canvas 雪花效果

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canvas

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canvas 画雪花效果

示例

example.html

如图：

源码

注意源码中引用了一个图片，链接在此：snowflake1.png

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<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8" />
  <title>canvas 雪花效果</title>
  <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0, user-scalable=no">
  <style type="text/css">
    body {
      margin: 0;
      padding: 0;
      background: #000;
    }

    canvas {
      display: block;
      width: 100%;
      height: 100%;
    }
  </style>
</head>

<body>
  <canvas id="canvas"></canvas>
  <script>
    //canvas init
    var snowflake = {
      number: 200,
      particles: [],
      angle: 0,
      timer: null,
      canvas: document.getElementById("canvas"),
      ctx: document.getElementById("canvas").getContext("2d"),
      loadLength: 0, //当前图片加载了多少个
      image: [
        './snowflake1.png',
      ],
      winWidth: window.innerWidth,
      winHeight: window.innerHeight,
      minSize: 5,
      maxSize: 12,
      init: function () {
        var __this = this;
        __this.canvas.width = __this.winWidth;
        __this.canvas.height = __this.winHeight;
        __this.createParticles();
        __this.loadImage();
      },
      loadImage: function () {
        var __this = this;
        for (var i = 0; i < __this.image.length; i++) {
          (function (i) {
            var img = new Image();
            img.src = __this.image[i];
            img.onload = function () {
              __this.image[i] = img;
              __this.loadLength++;
              if (__this.loadLength == __this.image.length) {
                __this.loopDraw();
              }
            }
          })(i)
        }
      },
      loopDraw: function () {
        var __this = this;
        __this.timer = setInterval(function () {
          __this.draw();
        }, 33);
      },
      createParticles: function () {
        var __this = this;
        var width = __this.winWidth;
        var height = __this.winHeight;
        for (var i = 0; i < __this.number; i++) {
          __this.particles.push({
            x: __this.rand(10, __this.winWidth - 10),
            y: __this.rand(0, __this.winHeight),
            imgIndex: __this.rand(0, __this.image.length - 1),
            size: __this.rand(__this.minSize, __this.maxSize),
            d: Math.random() * __this.number,
            dir: __this.rand(0, 1) == 0 ? -1 : 1
          });
        }
      },
      draw: function () {
        var __this = this;
        var width = __this.winWidth;
        var height = __this.winHeight;
        __this.ctx.clearRect(0, 0, width, height);
        for (var i = 0; i < this.number; i++) {
          var p = __this.particles[i];
          var img = __this.image[p.imgIndex];
          try {
            __this.ctx.drawImage(img, p.x, p.y, p.size, p.size);
          } catch (e) {
            console.log(e, p)
            clearInterval(__this.timer);
          }
        }
        __this.update();
      },
      update: function () {
        var __this = this;
        var width = __this.winWidth;
        var height = __this.winHeight;
        __this.angle += 0.01;
        for (var i = 0; i < this.number; i++) {
          var p = __this.particles[i];
          p.y += (Math.cos(__this.angle + p.d) + 1 + p.size) / 10;
          p.x += (Math.sin(__this.angle) + 1) / 10 * p.dir;

          if (p.x > width + __this.maxSize || p.x < -__this.maxSize || p.y > height) {
            if (i % 3 > 0) {
              __this.particles[i] = {
                x: Math.random() * width,
                y: -10,
                size: p.size,
                imgIndex: __this.rand(0, __this.image.length - 1),
                d: p.d,
                dir: __this.rand(0, 1) == 0 ? -1 : 1
              };
            } else {
              if (Math.sin(__this.angle) > 0) {
                __this.particles[i] = {
                  x: -__this.maxSize,
                  y: Math.random() * height,
                  size: p.size,
                  imgIndex: __this.rand(0, __this.image.length - 1),
                  d: p.d,
                  dir: __this.rand(0, 1) == 0 ? -1 : 1
                };
              } else {
                __this.particles[i] = {
                  x: width + __this.maxSize,
                  y: Math.random() * height,
                  size: p.size,
                  imgIndex: __this.rand(0, __this.image.length - 1),
                  d: p.d,
                  dir: __this.rand(0, 1) == 0 ? -1 : 1
                };
              }
            }
          }
        }
      },
      rand: function (min, max) {
        return parseInt(Math.random() * (max - min + 1) + min);
      },
    };

    snowflake.init();
  </script>
</body>

</html>
本文由 linx(544819896@qq.com) 创作，采用 CC BY 4.0 CN协议 进行许可。 可自由转载、引用，但需署名作者且注明文章出处。本文链接为： https://blog.jijian.link/2020-03-21/canvas-snowflake/

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