# Three.js Shaders

## Overview

Three.js shaders - GLSL, ShaderMaterial, uniforms, custom effects. Use when creating custom visual effects, modifying vertices, writing fragment shaders, or extending built-in materials.

## Quick Start

```javascript
import * as THREE from "three";

const material = new THREE.ShaderMaterial({
  uniforms: {
    time: { value: 0 },
    color: { value: new THREE.Color(0xff0000) },
  },
  vertexShader: `
    void main() {
      gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
    }
  `,
  fragmentShader: `
    uniform vec3 color;

    void main() {
      gl_FragColor = vec4(color, 1.0);
    }
  `,
});

// Update in animation loop
material.uniforms.time.value = clock.getElapsedTime();
```

## ShaderMaterial vs RawShaderMaterial

### ShaderMaterial

Three.js provides built-in uniforms and attributes.

```javascript
const material = new THREE.ShaderMaterial({
  vertexShader: `
    // Built-in uniforms available:
    // uniform mat4 modelMatrix;
    // uniform mat4 modelViewMatrix;
    // uniform mat4 projectionMatrix;
    // uniform mat4 viewMatrix;
    // uniform mat3 normalMatrix;
    // uniform vec3 cameraPosition;

    // Built-in attributes available:
    // attribute vec3 position;
    // attribute vec3 normal;
    // attribute vec2 uv;

    void main() {
      gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
    }
  `,
  fragmentShader: `
    void main() {
      gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
    }
  `,
});
```

### RawShaderMaterial

Full control - you define everything.

```javascript
const material = new THREE.RawShaderMaterial({
  uniforms: {
    projectionMatrix: { value: camera.projectionMatrix },
    modelViewMatrix: { value: new THREE.Matrix4() },
  },
  vertexShader: `
    precision highp float;

    attribute vec3 position;
    uniform mat4 projectionMatrix;
    uniform mat4 modelViewMatrix;

    void main() {
      gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
    }
  `,
  fragmentShader: `
    precision highp float;

    void main() {
      gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
    }
  `,
});
```

## Uniforms

### Uniform Types

```javascript
const material = new THREE.ShaderMaterial({
  uniforms: {
    // Numbers
    floatValue: { value: 1.5 },
    intValue: { value: 1 },

    // Vectors
    vec2Value: { value: new THREE.Vector2(1, 2) },
    vec3Value: { value: new THREE.Vector3(1, 2, 3) },
    vec4Value: { value: new THREE.Vector4(1, 2, 3, 4) },

    // Colors (converted to vec3)
    colorValue: { value: new THREE.Color(0xff0000) },

    // Matrices
    mat3Value: { value: new THREE.Matrix3() },
    mat4Value: { value: new THREE.Matrix4() },

    // Textures
    textureValue: { value: texture },
    cubeTextureValue: { value: cubeTexture },

    // Arrays
    floatArray: { value: [1.0, 2.0, 3.0] },
    vec3Array: {
      value: [new THREE.Vector3(1, 0, 0), new THREE.Vector3(0, 1, 0)],
    },
  },
});
```

### GLSL Declarations

```glsl
// In shader
uniform float floatValue;
uniform int intValue;
uniform vec2 vec2Value;
uniform vec3 vec3Value;
uniform vec3 colorValue;    // Color becomes vec3
uniform vec4 vec4Value;
uniform mat3 mat3Value;
uniform mat4 mat4Value;
uniform sampler2D textureValue;
uniform samplerCube cubeTextureValue;
uniform float floatArray[3];
uniform vec3 vec3Array[2];
```

### Updating Uniforms

```javascript
// Direct assignment
material.uniforms.time.value = clock.getElapsedTime();

// Vector/Color updates
material.uniforms.position.value.set(x, y, z);
material.uniforms.color.value.setHSL(hue, 1, 0.5);

// Matrix updates
material.uniforms.matrix.value.copy(mesh.matrixWorld);
```

## Varyings

Pass data from vertex to fragment shader.

```javascript
const material = new THREE.ShaderMaterial({
  vertexShader: `
    varying vec2 vUv;
    varying vec3 vNormal;
    varying vec3 vPosition;

    void main() {
      vUv = uv;
      vNormal = normalize(normalMatrix * normal);
      vPosition = (modelViewMatrix * vec4(position, 1.0)).xyz;

      gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
    }
  `,
  fragmentShader: `
    varying vec2 vUv;
    varying vec3 vNormal;
    varying vec3 vPosition;

    void main() {
      // Use interpolated values
      gl_FragColor = vec4(vNormal * 0.5 + 0.5, 1.0);
    }
  `,
});
```

## Common Shader Patterns

### Texture Sampling

```javascript
const material = new THREE.ShaderMaterial({
  uniforms: {
    map: { value: texture },
  },
  vertexShader: `
    varying vec2 vUv;

    void main() {
      vUv = uv;
      gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
    }
  `,
  fragmentShader: `
    uniform sampler2D map;
    varying vec2 vUv;

    void main() {
      vec4 texColor = texture2D(map, vUv);
      gl_FragColor = texColor;
    }
  `,
});
```

### Vertex Displacement

```javascript
const material = new THREE.ShaderMaterial({
  uniforms: {
    time: { value: 0 },
    amplitude: { value: 0.5 },
  },
  vertexShader: `
    uniform float time;
    uniform float amplitude;

    void main() {
      vec3 pos = position;

      // Wave displacement
      pos.z += sin(pos.x * 5.0 + time) * amplitude;
      pos.z += sin(pos.y * 5.0 + time) * amplitude;

      gl_Position = projectionMatrix * modelViewMatrix * vec4(pos, 1.0);
    }
  `,
  fragmentShader: `
    void main() {
      gl_FragColor = vec4(0.5, 0.8, 1.0, 1.0);
    }
  `,
});
```

### Fresnel Effect

```javascript
const material = new THREE.ShaderMaterial({
  vertexShader: `
    varying vec3 vNormal;
    varying vec3 vWorldPosition;

    void main() {
      vNormal = normalize(normalMatrix * normal);
      vWorldPosition = (modelMatrix * vec4(position, 1.0)).xyz;
      gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
    }
  `,
  fragmentShader: `
    varying vec3 vNormal;
    varying vec3 vWorldPosition;

    void main() {
      // cameraPosition is auto-provided by ShaderMaterial
      vec3 viewDirection = normalize(cameraPosition - vWorldPosition);
      float fresnel = pow(1.0 - dot(viewDirection, vNormal), 3.0);

      vec3 baseColor = vec3(0.0, 0.0, 0.5);
      vec3 fresnelColor = vec3(0.5, 0.8, 1.0);

      gl_FragColor = vec4(mix(baseColor, fresnelColor, fresnel), 1.0);
    }
  `,
});
```

### Noise-Based Effects

```glsl
// Simple noise function
float random(vec2 st) {
  return fract(sin(dot(st.xy, vec2(12.9898, 78.233))) * 43758.5453);
}

// Value noise
float noise(vec2 st) {
  vec2 i = floor(st);
  vec2 f = fract(st);

  float a = random(i);
  float b = random(i + vec2(1.0, 0.0));
  float c = random(i + vec2(0.0, 1.0));
  float d = random(i + vec2(1.0, 1.0));

  vec2 u = f * f * (3.0 - 2.0 * f);

  return mix(a, b, u.x) + (c - a) * u.y * (1.0 - u.x) + (d - b) * u.x * u.y;
}

// Usage
float n = noise(vUv * 10.0 + time);
```

### Gradient

```glsl
// Linear gradient
vec3 color = mix(colorA, colorB, vUv.y);

// Radial gradient
float dist = distance(vUv, vec2(0.5));
vec3 color = mix(centerColor, edgeColor, dist * 2.0);

// Smooth gradient with custom curve
float t = smoothstep(0.0, 1.0, vUv.y);
vec3 color = mix(colorA, colorB, t);
```

### Rim Lighting

```javascript
const material = new THREE.ShaderMaterial({
  vertexShader: `
    varying vec3 vNormal;
    varying vec3 vViewPosition;

    void main() {
      vNormal = normalize(normalMatrix * normal);
      vec4 mvPosition = modelViewMatrix * vec4(position, 1.0);
      vViewPosition = mvPosition.xyz;
      gl_Position = projectionMatrix * mvPosition;
    }
  `,
  fragmentShader: `
    varying vec3 vNormal;
    varying vec3 vViewPosition;

    void main() {
      vec3 viewDir = normalize(-vViewPosition);
      float rim = 1.0 - max(0.0, dot(viewDir, vNormal));
      rim = pow(rim, 4.0);

      vec3 baseColor = vec3(0.2, 0.2, 0.8);
      vec3 rimColor = vec3(1.0, 0.5, 0.0);

      gl_FragColor = vec4(baseColor + rimColor * rim, 1.0);
    }
  `,
});
```

### Dissolve Effect

```glsl
uniform float progress;
uniform sampler2D noiseMap;

void main() {
  float noise = texture2D(noiseMap, vUv).r;

  if (noise < progress) {
    discard;
  }

  // Edge glow
  float edge = smoothstep(progress, progress + 0.1, noise);
  vec3 edgeColor = vec3(1.0, 0.5, 0.0);
  vec3 baseColor = vec3(0.5);

  gl_FragColor = vec4(mix(edgeColor, baseColor, edge), 1.0);
}
```

## Extending Built-in Materials

### onBeforeCompile

Modify existing material shaders.

```javascript
const material = new THREE.MeshStandardMaterial({ color: 0x00ff00 });

material.onBeforeCompile = (shader) => {
  // Add custom uniform
  shader.uniforms.time = { value: 0 };

  // Store reference for updates
  material.userData.shader = shader;

  // Modify vertex shader
  shader.vertexShader = shader.vertexShader.replace(
    "#include <begin_vertex>",
    `
    #include <begin_vertex>
    transformed.y += sin(position.x * 10.0 + time) * 0.1;
    `,
  );

  // Add uniform declaration
  shader.vertexShader = "uniform float time;\n" + shader.vertexShader;
};

// Update in animation loop
if (material.userData.shader) {
  material.userData.shader.uniforms.time.value = clock.getElapsedTime();
}
```

### Common Injection Points

```javascript
// Vertex shader chunks
"#include <begin_vertex>"; // After position is calculated
"#include <project_vertex>"; // After gl_Position
"#include <beginnormal_vertex>"; // Normal calculation start

// Fragment shader chunks
"#include <color_fragment>"; // After diffuse color
"#include <output_fragment>"; // Final output
"#include <fog_fragment>"; // After fog applied
```

## GLSL Built-in Functions

### Math Functions

```glsl
// Basic
abs(x), sign(x), floor(x), ceil(x), fract(x)
mod(x, y), min(x, y), max(x, y), clamp(x, min, max)
mix(a, b, t), step(edge, x), smoothstep(edge0, edge1, x)

// Trigonometry
sin(x), cos(x), tan(x)
asin(x), acos(x), atan(y, x), atan(x)
radians(degrees), degrees(radians)

// Exponential
pow(x, y), exp(x), log(x), exp2(x), log2(x)
sqrt(x), inversesqrt(x)
```

### Vector Functions

```glsl
// Length and distance
length(v), distance(p0, p1), dot(x, y), cross(x, y)

// Normalization
normalize(v)

// Reflection and refraction
reflect(I, N), refract(I, N, eta)

// Component-wise
lessThan(x, y), lessThanEqual(x, y)
greaterThan(x, y), greaterThanEqual(x, y)
equal(x, y), notEqual(x, y)
any(bvec), all(bvec)
```

### Texture Functions

```glsl
// GLSL 1.0 (default) - use texture2D/textureCube
texture2D(sampler, coord)
texture2D(sampler, coord, bias)
textureCube(sampler, coord)

// GLSL 3.0 (glslVersion: THREE.GLSL3) - use texture()
// texture(sampler, coord) replaces texture2D/textureCube
// Also use: out vec4 fragColor instead of gl_FragColor

// Texture size (GLSL 1.30+)
textureSize(sampler, lod)
```

## Common Material Properties

```javascript
const material = new THREE.ShaderMaterial({
  uniforms: {
    /* ... */
  },
  vertexShader: "/* ... */",
  fragmentShader: "/* ... */",

  // Rendering
  transparent: true,
  opacity: 1.0,
  side: THREE.DoubleSide,
  depthTest: true,
  depthWrite: true,

  // Blending
  blending: THREE.NormalBlending,
  // AdditiveBlending, SubtractiveBlending, MultiplyBlending

  // Wireframe
  wireframe: false,
  wireframeLinewidth: 1, // Note: >1 has no effect on most platforms (WebGL limitation)

  // Extensions
  extensions: {
    derivatives: true, // For fwidth, dFdx, dFdy
    fragDepth: true, // gl_FragDepth
    drawBuffers: true, // Multiple render targets
    shaderTextureLOD: true, // texture2DLod
  },

  // GLSL version
  glslVersion: THREE.GLSL3, // For WebGL2 features
});
```

## Shader Includes

### Using Three.js Shader Chunks

```javascript
import { ShaderChunk } from "three";

const fragmentShader = `
  ${ShaderChunk.common}
  ${ShaderChunk.packing}

  uniform sampler2D depthTexture;
  varying vec2 vUv;

  void main() {
    float depth = texture2D(depthTexture, vUv).r;
    float linearDepth = perspectiveDepthToViewZ(depth, 0.1, 1000.0);
    gl_FragColor = vec4(vec3(-linearDepth / 100.0), 1.0);
  }
`;
```

### External Shader Files

```javascript
// With vite/webpack
import vertexShader from "./shaders/vertex.glsl";
import fragmentShader from "./shaders/fragment.glsl";

const material = new THREE.ShaderMaterial({
  vertexShader,
  fragmentShader,
});
```

## Instanced Shaders

```javascript
// Instanced attribute
const offsets = new Float32Array(instanceCount * 3);
// Fill offsets...
geometry.setAttribute("offset", new THREE.InstancedBufferAttribute(offsets, 3));

const material = new THREE.ShaderMaterial({
  vertexShader: `
    attribute vec3 offset;

    void main() {
      vec3 pos = position + offset;
      gl_Position = projectionMatrix * modelViewMatrix * vec4(pos, 1.0);
    }
  `,
  fragmentShader: `
    void main() {
      gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
    }
  `,
});
```

## Debugging Shaders

```javascript
// Check for compile errors
material.onBeforeCompile = (shader) => {
  console.log("Vertex Shader:", shader.vertexShader);
  console.log("Fragment Shader:", shader.fragmentShader);
};

// Visual debugging
fragmentShader: `
  void main() {
    // Debug UV
    gl_FragColor = vec4(vUv, 0.0, 1.0);

    // Debug normals
    gl_FragColor = vec4(vNormal * 0.5 + 0.5, 1.0);

    // Debug position
    gl_FragColor = vec4(vPosition * 0.1 + 0.5, 1.0);
  }
`;

// Check WebGL errors
renderer.debug.checkShaderErrors = true;
```

## Performance Tips

1. **Minimize uniforms**: Group related values into vectors
2. **Avoid conditionals**: Use mix/step instead of if/else
3. **Precalculate**: Move calculations to JS when possible
4. **Use textures**: For complex functions, use lookup tables
5. **Limit overdraw**: Avoid transparent objects when possible

```glsl
// Instead of:
if (value > 0.5) {
  color = colorA;
} else {
  color = colorB;
}

// Use:
color = mix(colorB, colorA, step(0.5, value));
```

## See Also

- `threejs-materials` - Built-in material types
- `threejs-postprocessing` - Full-screen shader effects
- `threejs-textures` - Texture sampling in shaders