My 3D WebGL JS Engine: 5 Brutal Lessons for 2025

Introduction: The Allure and Agony of a Custom Engine

Every ambitious JavaScript developer with a penchant for visuals has had the thought: "I'll build my own 3D engine." It’s a siren song, promising ultimate control, deep learning, and a masterpiece of personal engineering. I answered that call. For the past few years, I’ve been wrestling with vertices, matrices, and the notoriously verbose WebGL API to create my own engine from scratch. It's been an odyssey of triumph and frustration.

Now, looking towards 2025, the landscape is shifting. WebGPU is on the horizon, performance expectations are higher than ever, and the lessons learned feel more critical. Forget the gentle tutorials. These are the five brutal, hard-won truths I wish I'd known before writing a single line of code. This is the stuff that separates a cool tech demo from a robust, performant engine.

Lesson 1: The Premature Abstraction Trap

When you start, the temptation is to build beautiful, high-level abstractions immediately. You envision a clean API: scene.add(new Mesh(geometry, material)). It looks like Three.js, it feels professional. This is a trap.

WebGL is, at its core, a giant, unforgiving state machine. You bind a buffer, you set a uniform, you enable an attribute, you make a draw call. If you abstract this away before you intimately understand the cost and consequence of every `gl.bindBuffer()` and `gl.uniformMatrix4fv()`, you will architect yourself into a performance corner. Your elegant `material.setColor()` method might be thrashing the GPU by unnecessarily switching shader programs or re-binding uniforms every frame for thousands of objects.

The Brutal Reality

Early on, your render loop should be ugly. It should be explicit. You should feel the pain of managing state. Why? Because this pain teaches you how to batch. You'll quickly realize that sorting your objects by shader program, then by material, then by geometry is the key to minimizing state changes and maximizing performance. Only after you've built an efficient, batch-oriented renderer should you begin to layer on the clean, user-facing abstractions.

• Don't: Create a `Mesh` class that holds its own VAO, shader, and material, and renders itself in a `mesh.render()` call.
• Do: Create a renderer that takes lists of objects, sorts them into batches, and then iterates through those batches, binding the necessary state only when it changes.

Lesson 2: WebGPU's Shadow is a Harbinger, Not a Ghost

For years, WebGL has been the only game in town. It's easy to think, "I'll just stick with what's stable and has universal support." In 2025, this is a strategic error. WebGPU isn't just "the next WebGL"; it's a fundamental paradigm shift modeled after modern graphics APIs like Vulkan, Metal, and DirectX 12.

Ignoring WebGPU means you are building on a foundation that is philosophically obsolete. The core difference is moving from WebGL's retained state machine to WebGPU's command buffer and pipeline state object (PSO) model. This shift gives developers significantly more control, reduces driver overhead, and enables true multi-threaded rendering capabilities via web workers.

Even if you decide to build a WebGL-first engine, your architecture should be designed with a WebGPU backend in mind. This means separating your scene logic from the low-level rendering API. Create a rendering interface that can be implemented by both a `WebGLRenderer` and a `WebGPURenderer`. Future-proofing is no longer optional.

WebGL vs. WebGPU: A 2025 Perspective

Lesson 3: Garbage Collection is the Silent Frame Killer

JavaScript is a garbage-collected language, which is a blessing for general web development but a curse for real-time graphics. A "stop-the-world" garbage collection (GC) pause that lasts just 10ms will drop your frame rate from a buttery 60 FPS (16.67ms/frame) to an effective 37 FPS. Users feel this as a stutter or jank.

The number one source of GC pressure in a 3D engine? Creating new objects in the main render loop. Every `new Vector3()`, `new Matrix4()`, or temporary object you create to pass data around is a ticking time bomb.

Starving the Garbage Collector

The solution is aggressive memory management. This feels unnatural in JavaScript, but it's mandatory.

• Object Pooling: Pre-allocate a pool of objects (like vectors or matrices) at initialization. When you need one, you `get()` it from the pool. When you're done, you `release()` it back. No `new` keywords in the render loop.
• Cache-Friendly Data: Instead of a scene graph of thousands of `Node` objects, consider an Entity Component System (ECS). Data for a given system (e.g., all positions, all velocities) is stored in contiguous arrays, which is much friendlier to the CPU cache and avoids object-hopping.
• Avoid Anonymous Functions: Defining anonymous functions or closures inside your render loop (`() => {...}`) can create new objects and add to GC pressure. Define your functions once and reuse them.

Lesson 4: The Monolithic "Uber-Shader" Fallacy

Your first instinct with shaders might be to write one giant, flexible shader program. It'll have `if` statements for every possible feature: `if (has_normal_map) { ... } else if (has_emissive_map) { ... }`. This is a performance disaster.

Branching (`if` statements) inside a shader can be slow, especially if threads in the same GPU warp take different paths (thread divergence). Furthermore, a monolithic shader becomes a nightmare to maintain and debug. A much better approach is to use shader permutations.

Modular Shaders with Preprocessors

Break your shader logic into smaller, reusable chunks. Then, at compile time (when the user's material is initialized), generate the final GLSL code by stitching these chunks together using preprocessor directives like `#define` and `#ifdef`.

For example, instead of `if (use_lighting)`, you compile a version of the shader that either has the lighting code or doesn't. Your engine might end up compiling dozens of slightly different shader programs, but each one is highly optimized for its specific task. This process, often called "ubershader with defines," gives you the best of both worlds: maintainability and runtime performance.

Lesson 5: Your Math Library Won't Save You

It's easy to grab `gl-matrix` or a similar library and assume the math is a "solved problem." While these libraries are essential and well-optimized, they are tools, not a substitute for understanding.

When a model is rotated incorrectly, when your camera gimbal locks, or when an object scales from the wrong pivot point, you can't debug it by looking at the library's source code. You need to understand the why behind the operations.

You must have a working knowledge of:

• Vector Operations: Dot products (for lighting, projections), cross products (for normals).
• Matrix Transformations: The specific order of operations (Scale -> Rotate -> Translate) and how they combine in a single transformation matrix.
• Quaternions: Why they are superior to Euler angles for representing rotation and avoiding gimbal lock. You don't need to derive them from first principles, but you must know how to use them for interpolation (slerp) and composition.
• Projection vs. View Matrix: The distinct roles of the camera's position/orientation (View) and its lens properties (Projection).

Without this fundamental knowledge, you're not an engine developer; you're just a user of a math library, and you'll be helpless when faced with the inevitable 3D math bugs.

Conclusion: Was It Worth It?

Absolutely. Despite the brutal lessons and moments of hair-pulling frustration, building a WebGL engine from the ground up has been the single most rewarding educational experience of my career. It forces you to confront the metal, to think about performance at a granular level, and to appreciate the incredible engineering that goes into frameworks like Three.js and Babylon.js.

My advice for anyone embarking on this journey in 2025 is to embrace the difficulty. Start low-level, keep an eye on WebGPU, be ruthless about memory, build modular shaders, and do your math homework. The engine you build might not power the next blockbuster game, but the skills you gain will be invaluable.