How to build a game engine: What most people get wrong

So, you want to learn how to build a game engine. Honestly? It’s a bit of a nightmare. But it is also probably the most rewarding thing a programmer can do. Most people think they can just sit down, open up a C++ file, and suddenly they're the next John Carmack. It doesn't work like that. If you go into this expecting to make the next Unreal Engine 5 in a weekend, you're going to burn out before you even get a triangle on the screen.

Building an engine is less about "making games" and more about building a laboratory where games could happen. You’re handling memory, talking to the GPU, and wrestling with linear algebra. It's deep. It's messy.

Why even bother when Unity and Godot exist?

Let’s be real for a second. If you just want to ship a game, do not build an engine. Use Godot. Use Unreal. Use Unity. You’ll save yourself three years of gray hair. But if you want to understand how software actually touches hardware, that’s why you do this. You do it because you want total control. You do it because you're tired of "black box" engines where a random bug in the source code ruins your performance and you can’t fix it.

Casey Muratori, the guy behind Handmade Hero, has spent years showing that "modern" engines are often bloated. When you build your own, you realize how fast things can actually be. You're not fighting a general-purpose beast; you’re building a specialized tool. It’s the difference between buying a mass-produced sedan and machining your own F1 car from scratch.

The scary first step: Choosing your stack

Don't overthink this, but don't underthink it either. Most purists will tell you C++ is the only way. They have a point. Most of the industry—we're talking id Tech, Frostbite, Unreal—is built on C++. Why? Because you need manual memory management. You need to know exactly where every byte lives.

But hey, if you hate C++, Rust is becoming a massive deal. The Bevy engine is proving that data-driven design in Rust is actually kind of incredible. It handles memory safety for you without a garbage collector, which is a huge win. Some people use C# with Silk.NET or OpenTK, but you’ll eventually hit the "Garbage Collection stutter" wall if you aren't careful.

Pick one:

• C++: The industry standard. Hard mode.
• Rust: The modern challenger. Great for ECS (Entity Component Systems).
• C: For the true masochists who want to write their own hash maps.

Graphics APIs: Picking your poison

You can't just tell a computer "draw a dog." You have to talk to the GPU. This is where how to build a game engine gets really technical. You have three main paths here.

OpenGL is the old reliable. It’s easier to learn, but it’s kind of a "legacy" vibe now. DirectX 11 is similar—great documentation, very stable. Then you have the modern "low-level" APIs: Vulkan and DirectX 12.

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Warning: Vulkan is brutal. To just clear the screen to a solid color in Vulkan, you might need 1,000 lines of code. It’s verbose. It’s intimidating. But it gives you insane power over the hardware. If this is your first engine, seriously, just start with OpenGL 4.5 or DX11. Don't drown in Vulkan boilerplate before you've even moved a sprite.

The Game Loop: The heartbeat of your engine

Every engine has a heart. It’s basically a while loop that runs until you hit the "X" button.

while (isRunning) {
    processInput();
    updatePhysics();
    renderFrame();
}

Sounds simple? It isn’t.

What happens if the game runs at 500 FPS on your machine but 30 FPS on your friend’s laptop? If your physics are tied to the frame rate, the character will move like a teleporting god on your PC and a snail on theirs. You need a "Fixed Timestep." You’ve probably heard of delta time. It’s the secret sauce. You calculate how long the last frame took and scale everything by that.

Memory management is where the pros live

If you use new or malloc every time you create a bullet in a shmup, your game will lag. Period. Real game engines use Memory Pool Allocators.

Basically, you grab a giant chunk of RAM at the start and say, "This is mine now." Then you manage it yourself. You carve out little pieces for your entities and reclaim them when they're done. This avoids "heap fragmentation." It’s basically like being an accountant for your computer’s brain. If you aren't thinking about cache hits and data locality, your engine is just a slow wrapper around a library.

Data-Oriented Design (DOD)

This is a huge shift in thinking. Old engines used Object-Oriented Programming (OOP). You’d have a Player class, and it would inherit from Entity, and so on.

Modern experts like Mike Acton (formerly of Insomniac Games) argue that this is terrible for performance. Instead, we use Entity Component Systems (ECS). You keep all your "Position" data in one big, flat array. Then you keep all your "Velocity" data in another. The CPU loves this. It can pre-fetch that data because it’s all lined up in a row. It's called "cache-friendly code." It’s the difference between a game that handles 100 enemies and one that handles 10,000.

The Architecture: Layers on layers

A good engine is like an onion.

1. Platform Layer: This handles Windows, Linux, or Mac. It opens the window and gets the input. You want this isolated so you can port the game later without rewriting the whole thing.
2. Renderer: This talks to the GPU. It shouldn't care what the game logic is doing. It just takes a list of meshes and textures and pushes them to the screen.
3. Physics/Collision: Are two boxes touching? This is mostly just heavy math. You can write your own SAT (Separating Axis Theorem) or integrate something like PhysX or Jolt.
4. Game Logic: This is where the actual "game" lives.

What about the math?

Yeah, there's no way around it. You need linear algebra. Vectors, matrices, quaternions—they are your bread and butter.

If you don't know why you'd use a Dot Product versus a Cross Product, go hit the books. A Dot Product tells you if an enemy is facing you. A Cross Product gives you the vector sticking out of a surface. Quaternions are used for rotation because Euler angles (pitch, yaw, roll) eventually hit "Gimbal Lock," where two axes align and you lose a degree of freedom. It’s a mess. Use quaternions. Don't try to understand how they work internally yet—just learn how to use them.

Handling Assets: The Pipeline

How do you get a 3D model from Blender into your engine? You don't just "load the .blend file." You need an asset pipeline.

Most engines use a format like glTF or FBX. You'll likely write a tool that "cooks" these assets into a custom binary format that your engine can read instantly. Speed is everything. You don't want your engine parsing text files while the player is waiting on a loading screen.

Common Pitfalls to Avoid

• Feature Creep: Don't try to build a level editor, a physics engine, a sound engine, and a scripting language all at once. Start with a window. Then a triangle. Then a moving square.
• Writing your own Physics: Unless you're a math genius, writing a robust 3D physics engine is a trap. Use an existing library like Bullet or PhysX for your first few tries.
• The "Perfect" Architecture: You will rewrite your engine four times. Accept it. Your first architecture will be garbage. Your second will be slightly better. By the third, you’ll start to see the patterns.

Putting it all together: The "First Triangle" milestone

In the graphics world, the "Hello World" is a colored triangle on a black background. It sounds pathetic, but when you see that triangle, it means your platform layer is working, your shaders are compiling, your GPU buffers are set up, and your render loop is humming.

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From there, you move to textures. Then to 3D models. Then to lighting. It’s a ladder. Each rung is a struggle, but each rung makes you a better engineer.

Actionable Steps for Your Engine Journey

If you are serious about how to build a game engine, here is your immediate roadmap. Don't skip steps.

1. Learn C++ or Rust deeply. Understand pointers, references, and memory layout. If you don't know what a "Pointer to a Pointer" is, you aren't ready.
2. Choose a library for windowing. Use GLFW or SDL2. They handle the annoying stuff like creating a window and getting keyboard input so you can focus on the engine.
3. Get a triangle on the screen using OpenGL 4.5. It's modern enough to be relevant but simple enough to not kill your motivation.
4. Implement a basic Math library. Write your own Vector3 and Matrix4 classes. It’s the best way to actually learn the math.
5. Build a simple Sprite Renderer. Make it so you can draw 1,000 sprites without the frame rate dropping.
6. Read "Game Programming Patterns" by Robert Nystrom. It’s the bible for engine architecture.
7. Check out the "Handmade Hero" series. Even if you don't follow it exactly, seeing how a professional builds everything from scratch is eye-opening.
8. Stop reading and start coding. You can spend forever in "tutorial hell." The best engine is the one you actually wrote, even if the code is ugly.

Building a game engine is a marathon. It’s about the journey of understanding the machine. Don't worry about the finish line—just focus on the next frame.