Building a 3D Renderer from Scratch

I’ve always been curious about what happens inside game engines when they render a 3D model. You know that feeling when you use Unity or Unreal without understanding what’s actually happening on the GPU? That’s exactly why I decided to build my own 3D renderer from scratch using C++ and OpenGL.

No engines. No magic. Just raw graphics programming.

Why Build a Renderer?

Here’s the thing - I’ve used game engines for years, but I never really understood how a 3D model actually gets converted into pixels on my screen. How do textures get applied? How does the camera move through space?

So I thought, why not build one myself? The goal wasn’t to compete with Unity or Unreal. It was to understand the fundamentals - to demystify what’s actually happening when you call Draw() on a mesh.

What I Built

The result is a real-time 3D model renderer that can:

• Load 3D models in OBJ format (using Assimp)
• Apply textures - diffuse, specular, and normal maps
• Compile custom GLSL shaders
• Move around with WASD + mouse look (first-person camera)
• Handle the complete rendering pipeline

The renderer runs at 60 FPS and shows a textured 3D model. That’s it. But the journey to get there taught me more about graphics programming than years of using game engines.

The Core Concepts

Let me walk you through what I learned along the way.

How a 3D Model Gets Rendered

It starts with vertices - points in 3D space that define a shape. These vertices get processed through what’s called the rendering pipeline:

1. Model transformation - Move vertices from model space to world space
2. View transformation - Move vertices to camera space
3. Projection transformation - Apply perspective (things get smaller as they get farther)
4. Rasterization - Convert those 3D points into 2D pixels on your screen

The magic happens in the shaders - little programs that run on your GPU for each vertex and each pixel.

The Code

Here’s how the main render loop looks:

while (!glfwWindowShouldClose(window)) {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    
    // Calculate matrices
    glm::mat4 view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp);
    glm::mat4 projection = glm::perspective(45.f, ratio, 0.1f, 100.f);
    
    // Upload to GPU
    shader->setMat4("view", view);
    shader->setMat4("projection", projection);
    
    // Draw!
    model->Draw(*shader);
    
    glfwSwapBuffers(window);
}

The key insight? Every frame, we’re recalculating matrices based on camera position, then uploading them to the GPU as “uniform variables” - values that stay the same for all vertices in that frame.

The Camera System

First-person camera control is actually pretty interesting math. You have:

• Yaw - rotation left/right
• Pitch - rotation up/down

And you convert those angles into a direction vector using spherical coordinates:

front.x = cos(yaw) * cos(pitch);
front.y = sin(pitch);  
front.z = sin(yaw) * cos(pitch);

Simple, but it works perfectly for WASD movement.

Key Takeaways

Building this renderer taught me several important things:

1. OpenGL is just an API - It’s not magic, it’s a standardized way to talk to your GPU. You give it data, it gives you pixels.

2. The rendering pipeline is everywhere - Model→View→Projection isn’t just for games. It’s the foundation of all 3D graphics.

3. Shaders are powerful - Those little GLSL programs are where all the visual magic happens.

4. Game engines hide a lot - Unity and Unreal do incredible things, but they hide all this complexity. There’s nothing wrong with that, but understanding it gives you more control.

What Would I Do Differently?

If I were to build this again, I’d:

• Add Blinn-Phong lighting earlier (makes models look much better)
• Use a proper scene graph instead of single-model rendering
• Add shadow mapping (still haven’t tackled that!)

Final Thoughts

This project took about 2 weeks of evenings to complete. It’s not perfect, but it works - and more importantly, I now understand what’s happening when I use any 3D engine.

If you’re curious about graphics programming, I’d highly recommend building something similar. You don’t need to write a full engine. Just start with rendering a single triangle, then add textures, then add a camera. Each step teaches you something new.

The code is available if you want to take a look. Happy rendering!