What a game engine is and why you might build one
A game engine is the software foundation that handles the core systems a game needs to run: rendering graphics to the screen, processing physics, managing sound, detecting collisions, and responding to player input. When you build your own engine instead of using an existing one like Unity or Unreal, you are writing the code that makes all of those things happen.
Most people starting out should use an existing engine. But there are real reasons to build your own: you want to understand how games actually work under the hood, you need an engine optimized for a very specific type of game, or you are learning programming and want a concrete project. Building an engine teaches you more about how computers work than using a pre-built one ever will.
This guide explains what systems you need to build, what languages and tools work for the job, and the realistic scope of the work involved. It does not walk you through writing the code line by line — that would be a book, not an article — but it shows you what you are actually taking on.
Key Takeaways
- A minimal game engine needs a graphics renderer, an input handler, a game loop that runs at a steady frame rate, and a way to organize game objects and their behavior.
- C++ is the industry standard for performance-critical engines, but Python, C#, or JavaScript are realistic choices if you are learning or building something small.
- You will spend most of your time on the renderer (drawing things to screen) and the physics or collision system, not on the fun parts like game design.
- Starting with a 2D engine is vastly simpler than 3D and teaches you the same core concepts with a fraction of the complexity.
- Most solo developers and small teams should use an existing engine and spend their time on the game itself, not rebuilding what Unity or Godot already do well.
The core systems every engine needs
A game engine, stripped to its essentials, is a loop that runs roughly 60 times per second. Each loop does the same thing: read input from the player, update the state of every game object, check for collisions, run physics calculations, and draw everything to the screen. If any of these steps is slow or broken, the whole game feels broken.
The renderer is the system that draws pixels to the screen. In 2D, this is often simpler — you load an image file, position it at coordinates, and tell the graphics card to draw it. In 3D, you are loading 3D models, positioning them in 3D space, calculating how light hits them, and converting that 3D world into a 2D image for the screen. The renderer is almost always the bottleneck, and it is where most of your optimization work will live.
The input handler listens for keyboard presses, mouse movement, gamepad buttons, and touch input. It stores the current state (is the spacebar down right now?) and passes that information to your game code so you can move the player when they press a key.
The physics and collision system detects when two objects touch and decides what happens. Does the player bounce off a wall, or pass through it? Does a bullet disappear when it hits an enemy? This system can be as simple as checking if two rectangles overlap, or as complex as simulating gravity, friction, and realistic object interactions.
The entity or object system is how you organize game objects — the player, enemies, projectiles, platforms. Each object needs properties (position, speed, health) and behavior (what happens each frame). Most engines use a class-based system where you define a Player class, an Enemy class, and so on.
Choosing a language and graphics library
C++ is what professional game studios use because it is fast and gives you direct control over memory. Unreal Engine is written in C++. But C++ is also the hardest language to learn and the easiest to crash. If you are new to programming, C++ will slow you down.
C# is a middle ground. It is faster than Python, easier than C++, and has good libraries for game development. MonoGame and FNA are C# frameworks that give you low-level control without forcing you to manage memory yourself.
Python is the easiest to learn and read, but it is slow. Pygame is the standard library for 2D games in Python. It works fine for small 2D games and learning, but you will hit performance limits quickly if you try anything complex.
JavaScript runs in a web browser, which means your game works on any computer without installation. Phaser and Babylon.js are popular frameworks. The downside is that web browsers are slower than native applications, so complex 3D games are not realistic.
For graphics, you need a library that talks to your graphics card. OpenGL is the industry standard and works on Windows, Mac, and Linux. DirectX is Windows-only and slightly faster. Vulkan is newer and more complex but offers better performance on modern hardware. Most beginners should start with OpenGL because it is well-documented and available everywhere.
2D engines are much simpler than 3D
A 2D engine draws sprites (flat images) at positions on a 2D grid. You load a PNG file, tell the engine where to draw it, and it appears on screen. Collision detection is checking if two rectangles overlap. Physics is moving objects in straight lines and bouncing them off walls.
A 3D engine loads 3D models (files that describe the shape of an object in three-dimensional space), positions them in 3D space, calculates how light bounces off them, and converts that 3D scene into a 2D image for your screen. The math is harder, the rendering is slower, and debugging is more difficult because you cannot see what is happening inside the 3D space the way you can in 2D.
If you are building an engine to learn, start with 2D. You will learn the same core concepts — the game loop, input handling, collision detection, entity management — without the added complexity of 3D math and lighting calculations. Many successful indie games are 2D: Celeste, Hollow Knight, Stardew Valley. You can make something real and fun in 2D.
The realistic scope of work
Building a minimal 2D engine that can run a simple game — a player character that moves and jumps, enemies that patrol, collision detection — takes a solo developer roughly 3 to 6 months of part-time work, depending on your programming experience. That is just the engine. The game itself — level design, art, sound, polish — is separate work on top of that.
The first month is usually the fastest: you get a window open, draw a sprite, make it move. The next two months are grinding through the systems that are not fun but are necessary: collision detection that works reliably, a physics system that feels right, an input system that is responsive. The last month is optimization and bug fixes.
Most of that time is spent on the renderer and physics. Drawing things to the screen efficiently is hard. Making collisions feel right is hard. Game design, level layout, and art are separate skills that take their own time. If you are building an engine, you are not spending that time on the game.
When to build your own versus using an existing engine
Use an existing engine if you want to make a game. Unity, Unreal, and Godot are free or low-cost, well-documented, and have large communities. They handle rendering, physics, input, and a hundred other systems you do not have to rebuild. You can focus on the game design, art, and story.
Build your own engine if you are learning programming and want a concrete project, if you need an engine optimized for a very specific type of game that existing engines do not handle well, or if you want to understand how games work at a deep level. Do not build your own engine because you think it will be faster or better than existing ones — it will not be, at least not for your first attempt.
A realistic middle ground is using a framework like Pygame, Phaser, or MonoGame. These give you the low-level control of building your own engine while handling the graphics and input for you. You still write the game loop, collision detection, and physics, but you do not have to write a graphics driver.
The tools and libraries you will need
A code editor is where you write the code. Visual Studio Code is free and works for most languages. Visual Studio (the full version, not Code) is free for C++ and has good debugging tools.
A graphics library handles drawing to the screen. OpenGL is the standard. GLFW is a small library that creates a window and handles input, which saves you from writing that yourself.
A math library handles vectors and matrices. GLM is a standard C++ library. Most languages have equivalents.
An asset pipeline is how you load images, sounds, and other files into your engine. You will write code that reads a PNG file from disk and converts it into a format your graphics card can use. This is tedious and easy to get wrong.
A debugger lets you pause your program, inspect variables, and step through code line by line. This is how you find bugs. Most code editors have a debugger built in.
Frequently Asked Questions
Do I need to know advanced math to build a game engine?
You need to understand vectors (direction and magnitude), basic trigonometry (angles and rotations), and matrix math (transformations in 3D space). For 2D, you can get by with less. There are libraries that handle the math for you, but understanding what is happening underneath makes debugging much easier.
How much faster is a game engine written in C++ than one in Python?
For a simple 2D game, the difference is not noticeable. For a complex 3D game with thousands of objects, C++ can be 10 to 100 times faster. The bottleneck is usually the graphics card, not the language, so language choice matters less than you might think for learning.
Can I use an existing engine and modify it to learn how it works?
Yes. Godot is open source and written in C++. You can read the source code and modify it. This teaches you how a real engine works without starting from zero. It is a good middle ground between using an engine as a black box and building one from scratch.
What is the difference between a game engine and a game framework?
A framework gives you libraries and tools but expects you to write the main loop and architecture. An engine provides more structure and handles more systems for you. The line is blurry. Pygame is a framework. Unity is an engine. MonoGame is somewhere in between.
Should I build a 3D engine or a 2D engine first?
Start with 2D. You will learn the same core concepts with a fraction of the complexity. Once you understand how a 2D engine works, moving to 3D is adding more math and graphics complexity on top of a foundation you already understand.