圣诞节快到啦～🎄🎄🎄🎄咱们也试着做做小程序版本的星星✨飘落效果吧～

先来个效果图：

484听起来很叼，看起来也就那样。
来咱们上手开始撸
页面内容wxml，先简单切个图吧。

<view class="container">
  <image src="https://image.wxopen.club/content_1b297d02-2ea4-11ea-8abd-a0999b08aadb.jpg" mode="widthFix"/>
  <image src="https://image.wxopen.club/content_1b60d7fc-2ea4-11ea-8abd-a0999b08aadb.jpg" alt="" mode="widthFix"/>
  <image src="https://image.wxopen.club/content_1b8c448c-2ea4-11ea-8abd-a0999b08aadb.jpg" alt="" mode="widthFix"/>
  <image src="https://image.wxopen.club/content_1bbb9494-2ea4-11ea-8abd-a0999b08aadb.jpg" alt="" mode="widthFix"/>
  <image src="https://image.wxopen.club/content_1c389ad4-2ea4-11ea-8abd-a0999b08aadb.jpg" alt="" mode="widthFix"/>
  <image src="https://image.wxopen.club/content_1c6ce014-2ea4-11ea-8abd-a0999b08aadb.jpg" alt="" mode="widthFix"/>
  <image src="https://image.wxopen.club/content_1c95dfbe-2ea4-11ea-8abd-a0999b08aadb.jpg" alt="" mode="widthFix"/>
</view>
<canvas  canvas-id="myCanvas" />

页面样式wxss，因为切片用的不太熟练，图片之间有个2rpx的空隙。

.container {
  height: 100%;
  box-sizing: border-box;
  min-height: 100vh;
}

image {
  width: 100%;
  display: block;
  margin-top: -2rpx;  //不会切图造的孽
}

canvas {
  width: 100%; 
  min-height:100vh; 
  position: fixed;
  top: 0;
  z-index: 888;
}

重点JS：

//获取应用实例
const app = getApp()
// 存储所有的星星
const stars = []
// 下落的加速度
const G = 0.01
const stime = 60

// 速度上限，避免速度过快
const SPEED_LIMIT_X = 1
const SPEED_LIMIT_Y = 1

const W = wx.getSystemInfoSync().windowWidth
const H = wx.getSystemInfoSync().windowHeight
var starImage = '' //星星素材
wx.getImageInfo({
  src: 'https://qiniu-image.qtshe.com/WechatIMG470.png',
  success: (res)=> {
    starImage = res.path
  }
})

Page({
  onLoad() {
    this.setAudioPlay()
  },
  onShow() {
    this.createStar()
  },
  createStar() {
    let starCount = 350 //星星总的数量
    let starNum = 0 //当前生成星星数
    let deltaTime = 0
    let ctx = wx.createCanvasContext('myCanvas')
    let requestAnimationFrame = (() => {
      return (callback) => {
        setTimeout(callback, 1000 / stime)
      }
    })()
    starLoop()

    function starLoop() {
      requestAnimationFrame(starLoop)
      ctx.clearRect(0, 0, W, H)
      deltaTime = 20 //每次增加的星星数量
      starNum += deltaTime
      if (starNum > starCount) {
        stars.push(
          new Star(Math.random() * W, 0, Math.random() * 5 + 5)
        );
        starNum %= starCount
      }
      stars.map((s, i) => { //重复绘制
        s.update()
        s.draw()
        if (s.y >= H) { //大于屏幕高度的就从数组里去掉
          stars.splice(i, 1)
        }
      })
      ctx.draw()
    }

    function Star(x, y, radius) {
      this.x = x
      this.y = y
      this.sx = 0
      this.sy = 0
      this.deg = 0
      this.radius = radius
      this.ax = Math.random() < 0.5 ? 0.005 : -0.005
    }

    Star.prototype.update = function() {
      const deltaDeg = Math.random() * 0.6 + 0.2

      this.sx += this.ax
      if (this.sx >= SPEED_LIMIT_X || this.sx <= -SPEED_LIMIT_X) {
        this.ax *= -1
      }

      if (this.sy < SPEED_LIMIT_Y) {
        this.sy += G
      }

      this.deg += deltaDeg
      this.x += this.sx
      this.y += this.sy
    }

    Star.prototype.draw = function() {
      const radius = this.radius
      ctx.save()
      ctx.translate(this.x, this.y)
      ctx.rotate(this.deg * Math.PI / 180)
      ctx.drawImage(starImage, -radius, -radius * 1.8, radius * 2, radius * 2)
      ctx.restore()
    }
  },
  setAudioPlay() {
    let adctx = wx.createInnerAudioContext()
    adctx.autoplay = true
    adctx.loop = true
    adctx.src = 'https://dn-qtshe.qbox.me/Jingle%20Bells.mp3'
    adctx.onPlay(() => {
      console.log('开始播放')
      adctx.play()
    })
  }
})

以上只是简单实现了一个星星飘落的效果，预览的时候需要开启不校验合法域名哦～
目前还有更优的h5版本，使用Three.js实现的，在小程序内使用Three.js对于我来说有点打脑壳，先把效果分享出来吧。
h5版本，手机看效果最佳

如果有需要的可以留言，我可以整理下发源码给你。