大家好，这里是 CSS兼WebGL 魔法使——alphardex。

本文我们将用three.js来实现风暴云特效，以下是最终实现的效果图

让我们开始吧！

为了实现这个特效，我们先简要了解一下FBM吧

FBM中文意思是分形布朗运动，另一种称呼是分形噪声（说明它也属于噪声的一种）。它常用于描绘各种自然之中的形状（山脉、云层、河流等）。概念是在一个for循环内叠加几次噪声（往往是6次，相当于一个八度octave），并在叠加的同时升高频率，降低振幅。以下是一个简易的fbm实现的噪声图案

#pragma glslify:centerUv=require(../modules/centerUv)
#pragma glslify:snoise=require(glsl-noise/simplex/2d)

uniform float uTime;
uniform vec2 uMouse;
uniform vec2 uResolution;

varying vec2 vUv;
varying vec3 vPosition;

#define OCTAVES 6

float fbm(vec2 p){
    float sum=0.;
    float amp=.5;
    for(int i=0;i<OCTAVES;i++){
        float noise=snoise(p)*amp;
        sum+=noise;
        p*=2.;
        amp*=.5;
    }
    return sum;
}

void main(){
    vec2 cUv=centerUv(vUv,uResolution);
    vec2 p=cUv*3.;
    float noise=fbm(p);
    vec3 color=vec3(noise);
    gl_FragColor=vec4(color,1.);
}
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笔者的three.js模板：点击右下角的fork即可复制一份

为了将着色器模块化，需要用到glslify

同时也需要安装如下的npm包：glsl-noise

创建一张铺满屏幕的平面，作为画布

class CloudySky extends Base {
  clock!: THREE.Clock;
  cloudySkyMaterial!: THREE.ShaderMaterial;
  params!: any;
  constructor(sel: string, debug: boolean) {
    super(sel, debug);
    this.clock = new THREE.Clock();
    this.cameraPosition = new THREE.Vector3(0, 0, 1);
    this.params = {
      velocity: 5,
      skyColor: "#324678",
    };
  }
  // 初始化
  init() {
    this.createScene();
    this.createOrthographicCamera();
    this.createRenderer();
    this.createCloudySkyMaterial();
    this.createPlane();
    this.createLight();
    this.trackMousePos();
    this.addListeners();
    this.setLoop();
  }
  // 创建材质
  createCloudySkyMaterial() {
    const cloudySkyMaterial = new THREE.ShaderMaterial({
      vertexShader: cloudySkyVertexShader,
      fragmentShader: cloudySkyFragmentShader,
      side: THREE.DoubleSide,
      uniforms: {
        uTime: {
          value: 0,
        },
        uMouse: {
          value: new THREE.Vector2(0, 0),
        },
        uResolution: {
          value: new THREE.Vector2(window.innerWidth, window.innerHeight),
        },
        uVelocity: {
          value: this.params.velocity,
        },
        uSkyColor: {
          value: new THREE.Color(this.params.skyColor),
        },
      },
    });
    this.cloudySkyMaterial = cloudySkyMaterial;
    this.shaderMaterial = cloudySkyMaterial;
  }
  // 创建平面
  createPlane() {
    const geometry = new THREE.PlaneBufferGeometry(2, 2, 100, 100);
    const material = this.cloudySkyMaterial;
    this.createMesh({
      geometry,
      material,
    });
  }
  // 动画
  update() {
    const elapsedTime = this.clock.getElapsedTime();
    const mousePos = this.mousePos;
    if (this.cloudySkyMaterial) {
      this.cloudySkyMaterial.uniforms.uTime.value = elapsedTime;
      this.cloudySkyMaterial.uniforms.uMouse.value = mousePos;
    }
  }
}
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顶点着色器直接用默认的就可以了

片元着色器

思路也是基本的fbm写法，只是在外层连续应用了16次（这样特别烧显卡，但是实现的效果很炫酷，帅就完事了），并且加上了随着时间的x轴位移

#pragma glslify:centerUv=require(../modules/centerUv)
#pragma glslify:snoise=require(glsl-noise/simplex/3d)
#pragma glslify:invert=require(../modules/invert)

uniform float uTime;
uniform vec2 uMouse;
uniform vec2 uResolution;
uniform float uVelocity;
uniform vec3 uSkyColor;

varying vec2 vUv;
varying vec3 vPosition;

#define OCTAVES 6

float fbm(vec3 p){
    float sum=0.;
    float amp=1.;
    for(int i=0;i<OCTAVES;i++){
        vec3 r=p/amp*.2;
        float noise=snoise(r)*amp;
        sum+=noise;
        amp*=.5;
    }
    return sum;
}

void main(){
    vec2 cUv=centerUv(vUv,uResolution);
    vec2 p=cUv;
    vec3 ray=vec3(0.);
    vec3 eye=normalize(vec3(p,2.));
    float displacement=uTime*uVelocity;
    ray.x+=displacement;
    float cloud=0.;
    float sum=0.;
    for(int i=0;i<16;i++){
        ray+=eye;
        sum=fbm(ray);
        sum=clamp(sum,0.,1.)*.1;
        cloud+=sum;
    }
    vec3 color=uSkyColor+cloud;
    gl_FragColor=vec4(color,1.);
}
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最终效果如下

Cloudy Sky