feat: implement contact listeners

destrum/include/destrum/ObjectModel/Component.h

@@ -59,6 +59,16 @@ public:
     virtual void ResolveReferences(const ObjectMap&) {
     }
 
+    // Trigger callbacks called when this component's owner overlaps a sensor.
+    // Only called when the owner has a Collider set as a trigger (or overlaps one).
+    virtual void OnTriggerEnter(GameObject* other) {
+        (void)other;
+    }
+
+    virtual void OnTriggerExit(GameObject* other) {
+        (void)other;
+    }
+
     bool HasStarted{false};
 
 protected:

destrum/include/destrum/Physics/JoltPhysicsWorld.h

@@ -55,6 +55,8 @@ public:
                  float maxDistance,
                  PhysicsRaycastHit& hit) const override;
 
+    std::vector<TriggerEvent> ConsumeTriggerEvents() override;
+
 private:
     class Impl;
     std::unique_ptr<Impl> m_Impl;

destrum/include/destrum/Physics/PhysicsSceneBridge.h

@@ -21,6 +21,7 @@ class PhysicsSceneBridge final {
 public:
     explicit PhysicsSceneBridge(std::unique_ptr<PhysicsWorld> world);
 
+    [[nodiscard]] bool IsValid() const { return m_World != nullptr; }
     [[nodiscard]] PhysicsWorld& GetWorld() { return *m_World; }
     [[nodiscard]] const PhysicsWorld& GetWorld() const { return *m_World; }
 

destrum/include/destrum/Physics/PhysicsTypes.h

@@ -116,3 +116,9 @@ struct PhysicsBodyDesc {
     bool useGravity{true};
     bool allowSleep{true};
 };
+
+struct TriggerEvent {
+    GameObject* owner{nullptr};
+    GameObject* other{nullptr};
+    bool entered{true};
+};

destrum/include/destrum/Physics/PhysicsWorld.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <vector>
+
 #include <glm/glm.hpp>
 
 #include <unordered_set>
@@ -49,6 +51,9 @@ public:
                          float maxDistance,
                          PhysicsRaycastHit& hit) const = 0;
 
+    // Trigger events accumulated during the last Step().
+    virtual std::vector<TriggerEvent> ConsumeTriggerEvents() { return {}; }
+
 private:
     std::unordered_set<Rigidbody*> m_RegisteredRigidbodies;
 };

destrum/include/destrum/Scene/Scene.h

@@ -3,6 +3,8 @@
 
 #include <functional>
 
+#include <memory>
+
 #include <destrum/Event.h>
 #include <destrum/ObjectModel/ObjectId.h>
 #include <destrum/Scene/SceneManager.h>
@@ -12,6 +14,7 @@
 
 class GameObject;
 class SceneSerializer;
+class PhysicsWorld;
 
 class Scene final {
     friend Scene& SceneManager::CreateScene(const std::string& name);
@@ -104,6 +107,7 @@ public:
     PhysicsSceneBridge& GetPhysics() { return m_Physics; }
 private:
     explicit Scene(const std::string& name);
+    explicit Scene(const std::string& name, std::unique_ptr<PhysicsWorld> physicsWorld);
 
     PhysicsSceneBridge m_Physics{std::make_unique<JoltPhysicsWorld>()};
 

destrum/include/destrum/Scene/SceneManager.h

@@ -16,6 +16,7 @@ public:
     Scene& CreateScene(const std::string& name);
 
     Scene& GetCurrentScene() const;
+    const std::vector<std::shared_ptr<Scene>>& GetActiveScenes() const { return m_activeScenes; }
 
     void Update(float dt);
     void FixedUpdate(float dt);
@@ -34,7 +35,9 @@ public:
     void Destroy();
 
     void SwitchScene(int index);
-    int GetActiveSceneId() const { return m_scenes.empty() ? -1 : m_ActiveSceneIndex; }
+    void AddActiveScene(int index);
+    void RemoveActiveScene(int index);
+    int GetActiveSceneId() const;
 
     [[nodiscard]] const std::vector<std::shared_ptr<Scene>>& GetScenes() const { return m_scenes; }
 
@@ -47,8 +50,7 @@ private:
 
     SceneManager() = default;
 
-    int m_ActiveSceneIndex{0};
+    std::vector<std::shared_ptr<Scene>> m_activeScenes;
-
     std::vector<std::shared_ptr<Scene>> m_scenes;
 };
 

destrum/include/destrum/Serialization/SceneSerializer.h

@@ -2,13 +2,37 @@
 #define DESTRUM_SCENESERIALIZER_H
 
 #include <filesystem>
+#include <functional>
+#include <future>
+
+#include <nlohmann/json.hpp>
 
 class Scene;
 
 class SceneSerializer final {
 public:
+    struct LoadResult {
+        bool success{false};
+        std::string errorMessage;
+        nlohmann::json root;
+    };
+
     static bool Save(Scene& scene, const std::filesystem::path& path);
-    static bool Load(Scene& scene, const std::filesystem::path& path);
+
+    static bool Load(Scene& scene, const std::filesystem::path& path,
+                     std::function<void(float)> progressCallback = nullptr);
+
+    // Thread-safe: parse and validate a scene file on any thread.
+    // No engine state is touched during parsing.
+    static LoadResult LoadSceneFile(const std::filesystem::path& path);
+
+    // Main-thread-only: construct a scene from pre-validated JSON.
+    static bool ConstructScene(Scene& scene, LoadResult& result,
+                               std::function<void(float)> progressCallback = nullptr);
+
+    // Parse the scene file on a background thread. Call LoadFromJson on the
+    // main thread once the future is ready.
+    static std::future<LoadResult> LoadSceneFileAsync(const std::filesystem::path& path);
 };
 
 #endif //DESTRUM_SCENESERIALIZER_H

destrum/src/Physics/JoltPhysicsWorld.cpp

@@ -26,9 +26,12 @@
 #include <cstdarg>
 #include <cstdio>
 #include <memory>
+#include <mutex>
 #include <stdexcept>
 #include <thread>
 #include <unordered_map>
+#include <unordered_set>
+#include <vector>
 
 #include <glm/gtx/norm.hpp>
 
@@ -276,6 +279,84 @@ namespace
             throw std::runtime_error("Cannot create Jolt body without a valid shape.");
         }
     }
+
+    class SensorContactListener final : public ContactListener
+    {
+    public:
+        using BodyPair = std::pair<BodyID, BodyID>;
+
+        struct PairHash {
+            std::size_t operator()(const BodyPair& p) const {
+                return std::hash<uint32_t>{}(
+                    p.first.GetIndexAndSequenceNumber() ^
+                    (p.second.GetIndexAndSequenceNumber() << 7));
+            }
+        };
+
+        struct PairData {
+            GameObject* objA{nullptr};
+            GameObject* objB{nullptr};
+            bool sensorA{false};
+            bool sensorB{false};
+        };
+
+        ValidateResult OnContactValidate(const Body&, const Body&, RVec3Arg,
+                                         const CollideShapeResult&) override
+        {
+            return ValidateResult::AcceptAllContactsForThisBodyPair;
+        }
+
+        void OnContactAdded(const Body& body1, const Body& body2,
+                            const ContactManifold&, ContactSettings& ioSettings) override
+        {
+            if (body1.IsSensor() || body2.IsSensor())
+            {
+                PairData data;
+                data.objA = reinterpret_cast<GameObject*>(body1.GetUserData());
+                data.objB = reinterpret_cast<GameObject*>(body2.GetUserData());
+                data.sensorA = body1.IsSensor();
+                data.sensorB = body2.IsSensor();
+                std::lock_guard<std::mutex> lock(m_Mutex);
+                m_Overlaps.insert_or_assign(MakePair(body1.GetID(), body2.GetID()), data);
+            }
+        }
+
+        void OnContactPersisted(const Body& body1, const Body& body2,
+                                const ContactManifold&, ContactSettings&) override
+        {
+        }
+
+        void OnContactRemoved(const SubShapeIDPair& subShapePair) override
+        {
+            std::lock_guard<std::mutex> lock(m_Mutex);
+            m_Overlaps.erase(MakePair(subShapePair.GetBody1ID(), subShapePair.GetBody2ID()));
+        }
+
+        void Clear()
+        {
+            std::lock_guard<std::mutex> lock(m_Mutex);
+            m_Overlaps.clear();
+        }
+
+        std::unordered_map<BodyPair, PairData, PairHash> SwapOverlaps()
+        {
+            std::lock_guard<std::mutex> lock(m_Mutex);
+            return std::move(m_Overlaps);
+        }
+
+    private:
+        static BodyPair MakePair(BodyID a, BodyID b)
+        {
+            if (a.GetIndexAndSequenceNumber() < b.GetIndexAndSequenceNumber())
+            {
+                return {a, b};
+            }
+            return {b, a};
+        }
+
+        std::mutex m_Mutex;
+        std::unordered_map<BodyPair, PairData, PairHash> m_Overlaps;
+    };
 } // namespace
 
 class JoltPhysicsWorld::Impl
@@ -307,6 +388,7 @@ public:
             m_ObjectVsBroadPhaseLayerFilter,
             m_ObjectLayerPairFilter);
 
+        m_PhysicsSystem.SetContactListener(&m_SensorListener);
         m_PhysicsSystem.SetGravity(ToJoltVec3(settings.gravity));
     }
 
@@ -426,6 +508,15 @@ public:
             collisionSteps,
             m_TempAllocator.get(),
             m_JobSystem.get());
+
+        ProcessSensorOverlaps();
+    }
+
+    std::vector<TriggerEvent> ConsumeTriggerEvents()
+    {
+        std::vector<TriggerEvent> events;
+        m_TriggerEvents.swap(events);
+        return events;
     }
 
     void SyncKinematicBodiesToPhysics()
@@ -626,6 +717,43 @@ private:
         return {};
     }
 
+    void ProcessSensorOverlaps()
+    {
+        const auto currentOverlaps = m_SensorListener.SwapOverlaps();
+
+        for (const auto& [pair, data] : currentOverlaps)
+        {
+            if (m_PreviousSensorOverlaps.find(pair) == m_PreviousSensorOverlaps.end())
+            {
+                if (data.sensorA && data.objA)
+                {
+                    m_TriggerEvents.push_back({data.objA, data.objB, true});
+                }
+                if (data.sensorB && data.objB)
+                {
+                    m_TriggerEvents.push_back({data.objB, data.objA, true});
+                }
+            }
+        }
+
+        for (const auto& [pair, data] : m_PreviousSensorOverlaps)
+        {
+            if (currentOverlaps.find(pair) == currentOverlaps.end())
+            {
+                if (data.sensorA && data.objA)
+                {
+                    m_TriggerEvents.push_back({data.objA, data.objB, false});
+                }
+                if (data.sensorB && data.objB)
+                {
+                    m_TriggerEvents.push_back({data.objB, data.objA, false});
+                }
+            }
+        }
+
+        m_PreviousSensorOverlaps = std::move(currentOverlaps);
+    }
+
     Settings m_Settings{};
 
     BPLayerInterfaceImpl m_BPLayerInterface{};
@@ -639,6 +767,10 @@ private:
 
     std::unordered_map<std::uint32_t, BodyRecord> m_Bodies;
     std::uint32_t m_NextHandle{0};
+
+    SensorContactListener m_SensorListener;
+    std::unordered_map<SensorContactListener::BodyPair, SensorContactListener::PairData, SensorContactListener::PairHash> m_PreviousSensorOverlaps;
+    std::vector<TriggerEvent> m_TriggerEvents;
 };
 
 JoltPhysicsWorld::JoltPhysicsWorld(const Settings& settings)
@@ -710,3 +842,8 @@ bool JoltPhysicsWorld::Raycast(const glm::vec3& origin,
 {
     return m_Impl->Raycast(origin, direction, maxDistance, hit);
 }
+
+std::vector<TriggerEvent> JoltPhysicsWorld::ConsumeTriggerEvents()
+{
+    return m_Impl->ConsumeTriggerEvents();
+}

destrum/src/Physics/PhysicsSceneBridge.cpp

@@ -1,6 +1,7 @@
 #include <destrum/Physics/PhysicsSceneBridge.h>
 
 #include <destrum/Components/Physics/Rigidbody.h>
+#include <destrum/ObjectModel/Component.h>
 #include <destrum/ObjectModel/GameObject.h>
 
 PhysicsSceneBridge::PhysicsSceneBridge(std::unique_ptr<PhysicsWorld> world)
@@ -8,14 +9,16 @@ PhysicsSceneBridge::PhysicsSceneBridge(std::unique_ptr<PhysicsWorld> world)
 }
 
 void PhysicsSceneBridge::RegisterGameObject(GameObject& object) {
+    if (!m_World) return;
     if (auto* rb = object.GetComponent<Rigidbody>()) {
-        if (!rb->HasPhysicsBody() || rb->GetPhysicsWorld() != &GetWorld()) {
+        if (!rb->HasPhysicsBody() || rb->GetPhysicsWorld() != m_World.get()) {
             m_World->RegisterRigidbody(*rb);
         }
     }
 }
 
 void PhysicsSceneBridge::UnregisterGameObject(GameObject& object) {
+    if (!m_World) return;
     if (auto* rb = object.GetComponent<Rigidbody>()) {
         if (rb->GetPhysicsWorld() == m_World.get()) {
             m_World->UnregisterRigidbody(*rb);
@@ -24,13 +27,29 @@ void PhysicsSceneBridge::UnregisterGameObject(GameObject& object) {
 }
 
 void PhysicsSceneBridge::RefreshGameObject(GameObject& object) {
+    if (!m_World) return;
     if (auto* rb = object.GetComponent<Rigidbody>()) {
         m_World->RefreshRigidbody(*rb);
     }
 }
 
 void PhysicsSceneBridge::FixedUpdate(float fixedDt) {
+    if (!m_World) return;
     m_World->SyncKinematicBodiesToPhysics();
     m_World->Step(fixedDt);
+
+    for (const auto& event : m_World->ConsumeTriggerEvents()) {
+        if (event.owner == nullptr) continue;
+        for (const auto& component : event.owner->GetComponents()) {
+            if (component && !component->IsBeingDestroyed() && component->isEnabled()) {
+                if (event.entered) {
+                    component->OnTriggerEnter(event.other);
+                } else {
+                    component->OnTriggerExit(event.other);
+                }
+            }
+        }
+    }
+
     m_World->SyncDynamicBodiesToTransforms();
 }

destrum/src/Scene/Scene.cpp

@@ -23,7 +23,12 @@ namespace {
 }
 
 Scene::Scene(const std::string& name)
-    : m_name(name),
+    : Scene(name, std::make_unique<JoltPhysicsWorld>()) {
+}
+
+Scene::Scene(const std::string& name, std::unique_ptr<PhysicsWorld> physicsWorld)
+    : m_Physics(std::move(physicsWorld)),
+      m_name(name),
       m_id(++m_idCounter) {
 }
 

destrum/src/Scene/SceneManager.cpp

@@ -8,51 +8,41 @@
 #include <destrum/Util/DeltaTime.h>
 
 Scene& SceneManager::GetCurrentScene() const {
-    if (m_scenes.empty()) {
+    if (m_activeScenes.empty()) {
-        throw std::out_of_range("No scenes are available");
+        throw std::out_of_range("No active scenes are available");
     }
-
+    return *m_activeScenes.front();
-    if (m_ActiveSceneIndex < 0 || m_ActiveSceneIndex >= static_cast<int>(m_scenes.size())) {
-        throw std::out_of_range("Active scene index is invalid");
-    }
-
-    return *m_scenes[static_cast<std::size_t>(m_ActiveSceneIndex)];
 }
 
 void SceneManager::Update(float dt) {
-    if (m_scenes.empty()) return;
+    for (const auto& scene : m_activeScenes) {
-    (void)GetCurrentScene();
-    const auto scene = m_scenes.at(static_cast<std::size_t>(m_ActiveSceneIndex));
         scene->Update(dt);
     }
+}
 
 void SceneManager::FixedUpdate(float dt) {
-    if (m_scenes.empty()) return;
+    for (const auto& scene : m_activeScenes) {
-    (void)GetCurrentScene();
-    const auto scene = m_scenes.at(static_cast<std::size_t>(m_ActiveSceneIndex));
         scene->FixedUpdate(dt);
     }
+}
 
 void SceneManager::LateUpdate(float dt) {
-    if (m_scenes.empty()) return;
+    for (const auto& scene : m_activeScenes) {
-    (void)GetCurrentScene();
-    const auto scene = m_scenes.at(static_cast<std::size_t>(m_ActiveSceneIndex));
         scene->LateUpdate(dt);
     }
+}
 
 void SceneManager::Render(const RenderContext& ctx) {
-    if (m_scenes.empty()) return;
+    for (const auto& scene : m_activeScenes) {
-    (void)GetCurrentScene();
-    const auto scene = m_scenes.at(static_cast<std::size_t>(m_ActiveSceneIndex));
         scene->Render(ctx);
     }
+}
 
 void SceneManager::RenderImgui() {
-    if (m_scenes.empty()) return;
+    for (const auto& scene : m_activeScenes) {
-    (void)GetCurrentScene();
-    const auto scene = m_scenes.at(static_cast<std::size_t>(m_ActiveSceneIndex));
         scene->RenderImgui();
     }
+}
 
 void SceneManager::HandleGameObjectDestroy() {
     for (const auto& scene : m_scenes) {
@@ -73,37 +63,22 @@ void SceneManager::UnloadAllScenes() {
 }
 
 void SceneManager::HandleSceneDestroy() {
-    const std::shared_ptr<Scene> activeScene =
-        m_ActiveSceneIndex >= 0 &&
-        m_ActiveSceneIndex < static_cast<int>(m_scenes.size())
-            ? m_scenes[static_cast<std::size_t>(m_ActiveSceneIndex)]
-            : nullptr;
-
     for (auto it = m_scenes.begin(); it != m_scenes.end();) {
         if ((*it)->IsBeingUnloaded()) {
+            const auto activeIt = std::find(m_activeScenes.begin(), m_activeScenes.end(), *it);
+            if (activeIt != m_activeScenes.end()) {
+                m_activeScenes.erase(activeIt);
+            }
             it = m_scenes.erase(it);
         } else {
             ++it;
         }
     }
 
-    if (m_scenes.empty()) {
+    // Remove any stale active scenes that are no longer in the scene list.
-        m_ActiveSceneIndex = 0;
+    std::erase_if(m_activeScenes, [this](const auto& scene) {
-        return;
+        return std::find(m_scenes.begin(), m_scenes.end(), scene) == m_scenes.end();
-    }
+    });
-
-    if (activeScene != nullptr) {
-        const auto activeIt = std::find(m_scenes.begin(), m_scenes.end(), activeScene);
-        if (activeIt != m_scenes.end()) {
-            m_ActiveSceneIndex = static_cast<int>(std::distance(m_scenes.begin(), activeIt));
-            return;
-        }
-    }
-
-    m_ActiveSceneIndex = std::clamp(
-        m_ActiveSceneIndex,
-        0,
-        static_cast<int>(m_scenes.size()) - 1);
 }
 
 void SceneManager::HandleScene() {
@@ -113,7 +88,6 @@ void SceneManager::HandleScene() {
 
 void SceneManager::Destroy() {
     if (m_scenes.empty()) {
-        m_ActiveSceneIndex = 0;
         return;
     }
 
@@ -124,25 +98,60 @@ void SceneManager::Destroy() {
 }
 
 void SceneManager::SwitchScene(int index) {
-    // InputManager::GetInstance().RemoveAllBindings();
-
     if (index < 0 || index >= static_cast<int>(m_scenes.size())) {
         throw std::out_of_range("Scene index out of range");
     }
-    if (index == m_ActiveSceneIndex) {
+
-        return;
+    for (const auto& scene : m_activeScenes) {
+        scene->UnloadBindings();
+    }
+    m_activeScenes.clear();
+    m_activeScenes.push_back(m_scenes[static_cast<std::size_t>(index)]);
+    m_activeScenes.back()->LoadBindings();
 }
 
-    m_scenes[static_cast<std::size_t>(m_ActiveSceneIndex)]->UnloadBindings();
+void SceneManager::AddActiveScene(int index) {
-    m_ActiveSceneIndex = index;
+    if (index < 0 || index >= static_cast<int>(m_scenes.size())) {
-    m_scenes[static_cast<std::size_t>(m_ActiveSceneIndex)]->LoadBindings();
+        throw std::out_of_range("Scene index out of range");
+    }
+
+    const auto& scene = m_scenes[static_cast<std::size_t>(index)];
+    if (std::find(m_activeScenes.begin(), m_activeScenes.end(), scene) == m_activeScenes.end()) {
+        scene->LoadBindings();
+        m_activeScenes.push_back(scene);
+    }
+}
+
+void SceneManager::RemoveActiveScene(int index) {
+    if (index < 0 || index >= static_cast<int>(m_scenes.size())) {
+        throw std::out_of_range("Scene index out of range");
+    }
+
+    const auto& scene = m_scenes[static_cast<std::size_t>(index)];
+    const auto it = std::find(m_activeScenes.begin(), m_activeScenes.end(), scene);
+    if (it != m_activeScenes.end()) {
+        (*it)->UnloadBindings();
+        m_activeScenes.erase(it);
+    }
+}
+
+int SceneManager::GetActiveSceneId() const {
+    if (m_scenes.empty() || m_activeScenes.empty()) {
+        return -1;
+    }
+
+    const auto it = std::find(m_scenes.begin(), m_scenes.end(), m_activeScenes.front());
+    if (it == m_scenes.end()) {
+        return -1;
+    }
+    return static_cast<int>(std::distance(m_scenes.begin(), it));
 }
 
 Scene& SceneManager::CreateScene(const std::string& name) {
     const auto scene = std::shared_ptr<Scene>(new Scene(name));
     m_scenes.push_back(scene);
     if (m_scenes.size() == 1) {
-        m_ActiveSceneIndex = 0;
+        m_activeScenes.push_back(scene);
     }
     return *scene;
 }

destrum/src/Serialization/SceneSerializer.cpp

@@ -16,8 +16,10 @@
 #include <destrum/ObjectModel/GameObject.h>
 #include <destrum/ObjectModel/ObjectId.h>
 #include <destrum/ObjectModel/Transform.h>
+#include <destrum/Assets/AssetReference.h>
 #include <destrum/Components/Physics/Collider.h>
 #include <destrum/Components/Physics/Rigidbody.h>
+#include <destrum/FS/AssetFS.h>
 #include <destrum/Serialization/ComponentFactory.h>
 #include <destrum/Serialization/ComponentRegistry.h>
 
@@ -201,6 +203,78 @@ namespace {
 
         return true;
     }
+
+    [[nodiscard]] bool AssetFileExists(const std::string& path) {
+        if (path.empty()) {
+            return true;
+        }
+
+        std::filesystem::path fullPath;
+        if (path.find("://") != std::string::npos) {
+            try {
+                fullPath = AssetFS::GetInstance().GetFullPath(path);
+            } catch (const std::exception&) {
+                return false;
+            }
+        } else {
+            fullPath = path;
+        }
+
+        return std::filesystem::exists(fullPath);
+    }
+
+    void ValidateAssetReferences(const json& root, const std::filesystem::path& scenePath) {
+        const auto report = [&](const std::string& objectName, const std::string& detail) {
+            std::cerr << "Scene asset warning (" << scenePath << "): " << objectName
+                      << " references \"" << detail << "\" which could not be found\n";
+        };
+
+        for (const auto& objectJson : root.at("objects")) {
+            const std::string objectName = objectJson.value("name", "GameObject");
+            if (!objectJson.contains("components")) {
+                continue;
+            }
+
+            for (const auto& componentJson : objectJson.at("components")) {
+                if (!componentJson.contains("data")) {
+                    continue;
+                }
+                const auto& data = componentJson.at("data");
+
+                // MeshRendererComponent: meshKey / materialKey are asset cache keys.
+                for (const char* key : {"meshKey", "materialKey"}) {
+                    if (data.contains(key) && data.at(key).is_string()) {
+                        const std::string cacheKey = data.at(key).get<std::string>();
+                        if (cacheKey.empty()) continue;
+                        const auto asset = AssetReference::fromCacheKey(cacheKey);
+                        if (asset && !AssetFileExists(asset->path)) {
+                            report(objectName, cacheKey);
+                        }
+                    }
+                }
+
+                // Generic: any nested object with a "path" field is an AssetReference.
+                std::function<void(const json&)> walk = [&](const json& node) {
+                    if (node.is_object()) {
+                        if (node.contains("path") && node.at("path").is_string()) {
+                            const std::string path = node.at("path").get<std::string>();
+                            if (!path.empty() && !AssetFileExists(path)) {
+                                report(objectName, path);
+                            }
+                        }
+                        for (auto it = node.begin(); it != node.end(); ++it) {
+                            walk(it.value());
+                        }
+                    } else if (node.is_array()) {
+                        for (const auto& element : node) {
+                            walk(element);
+                        }
+                    }
+                };
+                walk(data);
+            }
+        }
+    }
 }
 
 bool SceneSerializer::Save(Scene& scene, const std::filesystem::path& path) {
@@ -290,30 +364,45 @@ bool SceneSerializer::Save(Scene& scene, const std::filesystem::path& path) {
     return true;
 }
 
-bool SceneSerializer::Load(Scene& scene, const std::filesystem::path& path) {
+SceneSerializer::LoadResult SceneSerializer::LoadSceneFile(const std::filesystem::path& path) {
+    LoadResult result;
+
+    std::ifstream file(path);
+    if (!file.is_open()) {
+        result.errorMessage = "Failed to open scene file for reading: " + path.string();
+        std::cerr << result.errorMessage << '\n';
+        return result;
+    }
+
+    try {
+        file >> result.root;
+        if (!ValidateSceneJson(result.root)) {
+            result.errorMessage = "Invalid scene data: " + path.string();
+            std::cerr << result.errorMessage << '\n';
+            return result;
+        }
+    } catch (const std::exception& exception) {
+        result.errorMessage = "Failed to parse scene file: " + std::string(exception.what());
+        std::cerr << result.errorMessage << '\n';
+        return result;
+    }
+
+    ValidateAssetReferences(result.root, path);
+    result.success = true;
+    return result;
+}
+
+bool SceneSerializer::ConstructScene(Scene& scene, LoadResult& result,
+                                     std::function<void(float)> progressCallback) {
     if (scene.IsIterating()) {
         std::cerr << "Cannot load a scene during an update or render phase: "
                   << scene.GetName() << '\n';
         return false;
     }
 
-    RegisterEngineComponents();
+    if (!result.success) {
-
+        std::cerr << "Cannot construct scene from a failed load result: "
-    std::ifstream file(path);
+                  << result.errorMessage << '\n';
-    if (!file.is_open()) {
-        std::cerr << "Failed to open scene file for reading: " << path << '\n';
-        return false;
-    }
-
-    json root;
-    try {
-        file >> root;
-        if (!ValidateSceneJson(root)) {
-            std::cerr << "Invalid scene data: " << path << '\n';
-            return false;
-        }
-    } catch (const std::exception& exception) {
-        std::cerr << "Failed to parse scene file: " << exception.what() << '\n';
         return false;
     }
 
@@ -322,9 +411,16 @@ bool SceneSerializer::Load(Scene& scene, const std::filesystem::path& path) {
         return false;
     }
 
+    RegisterEngineComponents();
+    if (progressCallback) progressCallback(0.35f);
+
+    const json& root = result.root;
+
     // Build the replacement separately. The current scene is not touched
     // until all objects, transforms, and components have loaded successfully.
-    Scene stagingScene(scene.GetName());
+    // No physics world is created for the staging scene - physics bodies are
+    // registered directly in the live scene's world once loading succeeds.
+    Scene stagingScene(scene.GetName(), nullptr);
     std::unordered_map<ObjectId, GameObject*> idMap;
     std::vector<const json*> objectJsonList;
     std::vector<GameObject*> registeredObjects;
@@ -343,7 +439,16 @@ bool SceneSerializer::Load(Scene& scene, const std::filesystem::path& path) {
             objectJsonList.push_back(&objectJson);
         }
 
-        stagingScene.CommitPendingAdditions();
+        if (progressCallback) progressCallback(0.4f);
+
+        // Move objects from pending to objects list without physics registration
+        // (staging scene has no physics world).
+        for (auto& pending : stagingScene.m_pendingAdditions) {
+            if (pending) {
+                stagingScene.m_objects.emplace_back(std::move(pending));
+            }
+        }
+        stagingScene.m_pendingAdditions.clear();
 
         for (const json* objectJson : objectJsonList) {
             const ObjectId id = objectJson->at("id").get<ObjectId>();
@@ -392,6 +497,8 @@ bool SceneSerializer::Load(Scene& scene, const std::filesystem::path& path) {
             }
         }
 
+        if (progressCallback) progressCallback(0.5f);
+
         for (const json* objectJson : objectJsonList) {
             GameObject* object = idMap.at(objectJson->at("id").get<ObjectId>());
             if (!objectJson->contains("components")) {
@@ -412,6 +519,8 @@ bool SceneSerializer::Load(Scene& scene, const std::filesystem::path& path) {
             }
         }
 
+        if (progressCallback) progressCallback(0.6f);
+
         for (const auto& objectPtr : stagingScene.GetObjects()) {
             if (!objectPtr) {
                 continue;
@@ -424,6 +533,8 @@ bool SceneSerializer::Load(Scene& scene, const std::filesystem::path& path) {
             }
         }
 
+        if (progressCallback) progressCallback(0.7f);
+
         // Register the replacement bodies in the live physics world before
         // touching the current scene. If any body fails, the old scene and
         // its physics state can remain intact.
@@ -438,6 +549,8 @@ bool SceneSerializer::Load(Scene& scene, const std::filesystem::path& path) {
                 registeredObjects.push_back(objectPtr.get());
             }
         }
+
+        if (progressCallback) progressCallback(0.8f);
     } catch (const std::exception& exception) {
         std::cerr << "Failed to load scene: " << exception.what() << '\n';
         for (GameObject* object : registeredObjects) {
@@ -449,6 +562,7 @@ bool SceneSerializer::Load(Scene& scene, const std::filesystem::path& path) {
         return false;
     }
 
+    scene.UnloadBindings();
     scene.RemoveAll();
     scene.m_objects = std::move(stagingScene.m_objects);
     scene.m_pendingAdditions = std::move(stagingScene.m_pendingAdditions);
@@ -456,6 +570,8 @@ bool SceneSerializer::Load(Scene& scene, const std::filesystem::path& path) {
         scene.m_name = root.at("name").get<std::string>();
     }
 
+    if (progressCallback) progressCallback(0.9f);
+
     for (const auto& object : scene.m_objects) {
         if (object) {
             object->SetScene(&scene);
@@ -467,5 +583,27 @@ bool SceneSerializer::Load(Scene& scene, const std::filesystem::path& path) {
         }
     }
 
+    if (progressCallback) progressCallback(1.0f);
     return true;
 }
+
+bool SceneSerializer::Load(Scene& scene, const std::filesystem::path& path,
+                           std::function<void(float)> progressCallback) {
+    if (progressCallback) progressCallback(0.0f);
+
+    auto result = LoadSceneFile(path);
+    if (!result.success) {
+        if (progressCallback) progressCallback(1.0f);
+        return false;
+    }
+
+    if (progressCallback) progressCallback(0.3f);
+    return ConstructScene(scene, result, std::move(progressCallback));
+}
+
+std::future<SceneSerializer::LoadResult> SceneSerializer::LoadSceneFileAsync(
+    const std::filesystem::path& path) {
+    return std::async(std::launch::async, [path]() {
+        return LoadSceneFile(path);
+    });
+}

lightkeeper/CMakeLists.txt

@@ -9,6 +9,7 @@ set(GAME_SRC
 
     src/components/GameComponentRegistry.cpp
     src/components/PrintComponent.cpp
+    src/components/TriggerLoggerComponent.cpp
 )
 
 add_executable(lightkeeper ${GAME_SRC})

lightkeeper/include/components/GameComponentList.h

@@ -2,8 +2,10 @@
 #define LIGHTKEEPER_GAMECOMPONENTLIST_H
 
 #include <components/PrintComponent.h>
+#include <components/TriggerLoggerComponent.h>
 
 #define LIGHTKEEPER_GAME_COMPONENTS(X) \
-    X(PrintComponent)
+    X(PrintComponent) \
+    X(TriggerLoggerComponent)
 
 #endif // LIGHTKEEPER_GAMECOMPONENTLIST_H

lightkeeper/include/components/TriggerLoggerComponent.h

@@ -0,0 +1,22 @@
+#ifndef DESTRUM_TRIGGERLOGGERCOMPONENT_H
+#define DESTRUM_TRIGGERLOGGERCOMPONENT_H
+#include "destrum/ObjectModel/Component.h"
+
+class TriggerLoggerComponent: public Component {
+public:
+    TriggerLoggerComponent(GameObject& parent);
+
+    std::string GetTypeName() const override { return "TriggerLoggerComponent"; }
+
+    void OnTriggerEnter(GameObject* other) override;
+    void OnTriggerExit(GameObject* other) override;
+
+    nlohmann::json Serialize() const override;
+    void Deserialize(const nlohmann::json&) override;
+
+    int triggerEnterCount{0};
+    int triggerExitCount{0};
+    std::string lastOtherName;
+};
+
+#endif //DESTRUM_TRIGGERLOGGERCOMPONENT_H

lightkeeper/src/Lightkeeper.cpp

@@ -18,6 +18,7 @@
 #include "destrum/ObjectModel/GameObject.h"
 #include "destrum/Util/ModelDoc.h"
 #include "destrum/Components/Animator.h"
+#include <components/TriggerLoggerComponent.h>
 
 
 #include <filesystem>
@@ -433,9 +434,15 @@ void LightKeeper::customInit()
     sphereMaterial = resources.materials().addSimpleColorMaterial({0.5f, 0.3f, 0.8f}, "Blue");
 
 
-    auto obj = scene.CreateGameObject("GameObject");
+    // Trigger zone: a static box with a TriggerLoggerComponent.
-    auto printComp = obj->AddComponent<PrintComponent>();
+    // Spheres spawned via the "Spawn ball" button fall through it.
-    printComp->SetMessage("Testing");
+    auto triggerObj = scene.CreateGameObject("TriggerBox");
+    auto triggerBox = triggerObj->AddComponent<BoxCollider>(glm::vec3{3.0f, 3.0f, 3.0f});
+    triggerBox->SetTrigger(true);
+    auto triggerRb = triggerObj->AddComponent<Rigidbody>();
+    triggerRb->SetType(RigidbodyType::Static);
+    triggerObj->AddComponent<TriggerLoggerComponent>();
+    triggerObj->GetTransform().SetWorldPosition({0.0f, 0.0f, 0.0f});
 
 
 }

lightkeeper/src/components/TriggerLoggerComponent.cpp

@@ -0,0 +1,45 @@
+#include <components/TriggerLoggerComponent.h>
+
+#include "spdlog/spdlog.h"
+#include <destrum/ObjectModel/GameObject.h>
+
+TriggerLoggerComponent::TriggerLoggerComponent(GameObject& parent)
+    : Component(parent, "TriggerLoggerComponent") {}
+
+void TriggerLoggerComponent::OnTriggerEnter(GameObject* other) {
+    ++triggerEnterCount;
+    lastOtherName = other ? other->GetName() : "null";
+    spdlog::info(
+        "TriggerLogger: ENTER {} -> {} (enters: {}, exits: {})",
+        GetGameObject()->GetName(),
+        lastOtherName,
+        triggerEnterCount,
+        triggerExitCount);
+}
+
+void TriggerLoggerComponent::OnTriggerExit(GameObject* other) {
+    ++triggerExitCount;
+    lastOtherName = other ? other->GetName() : "null";
+    spdlog::info(
+        "TriggerLogger: EXIT {} -> {} (enters: {}, exits: {})",
+        GetGameObject()->GetName(),
+        lastOtherName,
+        triggerEnterCount,
+        triggerExitCount);
+}
+
+nlohmann::json TriggerLoggerComponent::Serialize() const {
+    return {
+        {"triggerEnterCount", triggerEnterCount},
+        {"triggerExitCount", triggerExitCount}
+    };
+}
+
+void TriggerLoggerComponent::Deserialize(const nlohmann::json& data) {
+    if (data.contains("triggerEnterCount")) {
+        triggerEnterCount = data.at("triggerEnterCount").get<int>();
+    }
+    if (data.contains("triggerExitCount")) {
+        triggerExitCount = data.at("triggerExitCount").get<int>();
+    }
+}

tests/destrum_tests.cpp

@@ -20,6 +20,7 @@
 #include <destrum/Physics/JoltPhysicsWorld.h>
 #include <destrum/Components/Physics/SphereCollider.h>
 #include <destrum/Components/Physics/BoxCollider.h>
+#include <destrum/Components/Physics/Collider.h>
 #include <destrum/Components/Animator.h>
 #include <destrum/Components/Physics/Rigidbody.h>
 #include <destrum/Graphics/Material.h>
@@ -483,6 +484,65 @@ namespace {
         check(!AssetReference::fromCacheKey("CharacterMedium.fbx").has_value(),
               "plain cache names must not be treated as file-backed assets");
     }
+
+    class TriggerTracker final : public Component {
+    public:
+        explicit TriggerTracker(GameObject& owner)
+            : Component(owner, "TriggerTracker") {}
+
+        void Update(float) override {}
+        std::string GetTypeName() const override { return "TriggerTracker"; }
+
+        void OnTriggerEnter(GameObject* other) override {
+            ++enterCount;
+            lastOther = other;
+            enterObjectName = other ? other->GetName() : "null";
+        }
+
+        void OnTriggerExit(GameObject* other) override {
+            ++exitCount;
+        }
+
+        int enterCount{0};
+        int exitCount{0};
+        GameObject* lastOther{nullptr};
+        std::string enterObjectName;
+    };
+
+    void testTriggerZone()
+    {
+        Scene& scene = SceneManager::GetInstance().CreateScene("trigger-test");
+
+        // Trigger box at origin (Static rigidbody + BoxCollider as trigger).
+        GameObject* triggerObj = scene.CreateGameObject("TriggerZone");
+        triggerObj->AddComponent<BoxCollider>(glm::vec3{3.0f, 3.0f, 3.0f});
+        triggerObj->GetComponent<BoxCollider>()->SetTrigger(true);
+        auto* triggerRb = triggerObj->AddComponent<Rigidbody>();
+        triggerRb->SetType(RigidbodyType::Static);
+        auto* tracker = triggerObj->AddComponent<TriggerTracker>();
+
+        // Falling sphere above the trigger.
+        GameObject* sphere = scene.CreateGameObject("FallingSphere");
+        sphere->AddComponent<SphereCollider>(0.5f);
+        sphere->AddComponent<Rigidbody>();
+        sphere->GetTransform().SetWorldPosition({0.0f, 8.0f, 0.0f});
+
+        scene.CommitPendingAdditions();
+
+        // Run physics for enough steps that the sphere falls into the trigger.
+        for (int step = 0; step < 120; ++step) {
+            scene.FixedUpdate(1.0f / 60.0f);
+        }
+
+        check(tracker->enterCount >= 1,
+              "falling sphere must trigger OnTriggerEnter at least once");
+        check(tracker->exitCount >= 1,
+              "falling sphere passing through trigger must exit");
+        check(tracker->enterObjectName == "FallingSphere",
+              "OnTriggerEnter must report the correct entering object");
+
+        SceneManager::GetInstance().Destroy();
+    }
 }
 
 int main()
@@ -503,6 +563,7 @@ int main()
     testAnimatorAssetReferences();
     testSimpleColorMaterial();
     testAssetReferenceCacheKeys();
+    testTriggerZone();
     std::cout << "destrum tests passed\n";
     return EXIT_SUCCESS;
 }