From 8318a9c1d033fa5f559fa74cbfdabef5f8e183ae Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Thu, 12 Mar 2026 13:39:01 +0100
Subject: [PATCH] Fix crash when unloading scene during tick of that scene

---
 Source/Engine/Level/Level.cpp              |  3 --
 Source/Engine/Level/Scene/Scene.cpp        |  3 ++
 Source/Engine/Level/Scene/SceneTicking.cpp | 40 +++++++++++-----------
 Source/Engine/Level/Scene/SceneTicking.h   |  8 +++++
 4 files changed, 31 insertions(+), 23 deletions(-)

diff --git a/Source/Engine/Level/Level.cpp b/Source/Engine/Level/Level.cpp
index 956005f57..a46ee52f6 100644
--- a/Source/Engine/Level/Level.cpp
+++ b/Source/Engine/Level/Level.cpp
@@ -958,9 +958,6 @@ bool LevelImpl::unloadScene(Scene* scene)
     // Simple enqueue scene root object to be deleted
     scene->DeleteObject();
 
-    // Force flush deleted objects so we actually delete unloaded scene objects (prevent from reloading their managed objects, etc.)
-    ObjectsRemovalService::Flush();
-
     return false;
 }
 
diff --git a/Source/Engine/Level/Scene/Scene.cpp b/Source/Engine/Level/Scene/Scene.cpp
index f60aa8d2f..b45424a3d 100644
--- a/Source/Engine/Level/Scene/Scene.cpp
+++ b/Source/Engine/Level/Scene/Scene.cpp
@@ -389,11 +389,14 @@ void Scene::BeginPlay(SceneBeginData* data)
         if (model == nullptr)
             CreateCsgModel();
     }
+
+    Ticking.SetTicking(true);
 }
 
 void Scene::EndPlay()
 {
     // Improve scene cleanup performance by removing all data from scene rendering and ticking containers
+    Ticking.SetTicking(false);
     Ticking.Clear();
     Rendering.Clear();
     Navigation.Clear();
diff --git a/Source/Engine/Level/Scene/SceneTicking.cpp b/Source/Engine/Level/Scene/SceneTicking.cpp
index 30a551117..2b0ccc506 100644
--- a/Source/Engine/Level/Scene/SceneTicking.cpp
+++ b/Source/Engine/Level/Scene/SceneTicking.cpp
@@ -44,7 +44,7 @@ void SceneTicking::TickData::Tick()
 {
     TickScripts(Scripts);
 
-    for (int32 i = 0; i < Ticks.Count(); i++)
+    for (int32 i = 0; i < Ticks.Count() && _canTick; i++)
         Ticks.Get()[i].Call();
 }
 
@@ -66,7 +66,7 @@ void SceneTicking::TickData::TickExecuteInEditor()
 {
     TickScripts(ScriptsExecuteInEditor);
 
-    for (int32 i = 0; i < TicksExecuteInEditor.Count(); i++)
+    for (int32 i = 0; i < TicksExecuteInEditor.Count() && _canTick; i++)
         TicksExecuteInEditor.Get()[i].Call();
 }
 
@@ -89,10 +89,8 @@ SceneTicking::FixedUpdateTickData::FixedUpdateTickData()
 
 void SceneTicking::FixedUpdateTickData::TickScripts(const Array<Script*>& scripts)
 {
-    for (auto* script : scripts)
-    {
-        script->OnFixedUpdate();
-    }
+    for (int32 i = 0; i < scripts.Count() && _canTick; i++)
+        scripts.Get()[i]->OnFixedUpdate();
 }
 
 SceneTicking::UpdateTickData::UpdateTickData()
@@ -102,36 +100,30 @@ SceneTicking::UpdateTickData::UpdateTickData()
 
 void SceneTicking::UpdateTickData::TickScripts(const Array<Script*>& scripts)
 {
-    for (auto* script : scripts)
-    {
-        script->OnUpdate();
-    }
+    for (int32 i = 0; i < scripts.Count() && _canTick; i++)
+        scripts.Get()[i]->OnUpdate();
 }
 
 SceneTicking::LateUpdateTickData::LateUpdateTickData()
-    : TickData(64)
+    : TickData(0)
 {
 }
 
 void SceneTicking::LateUpdateTickData::TickScripts(const Array<Script*>& scripts)
 {
-    for (auto* script : scripts)
-    {
-        script->OnLateUpdate();
-    }
+    for (int32 i = 0; i < scripts.Count() && _canTick; i++)
+        scripts.Get()[i]->OnLateUpdate();
 }
 
 SceneTicking::LateFixedUpdateTickData::LateFixedUpdateTickData()
-    : TickData(64)
+    : TickData(0)
 {
 }
 
 void SceneTicking::LateFixedUpdateTickData::TickScripts(const Array<Script*>& scripts)
 {
-    for (auto* script : scripts)
-    {
-        script->OnLateFixedUpdate();
-    }
+    for (int32 i = 0; i < scripts.Count() && _canTick; i++)
+        scripts.Get()[i]->OnLateFixedUpdate();
 }
 
 void SceneTicking::AddScript(Script* obj)
@@ -167,3 +159,11 @@ void SceneTicking::Clear()
     LateUpdate.Clear();
     LateFixedUpdate.Clear();
 }
+
+void SceneTicking::SetTicking(bool enable)
+{
+    FixedUpdate._canTick = enable;
+    Update._canTick = enable;
+    LateUpdate._canTick = enable;
+    LateFixedUpdate._canTick = enable;
+}
diff --git a/Source/Engine/Level/Scene/SceneTicking.h b/Source/Engine/Level/Scene/SceneTicking.h
index 78e028b8e..26040852b 100644
--- a/Source/Engine/Level/Scene/SceneTicking.h
+++ b/Source/Engine/Level/Scene/SceneTicking.h
@@ -46,6 +46,9 @@ public:
     /// </summary>
     class FLAXENGINE_API TickData
     {
+    protected:
+        friend SceneTicking;
+        bool _canTick = true;
     public:
         Array<Script*> Scripts;
         Array<Tick> Ticks;
@@ -134,6 +137,11 @@ public:
     /// </summary>
     void Clear();
 
+    /// <summary>
+    /// Changes the ability to tick. When disabled, the ticking functions won't be called. Can be called during ticking (eg. when scene is unloaded) to stp performing any more ticks.
+    /// </summary>
+    void SetTicking(bool enable);
+
 public:
     /// <summary>
     /// The fixed update tick function.