本文我们将用 Python 来画一棵圣诞树，效果如下图所示，先睹为快。（附源码，可直接复制）

下面展开来看一下主要代码实现。

1.turtle库

turtle库是Python语言中一个很流行的绘制图像的函数库，想象一个小乌龟，在一个横轴为x、纵轴为y的坐标系原点，(0,0)位置开始，它根据一组函数指令的控制，在这个平面坐标系中移动，从而在它爬行的路径上绘制了图形。

2.python函数的定义规则

（1）以 def 开头，后接定义函数的名称和圆括号（），以冒号结尾

（2）圆括号（）可为空，也可以传入参数

（3）定义函数的内容，与def有缩进关系

（4）调用自定义的函数的基本格式为：定义函数的名称（）；若圆括号（）为空，调用时，也为空，若若圆括号（）不为空，调用时需传入参数

(5)return [表达式] 结束函数，选择性地返回一个值给调用方。不带表达式的return相当于返回 None。

3.引入库

4.定义画彩灯函数

5.定义画圣诞树的函数

6.定义树下面小装饰的函数

7.定义一个画雪花的函数 

8.画五角星

9.写文字

10.全部源代码

以下为代码，可直接复制

 圣诞树

  * 

  {

   box-sizing: border-box;

  }

  body 

  {

   margin: 0;

   height: 100vh;

   overflow: hidden;

   display: flex;

   align-items: center;

   justify-content: center;

   background: #161616;

   color: #c5a880;

   font-family: sans-serif;

  }

  label

  {

   display: inline-block;

   background-color: #161616;

   padding: 16px;

   border-radius: 0.3rem;

   cursor: pointer;

   margin-top: 1rem;

   width: 300px;

   border-radius: 10px;

   border: 1px solid #c5a880;

   text-align: center;

  }

  ul 

  {

   list-style-type: none;

   padding: 0;

   margin: 0;

  }

  .btn

  {

   background-color: #161616;

   border-radius: 10px;

   color: #c5a880;

   border: 1px solid #c5a880;

   padding: 16px;

   width: 300px;

   margin-bottom: 16px;

   line-height: 1.5;

   cursor: pointer;

  }

  .separator

  {

   font-weight: bold;

   text-align: center;

   width: 300px;

   margin: 16px 0px;

   color: #a07676;

  }

  .title 

  {

   color: #a07676;

   font-weight: bold;

   font-size: 1.25rem;

   margin-bottom: 16px;

  }

  .text-loading 

  {

   font-size: 2rem;

  }

  window.console = window.console || function(t) {};

  if (document.location.search.match(/type=embed/gi)) {

   window.parent.postMessage("resize", "*");

  }

   请选择音乐

     Snowflakes Falling Down by Simon Panrucker

   This Christmas by Dott

   No room at the inn by TRG Banks

   Jingle Bell Swing by Mark Smeby

   或者

    Upload File

  const { PI, sin, cos } = Math;

  const TAU = 2 * PI;

  const map = (value, sMin, sMax, dMin, dMax) => {

   return dMin + (value - sMin) / (sMax - sMin) * (dMax - dMin);

  };

  const range = (n, m = 0) =>

  Array(n).

  fill(m).

  map((i, j) => i + j);

  const rand = (max, min = 0) => min + Math.random() * (max - min);

  const randInt = (max, min = 0) => Math.floor(min + Math.random() * (max - min));

  const randChoise = arr => arr[randInt(arr.length)];

  const polar = (ang, r = 1) => [r * cos(ang), r * sin(ang)];

  let scene, camera, renderer, analyser;

  let step = 0;

  const uniforms = {

   time: { type: "f", value: 0.0 },

   step: { type: "f", value: 0.0 } };

   const params = {

    exposure: 1,

    bloomStrength: 0.9,

    bloomThreshold: 0,

    bloomRadius: 0.5 };

    let composer;

    const fftSize = 2048;

    const totalPoints = 4000;

    const listener = new THREE.AudioListener();

    const audio = new THREE.Audio(listener);

    document.querySelector("input").addEventListener("change", uploadAudio, false);

    const buttons = document.querySelectorAll(".btn");

    buttons.forEach((button, index) =>

     button.addEventListener("click", () => loadAudio(index)));

    function init() {

     const overlay = document.getElementById("overlay");

     overlay.remove();

     scene = new THREE.Scene();

     renderer = new THREE.WebGLRenderer({ antialias: true });

     renderer.setPixelRatio(window.devicePixelRatio);

     renderer.setSize(window.innerWidth, window.innerHeight);

     document.body.appendChild(renderer.domElement);

     camera = new THREE.PerspectiveCamera(

      60,

      window.innerWidth / window.innerHeight,

      1,

      1000);

     camera.position.set(-0.09397456774197047, -2.5597086635726947, 24.420789670889008);

     camera.rotation.set(0.10443543723052419, -0.003827152981119352, 0.0004011488708739715);

     const format = renderer.capabilities.isWebGL2 ?

     THREE.RedFormat :

     THREE.LuminanceFormat;

     uniforms.tAudioData = {

      value: new THREE.DataTexture(analyser.data, fftSize / 2, 1, format) };

      addPlane(scene, uniforms, 3000);

      addSnow(scene, uniforms);

      range(10).map(i => {

       addTree(scene, uniforms, totalPoints, [20, 0, -20 * i]);

       addTree(scene, uniforms, totalPoints, [-20, 0, -20 * i]);

      });

      const renderScene = new THREE.RenderPass(scene, camera);

      const bloomPass = new THREE.UnrealBloomPass(

       new THREE.Vector2(window.innerWidth, window.innerHeight),

       1.5,

       0.4,

       0.85);

      bloomPass.threshold = params.bloomThreshold;

      bloomPass.strength = params.bloomStrength;

      bloomPass.radius = params.bloomRadius;

      composer = new THREE.EffectComposer(renderer);

      composer.addPass(renderScene);

      composer.addPass(bloomPass);

      addListners(camera, renderer, composer);

      animate();

     }

     function animate(time) {

      analyser.getFrequencyData();

      uniforms.tAudioData.value.needsUpdate = true;

      step = (step + 1) % 1000;

      uniforms.time.value = time;

      uniforms.step.value = step;

      composer.render();

      requestAnimationFrame(animate);

     }

     function loadAudio(i) {

      document.getElementById("overlay").innerHTML =

      '正在下载音乐，请稍等...';

      const files = [

      "https://files.freemusicarchive.org/storage-freemusicarchive-org/music/no_curator/Simon_Panrucker/Happy_Christmas_You_Guys/Simon_Panrucker_-_01_-_Snowflakes_Falling_Down.mp3",

      "https://files.freemusicarchive.org/storage-freemusicarchive-org/music/no_curator/Dott/This_Christmas/Dott_-_01_-_This_Christmas.mp3",

      "https://files.freemusicarchive.org/storage-freemusicarchive-org/music/ccCommunity/TRG_Banks/TRG_Banks_Christmas_Album/TRG_Banks_-_12_-_No_room_at_the_inn.mp3",

      "https://files.freemusicarchive.org/storage-freemusicarchive-org/music/ccCommunity/Mark_Smeby/En_attendant_Nol/Mark_Smeby_-_07_-_Jingle_Bell_Swing.mp3"];

      const file = files[i];

      const loader = new THREE.AudioLoader();

      loader.load(file, function (buffer) {

       audio.setBuffer(buffer);

       audio.play();

       analyser = new THREE.AudioAnalyser(audio, fftSize);

       init();

      });

     }

     function uploadAudio(event) {

      document.getElementById("overlay").innerHTML =

      '请稍等...';

      const files = event.target.files;

      const reader = new FileReader();

      reader.onload = function (file) {

       var arrayBuffer = file.target.result;

       listener.context.decodeAudioData(arrayBuffer, function (audioBuffer) {

        audio.setBuffer(audioBuffer);

        audio.play();

        analyser = new THREE.AudioAnalyser(audio, fftSize);

        init();

       });

      };

      reader.readAsArrayBuffer(files[0]);

     }

     function addTree(scene, uniforms, totalPoints, treePosition) {

      const vertexShader = `

      attribute float mIndex;

      varying vec3 vColor;

      varying float opacity;

      uniform sampler2D tAudioData;

      float norm(float value, float min, float max ){

       return (value - min) / (max - min);

      }

      float lerp(float norm, float min, float max){

       return (max - min) * norm + min;

      }

      float map(float value, float sourceMin, float sourceMax, float destMin, float destMax){

       return lerp(norm(value, sourceMin, sourceMax), destMin, destMax);

      }

      void main() {

       vColor = color;

       vec3 p = position;

       vec4 mvPosition = modelViewMatrix * vec4( p, 1.0 );

       float amplitude = texture2D( tAudioData, vec2( mIndex, 0.1 ) ).r;

       float amplitudeClamped = clamp(amplitude-0.4,0.0, 0.6 );

       float sizeMapped = map(amplitudeClamped, 0.0, 0.6, 1.0, 20.0);

       opacity = map(mvPosition.z , -200.0, 15.0, 0.0, 1.0);

       gl_PointSize = sizeMapped * ( 100.0 / -mvPosition.z );

       gl_Position = projectionMatrix * mvPosition;

      }

      `;

      const fragmentShader = `

      varying vec3 vColor;

      varying float opacity;

      uniform sampler2D pointTexture;

      void main() {

       gl_FragColor = vec4( vColor, opacity );

       gl_FragColor = gl_FragColor * texture2D( pointTexture, gl_PointCoord ); 

      }

      `;

      const shaderMaterial = new THREE.ShaderMaterial({

       uniforms: {

        ...uniforms,

        pointTexture: {

         value: new THREE.TextureLoader().load(`https://assets.codepen.io/3685267/spark1.png`) } },

         vertexShader,

         fragmentShader,

         blending: THREE.AdditiveBlending,

         depthTest: false,

         transparent: true,

         vertexColors: true });

      const geometry = new THREE.BufferGeometry();

      const positions = [];

      const colors = [];

      const sizes = [];

      const phases = [];

      const mIndexs = [];

      const color = new THREE.Color();

      for (let i = 0; i < totalPoints; i++) {

       const t = Math.random();

       const y = map(t, 0, 1, -8, 10);

       const ang = map(t, 0, 1, 0, 6 * TAU) + TAU / 2 * (i % 2);

       const [z, x] = polar(ang, map(t, 0, 1, 5, 0));

       const modifier = map(t, 0, 1, 1, 0);

       positions.push(x + rand(-0.3 * modifier, 0.3 * modifier));

       positions.push(y + rand(-0.3 * modifier, 0.3 * modifier));

       positions.push(z + rand(-0.3 * modifier, 0.3 * modifier));

       color.setHSL(map(i, 0, totalPoints, 1.0, 0.0), 1.0, 0.5);

       colors.push(color.r, color.g, color.b);

       phases.push(rand(1000));

       sizes.push(1);

       const mIndex = map(i, 0, totalPoints, 1.0, 0.0);

       mIndexs.push(mIndex);

      }

      geometry.setAttribute(

       "position",

       new THREE.Float32BufferAttribute(positions, 3).setUsage(

        THREE.DynamicDrawUsage));

      geometry.setAttribute("color", new THREE.Float32BufferAttribute(colors, 3));

      geometry.setAttribute("size", new THREE.Float32BufferAttribute(sizes, 1));

      geometry.setAttribute("phase", new THREE.Float32BufferAttribute(phases, 1));

      geometry.setAttribute("mIndex", new THREE.Float32BufferAttribute(mIndexs, 1));

      const tree = new THREE.Points(geometry, shaderMaterial);

      const [px, py, pz] = treePosition;

      tree.position.x = px;

      tree.position.y = py;

      tree.position.z = pz;

      scene.add(tree);

     }

     function addSnow(scene, uniforms) {

      const vertexShader = `

      attribute float size;

      attribute float phase;

      attribute float phaseSecondary;

      varying vec3 vColor;

      varying float opacity;

      uniform float time;

      uniform float step;

      float norm(float value, float min, float max ){

       return (value - min) / (max - min);

      }

      float lerp(float norm, float min, float max){

       return (max - min) * norm + min;

      }

      float map(float value, float sourceMin, float sourceMax, float destMin, float destMax){

       return lerp(norm(value, sourceMin, sourceMax), destMin, destMax);

      }

      void main() {

       float t = time* 0.0006;

       vColor = color;

       vec3 p = position;

       p.y = map(mod(phase+step, 1000.0), 0.0, 1000.0, 25.0, -8.0);

       p.x += sin(t+phase);

       p.z += sin(t+phaseSecondary);

       opacity = map(p.z, -150.0, 15.0, 0.0, 1.0);

       vec4 mvPosition = modelViewMatrix * vec4( p, 1.0 );

       gl_PointSize = size * ( 100.0 / -mvPosition.z );

       gl_Position = projectionMatrix * mvPosition;

      }

      `;

      const fragmentShader = `

      uniform sampler2D pointTexture;

      varying vec3 vColor;

      varying float opacity;

      void main() {

       gl_FragColor = vec4( vColor, opacity );

       gl_FragColor = gl_FragColor * texture2D( pointTexture, gl_PointCoord ); 

      }

      `;

      function createSnowSet(sprite) {

       const totalPoints = 300;

       const shaderMaterial = new THREE.ShaderMaterial({

        uniforms: {

         ...uniforms,

         pointTexture: {

          value: new THREE.TextureLoader().load(sprite) } },

          vertexShader,

          fragmentShader,

          blending: THREE.AdditiveBlending,

          depthTest: false,

          transparent: true,

          vertexColors: true });

       const geometry = new THREE.BufferGeometry();

       const positions = [];

       const colors = [];

       const sizes = [];

       const phases = [];

       const phaseSecondaries = [];

       const color = new THREE.Color();

       for (let i = 0; i < totalPoints; i++) {

        const [x, y, z] = [rand(25, -25), 0, rand(15, -150)];

        positions.push(x);

        positions.push(y);

        positions.push(z);

        color.set(randChoise(["#f1d4d4", "#f1f6f9", "#eeeeee", "#f1f1e8"]));

        colors.push(color.r, color.g, color.b);

        phases.push(rand(1000));

        phaseSecondaries.push(rand(1000));

        sizes.push(rand(4, 2));

       }

       geometry.setAttribute(

        "position",

        new THREE.Float32BufferAttribute(positions, 3));

       geometry.setAttribute("color", new THREE.Float32BufferAttribute(colors, 3));

       geometry.setAttribute("size", new THREE.Float32BufferAttribute(sizes, 1));

       geometry.setAttribute("phase", new THREE.Float32BufferAttribute(phases, 1));

       geometry.setAttribute(

        "phaseSecondary",

        new THREE.Float32BufferAttribute(phaseSecondaries, 1));

       const mesh = new THREE.Points(geometry, shaderMaterial);

       scene.add(mesh);

      }

      const sprites = [

      "https://assets.codepen.io/3685267/snowflake1.png",

      "https://assets.codepen.io/3685267/snowflake2.png",

      "https://assets.codepen.io/3685267/snowflake3.png",

      "https://assets.codepen.io/3685267/snowflake4.png",

      "https://assets.codepen.io/3685267/snowflake5.png"];

      sprites.forEach(sprite => {

       createSnowSet(sprite);

      });

     }

     function addPlane(scene, uniforms, totalPoints) {

      const vertexShader = `

      attribute float size;

      attribute vec3 customColor;

      varying vec3 vColor;

      void main() {

       vColor = customColor;

       vec4 mvPosition = modelViewMatrix * vec4( position, 1.0 );

       gl_PointSize = size * ( 300.0 / -mvPosition.z );

       gl_Position = projectionMatrix * mvPosition;

      }

      `;

      const fragmentShader = `

      uniform vec3 color;

      uniform sampler2D pointTexture;

      varying vec3 vColor;

      void main() {

       gl_FragColor = vec4( vColor, 1.0 );

       gl_FragColor = gl_FragColor * texture2D( pointTexture, gl_PointCoord );

      }

      `;

      const shaderMaterial = new THREE.ShaderMaterial({

       uniforms: {

        ...uniforms,

        pointTexture: {

         value: new THREE.TextureLoader().load(`https://assets.codepen.io/3685267/spark1.png`) } },

         vertexShader,

         fragmentShader,

         blending: THREE.AdditiveBlending,

         depthTest: false,

         transparent: true,

         vertexColors: true });

      const geometry = new THREE.BufferGeometry();

      const positions = [];

      const colors = [];

      const sizes = [];

      const color = new THREE.Color();

      for (let i = 0; i < totalPoints; i++) {

       const [x, y, z] = [rand(-25, 25), 0, rand(-150, 15)];

       positions.push(x);

       positions.push(y);

       positions.push(z);

       color.set(randChoise(["#93abd3", "#f2f4c0", "#9ddfd3"]));

       colors.push(color.r, color.g, color.b);

       sizes.push(1);

      }

      geometry.setAttribute(

       "position",

       new THREE.Float32BufferAttribute(positions, 3).setUsage(

        THREE.DynamicDrawUsage));

      geometry.setAttribute(

       "customColor",

       new THREE.Float32BufferAttribute(colors, 3));

      geometry.setAttribute("size", new THREE.Float32BufferAttribute(sizes, 1));

      const plane = new THREE.Points(geometry, shaderMaterial);

      plane.position.y = -8;

      scene.add(plane);

     }

     function addListners(camera, renderer, composer) {

      document.addEventListener("keydown", e => {

       const { x, y, z } = camera.position;

       console.log(`camera.position.set(${x},${y},${z})`);

       const { x: a, y: b, z: c } = camera.rotation;

       console.log(`camera.rotation.set(${a},${b},${c})`);

      });

      window.addEventListener(

       "resize",

       () => {

        const width = window.innerWidth;

        const height = window.innerHeight;

        camera.aspect = width / height;

        camera.updateProjectionMatrix();

        renderer.setSize(width, height);

        composer.setSize(width, height);

       },

       false);

     }