Crafting Your Own Universe: A Comprehensive Guide to Making a Game Engine

The allure of creating a game engine – the very foundation upon which interactive worlds are built – is undeniable. It’s a journey of deep technical understanding, creative problem-solving, and immense satisfaction. This article serves as a comprehensive roadmap for those brave enough to embark on this exciting endeavor. We’ll break down the essential components, guide you through the crucial steps, and equip you with the knowledge to build a game engine, albeit a basic one, from the ground up.

Why Build a Game Engine?

Before we dive into the nitty-gritty, let’s consider the ‘why’. Why invest the significant time and effort when powerful, readily available engines like Unity, Unreal Engine, and Godot exist? There are several compelling reasons:

• Deep Understanding: Building your own engine provides an unparalleled understanding of game development principles. You’ll grapple with low-level concepts like rendering pipelines, memory management, and physics simulation, fostering a profound appreciation for the intricacies involved.
• Customization and Control: Pre-built engines, while powerful, can sometimes feel restrictive. A custom engine allows you to tailor every aspect to your exact needs, whether it’s a specific rendering style, unique game mechanics, or a custom data format.
• Educational Experience: The sheer volume of knowledge acquired is invaluable. You’ll become proficient in various areas of programming, mathematics, and software architecture.
• Portfolio Building: A custom game engine is a remarkable addition to any portfolio, showcasing your technical prowess and passion for game development.
• Pure Satisfaction: The sense of accomplishment after creating something so intricate from scratch is truly rewarding.

The Essential Building Blocks of a Game Engine

A game engine is a complex system, but it can be broken down into several key components. Here’s a high-level overview:

1. Rendering Engine: This handles the visual output of your game. It takes 3D or 2D models and draws them onto the screen. This often involves using libraries like OpenGL, Vulkan, or DirectX.
2. Input Handling: This component manages user inputs such as keyboard presses, mouse clicks, and gamepad controls. It translates these inputs into commands that the game can understand.
3. Game Logic: This is the heart of your game, responsible for implementing the game rules, player interactions, and overall gameplay.
4. Physics Engine: This simulates the behavior of objects in the game world, handling collisions, gravity, and other physical interactions.
5. Audio Engine: Responsible for playing sound effects and music within the game.
6. Resource Management: This system manages game assets like textures, models, sounds, and scripts, ensuring efficient loading and use.
7. Scene Management: Manages different levels or sections of your game. It determines which assets and entities are active in each scene.
8. Scripting System: Allows you to write game logic and behaviors in a more user-friendly language, separate from the core engine code.
9. Editor Tools: Provides tools for level design, object placement, and game configuration.

Step-by-Step Guide to Building a Basic 2D Game Engine

Let’s dive into a practical approach, building a simple 2D game engine. We’ll use C++ as our primary programming language, along with the SDL2 library for windowing and graphics. This guide will provide the core concepts you’ll need and should be treated as an extendable foundation.

Step 1: Setting Up Your Development Environment

Before you start coding, you need to set up your development environment.

1. Install C++ Compiler: Ensure you have a C++ compiler installed. For Windows, MinGW is a popular choice. On macOS or Linux, you can use GCC.
2. Install SDL2: Download and install the SDL2 library. It’s available on the official SDL website. Make sure you install the development libraries (headers and .lib/.so files).
3. Choose an IDE or Text Editor: Select an IDE (like Visual Studio Code, CLion, or Code::Blocks) or a text editor (like Sublime Text or Atom) for writing and managing your code.
4. Create a New Project: Create a new C++ project in your IDE or set up the necessary project structure using CMake or your IDE’s build system.
5. Configure Project: Configure your project to find SDL2 libraries and headers, add appropriate compile flags, and linker options (check your IDE or compiler documentation to do this correctly).

Step 2: Creating the Window and Rendering Context

The first step in your game engine is creating a window and a rendering context where you’ll draw your game. In your `main.cpp` file or a similar file create code like:

cpp
#include
#include

int main(int argc, char* argv[]) {
if (SDL_Init(SDL_INIT_VIDEO) < 0) { std::cerr << "SDL could not initialize! SDL Error: " << SDL_GetError() << std::endl; return 1; } SDL_Window* window = SDL_CreateWindow( "My Game Engine", // Window title SDL_WINDOWPOS_UNDEFINED, // Initial x position SDL_WINDOWPOS_UNDEFINED, // Initial y position 800, // Width, in pixels 600, // Height, in pixels SDL_WINDOW_SHOWN // Flags ); if (window == nullptr) { std::cerr << "Window could not be created! SDL Error: " << SDL_GetError() << std::endl; SDL_Quit(); return 1; } SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED); if (renderer == nullptr) { std::cerr << "Renderer could not be created! SDL Error: " << SDL_GetError() << std::endl; SDL_DestroyWindow(window); SDL_Quit(); return 1; } bool quit = false; SDL_Event e; while (!quit) { while (SDL_PollEvent(&e) != 0) { if (e.type == SDL_QUIT) { quit = true; } } SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255); // Background color (black) SDL_RenderClear(renderer); // Draw something here later (like sprites) SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255); // White color for test SDL_Rect rect = { 100,100,50,50 }; //Draw a 50x50 white rectangle at (100,100) SDL_RenderFillRect(renderer, &rect); SDL_RenderPresent(renderer); } SDL_DestroyRenderer(renderer); SDL_DestroyWindow(window); SDL_Quit(); return 0; }

This code initializes SDL, creates a window, creates a renderer, and enters the main game loop. The loop clears the screen with a black color, and in this example draws a small white rectangle. It also handles the SDL_QUIT event which will close the window.

Step 3: Creating a Basic Sprite System

Sprites are fundamental to 2D games. Let’s create a simple sprite class:

First, create a `sprite.h`:

cpp
#pragma once
#include

class Sprite {
public:
Sprite(const char* texturePath, SDL_Renderer* renderer);
~Sprite();

void draw(SDL_Renderer* renderer, int x, int y);

int getWidth() const { return m_width; }
int getHeight() const { return m_height; }

private:
SDL_Texture* m_texture = nullptr;
int m_width = 0;
int m_height = 0;

};

Then create `sprite.cpp`:

cpp
#include “sprite.h”
#include
#include

Sprite::Sprite(const char* texturePath, SDL_Renderer* renderer) {
SDL_Surface* surface = IMG_Load(texturePath);

if (surface == nullptr) {
std::cerr << "Failed to load image: " << texturePath << " - SDL Error: " << IMG_GetError() << std::endl; return; } m_texture = SDL_CreateTextureFromSurface(renderer, surface); if (m_texture == nullptr) { std::cerr << "Failed to create texture: " << SDL_GetError() << std::endl; } m_width = surface->w;
m_height = surface->h;
SDL_FreeSurface(surface);
}

Sprite::~Sprite() {
if (m_texture) {
SDL_DestroyTexture(m_texture);
}
}

void Sprite::draw(SDL_Renderer* renderer, int x, int y) {
SDL_Rect destRect = { x, y, m_width, m_height };
SDL_RenderCopy(renderer, m_texture, nullptr, &destRect);
}

Important Note: You will need to install and include the SDL_image library to load images as this example is doing. Then you would use this sprite in your main loop to draw the loaded image on the screen.

Now, modify your `main.cpp` to include the sprite:

cpp
#include
#include
#include “sprite.h”
#include

int main(int argc, char* argv[]) {
if (SDL_Init(SDL_INIT_VIDEO) < 0) { std::cerr << "SDL could not initialize! SDL Error: " << SDL_GetError() << std::endl; return 1; } // Initialize SDL_image int imgFlags = IMG_INIT_PNG; // Use PNG images here if (!(IMG_Init(imgFlags) & imgFlags)) { std::cerr << "SDL_image could not initialize! SDL_image Error: " << IMG_GetError() << std::endl; SDL_Quit(); // Shut down any SDL systems return 1; } SDL_Window* window = SDL_CreateWindow( "My Game Engine", // Window title SDL_WINDOWPOS_UNDEFINED, // Initial x position SDL_WINDOWPOS_UNDEFINED, // Initial y position 800, // Width, in pixels 600, // Height, in pixels SDL_WINDOW_SHOWN // Flags ); if (window == nullptr) { std::cerr << "Window could not be created! SDL Error: " << SDL_GetError() << std::endl; SDL_Quit(); return 1; } SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED); if (renderer == nullptr) { std::cerr << "Renderer could not be created! SDL Error: " << SDL_GetError() << std::endl; SDL_DestroyWindow(window); SDL_Quit(); return 1; } Sprite sprite("my_sprite.png", renderer); //Make sure you have a file called my_sprite.png in the same directory bool quit = false; SDL_Event e; while (!quit) { while (SDL_PollEvent(&e) != 0) { if (e.type == SDL_QUIT) { quit = true; } } SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255); // Background color (black) SDL_RenderClear(renderer); // Draw the sprite at position (100, 100) sprite.draw(renderer, 100, 100); SDL_RenderPresent(renderer); } SDL_DestroyRenderer(renderer); SDL_DestroyWindow(window); SDL_Quit(); IMG_Quit(); return 0; }

Replace `”my_sprite.png”` with your own sprite image file name. Now you have a basic rendering engine that is able to draw images on the screen!

Step 4: Input Handling

We’ve already seen a bit of input handling with our `SDL_PollEvent` loop in the main function. Now let’s make a basic Input Manager that would help with managing more key events.

Create `input_manager.h` file:

cpp
#pragma once
#include

class InputManager {
public:
InputManager();
~InputManager();
void processInput();
bool isKeyPressed(SDL_Scancode key);

private:
const Uint8* m_keyboardState;
bool m_quit = false;
};

And `input_manager.cpp` file:

cpp
#include “input_manager.h”
#include

InputManager::InputManager() {
m_keyboardState = SDL_GetKeyboardState(nullptr);
}

InputManager::~InputManager() {
}

void InputManager::processInput() {
SDL_Event e;
while (SDL_PollEvent(&e) != 0) {
if (e.type == SDL_QUIT) {
m_quit = true;
}
}
}

bool InputManager::isKeyPressed(SDL_Scancode key) {
return m_keyboardState[key];
}

Now, modify your `main.cpp` to use the Input manager class, and make the sprite move:

cpp
#include
#include
#include “sprite.h”
#include “input_manager.h”
#include

int main(int argc, char* argv[]) {
if (SDL_Init(SDL_INIT_VIDEO) < 0) { std::cerr << "SDL could not initialize! SDL Error: " << SDL_GetError() << std::endl; return 1; } // Initialize SDL_image int imgFlags = IMG_INIT_PNG; // Use PNG images here if (!(IMG_Init(imgFlags) & imgFlags)) { std::cerr << "SDL_image could not initialize! SDL_image Error: " << IMG_GetError() << std::endl; SDL_Quit(); // Shut down any SDL systems return 1; } SDL_Window* window = SDL_CreateWindow( "My Game Engine", // Window title SDL_WINDOWPOS_UNDEFINED, // Initial x position SDL_WINDOWPOS_UNDEFINED, // Initial y position 800, // Width, in pixels 600, // Height, in pixels SDL_WINDOW_SHOWN // Flags ); if (window == nullptr) { std::cerr << "Window could not be created! SDL Error: " << SDL_GetError() << std::endl; SDL_Quit(); return 1; } SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED); if (renderer == nullptr) { std::cerr << "Renderer could not be created! SDL Error: " << SDL_GetError() << std::endl; SDL_DestroyWindow(window); SDL_Quit(); return 1; } InputManager inputManager; Sprite sprite("my_sprite.png", renderer); //Make sure you have a file called my_sprite.png in the same directory int x = 100; int y = 100; bool quit = false; while (!quit) { inputManager.processInput(); if (inputManager.isKeyPressed(SDL_SCANCODE_LEFT)) { x -= 2; } if (inputManager.isKeyPressed(SDL_SCANCODE_RIGHT)) { x += 2; } if (inputManager.isKeyPressed(SDL_SCANCODE_UP)) { y -= 2; } if (inputManager.isKeyPressed(SDL_SCANCODE_DOWN)) { y += 2; } SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255); // Background color (black) SDL_RenderClear(renderer); // Draw the sprite at position (x, y) sprite.draw(renderer, x, y); SDL_RenderPresent(renderer); if (inputManager.m_quit) { //check for SDL_QUIT event quit = true; } } SDL_DestroyRenderer(renderer); SDL_DestroyWindow(window); SDL_Quit(); IMG_Quit(); return 0; }

Now the sprite should move when you press the arrow keys!

Step 5: Game Loop and Time Management

Games are all about time and keeping the main loop ticking at a steady rate. To do this, we can use SDL’s time functions.

Modify your `main.cpp` main loop:

cpp
#include
#include
#include “sprite.h”
#include “input_manager.h”
#include

int main(int argc, char* argv[]) {
if (SDL_Init(SDL_INIT_VIDEO) < 0) { std::cerr << "SDL could not initialize! SDL Error: " << SDL_GetError() << std::endl; return 1; } // Initialize SDL_image int imgFlags = IMG_INIT_PNG; // Use PNG images here if (!(IMG_Init(imgFlags) & imgFlags)) { std::cerr << "SDL_image could not initialize! SDL_image Error: " << IMG_GetError() << std::endl; SDL_Quit(); // Shut down any SDL systems return 1; } SDL_Window* window = SDL_CreateWindow( "My Game Engine", // Window title SDL_WINDOWPOS_UNDEFINED, // Initial x position SDL_WINDOWPOS_UNDEFINED, // Initial y position 800, // Width, in pixels 600, // Height, in pixels SDL_WINDOW_SHOWN // Flags ); if (window == nullptr) { std::cerr << "Window could not be created! SDL Error: " << SDL_GetError() << std::endl; SDL_Quit(); return 1; } SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED); if (renderer == nullptr) { std::cerr << "Renderer could not be created! SDL Error: " << SDL_GetError() << std::endl; SDL_DestroyWindow(window); SDL_Quit(); return 1; } InputManager inputManager; Sprite sprite("my_sprite.png", renderer); //Make sure you have a file called my_sprite.png in the same directory int x = 100; int y = 100; bool quit = false; const int FPS = 60; // frames per second const int frameDelay = 1000 / FPS; // milliseconds while (!quit) { Uint32 frameStart = SDL_GetTicks(); // Get the start tick inputManager.processInput(); if (inputManager.isKeyPressed(SDL_SCANCODE_LEFT)) { x -= 2; } if (inputManager.isKeyPressed(SDL_SCANCODE_RIGHT)) { x += 2; } if (inputManager.isKeyPressed(SDL_SCANCODE_UP)) { y -= 2; } if (inputManager.isKeyPressed(SDL_SCANCODE_DOWN)) { y += 2; } SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255); // Background color (black) SDL_RenderClear(renderer); // Draw the sprite at position (x, y) sprite.draw(renderer, x, y); SDL_RenderPresent(renderer); if (inputManager.m_quit) { //check for SDL_QUIT event quit = true; } int frameTime = SDL_GetTicks() - frameStart; // Get time of loop execution if (frameDelay > frameTime) {
SDL_Delay(frameDelay – frameTime);
}
}

SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
IMG_Quit();

return 0;
}

The loop is now being limited by a 60 fps rate. You now have a basic engine that renders sprites, handles basic keyboard inputs and is limited by a frame rate.

Step 6: Building Up

From here, we continue to add more features to build up the engine:

• Game Objects and Components: Implement a basic game object system to organize entities and their associated components like Transform, Sprite, Collider etc.
• Basic Camera: Allow the user to specify a camera, which will allow for large level design.
• Basic Physics: For collision detection, start with AABB (Axis-Aligned Bounding Box) collision detection for simplicity.
• Audio: Use SDL_mixer to load and play basic sounds.
• Scene Management: Create a system to switch between levels and to organize your Game Objects in different scenes.
• Resource Manager: A better way to load and manage game resources like textures, sounds, and other assets.
• Editor: Once your engine starts being able to do a lot of things, it would be important to develop editor tooling to handle all of this, this is very big challenge but you will learn a lot.

Important Considerations

• Start Small: Don’t try to create a full-fledged engine right away. Begin with the basics and gradually add more features.
• Modular Design: Build your engine in a modular fashion, so it’s easier to maintain and extend.
• Use Libraries: Don’t reinvent the wheel. Utilize existing libraries like SDL, OpenGL/Vulkan/DirectX, and others to handle low-level tasks.
• Version Control: Use Git to track changes and collaborate if you’re working with a team.
• Testing: Thoroughly test each component as you build it to identify bugs early on.
• Community: The open source community is a great resource for learning and help.

Extending Your Engine

The provided guide is just a starting point. Here are some advanced concepts to explore:

• 3D Rendering: Move from 2D to 3D using a graphics API like OpenGL or Vulkan.
• Advanced Physics: Implement a robust physics engine using libraries like Box2D (2D) or Bullet (3D).
• Scripting: Add scripting capabilities using languages like Lua or C# to simplify game logic development.
• Networking: Enable multiplayer experiences by implementing networking features.
• Optimizations: Explore techniques to improve performance, such as batch rendering and memory management.

Conclusion

Building a game engine is a challenging but incredibly rewarding journey. It’s a deep dive into computer science, mathematics, and the art of game development. While it may seem daunting, breaking it down into smaller steps and focusing on a solid foundation will set you up for success. Embrace the learning process, experiment, and above all, have fun crafting your own interactive world! This article should equip you with enough information to start your journey of making your own game engine and we wish you the best of luck!