feat: add ObjectRef for scene loading to not rely on runtime id's

destrum/CMakeLists.txt

@@ -96,6 +96,7 @@ set(SRC_FILES
         "src/ObjectModel/Component.cpp"
         "src/ObjectModel/GameObject.cpp"
         "src/ObjectModel/Object.cpp"
+        "src/ObjectModel/ObjectRef.cpp"
         "src/ObjectModel/Transform.cpp"
 
         "src/Scene/Scene.cpp"

destrum/include/destrum/ObjectModel/GameObject.h

@@ -44,9 +44,6 @@ public:
 
     [[nodiscard]] ObjectId GetId() const { return m_Id; }
 
-    // Use this only while loading a scene.
-    void SetIdForDeserialization(ObjectId id);
-
     [[nodiscard]] Scene* GetScene() const { return m_Scene; }
 
     [[nodiscard]] std::vector<std::unique_ptr<Component>>& GetComponents() {

destrum/include/destrum/ObjectModel/ObjectRef.h

@@ -0,0 +1,37 @@
+#ifndef DESTRUM_OBJECTREF_H
+#define DESTRUM_OBJECTREF_H
+
+#include <unordered_map>
+
+#include <nlohmann/json_fwd.hpp>
+
+#include <destrum/ObjectModel/ObjectId.h>
+
+class GameObject;
+class Scene;
+
+class ObjectRef final {
+public:
+    using ObjectMap = std::unordered_map<ObjectId, GameObject*>;
+
+    ObjectRef() = default;
+    explicit ObjectRef(ObjectId id) : m_Id(id) {}
+    explicit ObjectRef(const GameObject& object);
+
+    [[nodiscard]] ObjectId GetId() const { return m_Id; }
+    [[nodiscard]] bool IsSet() const { return m_Id != InvalidObjectId; }
+
+    [[nodiscard]] GameObject* Get(const Scene& scene) const;
+
+    bool Resolve(const ObjectMap& objects);
+
+    bool operator==(const ObjectRef&) const = default;
+
+private:
+    ObjectId m_Id{InvalidObjectId};
+};
+
+void to_json(nlohmann::json& json, const ObjectRef& ref);
+void from_json(const nlohmann::json& json, ObjectRef& ref);
+
+#endif //DESTRUM_OBJECTREF_H

destrum/src/ObjectModel/GameObject.cpp

@@ -39,19 +39,6 @@ GameObject::GameObject(const std::string& name)
       m_Id(AllocateId()) {
 }
 
-void GameObject::SetIdForDeserialization(ObjectId id) {
-    if (id == InvalidObjectId || id >= std::numeric_limits<ObjectId>::max() - 1) {
-        throw std::out_of_range("Object ID is reserved or cannot be incremented");
-    }
-
-    m_Id = id;
-
-    // Prevent newly created objects from reusing loaded IDs.
-    if (id != std::numeric_limits<ObjectId>::max() && id >= s_NextId) {
-        s_NextId = id + 1;
-    }
-}
-
 ObjectId GameObject::AllocateId() {
     if (s_NextId == InvalidObjectId ||
         s_NextId >= std::numeric_limits<ObjectId>::max() - 1) {

destrum/src/ObjectModel/ObjectRef.cpp

@@ -0,0 +1,38 @@
+#include <destrum/ObjectModel/ObjectRef.h>
+
+#include <nlohmann/json.hpp>
+
+#include <destrum/ObjectModel/GameObject.h>
+#include <destrum/Scene/Scene.h>
+
+ObjectRef::ObjectRef(const GameObject& object)
+    : m_Id(object.GetId()) {
+}
+
+GameObject* ObjectRef::Get(const Scene& scene) const {
+    return scene.FindGameObject(m_Id);
+}
+
+bool ObjectRef::Resolve(const ObjectMap& objects) {
+    if (m_Id == InvalidObjectId) {
+        return true;
+    }
+
+    const auto it = objects.find(m_Id);
+    if (it == objects.end() || it->second == nullptr) {
+        // Keeping an unmatched file id would alias an unrelated runtime object.
+        m_Id = InvalidObjectId;
+        return false;
+    }
+
+    m_Id = it->second->GetId();
+    return true;
+}
+
+void to_json(nlohmann::json& json, const ObjectRef& ref) {
+    json = ref.GetId();
+}
+
+void from_json(const nlohmann::json& json, ObjectRef& ref) {
+    ref = json.is_number_unsigned() ? ObjectRef(json.get<ObjectId>()) : ObjectRef{};
+}

destrum/src/Serialization/SceneSerializer.cpp

@@ -563,8 +563,8 @@ bool SceneSerializer::ConstructScene(Scene& scene, LoadResult& result,
             const std::string name = objectJson.value("name", "GameObject");
             const bool active = objectJson.value("active", true);
 
+            // File ids are local to the file, every loaded object gets a fresh runtime id
             GameObject* object = stagingScene.CreateGameObject(name);
-            object->SetIdForDeserialization(id);
             object->SetActive(active);
 
             idMap.emplace(id, object);
@@ -687,11 +687,14 @@ bool SceneSerializer::ConstructScene(Scene& scene, LoadResult& result,
         scene.m_name = root.at("name").get<std::string>();
     }
     scene.m_SelectedObjectId = InvalidObjectId;
-    scene.m_CurrentCameraId = root.value("currentCamera", InvalidObjectId);
-    if (scene.m_CurrentCameraId != InvalidObjectId && !idMap.contains(scene.m_CurrentCameraId)) {
-        spdlog::warn("Scene \"{}\" current camera id {} does not exist, ignoring it",
-                     scene.m_name, scene.m_CurrentCameraId);
-        scene.m_CurrentCameraId = InvalidObjectId;
+    scene.m_CurrentCameraId = InvalidObjectId;
+    if (const ObjectId cameraFileId = root.value("currentCamera", InvalidObjectId); cameraFileId != InvalidObjectId) {
+        if (const auto it = idMap.find(cameraFileId); it != idMap.end()) {
+            scene.m_CurrentCameraId = it->second->GetId();
+        } else {
+            spdlog::warn("Scene \"{}\" current camera id {} does not exist, ignoring it",
+                         scene.m_name, cameraFileId);
+        }
     }
     scene.m_Environment = SceneEnvironment{};
     if (root.contains("environment") && root.at("environment").is_object()) {