Merge branch 'master' of https://github.com/lonkaars/crepe into wouter/events

40 files changed, 1294 insertions, 663 deletions

diff --git a/src/crepe/Component.h b/src/crepe/Component.h
index 5279fb3..dc17721 100644
--- a/src/crepe/Component.h
+++ b/src/crepe/Component.h
@@ -27,6 +27,11 @@ protected:
 	//! Only the ComponentManager can create components
 	friend class ComponentManager;
 
+	Component(const Component &) = delete;
+	Component(Component &&) = delete;
+	virtual Component & operator=(const Component &) = delete;
+	virtual Component & operator=(Component &&) = delete;
+
 public:
 	virtual ~Component() = default;
 
diff --git a/src/crepe/api/Color.cpp b/src/crepe/api/Color.cpp
index 9e5f187..29bd77a 100644
--- a/src/crepe/api/Color.cpp
+++ b/src/crepe/api/Color.cpp
@@ -2,32 +2,11 @@
 
 using namespace crepe;
 
-Color Color::white = Color(255, 255, 255, 0);
-Color Color::red = Color(255, 0, 0, 0);
-Color Color::green = Color(0, 255, 0, 0);
-Color Color::blue = Color(0, 0, 255, 0);
-Color Color::black = Color(0, 0, 0, 0);
-Color Color::cyan = Color(0, 255, 255, 0);
-Color Color::yellow = Color(255, 255, 0, 0);
-Color Color::magenta = Color(255, 0, 255, 0);
-
-Color::Color(uint8_t red, uint8_t green, uint8_t blue, uint8_t alpha) {
-	this->a = alpha;
-	this->r = red;
-	this->g = green;
-	this->b = blue;
-};
-
-const Color & Color::get_white() { return Color::white; };
-
-const Color & Color::get_red() { return Color::red; };
-const Color & Color::get_green() { return Color::green; };
-const Color & Color::get_blue() { return Color::blue; };
-
-const Color & Color::get_black() { return Color::black; };
-
-const Color & Color::get_cyan() { return Color::cyan; };
-
-const Color & Color::get_yellow() { return Color::yellow; };
-
-const Color & Color::get_magenta() { return Color::magenta; };
+const Color Color::WHITE{0xff, 0xff, 0xff};
+const Color Color::RED{0xff, 0x00, 0x00};
+const Color Color::GREEN{0x00, 0xff, 0x00};
+const Color Color::BLUE{0x00, 0x00, 0xff};
+const Color Color::BLACK{0x00, 0x00, 0x00};
+const Color Color::CYAN{0x00, 0xff, 0xff};
+const Color Color::YELLOW{0xff, 0xff, 0x00};
+const Color Color::MAGENTA{0xff, 0x00, 0xff};
diff --git a/src/crepe/api/Color.h b/src/crepe/api/Color.h
index aa47bf4..84edb5c 100644
--- a/src/crepe/api/Color.h
+++ b/src/crepe/api/Color.h
@@ -4,41 +4,20 @@
 
 namespace crepe {
 
-// TODO: make Color a struct w/o constructors/destructors
-class Color {
-
-	// FIXME: can't these colors be defined as a `static constexpr const Color`
-	// instead?
-
-public:
-	Color(uint8_t red, uint8_t green, uint8_t blue, uint8_t alpha);
-	static const Color & get_white();
-	static const Color & get_red();
-	static const Color & get_green();
-	static const Color & get_blue();
-	static const Color & get_cyan();
-	static const Color & get_magenta();
-	static const Color & get_yellow();
-	static const Color & get_black();
-
-private:
-	// TODO: why are these private!?
-	uint8_t r;
-	uint8_t g;
-	uint8_t b;
-	uint8_t a;
-
-	static Color white;
-	static Color red;
-	static Color green;
-	static Color blue;
-	static Color cyan;
-	static Color magenta;
-	static Color yellow;
-	static Color black;
-
-private:
-	friend class SDLContext;
+struct Color {
+	uint8_t r = 0x00;
+	uint8_t g = 0x00;
+	uint8_t b = 0x00;
+	uint8_t a = 0xff;
+
+	static const Color WHITE;
+	static const Color RED;
+	static const Color GREEN;
+	static const Color BLUE;
+	static const Color CYAN;
+	static const Color MAGENTA;
+	static const Color YELLOW;
+	static const Color BLACK;
 };
 
 } // namespace crepe
diff --git a/src/crepe/api/Sprite.h b/src/crepe/api/Sprite.h
index 0192793..74a55d4 100644
--- a/src/crepe/api/Sprite.h
+++ b/src/crepe/api/Sprite.h
@@ -2,8 +2,9 @@
 
 #include <memory>
 
+#include "../Component.h"
+
 #include "Color.h"
-#include "Component.h"
 #include "Texture.h"
 
 namespace crepe {
diff --git a/src/crepe/api/Texture.cpp b/src/crepe/api/Texture.cpp
index de0d0ea..734a5bb 100644
--- a/src/crepe/api/Texture.cpp
+++ b/src/crepe/api/Texture.cpp
@@ -35,5 +35,5 @@ int Texture::get_width() const {
 }
 int Texture::get_height() const {
 	if (this->texture == nullptr) return 0;
-	return SDLContext::get_instance().get_width(*this);
+	return SDLContext::get_instance().get_height(*this);
 }
diff --git a/src/crepe/facade/DB.cpp b/src/crepe/facade/DB.cpp
index d5d19dc..95cf606 100644
--- a/src/crepe/facade/DB.cpp
+++ b/src/crepe/facade/DB.cpp
@@ -18,8 +18,8 @@ DB::DB(const string & path) {
 	this->db = {db, [](libdb::DB * db) { db->close(db, 0); }};
 
 	// load or create database file
-	ret = this->db->open(this->db.get(), NULL, path.c_str(), NULL, libdb::DB_BTREE, DB_CREATE,
-						 0);
+	const char * file = path.empty() ? NULL : path.c_str();
+	ret = this->db->open(this->db.get(), NULL, file, NULL, libdb::DB_BTREE, DB_CREATE, 0);
 	if (ret != 0) throw runtime_error(format("db->open: {}", libdb::db_strerror(ret)));
 
 	// create cursor
diff --git a/src/crepe/facade/DB.h b/src/crepe/facade/DB.h
index 629b0eb..115c0f1 100644
--- a/src/crepe/facade/DB.h
+++ b/src/crepe/facade/DB.h
@@ -22,8 +22,10 @@ class DB {
 public:
 	/**
 	 * \param path  The path of the database (created if nonexistant)
+	 *
+	 * \note If \p path is empty, the database is entirely in-memory
 	 */
-	DB(const std::string & path);
+	DB(const std::string & path = "");
 	virtual ~DB() = default;
 
 public:
diff --git a/src/crepe/facade/SDLContext.cpp b/src/crepe/facade/SDLContext.cpp
index 9464c31..b8b2bda 100644
--- a/src/crepe/facade/SDLContext.cpp
+++ b/src/crepe/facade/SDLContext.cpp
@@ -1,5 +1,6 @@
 #include <SDL2/SDL.h>
 #include <SDL2/SDL_image.h>
+#include <SDL2/SDL_keycode.h>
 #include <SDL2/SDL_rect.h>
 #include <SDL2/SDL_render.h>
 #include <SDL2/SDL_surface.h>
@@ -7,13 +8,15 @@
 #include <cmath>
 #include <cstddef>
 #include <functional>
-#include <iostream>
 #include <memory>
+#include <stdexcept>
 #include <string>
 
+#include "../api/Camera.h"
 #include "../api/Sprite.h"
 #include "../api/Texture.h"
 #include "../api/Transform.h"
+#include "../api/Vector2.h"
 #include "../util/Log.h"
 
 #include "SDLContext.h"
@@ -30,29 +33,21 @@ SDLContext::SDLContext() {
 	dbg_trace();
 	// FIXME: read window defaults from config manager
 
-	if (SDL_Init(SDL_INIT_VIDEO) < 0) {
-		// FIXME: throw exception
-		std::cerr << "SDL could not initialize! SDL_Error: " << SDL_GetError() << std::endl;
-		return;
+	if (SDL_Init(SDL_INIT_VIDEO) != 0) {
+		throw runtime_error(format("SDLContext: SDL_Init error: {}", SDL_GetError()));
 	}
 	SDL_Window * tmp_window
 		= SDL_CreateWindow("Crepe Game Engine", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
 						   this->viewport.w, this->viewport.h, 0);
 	if (!tmp_window) {
-		// FIXME: throw exception
-		std::cerr << "Window could not be created! SDL_Error: " << SDL_GetError() << std::endl;
-		return;
+		throw runtime_error(format("SDLContext: SDL_Window error: {}", SDL_GetError()));
 	}
 	this->game_window = {tmp_window, [](SDL_Window * window) { SDL_DestroyWindow(window); }};
 
 	SDL_Renderer * tmp_renderer
 		= SDL_CreateRenderer(this->game_window.get(), -1, SDL_RENDERER_ACCELERATED);
 	if (!tmp_renderer) {
-		// FIXME: throw exception
-		std::cerr << "Renderer could not be created! SDL_Error: " << SDL_GetError()
-				  << std::endl;
-		SDL_DestroyWindow(this->game_window.get());
-		return;
+		throw runtime_error(format("SDLContext: SDL_CreateRenderer error: {}", SDL_GetError()));
 	}
 
 	this->game_renderer
@@ -60,9 +55,7 @@ SDLContext::SDLContext() {
 
 	int img_flags = IMG_INIT_PNG;
 	if (!(IMG_Init(img_flags) & img_flags)) {
-		// FIXME: throw exception
-		std::cout << "SDL_image could not initialize! SDL_image Error: " << IMG_GetError()
-				  << std::endl;
+		throw runtime_error("SDLContext: SDL_image could not initialize!");
 	}
 }
 
@@ -102,40 +95,63 @@ void SDLContext::handle_events(bool & running) {
 void SDLContext::clear_screen() { SDL_RenderClear(this->game_renderer.get()); }
 void SDLContext::present_screen() { SDL_RenderPresent(this->game_renderer.get()); }
 
-void SDLContext::draw(const Sprite & sprite, const Transform & transform, const Camera & cam) {
-
-	SDL_RendererFlip render_flip
-		= (SDL_RendererFlip) ((SDL_FLIP_HORIZONTAL * sprite.flip.flip_x)
-							  | (SDL_FLIP_VERTICAL * sprite.flip.flip_y));
-
-	double adjusted_x = (transform.position.x - cam.x) * cam.zoom;
-	double adjusted_y = (transform.position.y - cam.y) * cam.zoom;
-	double adjusted_w = sprite.sprite_rect.w * transform.scale * cam.zoom;
-	double adjusted_h = sprite.sprite_rect.h * transform.scale * cam.zoom;
-
-	SDL_Rect srcrect = {
+SDL_Rect SDLContext::get_src_rect(const Sprite & sprite) const {
+	return SDL_Rect{
 		.x = sprite.sprite_rect.x,
 		.y = sprite.sprite_rect.y,
 		.w = sprite.sprite_rect.w,
 		.h = sprite.sprite_rect.h,
 	};
+}
+SDL_Rect SDLContext::get_dst_rect(const Sprite & sprite, const Vector2 & pos,
+								  const double & scale, const Camera & cam) const {
+
+	double adjusted_x = (pos.x - cam.x) * cam.zoom;
+	double adjusted_y = (pos.y - cam.y) * cam.zoom;
+	double adjusted_w = sprite.sprite_rect.w * scale * cam.zoom;
+	double adjusted_h = sprite.sprite_rect.h * scale * cam.zoom;
 
-	SDL_Rect dstrect = {
+	return SDL_Rect{
 		.x = static_cast<int>(adjusted_x),
 		.y = static_cast<int>(adjusted_y),
 		.w = static_cast<int>(adjusted_w),
 		.h = static_cast<int>(adjusted_h),
 	};
+}
+
+void SDLContext::draw_particle(const Sprite & sprite, const Vector2 & pos,
+							   const double & angle, const double & scale,
+							   const Camera & camera) {
+
+	SDL_RendererFlip render_flip
+		= (SDL_RendererFlip) ((SDL_FLIP_HORIZONTAL * sprite.flip.flip_x)
+							  | (SDL_FLIP_VERTICAL * sprite.flip.flip_y));
+
+	SDL_Rect srcrect = this->get_src_rect(sprite);
+	SDL_Rect dstrect = this->get_dst_rect(sprite, pos, scale, camera);
+
+	SDL_RenderCopyEx(this->game_renderer.get(), sprite.sprite_image->texture.get(), &srcrect,
+					 &dstrect, angle, NULL, render_flip);
+}
+
+void SDLContext::draw(const Sprite & sprite, const Transform & transform, const Camera & cam) {
+
+	SDL_RendererFlip render_flip
+		= (SDL_RendererFlip) ((SDL_FLIP_HORIZONTAL * sprite.flip.flip_x)
+							  | (SDL_FLIP_VERTICAL * sprite.flip.flip_y));
+
+	SDL_Rect srcrect = this->get_src_rect(sprite);
+	SDL_Rect dstrect = this->get_dst_rect(sprite, transform.position, transform.scale, cam);
 
 	SDL_RenderCopyEx(this->game_renderer.get(), sprite.sprite_image->texture.get(), &srcrect,
 					 &dstrect, transform.rotation, NULL, render_flip);
 }
 
-void SDLContext::camera(const Camera & cam) {
+void SDLContext::set_camera(const Camera & cam) {
 	this->viewport.w = static_cast<int>(cam.aspect_width);
 	this->viewport.h = static_cast<int>(cam.aspect_height);
-	this->viewport.x = static_cast<int>(cam.x) - (SCREEN_WIDTH / 2);
-	this->viewport.y = static_cast<int>(cam.y) - (SCREEN_HEIGHT / 2);
+	this->viewport.x = static_cast<int>(cam.x) - (this->viewport.w / 2);
+	this->viewport.y = static_cast<int>(cam.y) - (this->viewport.h / 2);
 
 	SDL_SetRenderDrawColor(this->game_renderer.get(), cam.bg_color.r, cam.bg_color.g,
 						   cam.bg_color.b, cam.bg_color.a);
@@ -147,9 +163,8 @@ std::unique_ptr<SDL_Texture, std::function<void(SDL_Texture *)>>
 SDLContext::texture_from_path(const std::string & path) {
 
 	SDL_Surface * tmp = IMG_Load(path.c_str());
-	if (tmp == nullptr) {
-		tmp = IMG_Load("../asset/texture/ERROR.png");
-	}
+	if (tmp == nullptr)
+		throw runtime_error(format("SDLContext: IMG_Load error: {}", SDL_GetError()));
 
 	std::unique_ptr<SDL_Surface, std::function<void(SDL_Surface *)>> img_surface;
 	img_surface = {tmp, [](SDL_Surface * surface) { SDL_FreeSurface(surface); }};
@@ -158,7 +173,7 @@ SDLContext::texture_from_path(const std::string & path) {
 		= SDL_CreateTextureFromSurface(this->game_renderer.get(), img_surface.get());
 
 	if (tmp_texture == nullptr) {
-		throw runtime_error(format("Texture cannot be load from {}", path));
+		throw runtime_error(format("SDLContext: Texture cannot be load from {}", path));
 	}
 
 	std::unique_ptr<SDL_Texture, std::function<void(SDL_Texture *)>> img_texture;
diff --git a/src/crepe/facade/SDLContext.h b/src/crepe/facade/SDLContext.h
index 007092b..841ffc9 100644
--- a/src/crepe/facade/SDLContext.h
+++ b/src/crepe/facade/SDLContext.h
@@ -1,8 +1,10 @@
 #pragma once
 
 #include <SDL2/SDL_keycode.h>
+#include <SDL2/SDL_rect.h>
 #include <SDL2/SDL_render.h>
 #include <SDL2/SDL_video.h>
+#include <cmath>
 #include <functional>
 #include <memory>
 #include <string>
@@ -10,10 +12,7 @@
 #include "../api/Sprite.h"
 #include "../api/Transform.h"
 #include "api/Camera.h"
-
-// FIXME: this needs to be removed
-const int SCREEN_WIDTH = 640;
-const int SCREEN_HEIGHT = 480;
+#include "api/Vector2.h"
 
 namespace crepe {
 
@@ -21,9 +20,6 @@ namespace crepe {
 // typedef is unusable when crepe is packaged. Wouter will fix this later.
 typedef SDL_Keycode CREPE_KEYCODES;
 
-class Texture;
-class LoopManager;
-
 /**
  * \class SDLContext
  * \brief Facade for the SDL library
@@ -91,9 +87,6 @@ private:
 	//! Will use the funtions: texture_from_path, get_width,get_height.
 	friend class Texture;
 
-	//! Will use the funtions: texture_from_path, get_width,get_height.
-	friend class Animator;
-
 	/**
 	 * \brief Loads a texture from a file path.
 	 * \param path Path to the image file.
@@ -127,6 +120,9 @@ private:
 	 */
 	void draw(const Sprite & sprite, const Transform & transform, const Camera & camera);
 
+	void draw_particle(const Sprite & sprite, const Vector2 & pos, const double & angle,
+					   const double & scale, const Camera & camera);
+
 	//! Clears the screen, preparing for a new frame.
 	void clear_screen();
 
@@ -134,10 +130,31 @@ private:
 	void present_screen();
 
 	/**
-	 * \brief Sets the current camera for rendering.
+	 * \brief sets the background of the camera (will be adjusted in future PR)
 	 * \param camera Reference to the Camera object.
 	 */
-	void camera(const Camera & camera);
+	void set_camera(const Camera & camera);
+
+private:
+	/**
+	 * \brief calculates the sqaure size of the image
+	 *
+	 * \param sprite Reference to the sprite to calculate the rectangle
+	 * \return sdl rectangle to draw a src image
+	 */
+	SDL_Rect get_src_rect(const Sprite & sprite) const;
+	/**
+	 * \brief calculates the sqaure size of the image for an destination
+	 *
+	 * \param sprite Reference to the sprite to calculate the rectangle
+	 * \param pos the pos in pixel positions
+	 * \param scale the multiplier to increase of decrease for the specified sprite 
+	 * \param cam Reference to the current camera in the scene to calculate the position based
+	 * on the camera 
+	 * \return sdl rectangle to draw a dst image to draw on the screen
+	 */
+	SDL_Rect get_dst_rect(const Sprite & sprite, const Vector2 & pos, const double & scale,
+						  const Camera & cam) const;
 
 private:
 	//! sdl Window
diff --git a/src/crepe/system/RenderSystem.cpp b/src/crepe/system/RenderSystem.cpp
index fa3d0de..e379771 100644
--- a/src/crepe/system/RenderSystem.cpp
+++ b/src/crepe/system/RenderSystem.cpp
@@ -1,44 +1,104 @@
+#include <algorithm>
+#include <cassert>
+#include <cmath>
 #include <functional>
+#include <iostream>
+#include <stdexcept>
 #include <vector>
 
 #include "../ComponentManager.h"
+#include "../api/ParticleEmitter.h"
 #include "../api/Sprite.h"
 #include "../api/Transform.h"
+#include "../api/Vector2.h"
 #include "../facade/SDLContext.h"
-#include "../util/Log.h"
 
 #include "RenderSystem.h"
 
 using namespace crepe;
+using namespace std;
 
-void RenderSystem::clear_screen() const { SDLContext::get_instance().clear_screen(); }
+void RenderSystem::clear_screen() { this->context.clear_screen(); }
 
-void RenderSystem::present_screen() const { SDLContext::get_instance().present_screen(); }
+void RenderSystem::present_screen() { this->context.present_screen(); }
 void RenderSystem::update_camera() {
 	ComponentManager & mgr = this->component_manager;
 
 	std::vector<std::reference_wrapper<Camera>> cameras = mgr.get_components_by_type<Camera>();
 
+	if (cameras.size() == 0) throw std::runtime_error("No cameras in current scene");
+
 	for (Camera & cam : cameras) {
-		SDLContext::get_instance().camera(cam);
-		this->curr_cam = &cam;
+		if (!cam.active) continue;
+		this->context.set_camera(cam);
+		this->curr_cam_ref = &cam;
 	}
 }
-void RenderSystem::render_sprites() const {
-	ComponentManager & mgr = this->component_manager;
 
-	std::vector<std::reference_wrapper<Sprite>> sprites = mgr.get_components_by_type<Sprite>();
+bool sorting_comparison(const Sprite & a, const Sprite & b) {
+	if (a.sorting_in_layer < b.sorting_in_layer) return true;
+	if (a.sorting_in_layer == b.sorting_in_layer) return a.order_in_layer < b.order_in_layer;
 
-	SDLContext & render = SDLContext::get_instance();
-	for (const Sprite & sprite : sprites) {
-		auto transforms = mgr.get_components_by_id<Transform>(sprite.game_object_id);
-		render.draw(sprite, transforms[0], *curr_cam);
-	}
+	return false;
+}
+
+std::vector<std::reference_wrapper<Sprite>>
+RenderSystem::sort(std::vector<std::reference_wrapper<Sprite>> & objs) const {
+
+	std::vector<std::reference_wrapper<Sprite>> sorted_objs(objs);
+	std::sort(sorted_objs.begin(), sorted_objs.end(), sorting_comparison);
+
+	return sorted_objs;
 }
 
 void RenderSystem::update() {
 	this->clear_screen();
 	this->update_camera();
-	this->render_sprites();
+	this->render();
 	this->present_screen();
 }
+
+bool RenderSystem::render_particle(const Sprite & sprite, const double & scale) {
+
+	ComponentManager & mgr = this->component_manager;
+
+	vector<reference_wrapper<ParticleEmitter>> emitters
+		= mgr.get_components_by_id<ParticleEmitter>(sprite.game_object_id);
+
+	bool rendering_particles = false;
+
+	for (const ParticleEmitter & em : emitters) {
+		if (!(&em.data.sprite == &sprite)) continue;
+		rendering_particles = true;
+		if (!em.active) continue;
+
+		for (const Particle & p : em.data.particles) {
+			if (!p.active) continue;
+			this->context.draw_particle(sprite, p.position, p.angle, scale,
+										*this->curr_cam_ref);
+		}
+	}
+	return rendering_particles;
+}
+void RenderSystem::render_normal(const Sprite & sprite, const Transform & tm) {
+	this->context.draw(sprite, tm, *this->curr_cam_ref);
+}
+
+void RenderSystem::render() {
+
+	ComponentManager & mgr = this->component_manager;
+	vector<reference_wrapper<Sprite>> sprites = mgr.get_components_by_type<Sprite>();
+	vector<reference_wrapper<Sprite>> sorted_sprites = this->sort(sprites);
+
+	for (const Sprite & sprite : sorted_sprites) {
+		if (!sprite.active) continue;
+		const Transform & transform
+			= mgr.get_components_by_id<Transform>(sprite.game_object_id).front().get();
+
+		bool rendered_particles = this->render_particle(sprite, transform.scale);
+
+		if (rendered_particles) continue;
+
+		this->render_normal(sprite, transform);
+	}
+}
diff --git a/src/crepe/system/RenderSystem.h b/src/crepe/system/RenderSystem.h
index 87ec494..d25a6e3 100644
--- a/src/crepe/system/RenderSystem.h
+++ b/src/crepe/system/RenderSystem.h
@@ -1,18 +1,24 @@
 #pragma once
 
-#include "api/Camera.h"
+#include <functional>
+#include <vector>
+
+#include "facade/SDLContext.h"
 
 #include "System.h"
+#include <cmath>
 
 namespace crepe {
 
+class Camera;
+class Sprite;
+
 /**
  * \class RenderSystem
  * \brief Manages rendering operations for all game objects.
  *
- * RenderSystem is responsible for rendering sprites, clearing and presenting the screen, and
- * managing the active camera. It functions as a singleton, providing centralized rendering
- * services for the application.
+ * RenderSystem is responsible for rendering, clearing and presenting the screen, and
+ * managing the active camera. 
  */
 class RenderSystem : public System {
 public:
@@ -25,20 +31,45 @@ public:
 
 private:
 	//! Clears the screen in preparation for rendering.
-	void clear_screen() const;
+	void clear_screen();
 
 	//! Presents the rendered frame to the display.
-	void present_screen() const;
+	void present_screen();
 
 	//! Updates the active camera used for rendering.
 	void update_camera();
 
-	//! Renders all active sprites to the screen.
-	void render_sprites() const;
+	//! Renders the whole screen
+	void render();
+
+	/**
+	 * \brief Renders all the particles on the screen from a given sprite.
+	 *
+	 * \param sprite renders the particles with given texture
+	 * \param tm the Transform component for scale
+	 * \return true if particles have been rendered
+	 */
+	bool render_particle(const Sprite & sprite, const double & scale);
+
+	/**
+	 * \brief renders a sprite with a Transform component on the screen 
+	 *
+	 * \param sprite  the sprite component that holds all the data
+	 * \param tm the Transform component that holds the position,rotation and scale 
+	 */
+	void render_normal(const Sprite & sprite, const Transform & tm);
+
+	/**
+	 * \brief sort a vector sprite objects with
+	 *
+	 * \param objs the vector that will do a sorting algorithm on 
+	 * \return returns a sorted reference vector
+	 */
+	std::vector<std::reference_wrapper<Sprite>>
+	sort(std::vector<std::reference_wrapper<Sprite>> & objs) const;
 
 	/**
 	 * \todo Include color handling for sprites.
-	 * \todo Implement particle emitter rendering with sprites.
 	 * \todo Add text rendering using SDL_ttf for text components.
 	 * \todo Implement a text component and a button component.
 	 * \todo Ensure each sprite is checked for active status before rendering.
@@ -48,8 +79,10 @@ private:
 
 private:
 	//! Pointer to the current active camera for rendering
-	Camera * curr_cam = nullptr;
+	Camera * curr_cam_ref = nullptr;
 	// TODO: needs a better solution
+
+	SDLContext & context = SDLContext::get_instance();
 };
 
 } // namespace crepe
diff --git a/src/crepe/util/Proxy.h b/src/crepe/util/Proxy.h
index b34f7c6..789144a 100644
--- a/src/crepe/util/Proxy.h
+++ b/src/crepe/util/Proxy.h
@@ -16,6 +16,8 @@ template <typename T>
 class Proxy {
 public:
 	//! Set operator
+	Proxy & operator=(Proxy &);
+	//! Set operator
 	Proxy & operator=(const T &);
 	//! Get operator
 	operator const T &();
diff --git a/src/crepe/util/Proxy.hpp b/src/crepe/util/Proxy.hpp
index b9923db..ef2b69f 100644
--- a/src/crepe/util/Proxy.hpp
+++ b/src/crepe/util/Proxy.hpp
@@ -14,6 +14,12 @@ Proxy<T> & Proxy<T>::operator=(const T & val) {
 }
 
 template <typename T>
+Proxy<T> & Proxy<T>::operator=(Proxy & proxy) {
+	this->broker.set(T(proxy));
+	return *this;
+}
+
+template <typename T>
 Proxy<T>::operator const T &() {
 	return this->broker.get();
 }
diff --git a/src/doc/feature/script.dox b/src/doc/feature/script.dox
new file mode 100644
index 0000000..d25a63b
--- /dev/null
+++ b/src/doc/feature/script.dox
@@ -0,0 +1,62 @@
+// vim:ft=doxygen
+namespace crepe {
+/**
+
+\defgroup feature_script Scripting
+\ingroup feature
+\brief User-defined scripts for game objects
+
+Scripts can be used to implement game behavior, and allow arbitrary code to run
+as part of the game loop. Scripts are implemented as derivative classes of
+Script, which are added to game objects using the BehaviorScript \ref Component
+"component".
+
+\todo This section is incomplete:
+- Utility functions to get components/events/etc inside script
+- How to listen for events
+- Extensions of script (keylistener)
+
+\see Script
+\see BehaviorScript
+\see GameObject
+
+\par Example
+
+First, define a class that inherits from Script. This class acts as an
+interface, and has two functions (\ref Script::init "\c init()" and \ref
+Script::update "\c update()"), which may be implemented (they are empty by
+default). From now on, this derivative class will be referred to as a *concrete
+script*.
+
+```cpp
+#include <crepe/api/Script.h>
+#include <crepe/api/BehaviorScript.h>
+
+class MyScript : public crepe::Script {
+	void init() {
+		// called once
+	}
+	void update() {
+		// called on fixed update
+	}
+};
+```
+
+Concrete scripts can be instantiated and attached to \ref GameObject
+"game objects" using the BehaviorScript \ref Component "component".
+
+```cpp
+using namespace crepe;
+GameObject obj = component_manager.new_object("name");
+
+// create BehaviorScript instance
+BehaviorScript & behavior_script = obj.add_component<BehaviorScript>();
+// attach (and instantiate) MyScript to behavior_script
+behavior_script.set_script<MyScript>();
+
+// the above can also be done in a single call for convenience:
+obj.add_component<BehaviorScript>().set_script<MyScript>();
+```
+
+*/
+}
diff --git a/src/doc/features.dox b/src/doc/features.dox
new file mode 100644
index 0000000..4786bed
--- /dev/null
+++ b/src/doc/features.dox
@@ -0,0 +1,10 @@
+// vim:ft=doxygen
+/**
+
+\defgroup feature Features
+\brief Engine components
+
+This page lists engine features and contains usage instructions for each
+feature.
+
+*/
diff --git a/src/doc/index.dox b/src/doc/index.dox
new file mode 100644
index 0000000..5ec7889
--- /dev/null
+++ b/src/doc/index.dox
@@ -0,0 +1,10 @@
+// vim:ft=doxygen
+/**
+
+\mainpage crêpe game engine
+
+Welcome to the documentation for the crêpe game engine.
+
+\see feature
+
+*/
diff --git a/src/doc/installing.dox b/src/doc/installing.dox
new file mode 100644
index 0000000..48b27d7
--- /dev/null
+++ b/src/doc/installing.dox
@@ -0,0 +1,9 @@
+// vim:ft=doxygen
+/**
+
+\defgroup install Installation
+\brief Engine installation instructions
+
+\todo This entire page
+
+*/
diff --git a/src/doc/layout.xml b/src/doc/layout.xml
new file mode 100644
index 0000000..2244fa7
--- /dev/null
+++ b/src/doc/layout.xml
@@ -0,0 +1,252 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<doxygenlayout version="1.0">
+	<navindex>
+		<tab type="mainpage" visible="yes" title=""/>
+		<tab type="pages" visible="no" title="" intro=""/>
+		<tab type="topics" visible="yes" title="" intro=""/>
+		<tab type="modules" visible="yes" title="" intro="">
+			<tab type="modulelist" visible="yes" title="" intro=""/>
+			<tab type="modulemembers" visible="yes" title="" intro=""/>
+		</tab>
+		<tab type="namespaces" visible="no" title="">
+			<tab type="namespacelist" visible="yes" title="" intro=""/>
+			<tab type="namespacemembers" visible="yes" title="" intro=""/>
+		</tab>
+		<tab type="concepts" visible="yes" title="">
+		</tab>
+		<tab type="interfaces" visible="yes" title="">
+			<tab type="interfacelist" visible="yes" title="" intro=""/>
+			<tab type="interfaceindex" visible="$ALPHABETICAL_INDEX" title=""/>
+			<tab type="interfacehierarchy" visible="yes" title="" intro=""/>
+		</tab>
+		<tab type="classes" visible="yes" title="">
+			<tab type="classlist" visible="yes" title="" intro=""/>
+			<tab type="classindex" visible="$ALPHABETICAL_INDEX" title=""/>
+			<tab type="hierarchy" visible="yes" title="" intro=""/>
+			<tab type="classmembers" visible="yes" title="" intro=""/>
+		</tab>
+		<tab type="structs" visible="yes" title="">
+			<tab type="structlist" visible="yes" title="" intro=""/>
+			<tab type="structindex" visible="$ALPHABETICAL_INDEX" title=""/>
+		</tab>
+		<tab type="exceptions" visible="yes" title="">
+			<tab type="exceptionlist" visible="yes" title="" intro=""/>
+			<tab type="exceptionindex" visible="$ALPHABETICAL_INDEX" title=""/>
+			<tab type="exceptionhierarchy" visible="yes" title="" intro=""/>
+		</tab>
+		<tab type="files" visible="yes" title="">
+			<tab type="filelist" visible="yes" title="" intro=""/>
+			<tab type="globals" visible="yes" title="" intro=""/>
+		</tab>
+		<tab type="examples" visible="yes" title="" intro=""/>
+	</navindex>
+	<class>
+		<briefdescription visible="yes"/>
+		<includes visible="$SHOW_HEADERFILE"/>
+		<inheritancegraph visible="yes"/>
+		<collaborationgraph visible="yes"/>
+		<memberdecl>
+			<nestedclasses visible="yes" title=""/>
+			<publictypes title=""/>
+			<services title=""/>
+			<interfaces title=""/>
+			<publicslots title=""/>
+			<signals title=""/>
+			<publicmethods title=""/>
+			<publicstaticmethods title=""/>
+			<publicattributes title=""/>
+			<publicstaticattributes title=""/>
+			<protectedtypes title=""/>
+			<protectedslots title=""/>
+			<protectedmethods title=""/>
+			<protectedstaticmethods title=""/>
+			<protectedattributes title=""/>
+			<protectedstaticattributes title=""/>
+			<packagetypes title=""/>
+			<packagemethods title=""/>
+			<packagestaticmethods title=""/>
+			<packageattributes title=""/>
+			<packagestaticattributes title=""/>
+			<properties title=""/>
+			<events title=""/>
+			<privatetypes title=""/>
+			<privateslots title=""/>
+			<privatemethods title=""/>
+			<privatestaticmethods title=""/>
+			<privateattributes title=""/>
+			<privatestaticattributes title=""/>
+			<friends title=""/>
+			<related title="" subtitle=""/>
+			<membergroups visible="yes"/>
+		</memberdecl>
+		<detaileddescription title=""/>
+		<memberdef>
+			<inlineclasses title=""/>
+			<typedefs title=""/>
+			<enums title=""/>
+			<services title=""/>
+			<interfaces title=""/>
+			<constructors title=""/>
+			<functions title=""/>
+			<related title=""/>
+			<variables title=""/>
+			<properties title=""/>
+			<events title=""/>
+		</memberdef>
+		<allmemberslink visible="yes"/>
+		<usedfiles visible="$SHOW_USED_FILES"/>
+		<authorsection visible="yes"/>
+	</class>
+	<namespace>
+		<briefdescription visible="yes"/>
+		<memberdecl>
+			<nestednamespaces visible="yes" title=""/>
+			<constantgroups visible="yes" title=""/>
+			<interfaces visible="yes" title=""/>
+			<classes visible="yes" title=""/>
+			<concepts visible="yes" title=""/>
+			<structs visible="yes" title=""/>
+			<exceptions visible="yes" title=""/>
+			<typedefs title=""/>
+			<sequences title=""/>
+			<dictionaries title=""/>
+			<enums title=""/>
+			<functions title=""/>
+			<variables title=""/>
+			<properties title=""/>
+			<membergroups visible="yes"/>
+		</memberdecl>
+		<detaileddescription title=""/>
+		<memberdef>
+			<inlineclasses title=""/>
+			<typedefs title=""/>
+			<sequences title=""/>
+			<dictionaries title=""/>
+			<enums title=""/>
+			<functions title=""/>
+			<variables title=""/>
+			<properties title=""/>
+		</memberdef>
+		<authorsection visible="yes"/>
+	</namespace>
+	<concept>
+		<briefdescription visible="yes"/>
+		<includes visible="$SHOW_HEADERFILE"/>
+		<definition visible="yes" title=""/>
+		<detaileddescription title=""/>
+		<authorsection visible="yes"/>
+	</concept>
+	<file>
+		<briefdescription visible="yes"/>
+		<includes visible="$SHOW_INCLUDE_FILES"/>
+		<includegraph visible="yes"/>
+		<includedbygraph visible="yes"/>
+		<sourcelink visible="yes"/>
+		<memberdecl>
+			<interfaces visible="yes" title=""/>
+			<classes visible="yes" title=""/>
+			<structs visible="yes" title=""/>
+			<exceptions visible="yes" title=""/>
+			<namespaces visible="yes" title=""/>
+			<concepts visible="yes" title=""/>
+			<constantgroups visible="yes" title=""/>
+			<defines title=""/>
+			<typedefs title=""/>
+			<sequences title=""/>
+			<dictionaries title=""/>
+			<enums title=""/>
+			<functions title=""/>
+			<variables title=""/>
+			<properties title=""/>
+			<membergroups visible="yes"/>
+		</memberdecl>
+		<detaileddescription title=""/>
+		<memberdef>
+			<inlineclasses title=""/>
+			<defines title=""/>
+			<typedefs title=""/>
+			<sequences title=""/>
+			<dictionaries title=""/>
+			<enums title=""/>
+			<functions title=""/>
+			<variables title=""/>
+			<properties title=""/>
+		</memberdef>
+		<authorsection/>
+	</file>
+	<group>
+		<detaileddescription title=""/>
+		<groupgraph visible="yes"/>
+		<memberdecl>
+			<nestedgroups visible="yes" title=""/>
+			<modules visible="yes" title=""/>
+			<dirs visible="yes" title=""/>
+			<files visible="yes" title=""/>
+			<namespaces visible="yes" title=""/>
+			<concepts visible="yes" title=""/>
+			<classes visible="yes" title=""/>
+			<defines title=""/>
+			<typedefs title=""/>
+			<sequences title=""/>
+			<dictionaries title=""/>
+			<enums title=""/>
+			<enumvalues title=""/>
+			<functions title=""/>
+			<variables title=""/>
+			<signals title=""/>
+			<publicslots title=""/>
+			<protectedslots title=""/>
+			<privateslots title=""/>
+			<events title=""/>
+			<properties title=""/>
+			<friends title=""/>
+			<membergroups visible="yes"/>
+		</memberdecl>
+		<memberdef>
+			<pagedocs/>
+			<inlineclasses title=""/>
+			<defines title=""/>
+			<typedefs title=""/>
+			<sequences title=""/>
+			<dictionaries title=""/>
+			<enums title=""/>
+			<enumvalues title=""/>
+			<functions title=""/>
+			<variables title=""/>
+			<signals title=""/>
+			<publicslots title=""/>
+			<protectedslots title=""/>
+			<privateslots title=""/>
+			<events title=""/>
+			<properties title=""/>
+			<friends title=""/>
+		</memberdef>
+		<authorsection visible="yes"/>
+	</group>
+	<module>
+		<briefdescription visible="yes"/>
+		<exportedmodules visible="yes"/>
+		<memberdecl>
+			<concepts visible="yes" title=""/>
+			<classes visible="yes" title=""/>
+			<enums title=""/>
+			<typedefs title=""/>
+			<functions title=""/>
+			<variables title=""/>
+			<membergroups title=""/>
+		</memberdecl>
+		<detaileddescription title=""/>
+		<memberdecl>
+			<files visible="yes"/>
+		</memberdecl>
+	</module>
+	<directory>
+		<briefdescription visible="yes"/>
+		<directorygraph visible="yes"/>
+		<memberdecl>
+			<dirs visible="yes"/>
+			<files visible="yes"/>
+		</memberdecl>
+		<detaileddescription title=""/>
+	</directory>
+</doxygenlayout>
diff --git a/src/doc/style.css b/src/doc/style.css
new file mode 100644
index 0000000..08bc9f5
--- /dev/null
+++ b/src/doc/style.css
@@ -0,0 +1,4 @@
+#titlearea,
+address {
+	display: none;
+}
diff --git a/src/example/CMakeLists.txt b/src/example/CMakeLists.txt
index ddb0262..7b4cc43 100644
--- a/src/example/CMakeLists.txt
+++ b/src/example/CMakeLists.txt
@@ -16,13 +16,7 @@ function(add_example target_name)
 	add_dependencies(examples ${target_name})
 endfunction()
 
-add_example(audio_internal)
-# add_example(components_internal)
-add_example(script)
-add_example(log)
-add_example(rendering)
 add_example(asset_manager)
-add_example(physics)
 add_example(savemgr)
 add_example(proxy)
 add_example(db)
@@ -30,5 +24,6 @@ add_example(ecs)
 add_example(scene_manager)
 add_example(events)
 add_example(particles)
+add_example(rendering_particle)
 add_example(gameloop)
 
diff --git a/src/example/audio_internal.cpp b/src/example/audio_internal.cpp
deleted file mode 100644
index 661161a..0000000
--- a/src/example/audio_internal.cpp
+++ /dev/null
@@ -1,56 +0,0 @@
-/** \file
- * 
- * Standalone example for usage of the internal \c Sound class.
- */
-
-#include <crepe/api/Config.h>
-#include <crepe/facade/Sound.h>
-#include <crepe/util/Log.h>
-
-#include <thread>
-
-using namespace crepe;
-using namespace std;
-using namespace std::chrono_literals;
-using std::make_unique;
-
-// Unrelated stuff that is not part of this POC
-int _ = []() {
-	// Show dbg_trace() output
-	auto & cfg = Config::get_instance();
-	cfg.log.level = Log::Level::TRACE;
-
-	return 0; // satisfy compiler
-}();
-
-int main() {
-	// Load a background track (Ogg Vorbis)
-	auto bgm = Sound("../mwe/audio/bgm.ogg");
-	// Load three short samples (WAV)
-	auto sfx1 = Sound("../mwe/audio/sfx1.wav");
-	auto sfx2 = Sound("../mwe/audio/sfx2.wav");
-	auto sfx3 = Sound("../mwe/audio/sfx3.wav");
-
-	// Start the background track
-	bgm.play();
-
-	// Play each sample sequentially while pausing and resuming the background track
-	this_thread::sleep_for(500ms);
-	sfx1.play();
-	this_thread::sleep_for(500ms);
-	sfx2.play();
-	bgm.pause();
-	this_thread::sleep_for(500ms);
-	sfx3.play();
-	bgm.play();
-	this_thread::sleep_for(500ms);
-
-	// Play all samples simultaniously
-	sfx1.play();
-	sfx2.play();
-	sfx3.play();
-	this_thread::sleep_for(1000ms);
-
-	// Stop all audio and exit
-	return EXIT_SUCCESS;
-}
diff --git a/src/example/components_internal.cpp b/src/example/components_internal.cpp
deleted file mode 100644
index 2a232a9..0000000
--- a/src/example/components_internal.cpp
+++ /dev/null
@@ -1,51 +0,0 @@
-/** \file
- * 
- * Standalone example for usage of the internal ECS
- */
-
-#include <cassert>
-#include <chrono>
-
-#include <crepe/Component.h>
-#include <crepe/ComponentManager.h>
-
-#include <crepe/api/GameObject.h>
-#include <crepe/api/Rigidbody.h>
-#include <crepe/api/Sprite.h>
-
-#include <crepe/util/Log.h>
-
-using namespace crepe;
-using namespace std;
-
-#define OBJ_COUNT 100000
-
-int main() {
-	dbg_trace();
-
-	ComponentManager mgr{};
-
-	auto start_adding = chrono::high_resolution_clock::now();
-
-	for (int i = 0; i < OBJ_COUNT; ++i) {
-		GameObject obj = mgr.new_object("Name", "Tag");
-		obj.add_component<Sprite>("test");
-		obj.add_component<Rigidbody>(0, 0, i);
-	}
-
-	auto stop_adding = chrono::high_resolution_clock::now();
-
-	auto sprites = mgr.get_components_by_type<Sprite>();
-	for (auto sprite : sprites) {
-		assert(true);
-	}
-
-	auto stop_looping = chrono::high_resolution_clock::now();
-
-	auto add_time = chrono::duration_cast<chrono::microseconds>(stop_adding - start_adding);
-	auto loop_time = chrono::duration_cast<chrono::microseconds>(stop_looping - stop_adding);
-	printf("add time:  %ldus\n", add_time.count());
-	printf("loop time: %ldus\n", loop_time.count());
-
-	return 0;
-}
diff --git a/src/example/db.cpp b/src/example/db.cpp
deleted file mode 100644
index ee4e8fc..0000000
--- a/src/example/db.cpp
+++ /dev/null
@@ -1,30 +0,0 @@
-#include <crepe/api/Config.h>
-#include <crepe/facade/DB.h>
-#include <crepe/util/Log.h>
-
-using namespace crepe;
-using namespace std;
-
-// run before main
-static auto _ = []() {
-	auto & cfg = Config::get_instance();
-	cfg.log.level = Log::Level::TRACE;
-	return 0;
-}();
-
-int main() {
-	dbg_trace();
-
-	DB db("file.db");
-
-	const char * test_key = "test-key";
-	string test_data = "Hello world!";
-
-	dbg_logf("DB has key = {}", db.has(test_key));
-
-	db.set(test_key, test_data);
-
-	dbg_logf("key = \"{}\"", db.get(test_key));
-
-	return 0;
-}
diff --git a/src/example/ecs.cpp b/src/example/ecs.cpp
deleted file mode 100644
index d5ba51b..0000000
--- a/src/example/ecs.cpp
+++ /dev/null
@@ -1,53 +0,0 @@
-#include <iostream>
-
-#include <crepe/ComponentManager.h>
-#include <crepe/api/GameObject.h>
-#include <crepe/api/Metadata.h>
-#include <crepe/api/Transform.h>
-
-using namespace crepe;
-using namespace std;
-
-int main() {
-	ComponentManager mgr{};
-
-	// Create a few GameObjects
-	try {
-		GameObject body = mgr.new_object("body", "person", Vector2{0, 0}, 0, 1);
-		GameObject right_leg = mgr.new_object("rightLeg", "person", Vector2{1, 1}, 0, 1);
-		GameObject left_leg = mgr.new_object("leftLeg", "person", Vector2{1, 1}, 0, 1);
-		GameObject right_foot = mgr.new_object("rightFoot", "person", Vector2{2, 2}, 0, 1);
-		GameObject left_foot = mgr.new_object("leftFoot", "person", Vector2{2, 2}, 0, 1);
-
-		// Set the parent of each GameObject
-		right_foot.set_parent(right_leg);
-		left_foot.set_parent(left_leg);
-		right_leg.set_parent(body);
-		left_leg.set_parent(body);
-
-		// Adding a second Transform component is not allowed and will invoke an exception
-		body.add_component<Transform>(Vector2{10, 10}, 0, 1);
-	} catch (const exception & e) {
-		cerr << e.what() << endl;
-	}
-
-	// Get the Metadata and Transform components of each GameObject
-	vector<reference_wrapper<Metadata>> metadata = mgr.get_components_by_type<Metadata>();
-	vector<reference_wrapper<Transform>> transform = mgr.get_components_by_type<Transform>();
-
-	// Print the Metadata and Transform components
-	for (auto & m : metadata) {
-		cout << "Id: " << m.get().game_object_id << " Name: " << m.get().name
-			 << " Tag: " << m.get().tag << " Parent: " << m.get().parent << " Children: ";
-		for (auto & c : m.get().children) {
-			cout << c << " ";
-		}
-		cout << endl;
-	}
-	for (auto & t : transform) {
-		cout << "Id: " << t.get().game_object_id << " Position: [" << t.get().position.x
-			 << ", " << t.get().position.y << "]" << endl;
-	}
-
-	return 0;
-}
diff --git a/src/example/log.cpp b/src/example/log.cpp
deleted file mode 100644
index 5baa021..0000000
--- a/src/example/log.cpp
+++ /dev/null
@@ -1,28 +0,0 @@
-/** \file
- * 
- * Standalone example for usage of the logging functions
- */
-
-#include <crepe/api/Config.h>
-#include <crepe/util/Log.h>
-
-using namespace crepe;
-
-// unrelated setup code
-int _ = []() {
-	// make sure all log messages get printed
-	auto & cfg = Config::get_instance();
-	cfg.log.level = Log::Level::TRACE;
-
-	return 0; // satisfy compiler
-}();
-
-int main() {
-	dbg_trace();
-	dbg_log("debug message");
-	Log::logf("info message with variable: {}", 3);
-	Log::logf(Log::Level::WARNING, "warning");
-	Log::logf(Log::Level::ERROR, "error");
-
-	return 0;
-}
diff --git a/src/example/particles.cpp b/src/example/particles.cpp
deleted file mode 100644
index 3d5f676..0000000
--- a/src/example/particles.cpp
+++ /dev/null
@@ -1,43 +0,0 @@
-#include <crepe/ComponentManager.h>
-#include <crepe/api/AssetManager.h>
-
-#include <crepe/Component.h>
-#include <crepe/api/Color.h>
-#include <crepe/api/GameObject.h>
-#include <crepe/api/ParticleEmitter.h>
-#include <crepe/api/Rigidbody.h>
-#include <crepe/api/Sprite.h>
-#include <crepe/api/Texture.h>
-#include <crepe/api/Transform.h>
-
-using namespace crepe;
-using namespace std;
-
-int main(int argc, char * argv[]) {
-	ComponentManager mgr{};
-	GameObject game_object = mgr.new_object("", "", Vector2{0, 0}, 0, 0);
-	Color color(0, 0, 0, 0);
-	Sprite test_sprite = game_object.add_component<Sprite>(
-		make_shared<Texture>("../asset/texture/img.png"), color, FlipSettings{true, true});
-	game_object.add_component<ParticleEmitter>(ParticleEmitter::Data{
-		.position = {0, 0},
-		.max_particles = 100,
-		.emission_rate = 0,
-		.min_speed = 0,
-		.max_speed = 0,
-		.min_angle = 0,
-		.max_angle = 0,
-		.begin_lifespan = 0,
-		.end_lifespan = 0,
-		.force_over_time = Vector2{0, 0},
-		.boundary{
-			.width = 0,
-			.height = 0,
-			.offset = Vector2{0, 0},
-			.reset_on_exit = false,
-		},
-		.sprite = test_sprite,
-	});
-
-	return 0;
-}
diff --git a/src/example/physics.cpp b/src/example/physics.cpp
deleted file mode 100644
index ad663a0..0000000
--- a/src/example/physics.cpp
+++ /dev/null
@@ -1,24 +0,0 @@
-#include <crepe/Component.h>
-#include <crepe/ComponentManager.h>
-#include <crepe/api/GameObject.h>
-#include <crepe/api/Rigidbody.h>
-#include <crepe/api/Transform.h>
-#include <crepe/system/PhysicsSystem.h>
-
-using namespace crepe;
-using namespace std;
-
-int main(int argc, char * argv[]) {
-	ComponentManager mgr{};
-
-	GameObject game_object = mgr.new_object("Name", "Tag", Vector2{0, 0}, 0, 0);
-	game_object.add_component<Rigidbody>(Rigidbody::Data{
-		.mass = 1,
-		.gravity_scale = 1,
-		.body_type = Rigidbody::BodyType::DYNAMIC,
-		.constraints = {0, 0, 0},
-		.use_gravity = true,
-		.bounce = false,
-	});
-	return 0;
-}
diff --git a/src/example/proxy.cpp b/src/example/proxy.cpp
deleted file mode 100644
index 69451f8..0000000
--- a/src/example/proxy.cpp
+++ /dev/null
@@ -1,45 +0,0 @@
-/** \file
- * 
- * Standalone example for usage of the proxy type
- */
-
-#include <crepe/ValueBroker.h>
-#include <crepe/api/Config.h>
-#include <crepe/util/Log.h>
-#include <crepe/util/Proxy.h>
-
-using namespace std;
-using namespace crepe;
-
-void test_ro_ref(const int & val) {}
-void test_rw_ref(int & val) {}
-void test_ro_val(int val) {}
-
-int main() {
-	auto & cfg = Config::get_instance();
-	cfg.log.level = Log::Level::DEBUG;
-
-	int real_value = 0;
-
-	ValueBroker<int> broker{
-		[&real_value](const int & target) {
-			dbg_logf("set {} to {}", real_value, target);
-			real_value = target;
-		},
-		[&real_value]() -> const int & {
-			dbg_logf("get {}", real_value);
-			return real_value;
-		},
-	};
-
-	Proxy<int> proxy{broker};
-
-	broker.set(54);
-	proxy = 84;
-
-	test_ro_ref(proxy); // this is allowed
-	// test_rw_ref(proxy); // this should throw a compile error
-	test_ro_val(proxy);
-
-	return 0;
-}
diff --git a/src/example/rendering.cpp b/src/example/rendering.cpp
deleted file mode 100644
index c9e62f1..0000000
--- a/src/example/rendering.cpp
+++ /dev/null
@@ -1,55 +0,0 @@
-#include "api/Camera.h"
-#include <crepe/ComponentManager.h>
-#include <crepe/api/GameObject.h>
-#include <crepe/system/RenderSystem.h>
-#include <crepe/util/Log.h>
-
-#include <crepe/api/AssetManager.h>
-#include <crepe/api/Color.h>
-#include <crepe/api/Sprite.h>
-#include <crepe/api/Texture.h>
-#include <crepe/api/Transform.h>
-#include <crepe/api/Vector2.h>
-
-#include <chrono>
-#include <memory>
-
-using namespace std;
-using namespace crepe;
-
-int main() {
-	dbg_trace();
-
-	ComponentManager mgr{};
-	RenderSystem sys{mgr};
-
-	GameObject obj = mgr.new_object("name", "tag", Vector2{0, 0}, 1, 1);
-	GameObject obj1 = mgr.new_object("name", "tag", Vector2{500, 0}, 1, 0.1);
-	GameObject obj2 = mgr.new_object("name", "tag", Vector2{800, 0}, 1, 0.1);
-
-	// Normal adding components
-	{
-		Color color(0, 0, 0, 0);
-		obj.add_component<Sprite>(make_shared<Texture>("../asset/texture/img.png"), color,
-								  FlipSettings{false, false});
-		obj.add_component<Camera>(Color::get_red());
-	}
-	{
-		Color color(0, 0, 0, 0);
-		obj1.add_component<Sprite>(make_shared<Texture>("../asset/texture/second.png"), color,
-								   FlipSettings{true, true});
-	}
-
-	/*
-	{
-		Color color(0, 0, 0, 0);
-		auto img = mgr.cache<Texture>("../asset/texture/second.png");
-		obj2.add_component<Sprite>(img, color, FlipSettings{true, true});
-	}
-	*/
-
-	auto start = std::chrono::steady_clock::now();
-	while (std::chrono::steady_clock::now() - start < std::chrono::seconds(5)) {
-		sys.update();
-	}
-}
diff --git a/src/example/rendering_particle.cpp b/src/example/rendering_particle.cpp
new file mode 100644
index 0000000..4571afb
--- /dev/null
+++ b/src/example/rendering_particle.cpp
@@ -0,0 +1,71 @@
+#include "api/Camera.h"
+#include "system/ParticleSystem.h"
+#include <SDL2/SDL_timer.h>
+#include <crepe/ComponentManager.h>
+
+#include <crepe/Component.h>
+#include <crepe/api/Color.h>
+#include <crepe/api/GameObject.h>
+#include <crepe/api/ParticleEmitter.h>
+#include <crepe/api/Rigidbody.h>
+#include <crepe/api/Sprite.h>
+#include <crepe/api/Texture.h>
+#include <crepe/api/Transform.h>
+#include <crepe/api/Vector2.h>
+#include <crepe/system/RenderSystem.h>
+
+#include <chrono>
+#include <iostream>
+#include <memory>
+
+using namespace crepe;
+using namespace std;
+
+int main(int argc, char * argv[]) {
+	ComponentManager mgr;
+	GameObject game_object = mgr.new_object("", "", Vector2{100, 100}, 0, 0.1);
+	RenderSystem sys{mgr};
+	ParticleSystem psys{mgr};
+
+	Color color(255, 255, 255, 255);
+
+	Sprite & test_sprite = game_object.add_component<Sprite>(
+		make_shared<Texture>("../asset/texture/img.png"), color, FlipSettings{false, false});
+	test_sprite.order_in_layer = 5;
+
+	auto & test = game_object.add_component<ParticleEmitter>(ParticleEmitter::Data{
+		.position = {0, 0},
+		.max_particles = 10,
+		.emission_rate = 0.1,
+		.min_speed = 6,
+		.max_speed = 20,
+		.min_angle = -20,
+		.max_angle = 20,
+		.begin_lifespan = 0,
+		.end_lifespan = 60,
+		.force_over_time = Vector2{0, 0},
+		.boundary{
+			.width = 1000,
+			.height = 1000,
+			.offset = Vector2{0, 0},
+			.reset_on_exit = false,
+		},
+		.sprite = test_sprite,
+	});
+	game_object.add_component<Camera>(Color::WHITE);
+
+	game_object
+		.add_component<Sprite>(make_shared<Texture>("../asset/texture/img.png"), color,
+							   FlipSettings{false, false})
+		.order_in_layer
+		= 6;
+
+	auto start = std::chrono::steady_clock::now();
+	while (std::chrono::steady_clock::now() - start < std::chrono::seconds(5)) {
+		psys.update();
+		sys.update();
+		SDL_Delay(10);
+	}
+
+	return 0;
+}
diff --git a/src/example/scene_manager.cpp b/src/example/scene_manager.cpp
deleted file mode 100644
index accec7d..0000000
--- a/src/example/scene_manager.cpp
+++ /dev/null
@@ -1,79 +0,0 @@
-#include <iostream>
-
-#include <crepe/ComponentManager.h>
-#include <crepe/api/GameObject.h>
-#include <crepe/api/Metadata.h>
-#include <crepe/api/Scene.h>
-#include <crepe/api/SceneManager.h>
-#include <crepe/api/Vector2.h>
-
-using namespace crepe;
-using namespace std;
-
-class ConcreteScene1 : public Scene {
-public:
-	using Scene::Scene;
-
-	void load_scene() {
-		auto & mgr = this->component_manager;
-		GameObject object1 = mgr.new_object("scene_1", "tag_scene_1", Vector2{0, 0}, 0, 1);
-		GameObject object2 = mgr.new_object("scene_1", "tag_scene_1", Vector2{1, 0}, 0, 1);
-		GameObject object3 = mgr.new_object("scene_1", "tag_scene_1", Vector2{2, 0}, 0, 1);
-	}
-};
-
-class ConcreteScene2 : public Scene {
-public:
-	using Scene::Scene;
-
-	void load_scene() {
-		auto & mgr = this->component_manager;
-		GameObject object1 = mgr.new_object("scene_2", "tag_scene_2", Vector2{0, 0}, 0, 1);
-		GameObject object2 = mgr.new_object("scene_2", "tag_scene_2", Vector2{0, 1}, 0, 1);
-		GameObject object3 = mgr.new_object("scene_2", "tag_scene_2", Vector2{0, 2}, 0, 1);
-		GameObject object4 = mgr.new_object("scene_2", "tag_scene_2", Vector2{0, 3}, 0, 1);
-	}
-};
-
-int main() {
-	ComponentManager component_mgr{};
-	SceneManager scene_mgr{component_mgr};
-
-	// Add the scenes to the scene manager
-	scene_mgr.add_scene<ConcreteScene1>("scene1");
-	scene_mgr.add_scene<ConcreteScene2>("scene2");
-
-	// There is no need to call set_next_scene() at the beginnen, because the first scene will be
-	// automatically set as the next scene
-
-	// Load scene1 (the first scene added)
-	scene_mgr.load_next_scene();
-
-	// Get the Metadata components of each GameObject of Scene1
-	vector<reference_wrapper<Metadata>> metadata
-		= component_mgr.get_components_by_type<Metadata>();
-
-	cout << "Metadata components of Scene1:" << endl;
-	// Print the Metadata
-	for (auto & m : metadata) {
-		cout << "Id: " << m.get().game_object_id << " Name: " << m.get().name
-			 << " Tag: " << m.get().tag << endl;
-	}
-
-	// Set scene2 as the next scene
-	scene_mgr.set_next_scene("scene2");
-	// Load scene2
-	scene_mgr.load_next_scene();
-
-	// Get the Metadata components of each GameObject of Scene2
-	metadata = component_mgr.get_components_by_type<Metadata>();
-
-	cout << "Metadata components of Scene2:" << endl;
-	// Print the Metadata
-	for (auto & m : metadata) {
-		cout << "Id: " << m.get().game_object_id << " Name: " << m.get().name
-			 << " Tag: " << m.get().tag << endl;
-	}
-
-	return 0;
-}
diff --git a/src/example/script.cpp b/src/example/script.cpp
deleted file mode 100644
index a23295b..0000000
--- a/src/example/script.cpp
+++ /dev/null
@@ -1,49 +0,0 @@
-/** \file
- * 
- * Standalone example for usage of the script component and system
- */
-
-#include <crepe/ComponentManager.h>
-#include <crepe/system/ScriptSystem.h>
-#include <crepe/util/Log.h>
-
-#include <crepe/api/BehaviorScript.h>
-#include <crepe/api/Config.h>
-#include <crepe/api/GameObject.h>
-#include <crepe/api/Script.h>
-#include <crepe/api/Transform.h>
-
-using namespace crepe;
-using namespace std;
-
-// Unrelated stuff that is not part of this POC
-int _ = []() {
-	// Show dbg_trace() output
-	auto & cfg = Config::get_instance();
-	cfg.log.level = Log::Level::TRACE;
-
-	return 0; // satisfy compiler
-}();
-
-// User-defined script:
-class MyScript : public Script {
-	void update() {
-		// Retrieve component from the same GameObject this script is on
-		Transform & test = get_component<Transform>();
-		dbg_logf("Transform({:.2f}, {:.2f})", test.position.x, test.position.y);
-	}
-};
-
-int main() {
-	ComponentManager component_manager{};
-	ScriptSystem system{component_manager};
-
-	// Create game object with Transform and BehaviorScript components
-	GameObject obj = component_manager.new_object("name");
-	obj.add_component<BehaviorScript>().set_script<MyScript>();
-
-	// Update all scripts. This should result in MyScript::update being called
-	system.update();
-
-	return EXIT_SUCCESS;
-}
diff --git a/src/makefile b/src/makefile
index 5f80204..a0e8f02 100644
--- a/src/makefile
+++ b/src/makefile
@@ -1,6 +1,9 @@
 .PHONY: FORCE
 
-FMT := $(shell git ls-files '*.c' '*.cpp' '*.h' '*.hpp')
 format: FORCE
-	clang-tidy -p build/compile_commands.json --fix-errors $(FMT)
+	$(MAKE) -C .. $@
+
+LINT := $(shell git ls-files '*.c' '*.cpp' '*.h' '*.hpp')
+lint: FORCE
+	clang-tidy -p build/compile_commands.json --fix-errors $(LINT)
 
diff --git a/src/test/CMakeLists.txt b/src/test/CMakeLists.txt
index 6f6ad79..dc985a3 100644
--- a/src/test/CMakeLists.txt
+++ b/src/test/CMakeLists.txt
@@ -4,5 +4,9 @@ target_sources(test_main PUBLIC
 	ScriptTest.cpp
 	ParticleTest.cpp
 	EventTest.cpp
+	ECSTest.cpp
+	SceneManagerTest.cpp
+	ValueBrokerTest.cpp
+	DBTest.cpp
 )
 
diff --git a/src/test/DBTest.cpp b/src/test/DBTest.cpp
new file mode 100644
index 0000000..b57eba9
--- /dev/null
+++ b/src/test/DBTest.cpp
@@ -0,0 +1,29 @@
+#include <gtest/gtest.h>
+#include <crepe/facade/DB.h>
+
+using namespace std;
+using namespace crepe;
+using namespace testing;
+
+class DBTest : public Test {
+public:
+	DB db;
+};
+
+TEST_F(DBTest, ReadWrite) {
+	db.set("foo", "bar");
+	EXPECT_EQ(db.get("foo"), "bar");
+}
+
+TEST_F(DBTest, Nonexistant) {
+	EXPECT_THROW(db.get("foo"), std::out_of_range);
+	db.set("foo", "bar");
+	EXPECT_NO_THROW(db.get("foo"));
+}
+
+TEST_F(DBTest, Has) {
+	EXPECT_EQ(db.has("foo"), false);
+	db.set("foo", "bar");
+	EXPECT_EQ(db.has("foo"), true);
+}
+
diff --git a/src/test/ECSTest.cpp b/src/test/ECSTest.cpp
new file mode 100644
index 0000000..d5a5826
--- /dev/null
+++ b/src/test/ECSTest.cpp
@@ -0,0 +1,236 @@
+#include <gtest/gtest.h>
+
+#define protected public
+
+#include <crepe/ComponentManager.h>
+#include <crepe/api/GameObject.h>
+#include <crepe/api/Metadata.h>
+#include <crepe/api/Transform.h>
+#include <crepe/api/Vector2.h>
+
+using namespace std;
+using namespace crepe;
+
+class ECSTest : public ::testing::Test {
+public:
+	ComponentManager mgr{};
+};
+
+TEST_F(ECSTest, createGameObject) {
+	GameObject obj = mgr.new_object("body", "person", Vector2{0, 0}, 0, 1);
+
+	vector<reference_wrapper<Metadata>> metadata = mgr.get_components_by_type<Metadata>();
+	vector<reference_wrapper<Transform>> transform = mgr.get_components_by_type<Transform>();
+
+	EXPECT_EQ(metadata.size(), 1);
+	EXPECT_EQ(transform.size(), 1);
+
+	EXPECT_EQ(metadata[0].get().name, "body");
+	EXPECT_EQ(metadata[0].get().tag, "person");
+	EXPECT_EQ(metadata[0].get().parent, -1);
+	EXPECT_EQ(metadata[0].get().children.size(), 0);
+
+	EXPECT_EQ(transform[0].get().position.x, 0);
+	EXPECT_EQ(transform[0].get().position.y, 0);
+	EXPECT_EQ(transform[0].get().rotation, 0);
+	EXPECT_EQ(transform[0].get().scale, 1);
+}
+
+TEST_F(ECSTest, deleteAllGameObjects) {
+	GameObject obj0 = mgr.new_object("body", "person", Vector2{0, 0}, 0, 1);
+	GameObject obj1 = mgr.new_object("body", "person", Vector2{0, 0}, 0, 1);
+
+	mgr.delete_all_components();
+
+	vector<reference_wrapper<Metadata>> metadata = mgr.get_components_by_type<Metadata>();
+	vector<reference_wrapper<Transform>> transform = mgr.get_components_by_type<Transform>();
+
+	EXPECT_EQ(metadata.size(), 0);
+	EXPECT_EQ(transform.size(), 0);
+
+	GameObject obj2 = mgr.new_object("body2", "person2", Vector2{1, 0}, 5, 1);
+
+	metadata = mgr.get_components_by_type<Metadata>();
+	transform = mgr.get_components_by_type<Transform>();
+
+	EXPECT_EQ(metadata.size(), 1);
+	EXPECT_EQ(transform.size(), 1);
+
+	EXPECT_EQ(metadata[0].get().game_object_id, 0);
+	EXPECT_EQ(metadata[0].get().name, "body2");
+	EXPECT_EQ(metadata[0].get().tag, "person2");
+	EXPECT_EQ(metadata[0].get().parent, -1);
+	EXPECT_EQ(metadata[0].get().children.size(), 0);
+
+	EXPECT_EQ(transform[0].get().game_object_id, 0);
+	EXPECT_EQ(transform[0].get().position.x, 1);
+	EXPECT_EQ(transform[0].get().position.y, 0);
+	EXPECT_EQ(transform[0].get().rotation, 5);
+	EXPECT_EQ(transform[0].get().scale, 1);
+}
+
+TEST_F(ECSTest, deleteGameObject) {
+	GameObject obj0 = mgr.new_object("body", "person", Vector2{0, 0}, 0, 1);
+	GameObject obj1 = mgr.new_object("body", "person", Vector2{0, 0}, 0, 1);
+
+	mgr.delete_all_components_of_id(0);
+
+	vector<reference_wrapper<Metadata>> metadata = mgr.get_components_by_type<Metadata>();
+	vector<reference_wrapper<Transform>> transform = mgr.get_components_by_type<Transform>();
+
+	EXPECT_EQ(metadata.size(), 1);
+	EXPECT_EQ(transform.size(), 1);
+
+	EXPECT_EQ(metadata[0].get().game_object_id, 1);
+	EXPECT_EQ(metadata[0].get().name, "body");
+	EXPECT_EQ(metadata[0].get().tag, "person");
+	EXPECT_EQ(metadata[0].get().parent, -1);
+	EXPECT_EQ(metadata[0].get().children.size(), 0);
+
+	EXPECT_EQ(transform[0].get().game_object_id, 1);
+	EXPECT_EQ(transform[0].get().position.x, 0);
+	EXPECT_EQ(transform[0].get().position.y, 0);
+	EXPECT_EQ(transform[0].get().rotation, 0);
+	EXPECT_EQ(transform[0].get().scale, 1);
+}
+
+TEST_F(ECSTest, manyGameObjects) {
+	for (int i = 0; i < 5000; i++) {
+		GameObject obj = mgr.new_object("body", "person", Vector2{0, 0}, 0, i);
+	}
+
+	vector<reference_wrapper<Metadata>> metadata = mgr.get_components_by_type<Metadata>();
+	vector<reference_wrapper<Transform>> transform = mgr.get_components_by_type<Transform>();
+
+	EXPECT_EQ(metadata.size(), 5000);
+	EXPECT_EQ(transform.size(), 5000);
+	for (int i = 0; i < 5000; i++) {
+		EXPECT_EQ(metadata[i].get().game_object_id, i);
+		EXPECT_EQ(metadata[i].get().name, "body");
+		EXPECT_EQ(metadata[i].get().tag, "person");
+		EXPECT_EQ(metadata[i].get().parent, -1);
+		EXPECT_EQ(metadata[i].get().children.size(), 0);
+
+		EXPECT_EQ(transform[i].get().game_object_id, i);
+		EXPECT_EQ(transform[i].get().position.x, 0);
+		EXPECT_EQ(transform[i].get().position.y, 0);
+		EXPECT_EQ(transform[i].get().rotation, 0);
+		EXPECT_EQ(transform[i].get().scale, i);
+	}
+
+	mgr.delete_components<Metadata>();
+
+	metadata = mgr.get_components_by_type<Metadata>();
+	transform = mgr.get_components_by_type<Transform>();
+
+	EXPECT_EQ(metadata.size(), 0);
+	EXPECT_EQ(transform.size(), 5000);
+
+	for (int i = 0; i < 10000 - 5000; i++) {
+		string tag = "person" + to_string(i);
+		GameObject obj = mgr.new_object("body", tag, Vector2{0, 0}, i, 0);
+	}
+
+	metadata = mgr.get_components_by_type<Metadata>();
+	transform = mgr.get_components_by_type<Transform>();
+
+	EXPECT_EQ(metadata.size(), 10000 - 5000);
+	EXPECT_EQ(transform.size(), 10000);
+}
+
+TEST_F(ECSTest, getComponentsByID) {
+	GameObject obj0 = mgr.new_object("body", "person", Vector2{0, 0}, 0, 1);
+	GameObject obj1 = mgr.new_object("body", "person", Vector2{0, 0}, 0, 1);
+
+	vector<reference_wrapper<Metadata>> metadata = mgr.get_components_by_id<Metadata>(0);
+	vector<reference_wrapper<Transform>> transform = mgr.get_components_by_id<Transform>(1);
+
+	EXPECT_EQ(metadata.size(), 1);
+	EXPECT_EQ(transform.size(), 1);
+
+	EXPECT_EQ(metadata[0].get().game_object_id, 0);
+	EXPECT_EQ(metadata[0].get().name, "body");
+	EXPECT_EQ(metadata[0].get().tag, "person");
+	EXPECT_EQ(metadata[0].get().parent, -1);
+	EXPECT_EQ(metadata[0].get().children.size(), 0);
+
+	EXPECT_EQ(transform[0].get().game_object_id, 1);
+	EXPECT_EQ(transform[0].get().position.x, 0);
+	EXPECT_EQ(transform[0].get().position.y, 0);
+	EXPECT_EQ(transform[0].get().rotation, 0);
+	EXPECT_EQ(transform[0].get().scale, 1);
+}
+
+TEST_F(ECSTest, tooMuchComponents) {
+	try {
+		GameObject obj0 = mgr.new_object("body", "person", Vector2{0, 0}, 0, 1);
+		obj0.add_component<Transform>(Vector2{10, 10}, 0, 1);
+	} catch (const exception & e) {
+		EXPECT_EQ(e.what(),
+				  string("Exceeded maximum number of instances for this component type"));
+	}
+
+	try {
+		GameObject obj1 = mgr.new_object("body", "person", Vector2{0, 0}, 0, 1);
+		obj1.add_component<Metadata>("body", "person");
+	} catch (const exception & e) {
+		EXPECT_EQ(e.what(),
+				  string("Exceeded maximum number of instances for this component type"));
+	}
+
+	vector<reference_wrapper<Metadata>> metadata = mgr.get_components_by_type<Metadata>();
+
+	EXPECT_EQ(metadata.size(), 2);
+	EXPECT_EQ(metadata[0].get().name, "body");
+	EXPECT_EQ(metadata[1].get().name, "body");
+}
+
+TEST_F(ECSTest, partentChild) {
+	{
+		GameObject body = mgr.new_object("body", "person", Vector2{0, 0}, 0, 1);
+		GameObject right_leg = mgr.new_object("rightLeg", "person", Vector2{1, 1}, 0, 1);
+		GameObject left_leg = mgr.new_object("leftLeg", "person", Vector2{1, 1}, 0, 1);
+		GameObject right_foot = mgr.new_object("rightFoot", "person", Vector2{2, 2}, 0, 1);
+		GameObject left_foot = mgr.new_object("leftFoot", "person", Vector2{2, 2}, 0, 1);
+
+		// Set the parent of each GameObject
+		right_foot.set_parent(right_leg);
+		left_foot.set_parent(left_leg);
+		right_leg.set_parent(body);
+		left_leg.set_parent(body);
+	}
+
+	// Get the Metadata and Transform components of each GameObject
+	vector<reference_wrapper<Metadata>> metadata = mgr.get_components_by_type<Metadata>();
+
+	// Check IDs
+	EXPECT_EQ(metadata[0].get().game_object_id, 0);
+	EXPECT_EQ(metadata[1].get().game_object_id, 1);
+	EXPECT_EQ(metadata[2].get().game_object_id, 2);
+	EXPECT_EQ(metadata[3].get().game_object_id, 3);
+	EXPECT_EQ(metadata[4].get().game_object_id, 4);
+
+	// Check the parent-child relationships
+	EXPECT_EQ(metadata[0].get().name, "body");
+	EXPECT_EQ(metadata[1].get().name, "rightLeg");
+	EXPECT_EQ(metadata[2].get().name, "leftLeg");
+	EXPECT_EQ(metadata[3].get().name, "rightFoot");
+	EXPECT_EQ(metadata[4].get().name, "leftFoot");
+
+	EXPECT_EQ(metadata[0].get().parent, -1);
+	EXPECT_EQ(metadata[1].get().parent, 0);
+	EXPECT_EQ(metadata[2].get().parent, 0);
+	EXPECT_EQ(metadata[3].get().parent, 1);
+	EXPECT_EQ(metadata[4].get().parent, 2);
+
+	EXPECT_EQ(metadata[0].get().children.size(), 2);
+	EXPECT_EQ(metadata[1].get().children.size(), 1);
+	EXPECT_EQ(metadata[2].get().children.size(), 1);
+	EXPECT_EQ(metadata[3].get().children.size(), 0);
+	EXPECT_EQ(metadata[4].get().children.size(), 0);
+
+	EXPECT_EQ(metadata[0].get().children[0], 1);
+	EXPECT_EQ(metadata[0].get().children[1], 2);
+	EXPECT_EQ(metadata[1].get().children[0], 3);
+	EXPECT_EQ(metadata[2].get().children[0], 4);
+}
diff --git a/src/test/ParticleTest.cpp b/src/test/ParticleTest.cpp
index 4e655a9..d9bbba0 100644
--- a/src/test/ParticleTest.cpp
+++ b/src/test/ParticleTest.cpp
@@ -28,7 +28,7 @@ public:
 			GameObject game_object = mgr.new_object("", "", Vector2{0, 0}, 0, 0);
 
 			Color color(0, 0, 0, 0);
-			Sprite test_sprite = game_object.add_component<Sprite>(
+			Sprite & test_sprite = game_object.add_component<Sprite>(
 				make_shared<Texture>("../asset/texture/img.png"), color,
 				FlipSettings{true, true});
 
diff --git a/src/test/RenderSystemTest.cpp b/src/test/RenderSystemTest.cpp
new file mode 100644
index 0000000..ac479d3
--- /dev/null
+++ b/src/test/RenderSystemTest.cpp
@@ -0,0 +1,174 @@
+#include "api/Camera.h"
+#include <functional>
+#include <gtest/gtest.h>
+#include <memory>
+#include <vector>
+
+#define private public
+#define protected public
+
+#include <crepe/ComponentManager.h>
+#include <crepe/api/Color.h>
+#include <crepe/api/GameObject.h>
+#include <crepe/api/Sprite.h>
+#include <crepe/api/Texture.h>
+
+#include <crepe/system/RenderSystem.h>
+
+using namespace std;
+using namespace crepe;
+using namespace testing;
+
+class RenderSystemTest : public Test {
+public:
+	ComponentManager mgr{};
+	RenderSystem sys{mgr};
+	GameObject entity1 = this->mgr.new_object("name");
+	GameObject entity2 = this->mgr.new_object("name");
+	GameObject entity3 = this->mgr.new_object("name");
+	GameObject entity4 = this->mgr.new_object("name");
+
+	void SetUp() override {
+		auto & sprite1
+			= entity1.add_component<Sprite>(make_shared<Texture>("../asset/texture/img.png"),
+											Color(0, 0, 0, 0), FlipSettings{false, false});
+		ASSERT_NE(sprite1.sprite_image.get(), nullptr);
+		sprite1.order_in_layer = 5;
+		sprite1.sorting_in_layer = 5;
+		EXPECT_EQ(sprite1.order_in_layer, 5);
+		EXPECT_EQ(sprite1.sorting_in_layer, 5);
+		auto & sprite2
+			= entity2.add_component<Sprite>(make_shared<Texture>("../asset/texture/img.png"),
+											Color(0, 0, 0, 0), FlipSettings{false, false});
+		ASSERT_NE(sprite2.sprite_image.get(), nullptr);
+		sprite2.sorting_in_layer = 2;
+		sprite2.order_in_layer = 1;
+
+		EXPECT_EQ(sprite2.sorting_in_layer, 2);
+		EXPECT_EQ(sprite2.order_in_layer, 1);
+
+		auto & sprite3
+			= entity3.add_component<Sprite>(make_shared<Texture>("../asset/texture/img.png"),
+											Color(0, 0, 0, 0), FlipSettings{false, false});
+		ASSERT_NE(sprite3.sprite_image.get(), nullptr);
+		sprite3.sorting_in_layer = 1;
+		sprite3.order_in_layer = 2;
+
+		EXPECT_EQ(sprite3.sorting_in_layer, 1);
+		EXPECT_EQ(sprite3.order_in_layer, 2);
+
+		auto & sprite4
+			= entity4.add_component<Sprite>(make_shared<Texture>("../asset/texture/img.png"),
+											Color(0, 0, 0, 0), FlipSettings{false, false});
+		ASSERT_NE(sprite4.sprite_image.get(), nullptr);
+		sprite4.sorting_in_layer = 1;
+		sprite4.order_in_layer = 1;
+		EXPECT_EQ(sprite4.sorting_in_layer, 1);
+		EXPECT_EQ(sprite4.order_in_layer, 1);
+	}
+};
+
+TEST_F(RenderSystemTest, expected_throws) {
+	GameObject entity1 = this->mgr.new_object("NAME");
+
+	// no texture img
+	EXPECT_ANY_THROW({
+		entity1.add_component<Sprite>(make_shared<Texture>("NO_IMAGE"), Color(0, 0, 0, 0),
+									  FlipSettings{false, false});
+	});
+
+	// No camera
+	EXPECT_ANY_THROW({ this->sys.update(); });
+}
+
+TEST_F(RenderSystemTest, make_sprites) {}
+
+TEST_F(RenderSystemTest, sorting_sprites) {
+	vector<reference_wrapper<Sprite>> sprites = this->mgr.get_components_by_type<Sprite>();
+	ASSERT_EQ(sprites.size(), 4);
+
+	vector<reference_wrapper<Sprite>> sorted_sprites = this->sys.sort(sprites);
+	ASSERT_EQ(sorted_sprites.size(), 4);
+
+	// Expected order after sorting:
+	// 1. sorting_in_layer: 1, order_in_layer: 1 (entity4)
+	// 2. sorting_in_layer: 1, order_in_layer: 2 (entity3)
+	// 3. sorting_in_layer: 2, order_in_layer: 1 (entity2)
+	// 4. sorting_in_layer: 5, order_in_layer: 5 (entity1)
+
+	EXPECT_EQ(sorted_sprites[0].get().sorting_in_layer, 1);
+	EXPECT_EQ(sorted_sprites[0].get().order_in_layer, 1);
+
+	EXPECT_EQ(sorted_sprites[1].get().sorting_in_layer, 1);
+	EXPECT_EQ(sorted_sprites[1].get().order_in_layer, 2);
+
+	EXPECT_EQ(sorted_sprites[2].get().sorting_in_layer, 2);
+	EXPECT_EQ(sorted_sprites[2].get().order_in_layer, 1);
+
+	EXPECT_EQ(sorted_sprites[3].get().sorting_in_layer, 5);
+	EXPECT_EQ(sorted_sprites[3].get().order_in_layer, 5);
+
+	for (size_t i = 1; i < sorted_sprites.size(); ++i) {
+		const Sprite & prev = sorted_sprites[i - 1].get();
+		const Sprite & curr = sorted_sprites[i].get();
+
+		if (prev.sorting_in_layer == curr.sorting_in_layer) {
+			EXPECT_LE(prev.order_in_layer, curr.order_in_layer);
+		} else {
+			EXPECT_LE(prev.sorting_in_layer, curr.sorting_in_layer);
+		}
+	}
+}
+
+TEST_F(RenderSystemTest, Update) {
+	entity1.add_component<Camera>(Color::WHITE);
+	{
+		vector<reference_wrapper<Sprite>> sprites = this->mgr.get_components_by_type<Sprite>();
+		ASSERT_EQ(sprites.size(), 4);
+
+		EXPECT_EQ(sprites[0].get().game_object_id, 0);
+		EXPECT_EQ(sprites[1].get().game_object_id, 1);
+		EXPECT_EQ(sprites[2].get().game_object_id, 2);
+		EXPECT_EQ(sprites[3].get().game_object_id, 3);
+	}
+	this->sys.update();
+	{
+		vector<reference_wrapper<Sprite>> sprites = this->mgr.get_components_by_type<Sprite>();
+		ASSERT_EQ(sprites.size(), 4);
+
+		EXPECT_EQ(sprites[0].get().game_object_id, 0);
+		EXPECT_EQ(sprites[1].get().game_object_id, 1);
+		EXPECT_EQ(sprites[2].get().game_object_id, 2);
+		EXPECT_EQ(sprites[3].get().game_object_id, 3);
+	}
+}
+
+TEST_F(RenderSystemTest, Camera) {
+	{
+		auto cameras = this->mgr.get_components_by_type<Camera>();
+		EXPECT_NE(cameras.size(), 1);
+	}
+	{
+		entity1.add_component<Camera>(Color::WHITE);
+		auto cameras = this->mgr.get_components_by_type<Camera>();
+		EXPECT_EQ(cameras.size(), 1);
+	}
+
+	//TODO improve with newer version
+}
+TEST_F(RenderSystemTest, Color) {
+	entity1.add_component<Camera>(Color::WHITE);
+	auto & sprite = this->mgr.get_components_by_id<Sprite>(entity1.id).front().get();
+	ASSERT_NE(sprite.sprite_image.get(), nullptr);
+
+	sprite.color = Color::GREEN;
+	EXPECT_EQ(sprite.color.r, Color::GREEN.r);
+	EXPECT_EQ(sprite.color.g, Color::GREEN.g);
+	EXPECT_EQ(sprite.color.b, Color::GREEN.b);
+	EXPECT_EQ(sprite.color.a, Color::GREEN.a);
+	this->sys.update();
+	EXPECT_EQ(sprite.color.r, Color::GREEN.r);
+	EXPECT_EQ(sprite.color.g, Color::GREEN.g);
+	EXPECT_EQ(sprite.color.b, Color::GREEN.b);
+	EXPECT_EQ(sprite.color.a, Color::GREEN.a);
+}
diff --git a/src/test/SceneManagerTest.cpp b/src/test/SceneManagerTest.cpp
new file mode 100644
index 0000000..69e1171
--- /dev/null
+++ b/src/test/SceneManagerTest.cpp
@@ -0,0 +1,122 @@
+#include <crepe/ComponentManager.h>
+#include <crepe/api/GameObject.h>
+#include <crepe/api/Metadata.h>
+#include <crepe/api/Scene.h>
+#include <crepe/api/SceneManager.h>
+#include <crepe/api/Transform.h>
+#include <crepe/api/Vector2.h>
+#include <gtest/gtest.h>
+
+using namespace std;
+using namespace crepe;
+
+class ConcreteScene1 : public Scene {
+public:
+	using Scene::Scene;
+
+	void load_scene() {
+		auto & mgr = this->component_manager;
+		GameObject object1 = mgr.new_object("scene_1", "tag_scene_1", Vector2{0, 0}, 0, 1);
+		GameObject object2 = mgr.new_object("scene_1", "tag_scene_1", Vector2{1, 0}, 0, 1);
+		GameObject object3 = mgr.new_object("scene_1", "tag_scene_1", Vector2{2, 0}, 0, 1);
+	}
+};
+
+class ConcreteScene2 : public Scene {
+public:
+	using Scene::Scene;
+
+	void load_scene() {
+		auto & mgr = this->component_manager;
+		GameObject object1 = mgr.new_object("scene_2", "tag_scene_2", Vector2{0, 0}, 0, 1);
+		GameObject object2 = mgr.new_object("scene_2", "tag_scene_2", Vector2{0, 1}, 0, 1);
+		GameObject object3 = mgr.new_object("scene_2", "tag_scene_2", Vector2{0, 2}, 0, 1);
+		GameObject object4 = mgr.new_object("scene_2", "tag_scene_2", Vector2{0, 3}, 0, 1);
+	}
+};
+
+class SceneManagerTest : public ::testing::Test {
+public:
+	ComponentManager component_mgr{};
+	SceneManager scene_mgr{component_mgr};
+};
+
+TEST_F(SceneManagerTest, loadScene) {
+	scene_mgr.add_scene<ConcreteScene1>("scene1");
+	scene_mgr.add_scene<ConcreteScene2>("scene2");
+
+	scene_mgr.load_next_scene();
+
+	vector<reference_wrapper<Metadata>> metadata
+		= component_mgr.get_components_by_type<Metadata>();
+	vector<reference_wrapper<Transform>> transform
+		= component_mgr.get_components_by_type<Transform>();
+
+	EXPECT_EQ(metadata.size(), 3);
+	EXPECT_EQ(transform.size(), 3);
+
+	EXPECT_EQ(metadata[0].get().game_object_id, 0);
+	EXPECT_EQ(metadata[0].get().name, "scene_1");
+	EXPECT_EQ(metadata[0].get().tag, "tag_scene_1");
+	EXPECT_EQ(metadata[0].get().parent, -1);
+	EXPECT_EQ(metadata[0].get().children.size(), 0);
+	EXPECT_EQ(transform[0].get().position.x, 0);
+	EXPECT_EQ(transform[0].get().position.y, 0);
+
+	EXPECT_EQ(metadata[1].get().game_object_id, 1);
+	EXPECT_EQ(metadata[1].get().name, "scene_1");
+	EXPECT_EQ(metadata[1].get().tag, "tag_scene_1");
+	EXPECT_EQ(metadata[1].get().parent, -1);
+	EXPECT_EQ(metadata[1].get().children.size(), 0);
+	EXPECT_EQ(transform[1].get().position.x, 1);
+	EXPECT_EQ(transform[1].get().position.y, 0);
+
+	EXPECT_EQ(metadata[2].get().game_object_id, 2);
+	EXPECT_EQ(metadata[2].get().name, "scene_1");
+	EXPECT_EQ(metadata[2].get().tag, "tag_scene_1");
+	EXPECT_EQ(metadata[2].get().parent, -1);
+	EXPECT_EQ(metadata[2].get().children.size(), 0);
+	EXPECT_EQ(transform[2].get().position.x, 2);
+	EXPECT_EQ(transform[2].get().position.y, 0);
+
+	scene_mgr.set_next_scene("scene2");
+	scene_mgr.load_next_scene();
+
+	metadata = component_mgr.get_components_by_type<Metadata>();
+	transform = component_mgr.get_components_by_type<Transform>();
+
+	EXPECT_EQ(metadata.size(), 4);
+	EXPECT_EQ(transform.size(), 4);
+
+	EXPECT_EQ(metadata[0].get().game_object_id, 0);
+	EXPECT_EQ(metadata[0].get().name, "scene_2");
+	EXPECT_EQ(metadata[0].get().tag, "tag_scene_2");
+	EXPECT_EQ(metadata[0].get().parent, -1);
+	EXPECT_EQ(metadata[0].get().children.size(), 0);
+	EXPECT_EQ(transform[0].get().position.x, 0);
+	EXPECT_EQ(transform[0].get().position.y, 0);
+
+	EXPECT_EQ(metadata[1].get().game_object_id, 1);
+	EXPECT_EQ(metadata[1].get().name, "scene_2");
+	EXPECT_EQ(metadata[1].get().tag, "tag_scene_2");
+	EXPECT_EQ(metadata[1].get().parent, -1);
+	EXPECT_EQ(metadata[1].get().children.size(), 0);
+	EXPECT_EQ(transform[1].get().position.x, 0);
+	EXPECT_EQ(transform[1].get().position.y, 1);
+
+	EXPECT_EQ(metadata[2].get().game_object_id, 2);
+	EXPECT_EQ(metadata[2].get().name, "scene_2");
+	EXPECT_EQ(metadata[2].get().tag, "tag_scene_2");
+	EXPECT_EQ(metadata[2].get().parent, -1);
+	EXPECT_EQ(metadata[2].get().children.size(), 0);
+	EXPECT_EQ(transform[2].get().position.x, 0);
+	EXPECT_EQ(transform[2].get().position.y, 2);
+
+	EXPECT_EQ(metadata[3].get().game_object_id, 3);
+	EXPECT_EQ(metadata[3].get().name, "scene_2");
+	EXPECT_EQ(metadata[3].get().tag, "tag_scene_2");
+	EXPECT_EQ(metadata[3].get().parent, -1);
+	EXPECT_EQ(metadata[3].get().children.size(), 0);
+	EXPECT_EQ(transform[3].get().position.x, 0);
+	EXPECT_EQ(transform[3].get().position.y, 3);
+}
diff --git a/src/test/ValueBrokerTest.cpp b/src/test/ValueBrokerTest.cpp
new file mode 100644
index 0000000..10a4654
--- /dev/null
+++ b/src/test/ValueBrokerTest.cpp
@@ -0,0 +1,64 @@
+#include <gtest/gtest.h>
+
+#include <crepe/ValueBroker.h>
+#include <crepe/util/Proxy.h>
+
+using namespace std;
+using namespace crepe;
+using namespace testing;
+
+class ValueBrokerTest : public Test {
+public:
+	int read_count = 0;
+	int write_count = 0;
+	int value = 0;
+
+	ValueBroker<int> broker {
+		[this](const int & target) -> void {
+			this->write_count++;
+			this->value = target;
+		},
+		[this]() -> const int & {
+			this->read_count++;
+			return this->value;
+		},
+	};
+	Proxy<int> proxy{broker};
+
+	void SetUp() override {
+		ASSERT_EQ(read_count, 0);
+		ASSERT_EQ(write_count, 0);
+	}
+};
+
+TEST_F(ValueBrokerTest, BrokerWrite) {
+	broker.set(0);
+	EXPECT_EQ(read_count, 0);
+	EXPECT_EQ(write_count, 1);
+}
+
+TEST_F(ValueBrokerTest, BrokerRead) {
+	broker.get();
+	EXPECT_EQ(read_count, 1);
+	EXPECT_EQ(write_count, 0);
+}
+
+TEST_F(ValueBrokerTest, ProxyWrite) {
+	proxy = 0;
+	EXPECT_EQ(read_count, 0);
+	EXPECT_EQ(write_count, 1);
+}
+
+void dummy(int) { }
+TEST_F(ValueBrokerTest, ProxyRead) {
+	dummy(proxy);
+	EXPECT_EQ(read_count, 1);
+	EXPECT_EQ(write_count, 0);
+}
+
+TEST_F(ValueBrokerTest, ProxyReadWrite) {
+	proxy = proxy;
+	ASSERT_EQ(read_count, 1);
+	ASSERT_EQ(write_count, 1);
+}
+