WebGL Fundamentals — Shaders and GLSL Explained

Understanding webgl fundamentals is the foundation of this guide. Below we break it down step by step so you can act with confidence.

Three.js hides WebGL behind a friendly API, but understanding the underlying pipeline makes you a far more capable graphics programmer. You will know why things are slow, how to write custom effects, and how to optimize rendering.

This lesson teaches the WebGL rendering pipeline, how shaders work, the GLSL language, and how to write your first custom shaders.

Webgl Fundamentals: The WebGL rendering pipeline

When Three.js calls renderer.render(), this is what happens on the GPU:

JavaScript sends vertex data (positions, normals, UVs) to GPU buffers
The vertex shader runs once per vertex — transforms 3D positions to 2D screen coordinates
The GPU rasterizes triangles — determines which pixels each triangle covers
The fragment shader runs once per pixel — calculates the final color
Depth testing, blending, and the framebuffer produce the final image

Shaders are programs that run on the GPU in parallel. A vertex shader processes millions of vertices simultaneously, and the fragment shader colors millions of pixels in parallel. This massive parallelism is why GPUs are so fast at graphics.

Vertex and fragment shaders in GLSL

GLSL (OpenGL Shading Language) is a C-like language for writing shaders:

🔬 Demo: Minimal WebGL shader pair

// Vertex shader — runs per vertex
attribute vec3 aPosition;
uniform mat4 uModelViewProjection;
varying vec2 vUv;

void main() {
  vUv = aPosition.xy * 0.5 + 0.5;
  gl_Position = uModelViewProjection * vec4(aPosition, 1.0);
}

// Fragment shader — runs per pixel
precision mediump float;
varying vec2 vUv;
uniform float uTime;

void main() {
  // Animated gradient
  float r = sin(vUv.x * 6.28 + uTime) * 0.5 + 0.5;
  float g = sin(vUv.y * 6.28 + uTime * 0.7) * 0.5 + 0.5;
  float b = 0.5;
  gl_FragColor = vec4(r, g, b, 1.0);
}

Custom shaders in Three.js

Three.js lets you write custom shaders via ShaderMaterial. The uniforms, attributes, and varyings bridge JavaScript and GLSL:

🔬 Demo: ShaderMaterial with animated effect

const customMaterial = new THREE.ShaderMaterial({
  uniforms: {
    uTime: { value: 0 },
    uColor1: { value: new THREE.Color(0xe94560) },
    uColor2: { value: new THREE.Color(0x533483) }
  },
  vertexShader: `
    varying vec2 vUv;
    void main() {
      vUv = uv;
      gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
    }
  `,
  fragmentShader: `
    precision mediump float;
    varying vec2 vUv;
    uniform float uTime;
    uniform vec3 uColor1;
    uniform vec3 uColor2;
    void main() {
      float wave = sin(vUv.x * 10.0 + uTime * 3.0) * 0.5 + 0.5;
      vec3 color = mix(uColor1, uColor2, wave);
      gl_FragColor = vec4(color, 1.0);
    }
  `
});

// In animate loop:
customMaterial.uniforms.uTime.value = clock.getElapsedTime();

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Common shader effects for games

Once you understand shaders, you can create effects that would be impossible in JavaScript alone:

🔬 Demo: Dissolve effect shader

// Fragment shader — dissolve effect
precision mediump float;
varying vec2 vUv;
uniform float uProgress; // 0.0 = solid, 1.0 = fully dissolved
uniform vec3 uColor;
uniform vec3 uEdgeColor;

// Simple noise function
float hash(vec2 p) {
  return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453);
}

void main() {
  float noise = hash(vUv * 20.0);
  if (noise < uProgress) discard;

  // Glow at dissolve edge
  float edge = smoothstep(uProgress - 0.05, uProgress, noise);
  vec3 color = mix(uEdgeColor, uColor, edge);
  gl_FragColor = vec4(color, 1.0);
}

When evaluating webgl fundamentals, start with the fundamentals: what problem it solves, who it serves, and how it compares to the alternatives buyers consider first.

Start with the fundamentals. Define who you are serving, the single outcome you want, and the budget you are comfortable committing before you compare any options.

A practical rule is to favour clarity over cleverness. The choice that is easiest to understand, spell, remember and act on tends to win over the long run.

Context changes the answer. What is optimal for a fast-moving startup is rarely optimal for an established brand, so weigh your own stage, market and ambitions.

Avoid the common mistakes: rushing the decision, copying competitors blindly, and ignoring the total cost of ownership beyond the very first year of use.

Think in terms of trade-offs rather than a single perfect answer. Every option trades memorability, cost, reach and flexibility in a slightly different mix.

Document your reasoning. Writing down why you chose one path makes it far easier to revisit the decision later and to explain it to partners and investors.

Test with real people. A quick check with a handful of your actual customers will surface problems that no amount of internal debate ever reveals.

Plan for growth. The option that fits today should still make sense when your audience, catalogue or team is several times larger than it is right now.

Finally, revisit the decision periodically. Markets, tools and best practices move quickly, and a choice that was ideal last year may deserve a fresh look today.