Add entity freeing and queued scene management

Works like Godot's queue_free

as6/Entity.hpp

@@ -33,6 +33,7 @@ class Component {
 struct Entity {
     std::vector<std::shared_ptr<Component>> components;
     GameContext *context = nullptr;
+    bool queuedForFree = false;
 
     /**
      * Injects the global game context/state so the entity and its components can
@@ -93,4 +94,20 @@ struct Entity {
             c->Update(dt);
         }
     }
+
+    /**
+     * Marks the entity for deferred destruction at the end of a systems tick.
+     * Inspired by Godot!
+     */
+    void QueueFree() { queuedForFree = true; }
+
+    /**
+     * Propagates cleanup call to all owned components so they can release any
+     * resources or references before the entity is destroyed.
+     */
+    void Cleanup() {
+        for (auto &c : components) {
+            c->Cleanup();
+        }
+    }
 };

as6/SceneManager.hpp

@@ -39,6 +39,7 @@ class SceneManager {
      * @param args Arguments forwarded to the constructor of the new scene.
      */
     template <typename T, typename... Args> void ChangeScene(Args &&...args);
+    template <typename T, typename... Args> void QueueSceneChange(Args &&...args);
 
     /**
      * @brief Changes to the provided next scene, invoking `Exit` on the old scene and
@@ -47,6 +48,7 @@ class SceneManager {
      * @param nextScene The new scene to switch to.
      */
     void ChangeScene(std::unique_ptr<Scene> nextScene);
+    void QueueSceneChange(std::unique_ptr<Scene> nextScene);
     void Update(float dt);
     void Draw();
 
@@ -54,6 +56,7 @@ class SceneManager {
     // use unique_ptr to enforce single ownership and ensure proper cleanup on
     // scene change
     std::unique_ptr<Scene> current;
+    std::unique_ptr<Scene> queued;
 };
 
 class StartMenuScene;
@@ -100,10 +103,22 @@ inline void SceneManager::ChangeScene(std::unique_ptr<Scene> nextScene) {
     }
 }
 
+inline void SceneManager::QueueSceneChange(std::unique_ptr<Scene> nextScene) {
+    queued = std::move(nextScene);
+}
+
 inline void SceneManager::Update(float dt) {
+    if (queued) {
+        ChangeScene(std::move(queued));
+    }
+
     if (current) {
         current->Update(dt);
     }
+
+    if (queued) {
+        ChangeScene(std::move(queued));
+    }
 }
 
 inline void SceneManager::Draw() {
@@ -114,7 +129,7 @@ inline void SceneManager::Draw() {
 
 inline void StartMenuScene::Update(float) {
     if (IsKeyPressed(KEY_ENTER) || IsMouseButtonPressed(MOUSE_BUTTON_LEFT)) {
-        manager.ChangeScene<GameplayScene>();
+        manager.QueueSceneChange<GameplayScene>();
     }
 }
 
@@ -154,7 +169,7 @@ inline void GameplayScene::Enter() {
 inline void GameplayScene::Update(float dt) {
     UpdateAllSystems(entities, context, dt);
     if (wantsDeathScene) {
-        manager.ChangeScene<DeathScene>();
+        manager.QueueSceneChange<DeathScene>();
     }
 }
 
@@ -198,12 +213,12 @@ inline void GameplayScene::Draw() {
 
 inline void DeathScene::Update(float) {
     if (IsKeyPressed(KEY_ENTER) || IsMouseButtonPressed(MOUSE_BUTTON_LEFT)) {
-        manager.ChangeScene<GameplayScene>();
+        manager.QueueSceneChange<GameplayScene>();
         return;
     }
 
     if (IsKeyPressed(KEY_ESCAPE)) {
-        manager.ChangeScene<StartMenuScene>();
+        manager.QueueSceneChange<StartMenuScene>();
     }
 }
 
@@ -217,3 +232,7 @@ inline void DeathScene::Draw() {
 template <typename T, typename... Args> inline void SceneManager::ChangeScene(Args &&...args) {
     ChangeScene(std::make_unique<T>(*this, std::forward<Args>(args)...));
 }
+
+template <typename T, typename... Args> inline void SceneManager::QueueSceneChange(Args &&...args) {
+    QueueSceneChange(std::make_unique<T>(*this, std::forward<Args>(args)...));
+}

as6/Systems.hpp

@@ -4,6 +4,7 @@
 #include "Entity.hpp"
 #include "GameContext.hpp"
 
+#include <algorithm>
 #include <memory>
 #include <vector>
 
@@ -60,4 +61,19 @@ void UpdateAllSystems(std::vector<std::shared_ptr<Entity>> &entities, GameContex
             }
         }
     }
+
+    auto remover = [](const std::shared_ptr<Entity> &entity) {
+        if (!entity) {
+            return true;
+        }
+
+        if (entity->queuedForFree) {
+            entity->Cleanup();
+            return true;
+        }
+
+        return false;
+    };
+
+    entities.erase(std::remove_if(entities.begin(), entities.end(), remover), entities.end());
 }