 @@ class TinyGLTF {
 #include "writer.h"
 #endif
 #endif
+#endif
 
 #ifdef TINYGLTF_ENABLE_DRACO
 #include "draco/compression/decode.h"
@@ -4470,6 +4472,7 @@ static bool GetAttributeForAllPoints(uint32_t componentType, draco::Mesh *mesh,
 static bool ParseDracoExtension(Primitive *primitive, Model *model,
                                 std::string *err,
                                 const Value &dracoExtensionValue) {
+  (void)err;
   auto bufferViewValue = dracoExtensionValue.Get("bufferView");
   if (!bufferViewValue.IsInt()) return false;
   auto attributesValue = dracoExtensionValue.Get("attributes");
@@ -4530,7 +4533,6 @@ static bool ParseDracoExtension(Primitive *primitive, Model *model,
 
     int dracoAttributeIndex = attribute.second.Get<int>();
     const auto pAttribute = mesh->GetAttributeByUniqueId(dracoAttributeIndex);
-    const auto pBuffer = pAttribute->buffer();
     const auto componentType =
         model->accessors[primitiveAttribute->second].componentType;
 
@@ -7241,11 +7243,17 @@ static void SerializeGltfScene(Scene &scene, json &o) {
 }
 
 static void SerializeGltfSkin(Skin &skin, json &o) {
-  if (skin.inverseBindMatrices != -1)
-    SerializeNumberProperty("inverseBindMatrices", skin.inverseBindMatrices, o);
-
+  // required
   SerializeNumberArrayProperty<int>("joints", skin.joints, o);
-  SerializeNumberProperty("skeleton", skin.skeleton, o);
+
+  if (skin.inverseBindMatrices >= 0) {
+    SerializeNumberProperty("inverseBindMatrices", skin.inverseBindMatrices, o);
+  }
+
+  if (skin.skeleton >= 0) {
+    SerializeNumberProperty("skeleton", skin.skeleton, o);
+  }
+
   if (skin.name.size()) {
     SerializeStringProperty("name", skin.name, o);
   }