fix physics test

39 files changed, 164 insertions, 158 deletions

diff --git a/src/crepe/Component.cpp b/src/crepe/Component.cpp
index c133739..d11a37e 100644
--- a/src/crepe/Component.cpp
+++ b/src/crepe/Component.cpp
@@ -2,5 +2,5 @@
 
 using namespace crepe;
 
-Component::Component(const Data & data) : data(data) {}
+Component::Component(game_object_id_t id) : game_object_id(id) {}
 
diff --git a/src/crepe/Component.h b/src/crepe/Component.h
index c6d72df..12c10cb 100644
--- a/src/crepe/Component.h
+++ b/src/crepe/Component.h
@@ -14,23 +14,20 @@ class ComponentManager;
  */
 class Component {
 public:
-	struct Data {
-		//! The ID of the GameObject this component belongs to
-		const game_object_id_t id;
-		//! The manager of this component
-		ComponentManager & component_manager;
-	};
+	//! Whether the component is active
+	bool active = true;
+	//! The id of the GameObject this component belongs to
+	const game_object_id_t game_object_id;
 
 protected:
 	/**
-	 * \param base Data
+	 * \param id The id of the GameObject this component belongs to
 	 */
-	Component(const Data & base);
+	Component(game_object_id_t id);
 	//! Only the ComponentManager can create components
-	friend class crepe::ComponentManager;
+	friend class ComponentManager;
 
 public:
-	virtual ~Component() = default;
 	/**
 	 * \brief Get the maximum number of instances for this component
 	 *
@@ -41,11 +38,6 @@ public:
 	 * \return The maximum number of instances for this component
 	 */
 	virtual int get_instances_max() const { return -1; }
-
-public:
-	Data data;
-	//! Whether the component is active
-	bool active = true;
 };
 
 } // namespace crepe
diff --git a/src/crepe/ComponentManager.h b/src/crepe/ComponentManager.h
index e37bc4a..1d67e69 100644
--- a/src/crepe/ComponentManager.h
+++ b/src/crepe/ComponentManager.h
@@ -24,7 +24,7 @@ public:
 	ComponentManager(); // dbg_trace
 	~ComponentManager(); // dbg_trace
 
-public:
+protected:
 	/**
 	 * \brief Add a component to the ComponentManager
 	 * 
@@ -39,6 +39,11 @@ public:
 	 */
 	template <typename T, typename... Args>
 	T & add_component(game_object_id_t id, Args &&... args);
+	//! GameObject is used as an interface to add components instead of the
+	// component manager directly
+	friend class GameObject;
+
+public:
 	/**
 	 * \brief Delete all components of a specific type and id
 	 * 
diff --git a/src/crepe/ComponentManager.hpp b/src/crepe/ComponentManager.hpp
index 89a8536..98efb49 100644
--- a/src/crepe/ComponentManager.hpp
+++ b/src/crepe/ComponentManager.hpp
@@ -31,10 +31,7 @@ T & ComponentManager::add_component(game_object_id_t id, Args &&... args) {
 
 	// Create a new component of type T (arguments directly forwarded). The
 	// constructor must be called by ComponentManager.
-	T * instance_ptr = new T(Component::Data {
-		.id = id,
-		.component_manager = *this,
-	}, forward<Args>(args)...);
+	T * instance_ptr = new T(id, forward<Args>(args)...);
 	if (instance_ptr == nullptr) throw std::bad_alloc();
 
 	T & instance_ref = *instance_ptr;
diff --git a/src/crepe/api/Animator.cpp b/src/crepe/api/Animator.cpp
index ad60981..cbf415d 100644
--- a/src/crepe/api/Animator.cpp
+++ b/src/crepe/api/Animator.cpp
@@ -9,8 +9,8 @@
 
 using namespace crepe;
 
-Animator::Animator(const Component::Data & data, Sprite & ss, int row, int col, int col_animator)
-	: Component(data),
+Animator::Animator(game_object_id_t id, Sprite & ss, int row, int col, int col_animator)
+	: Component(id),
 	  spritesheet(ss),
 	  row(row),
 	  col(col) {
diff --git a/src/crepe/api/Animator.h b/src/crepe/api/Animator.h
index f66dc1a..75b8139 100644
--- a/src/crepe/api/Animator.h
+++ b/src/crepe/api/Animator.h
@@ -36,7 +36,7 @@ public:
 	 *
 	 * This constructor sets up the Animator with the given parameters, and initializes the animation system.
 	 */
-	Animator(const Component::Data & data, Sprite & spritesheet, int row, int col,
+	Animator(game_object_id_t id, Sprite & spritesheet, int row, int col,
 			 int col_animate);
 
 	~Animator(); // dbg_trace
diff --git a/src/crepe/api/BehaviorScript.cpp b/src/crepe/api/BehaviorScript.cpp
index ce1cfde..41c144c 100644
--- a/src/crepe/api/BehaviorScript.cpp
+++ b/src/crepe/api/BehaviorScript.cpp
@@ -1,4 +1,7 @@
 #include "BehaviorScript.h"
+#include "Component.h"
 
 using namespace crepe;
 
+BehaviorScript::BehaviorScript(game_object_id_t id, ComponentManager & mgr) : Component(id), component_manager(mgr) {}
+
diff --git a/src/crepe/api/BehaviorScript.h b/src/crepe/api/BehaviorScript.h
index 8d21a72..f156081 100644
--- a/src/crepe/api/BehaviorScript.h
+++ b/src/crepe/api/BehaviorScript.h
@@ -12,7 +12,7 @@ class Script;
 
 class BehaviorScript : public Component {
 protected:
-	using Component::Component;
+	BehaviorScript(game_object_id_t id, ComponentManager & component_manager);
 	//! Only ComponentManager is allowed to instantiate BehaviorScript
 	friend class ComponentManager;
 
@@ -36,6 +36,7 @@ protected:
 	//! Flag to indicate if script->init() has been called already
 	bool initialized = false;
 	std::unique_ptr<Script> script = nullptr;
+	ComponentManager & component_manager;
 
 private:
 	//! Script accesses the component manager directly via its parent
diff --git a/src/crepe/api/BehaviorScript.hpp b/src/crepe/api/BehaviorScript.hpp
index bb5d829..2bed1b7 100644
--- a/src/crepe/api/BehaviorScript.hpp
+++ b/src/crepe/api/BehaviorScript.hpp
@@ -15,6 +15,7 @@ BehaviorScript & BehaviorScript::set_script() {
 	static_assert(std::is_base_of<Script, T>::value);
 	Script * s = new T();
 	s->parent_ref = this;
+	s->component_manager_ref = &this->component_manager;
 	this->script = std::unique_ptr<Script>(s);
 	return *this;
 }
diff --git a/src/crepe/api/CMakeLists.txt b/src/crepe/api/CMakeLists.txt
index d9cda57..ee77947 100644
--- a/src/crepe/api/CMakeLists.txt
+++ b/src/crepe/api/CMakeLists.txt
@@ -14,7 +14,7 @@ target_sources(crepe PUBLIC
 	Config.cpp
 	Metadata.cpp
 	Scene.cpp
-	# SceneManager.cpp
+	SceneManager.cpp
 	Vector2.cpp
 	Camera.cpp
 	Animator.cpp
@@ -40,8 +40,8 @@ target_sources(crepe PUBLIC FILE_SET HEADERS FILES
 	SaveManager.h
 	Scene.h
 	Metadata.h
-	# SceneManager.h
-	# SceneManager.hpp
+	SceneManager.h
+	SceneManager.hpp
 	Camera.h
 	Animator.h
 	# LoopManager.h
diff --git a/src/crepe/api/Camera.cpp b/src/crepe/api/Camera.cpp
index fece199..232c922 100644
--- a/src/crepe/api/Camera.cpp
+++ b/src/crepe/api/Camera.cpp
@@ -6,8 +6,8 @@
 
 using namespace crepe;
 
-Camera::Camera(const Component::Data & data, const Color & bg_color)
-	: Component(data),
+Camera::Camera(game_object_id_t id, const Color & bg_color)
+	: Component(id),
 	  bg_color(bg_color) {
 	dbg_trace();
 }
diff --git a/src/crepe/api/Camera.h b/src/crepe/api/Camera.h
index a52f2f7..d8c08a6 100644
--- a/src/crepe/api/Camera.h
+++ b/src/crepe/api/Camera.h
@@ -23,7 +23,7 @@ public:
 	 * \param id Unique identifier for the camera component.
 	 * \param bg_color Background color for the camera view.
 	 */
-	Camera(const Component::Data & data, const Color & bg_color);
+	Camera(game_object_id_t id, const Color & bg_color);
 	~Camera(); // dbg_trace only
 
 public:
diff --git a/src/crepe/api/GameObject.cpp b/src/crepe/api/GameObject.cpp
index bba1f26..dd20b7f 100644
--- a/src/crepe/api/GameObject.cpp
+++ b/src/crepe/api/GameObject.cpp
@@ -2,6 +2,7 @@
 
 #include "GameObject.h"
 #include "Metadata.h"
+#include "BehaviorScript.h"
 
 using namespace crepe;
 using namespace std;
@@ -30,3 +31,10 @@ void GameObject::set_parent(const GameObject & parent) {
 		= mgr.get_components_by_id<Metadata>(parent.id);
 	parent_metadata.at(0).get().children.push_back(this->id);
 }
+
+template <>
+BehaviorScript & GameObject::add_component<BehaviorScript>() {
+	ComponentManager & mgr = this->component_manager;
+	return mgr.add_component<BehaviorScript>(this->id, mgr);
+}
+
diff --git a/src/crepe/api/GameObject.h b/src/crepe/api/GameObject.h
index d09938a..7751fd0 100644
--- a/src/crepe/api/GameObject.h
+++ b/src/crepe/api/GameObject.h
@@ -8,6 +8,7 @@
 namespace crepe {
 
 class ComponentManager;
+class BehaviorScript;
 
 /**
  * \brief Represents a GameObject
@@ -67,6 +68,18 @@ protected:
 	ComponentManager & component_manager;
 };
 
+/**
+ * \brief Add a BehaviorScript component to this game object
+ *
+ * The \c BehaviorScript class is the only exception to the ECS harmony, and
+ * requires a reference to the component manager passed to its constructor in
+ * order to function normally. This is because the \c BehaviorScript (and \c
+ * Script) classes are the only component-related classes that store
+ * implemented member functions as data.
+ */
+template <>
+BehaviorScript & GameObject::add_component<BehaviorScript>();
+
 } // namespace crepe
 
 #include "GameObject.hpp"
diff --git a/src/crepe/api/Metadata.cpp b/src/crepe/api/Metadata.cpp
index 6f0a280..d421de5 100644
--- a/src/crepe/api/Metadata.cpp
+++ b/src/crepe/api/Metadata.cpp
@@ -3,7 +3,7 @@
 using namespace crepe;
 using namespace std;
 
-Metadata::Metadata(const Component::Data & data, const string & name, const string & tag)
-	: Component(data),
+Metadata::Metadata(game_object_id_t id, const string & name, const string & tag)
+	: Component(id),
 	  name(name),
 	  tag(tag) {}
diff --git a/src/crepe/api/Metadata.h b/src/crepe/api/Metadata.h
index 8c91797..c61e006 100644
--- a/src/crepe/api/Metadata.h
+++ b/src/crepe/api/Metadata.h
@@ -20,7 +20,7 @@ public:
 	 * \param name The name of the GameObject
 	 * \param tag The tag of the GameObject
 	 */
-	Metadata(const Component::Data & data, const std::string & name,
+	Metadata(game_object_id_t id, const std::string & name,
 			 const std::string & tag);
 	/**
 	 * \brief Get the maximum number of instances for this component
diff --git a/src/crepe/api/ParticleEmitter.cpp b/src/crepe/api/ParticleEmitter.cpp
index ed4fec8..0bc2197 100644
--- a/src/crepe/api/ParticleEmitter.cpp
+++ b/src/crepe/api/ParticleEmitter.cpp
@@ -6,12 +6,12 @@
 
 using namespace crepe;
 
-ParticleEmitter::ParticleEmitter(const Component::Data & data, uint32_t max_particles,
+ParticleEmitter::ParticleEmitter(game_object_id_t id, uint32_t max_particles,
 								 uint32_t emission_rate, uint32_t speed,
 								 uint32_t speed_offset, uint32_t angle,
 								 uint32_t angleOffset, float begin_lifespan,
 								 float end_lifespan)
-	: Component(data),
+	: Component(id),
 	  max_particles(max_particles),
 	  emission_rate(emission_rate),
 	  speed(speed),
diff --git a/src/crepe/api/ParticleEmitter.h b/src/crepe/api/ParticleEmitter.h
index ba89538..5939723 100644
--- a/src/crepe/api/ParticleEmitter.h
+++ b/src/crepe/api/ParticleEmitter.h
@@ -10,7 +10,7 @@ namespace crepe {
 
 class ParticleEmitter : public Component {
 public:
-	ParticleEmitter(const Component::Data & data, uint32_t max_particles,
+	ParticleEmitter(game_object_id_t id, uint32_t max_particles,
 					uint32_t emission_rate, uint32_t speed,
 					uint32_t speed_offset, uint32_t angle, uint32_t angleOffset,
 					float begin_lifespan, float end_lifespan);
diff --git a/src/crepe/api/Rigidbody.cpp b/src/crepe/api/Rigidbody.cpp
index be6bb93..6b87695 100644
--- a/src/crepe/api/Rigidbody.cpp
+++ b/src/crepe/api/Rigidbody.cpp
@@ -2,8 +2,8 @@
 
 using namespace crepe;
 
-crepe::Rigidbody::Rigidbody(const Component::Data & component_data, const Data & data)
-	: Component(component_data),
+crepe::Rigidbody::Rigidbody(game_object_id_t id, const Data & data)
+	: Component(id),
 	  data(data) {}
 
 void crepe::Rigidbody::add_force_linear(const Vector2 & force) {
diff --git a/src/crepe/api/Rigidbody.h b/src/crepe/api/Rigidbody.h
index 99837a6..2e20288 100644
--- a/src/crepe/api/Rigidbody.h
+++ b/src/crepe/api/Rigidbody.h
@@ -82,7 +82,7 @@ public:
 	 * \param game_object_id id of the gameobject the rigibody is added to.
 	 * \param data struct to configure the rigidbody.
 	 */
-	Rigidbody(const Component::Data & component_data, const Data & data);
+	Rigidbody(game_object_id_t id, const Data & data);
 	//! struct to hold data of rigidbody
 	Data data;
 
diff --git a/src/crepe/api/SceneManager.cpp b/src/crepe/api/SceneManager.cpp
index dfed6ee..814b7d7 100644
--- a/src/crepe/api/SceneManager.cpp
+++ b/src/crepe/api/SceneManager.cpp
@@ -8,10 +8,7 @@
 using namespace crepe;
 using namespace std;
 
-SceneManager & SceneManager::get_instance() {
-	static SceneManager instance;
-	return instance;
-}
+SceneManager::SceneManager(ComponentManager & mgr) : component_manager(mgr) {}
 
 void SceneManager::set_next_scene(const string & name) { next_scene = name; }
 
@@ -19,18 +16,18 @@ void SceneManager::load_next_scene() {
 	// next scene not set
 	if (this->next_scene.empty()) return;
 
-	auto it
-		= find_if(this->scenes.begin(), this->scenes.end(),
-				  [&next_scene = this->next_scene](unique_ptr<Scene> & scene) {
-					  return scene->name == next_scene;
-				  });
+	auto it = find_if(this->scenes.begin(), this->scenes.end(),
+		[&next_scene = this->next_scene](unique_ptr<Scene> & scene) {
+			return scene->name == next_scene;
+		}
+	);
 
 	// next scene not found
 	if (it == this->scenes.end()) return;
 	unique_ptr<Scene> & scene = *it;
 
 	// Delete all components of the current scene
-	ComponentManager & mgr = ComponentManager::get_instance();
+	ComponentManager & mgr = this->component_manager;
 	mgr.delete_all_components();
 
 	// Load the new scene
diff --git a/src/crepe/api/SceneManager.h b/src/crepe/api/SceneManager.h
index 1e0e670..553194f 100644
--- a/src/crepe/api/SceneManager.h
+++ b/src/crepe/api/SceneManager.h
@@ -8,14 +8,12 @@
 
 namespace crepe {
 
+class ComponentManager;
+
 class SceneManager {
 public:
-	// Singleton
-	static SceneManager & get_instance();
-	SceneManager(const SceneManager &) = delete;
-	SceneManager(SceneManager &&) = delete;
-	SceneManager & operator=(const SceneManager &) = delete;
-	SceneManager & operator=(SceneManager &&) = delete;
+	SceneManager(ComponentManager & mgr);
+	virtual ~SceneManager() = default;
 
 public:
 	/**
@@ -38,11 +36,11 @@ public:
 	void load_next_scene();
 
 private:
-	SceneManager() = default;
-
-private:
 	std::vector<std::unique_ptr<Scene>> scenes;
 	std::string next_scene;
+
+protected:
+	ComponentManager & component_manager;
 };
 
 } // namespace crepe
diff --git a/src/crepe/api/Script.h b/src/crepe/api/Script.h
index d543df8..c5e3cc4 100644
--- a/src/crepe/api/Script.h
+++ b/src/crepe/api/Script.h
@@ -9,6 +9,7 @@ class ScriptSystem;
 namespace crepe {
 
 class BehaviorScript;
+class ComponentManager;
 
 class Script {
 	//! ScriptSystem calls \c update()
@@ -31,14 +32,18 @@ protected:
 	template <typename T>
 	std::vector<std::reference_wrapper<T>> get_components();
 
-protected:
+private:
 	// NOTE: Script must have a constructor without arguments so the game
 	// programmer doesn't need to manually add `using Script::Script` to their
 	// concrete script class.
 	Script() = default;
 	//! Only \c BehaviorScript instantiates Script
 	friend class BehaviorScript;
+
+	// These references are set by BehaviorScript immediately after calling the
+	// constructor of Script.
 	BehaviorScript * parent_ref = nullptr;
+	ComponentManager * component_manager_ref = nullptr;
 };
 
 } // namespace crepe
diff --git a/src/crepe/api/Script.hpp b/src/crepe/api/Script.hpp
index 68bcc29..ee8c380 100644
--- a/src/crepe/api/Script.hpp
+++ b/src/crepe/api/Script.hpp
@@ -19,9 +19,9 @@ T & Script::get_component() {
 template <typename T>
 std::vector<std::reference_wrapper<T>> Script::get_components() {
 	auto & parent = *this->parent_ref;
-	auto & mgr = parent.data.component_manager;
+	auto & mgr = *this->component_manager_ref;
 
-	return mgr.get_components_by_id<T>(parent.data.id);
+	return mgr.get_components_by_id<T>(parent.game_object_id);
 }
 
 } // namespace crepe
diff --git a/src/crepe/api/Sprite.cpp b/src/crepe/api/Sprite.cpp
index 716609f..6f0433f 100644
--- a/src/crepe/api/Sprite.cpp
+++ b/src/crepe/api/Sprite.cpp
@@ -10,9 +10,9 @@
 using namespace std;
 using namespace crepe;
 
-Sprite::Sprite(const Component::Data & data, const shared_ptr<Texture> image,
+Sprite::Sprite(game_object_id_t id, const shared_ptr<Texture> image,
 			   const Color & color, const FlipSettings & flip)
-	: Component(data),
+	: Component(id),
 	  color(color),
 	  flip(flip),
 	  sprite_image(image) {
diff --git a/src/crepe/api/Sprite.h b/src/crepe/api/Sprite.h
index 171dfeb..deb3f93 100644
--- a/src/crepe/api/Sprite.h
+++ b/src/crepe/api/Sprite.h
@@ -43,7 +43,7 @@ public:
 	 * \param color Color tint applied to the sprite.
 	 * \param flip Flip settings for horizontal and vertical orientation.
 	 */
-	Sprite(const Component::Data & data, const std::shared_ptr<Texture> image,
+	Sprite(game_object_id_t id, const std::shared_ptr<Texture> image,
 		   const Color & color, const FlipSettings & flip);
 
 	/**
diff --git a/src/crepe/api/Transform.cpp b/src/crepe/api/Transform.cpp
index 9645d03..e401120 100644
--- a/src/crepe/api/Transform.cpp
+++ b/src/crepe/api/Transform.cpp
@@ -4,9 +4,9 @@
 
 using namespace crepe;
 
-Transform::Transform(const Component::Data & data, const Vector2 & point,
+Transform::Transform(game_object_id_t id, const Vector2 & point,
 					 double rotation, double scale)
-	: Component(data),
+	: Component(id),
 	  position(point),
 	  rotation(rotation),
 	  scale(scale) {
diff --git a/src/crepe/api/Transform.h b/src/crepe/api/Transform.h
index a7bcd89..a1ef406 100644
--- a/src/crepe/api/Transform.h
+++ b/src/crepe/api/Transform.h
@@ -14,28 +14,26 @@ namespace crepe {
  */
 class Transform : public Component {
 public:
+	//! Translation (shift)
+	Vector2 position = { 0, 0 };
+	//! Rotation, in degrees
+	double rotation = 0;
+	//! Multiplication factor
+	double scale = 0;
+
+protected:
 	/**
 	 * \param id The id of the GameObject this component belongs to
 	 * \param point The position of the GameObject
 	 * \param rotation The rotation of the GameObject
 	 * \param scale The scale of the GameObject
 	 */
-	Transform(const Component::Data & data, const Vector2 & point, double rotation,
-			  double scale);
-	/**
-	 * \brief Get the maximum number of instances for this component
-	 *
-	 * \return The maximum number of instances for this component
-	 */
+	Transform(game_object_id_t id, const Vector2 & point, double rotation = 0,
+			  double scale = 0);
+	//! There is always exactly one transform component per entity
 	virtual int get_instances_max() const { return 1; }
-
-public:
-	//! Translation (shift)
-	Vector2 position;
-	//! Rotation, in degrees
-	double rotation;
-	//! Multiplication factor
-	double scale;
+	//! ComponentManager instantiates all components
+	friend class ComponentManager;
 };
 
 } // namespace crepe
diff --git a/src/crepe/api/Vector2.cpp b/src/crepe/api/Vector2.cpp
index 09bb59b..aa391fa 100644
--- a/src/crepe/api/Vector2.cpp
+++ b/src/crepe/api/Vector2.cpp
@@ -1,57 +1,44 @@
 #include "Vector2.h"
 
-namespace crepe {
+using namespace crepe;
 
-// Constructor with initial values
-Vector2::Vector2(float x, float y) : x(x), y(y) {}
-
-// Subtracts another vector from this vector and returns the result.
 Vector2 Vector2::operator-(const Vector2 & other) const {
 	return {x - other.x, y - other.y};
 }
 
-// Adds another vector to this vector and returns the result.
 Vector2 Vector2::operator+(const Vector2 & other) const {
 	return {x + other.x, y + other.y};
 }
 
-// Multiplies this vector by a scalar and returns the result.
 Vector2 Vector2::operator*(float scalar) const {
 	return {x * scalar, y * scalar};
 }
 
-// Multiplies this vector by another vector element-wise and updates this vector.
 Vector2 & Vector2::operator*=(const Vector2 & other) {
 	x *= other.x;
 	y *= other.y;
 	return *this;
 }
 
-// Adds another vector to this vector and updates this vector.
 Vector2 & Vector2::operator+=(const Vector2 & other) {
 	x += other.x;
 	y += other.y;
 	return *this;
 }
 
-// Adds a scalar value to both components of this vector and updates this vector.
 Vector2 & Vector2::operator+=(float other) {
 	x += other;
 	y += other;
 	return *this;
 }
 
-// Returns the negation of this vector.
 Vector2 Vector2::operator-() const { return {-x, -y}; }
 
-// Checks if this vector is equal to another vector.
 bool Vector2::operator==(const Vector2 & other) const {
 	return x == other.x && y == other.y;
 }
 
-// Checks if this vector is not equal to another vector.
 bool Vector2::operator!=(const Vector2 & other) const {
 	return !(*this == other);
 }
 
-} // namespace crepe
diff --git a/src/crepe/api/Vector2.h b/src/crepe/api/Vector2.h
index 741951b..a069a57 100644
--- a/src/crepe/api/Vector2.h
+++ b/src/crepe/api/Vector2.h
@@ -2,19 +2,12 @@
 
 namespace crepe {
 
-//! Vector2 class
-class Vector2 {
-public:
+//! 2D vector
+struct Vector2 {
 	//! X component of the vector
-	float x;
+	float x = 0;
 	//! Y component of the vector
-	float y;
-
-	//! Default constructor
-	Vector2() = default;
-
-	//! Constructor with initial values
-	Vector2(float x, float y);
+	float y = 0;
 
 	//! Subtracts another vector from this vector and returns the result.
 	Vector2 operator-(const Vector2 & other) const;
diff --git a/src/crepe/system/CMakeLists.txt b/src/crepe/system/CMakeLists.txt
index 9ee12f6..2fb58dc 100644
--- a/src/crepe/system/CMakeLists.txt
+++ b/src/crepe/system/CMakeLists.txt
@@ -1,8 +1,8 @@
 target_sources(crepe PUBLIC
 	System.cpp
-	# ParticleSystem.cpp
+	ParticleSystem.cpp
 	ScriptSystem.cpp
-	# PhysicsSystem.cpp
+	PhysicsSystem.cpp
 	# CollisionSystem.cpp
 	# RenderSystem.cpp
 	# AnimatorSystem.cpp
@@ -11,7 +11,7 @@ target_sources(crepe PUBLIC
 target_sources(crepe PUBLIC FILE_SET HEADERS FILES
 	System.h
 	ScriptSystem.h
-	# PhysicsSystem.h
+	PhysicsSystem.h
 	# CollisionSystem.h
 	# RenderSystem.h
 	# AnimatorSystem.h
diff --git a/src/crepe/system/ParticleSystem.cpp b/src/crepe/system/ParticleSystem.cpp
index 397b586..64fee4e 100644
--- a/src/crepe/system/ParticleSystem.cpp
+++ b/src/crepe/system/ParticleSystem.cpp
@@ -8,10 +8,8 @@
 
 using namespace crepe;
 
-ParticleSystem::ParticleSystem() : elapsed_time(0.0f) {}
-
 void ParticleSystem::update() {
-	ComponentManager & mgr = ComponentManager::get_instance();
+	ComponentManager & mgr = this->component_manager;
 	std::vector<std::reference_wrapper<ParticleEmitter>> emitters
 		= mgr.get_components_by_type<ParticleEmitter>();
 	float delta_time = 0.10;
@@ -60,3 +58,4 @@ void ParticleSystem::emit_particle(ParticleEmitter & emitter) {
 		}
 	}
 }
+
diff --git a/src/crepe/system/ParticleSystem.h b/src/crepe/system/ParticleSystem.h
index 3ac1d3f..f171c62 100644
--- a/src/crepe/system/ParticleSystem.h
+++ b/src/crepe/system/ParticleSystem.h
@@ -2,17 +2,22 @@
 
 #include "../api/ParticleEmitter.h"
 
+#include "System.h"
+
 namespace crepe {
 
-class ParticleSystem {
+class ParticleSystem : public System {
 public:
-	ParticleSystem();
-	void update();
+	using System::System;
+	void update() override;
 
 private:
-	void emit_particle(ParticleEmitter & emitter); //emits a new particle
+	//! Emits a new particle
+	void emit_particle(ParticleEmitter & emitter);
 
-	float elapsed_time; //elapsed time since the last emission
+	//! Elapsed time since the last emission
+	float elapsed_time = 0.0;
+	// TODO: to std::chrono::duration
 };
 
 } // namespace crepe
diff --git a/src/crepe/system/PhysicsSystem.cpp b/src/crepe/system/PhysicsSystem.cpp
index eb54ad3..da79707 100644
--- a/src/crepe/system/PhysicsSystem.cpp
+++ b/src/crepe/system/PhysicsSystem.cpp
@@ -11,7 +11,7 @@
 using namespace crepe;
 
 void PhysicsSystem::update() {
-	ComponentManager & mgr = ComponentManager::get_instance();
+	ComponentManager & mgr = this->component_manager;
 	std::vector<std::reference_wrapper<Rigidbody>> rigidbodies
 		= mgr.get_components_by_type<Rigidbody>();
 	std::vector<std::reference_wrapper<Transform>> transforms
diff --git a/src/crepe/system/PhysicsSystem.h b/src/crepe/system/PhysicsSystem.h
index cc13b70..5433a0f 100644
--- a/src/crepe/system/PhysicsSystem.h
+++ b/src/crepe/system/PhysicsSystem.h
@@ -1,24 +1,24 @@
 #pragma once
 
+#include "System.h"
+
 namespace crepe {
+
 /**
  * \brief System that controls all physics
  * 
  * This class is a physics system that uses a rigidbody and transform
  * to add physics to a game object.
  */
-class PhysicsSystem {
+class PhysicsSystem : public System {
 public:
-	/**
-	 * Constructor is default
-	 */
-	PhysicsSystem() = default;
+	using System::System;
 	/**
 	 * \brief updates the physics system.
 	 * 
 	 * It calculates new velocties and changes the postion in the transform.
 	 */
-	void update();
+	void update() override;
 };
 
 } // namespace crepe
diff --git a/src/crepe/system/ScriptSystem.h b/src/crepe/system/ScriptSystem.h
index b52e825..b0b4185 100644
--- a/src/crepe/system/ScriptSystem.h
+++ b/src/crepe/system/ScriptSystem.h
@@ -7,12 +7,11 @@
 namespace crepe {
 
 class Script;
-class BehaviorScript;
 
 class ScriptSystem : public System {
 public:
 	using System::System;
-	void update();
+	void update() override;
 
 private:
 	std::forward_list<std::reference_wrapper<Script>> get_scripts();
diff --git a/src/example/script.cpp b/src/example/script.cpp
index 9e8b147..4ba2b4b 100644
--- a/src/example/script.cpp
+++ b/src/example/script.cpp
@@ -35,15 +35,15 @@ class MyScript : public Script {
 };
 
 int main() {
+	ComponentManager component_manager {};
+	ScriptSystem system { component_manager };
+
 	// Create game object with Transform and BehaviorScript components
-	auto obj = GameObject(0, "name", "tag", Vector2{1.2, 3.4}, 0, 1);
+	auto & obj = component_manager.new_object("name");
 	obj.add_component<BehaviorScript>().set_script<MyScript>();
 
-	// Get ScriptSystem singleton instance (this would normally be done from the
-	// game loop)
-	ScriptSystem sys;
 	// Update all scripts. This should result in MyScript::update being called
-	sys.update();
+	system.update();
 
 	return EXIT_SUCCESS;
 }
diff --git a/src/test/CMakeLists.txt b/src/test/CMakeLists.txt
index 9d303bc..4dd5010 100644
--- a/src/test/CMakeLists.txt
+++ b/src/test/CMakeLists.txt
@@ -1,6 +1,6 @@
 target_sources(test_main PUBLIC
 	main.cpp
-	# PhysicsTest.cpp
+	PhysicsTest.cpp
 	ScriptTest.cpp
 )
 
diff --git a/src/test/PhysicsTest.cpp b/src/test/PhysicsTest.cpp
index 538d244..5399d54 100644
--- a/src/test/PhysicsTest.cpp
+++ b/src/test/PhysicsTest.cpp
@@ -12,17 +12,16 @@ using namespace crepe;
 
 class PhysicsTest : public ::testing::Test {
 public:
-	GameObject * game_object;
 	ComponentManager component_manager;
-	PhysicsSystem physics_system;
+	PhysicsSystem system { component_manager };
 
 	void SetUp() override {
-		ComponentManager & mgr = ComponentManager::get_instance();
-		std::vector<std::reference_wrapper<Transform>> transforms
+		ComponentManager & mgr = this->component_manager;
+		vector<reference_wrapper<Transform>> transforms
 			= mgr.get_components_by_id<Transform>(0);
 		if (transforms.empty()) {
-			game_object = new GameObject(0, "", "", Vector2{0, 0}, 0, 0);
-			game_object->add_component<Rigidbody>(Rigidbody::Data{
+			auto & entity = mgr.new_object("", "", Vector2{0, 0}, 0, 0);
+			entity.add_component<Rigidbody>(Rigidbody::Data{
 				.mass = 1,
 				.gravity_scale = 1,
 				.body_type = Rigidbody::BodyType::DYNAMIC,
@@ -38,7 +37,7 @@ public:
 		transform.position.x = 0.0;
 		transform.position.y = 0.0;
 		transform.rotation = 0.0;
-		std::vector<std::reference_wrapper<Rigidbody>> rigidbodies
+		vector<reference_wrapper<Rigidbody>> rigidbodies
 			= mgr.get_components_by_id<Rigidbody>(0);
 		Rigidbody & rigidbody = rigidbodies.front().get();
 		rigidbody.data.angular_velocity = 0;
@@ -49,34 +48,37 @@ public:
 
 TEST_F(PhysicsTest, gravity) {
 	Config::get_instance().physics.gravity = 1;
-	ComponentManager & mgr = ComponentManager::get_instance();
-	std::vector<std::reference_wrapper<Transform>> transforms
-		= mgr.get_components_by_id<Transform>(0);
+	ComponentManager & mgr = this->component_manager;
+	vector<reference_wrapper<Transform>> transforms = mgr.get_components_by_id<Transform>(0);
 	const Transform & transform = transforms.front().get();
 	ASSERT_FALSE(transforms.empty());
 	EXPECT_EQ(transform.position.y, 0);
-	physics_system.update();
+
+	system.update();
 	EXPECT_EQ(transform.position.y, 1);
-	physics_system.update();
+
+	system.update();
 	EXPECT_EQ(transform.position.y, 3);
 }
 
 TEST_F(PhysicsTest, max_velocity) {
-	ComponentManager & mgr = ComponentManager::get_instance();
-	std::vector<std::reference_wrapper<Rigidbody>> rigidbodies
+	ComponentManager & mgr = this->component_manager;
+	vector<reference_wrapper<Rigidbody>> rigidbodies
 		= mgr.get_components_by_id<Rigidbody>(0);
 	Rigidbody & rigidbody = rigidbodies.front().get();
 	ASSERT_FALSE(rigidbodies.empty());
 	EXPECT_EQ(rigidbody.data.linear_velocity.y, 0);
+
 	rigidbody.add_force_linear({100, 100});
 	rigidbody.add_force_angular(100);
-	physics_system.update();
+	system.update();
 	EXPECT_EQ(rigidbody.data.linear_velocity.y, 10);
 	EXPECT_EQ(rigidbody.data.linear_velocity.x, 10);
 	EXPECT_EQ(rigidbody.data.angular_velocity, 10);
+
 	rigidbody.add_force_linear({-100, -100});
 	rigidbody.add_force_angular(-100);
-	physics_system.update();
+	system.update();
 	EXPECT_EQ(rigidbody.data.linear_velocity.y, -10);
 	EXPECT_EQ(rigidbody.data.linear_velocity.x, -10);
 	EXPECT_EQ(rigidbody.data.angular_velocity, -10);
@@ -84,39 +86,42 @@ TEST_F(PhysicsTest, max_velocity) {
 
 TEST_F(PhysicsTest, movement) {
 	Config::get_instance().physics.gravity = 0;
-	ComponentManager & mgr = ComponentManager::get_instance();
-	std::vector<std::reference_wrapper<Rigidbody>> rigidbodies
-		= mgr.get_components_by_id<Rigidbody>(0);
+	ComponentManager & mgr = this->component_manager;
+	vector<reference_wrapper<Rigidbody>> rigidbodies = mgr.get_components_by_id<Rigidbody>(0);
 	Rigidbody & rigidbody = rigidbodies.front().get();
-	std::vector<std::reference_wrapper<Transform>> transforms
-		= mgr.get_components_by_id<Transform>(0);
+	vector<reference_wrapper<Transform>> transforms = mgr.get_components_by_id<Transform>(0);
 	const Transform & transform = transforms.front().get();
 	ASSERT_FALSE(rigidbodies.empty());
 	ASSERT_FALSE(transforms.empty());
+
 	rigidbody.add_force_linear({1, 1});
 	rigidbody.add_force_angular(1);
-	physics_system.update();
+	system.update();
 	EXPECT_EQ(transform.position.x, 1);
 	EXPECT_EQ(transform.position.y, 1);
 	EXPECT_EQ(transform.rotation, 1);
+
 	rigidbody.data.constraints = {1, 1, 1};
 	EXPECT_EQ(transform.position.x, 1);
 	EXPECT_EQ(transform.position.y, 1);
 	EXPECT_EQ(transform.rotation, 1);
+
 	rigidbody.data.linear_damping.x = 0.5;
 	rigidbody.data.linear_damping.y = 0.5;
 	rigidbody.data.angular_damping = 0.5;
-	physics_system.update();
+	system.update();
 	EXPECT_EQ(rigidbody.data.linear_velocity.x, 0.5);
 	EXPECT_EQ(rigidbody.data.linear_velocity.y, 0.5);
 	EXPECT_EQ(rigidbody.data.angular_velocity, 0.5);
+
 	rigidbody.data.constraints = {1, 1, 0};
 	rigidbody.data.angular_damping = 0;
 	rigidbody.data.max_angular_velocity = 1000;
 	rigidbody.data.angular_velocity = 360;
-	physics_system.update();
+	system.update();
 	EXPECT_EQ(transform.rotation, 1);
+
 	rigidbody.data.angular_velocity = -360;
-	physics_system.update();
+	system.update();
 	EXPECT_EQ(transform.rotation, 1);
 }