A few things

Make child entites work.

z-sort entity list before rendering.

entites have a creation timestamp.

include/Engine/Level/Scene.h

@@ -18,6 +18,8 @@ protected:
     Camera* active_camera = nullptr;
     std::vector<Fixed*> fixed_list{};
     std::vector<Entity*> entity_list{};
+protected:
+    [[nodiscard]] std::vector<Entity*> GetFlatEntityList(const std::vector<Entity*>& entity_list) const;
 public:
     [[nodiscard]] bool EntityListContains(const Entity* entity) const;
     [[nodiscard]] bool FixedListContains(const Fixed* fixed) const;