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HTML

              
                <canvas width="800" height="600" id="canva1"></canvas>

              
            
!

CSS

              
                * {
  padding: 0;
  margin: 0;
}
canvas  {
  position: absolute;
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
}
              
            
!

JS

              
                  (function() {
    var VW = window.innerWidth
    var VH = window.innerHeight
    var canva1 = document.getElementById('canva1')
    canva1.width = VW
    canva1.height = VH
    var context1 = canva1.getContext('2d')
    var PI = Math.PI
    var sin = Math.sin
    var cos = Math.cos
    var random = Math.random
    var FULL_ANG = 360
    var HALF_ANG = 180

    // 浅 -> 深
    var colorList1 = [
      '#f0f0f0', '#ccc', '#c9c9c9',
      '#d9d9d9', '#dddddd', '#d0d0d0',
      '#bfbfbf', '#b5b5b5',
      '#bbb', '#8f8f8f', '#767676'
    ]

    var colorList2 = [
      '#f2e1c7', '#f9e7c3', '#fdd6af',
      '#fadcb6', '#e9b8ae', '#f7bcda',
      '#eb7bcf', '#eb7bcf', '#cf60c7',
      '#eb5998', '#d82066', '#e1337a'
    ]

    // 半径、与偏移角度计算相对坐标即相对于原点的偏移量
    // 因为在后面的 ctx.translate(this.x, this.y) 会将坐标原点设置为圆心所在位置
    function createPoint(ang, radius, offset = 0) {
      const rad = PI * (ang + offset) / HALF_ANG
      return {
        x: radius * sin(rad),
        y: radius * cos(rad)
      }
    }

    function getRandomColor(colorList) {
      return colorList[random() * colorList.length | 0]
    }

    // 画板的宽度高度、 坐标、半径、花瓣的数量
    function Flower(cw, ch, radius, colors, alpha, vy) {
      var count = 5
      var halfRadius = radius / 2
      var cacheCanvas = document.createElement('canvas')
      cacheCanvas.width = radius * 2
      cacheCanvas.height = radius * 2
      this.halfRadius = halfRadius
      this.x = random() * cw + halfRadius
      this.y = random() * ch + halfRadius
      this.vy = vy
      this.vx = random() * 1 - 0.5
      this.cw = cw
      this.ch = ch
      this.alpha = alpha
      this.scale = 1
      this.radius = radius
      this.color = '#fff'
      this.colors = colors
      this.count = count
      this.rotate = 0
      this.points = []
      this.canva = cacheCanvas
      this.ctx = cacheCanvas.getContext('2d')
      this.vertical = 1 // 换飘落的方向 1 向下 0 静止 -1 向上
      this.setColor()
      this.createPath()
      this.cache()
    }

    Flower.prototype.setColor = function setColor() {
      if (this.vertical === 1) {
        this.color = this.colors[0]
      } else {
        this.color = this.colors[1]
      }
    }

    Flower.prototype.zoom = function zoom() {
      this.vertical = 0
      this.setColor()
      this.cache()
    }

    Flower.prototype.reverse = function reverse() {
      this.vertical = -1
    }

    // 用于生成花瓣的路径
    Flower.prototype.createPath = function createPath() {
      var radius = this.radius
      var count = this.count
        // 单个花瓣的所占的角度
      var singleAng = 360 / count
      var halfAng = singleAng / 2
      var r3 = radius
      var r2 = radius * 0.9
      var r1 = radius * 0.3
      var r2Offset = r2 * 0.2
      var ponits = []
      for (var i = 0; i < this.count; i++) {
        ponits.push(createPoint(singleAng * i, r1))
        ponits.push(createPoint(singleAng * i, r2 + (random() * r2Offset - r2Offset / 2)))
        ponits.push(createPoint(singleAng * i, r3, halfAng))
        ponits.push(createPoint(singleAng * (i + 1), r2 + (random() * r2Offset - r2Offset / 2)))
      }
      // 首尾路径闭合
      ponits.push(ponits[0])
      this.ponits = ponits
    }

    // 先在自身的离屏 canvas 缓存绘制出花瓣图案
    Flower.prototype.cache = function cache() {
      var ctx = this.ctx
      var ponits = this.ponits
      var radius = this.radius
      ctx.clearRect(0, 0, radius * 2, radius * 2)
      ctx.save()
      ctx.translate(radius, radius)
      ctx.beginPath()
      ctx.globalAlpha = this.alpha
      ctx.strokeStyle = this.color
      ctx.fillStyle = this.color
      ctx.moveTo(ponits[0].x, ponits[0].y)
      for (var i = 2; i < ponits.length; i += 2) {
        var target = ponits[i]
        var cp = ponits[i - 1]
        ctx.quadraticCurveTo(cp.x, cp.y, target.x, target.y)
      }
      ctx.closePath()
      ctx.stroke()
      ctx.fill()
      ctx.restore()
    }

    // 绘制花瓣
    Flower.prototype.drow = function drow(context) {
      context.save()
      context.translate(this.x, this.y)
      context.rotate(this.rotate)
      context.scale(this.scale, this.scale)
      context.drawImage(this.canva, -this.radius, -this.radius)
      context.restore()
    }

    // 更新路径判断边界
    Flower.prototype.update = function update() {
      if (!this.vertical && this.scale >= 0.9) {
        this.scale *= 0.99
        return
      }
      var halfRadius = this.halfRadius + 10
      this.rotate += .02 * this.vertical
      this.x += this.vx * this.vertical
      this.y += this.vy * this.vertical
      if (this.x < -halfRadius || this.x > this.cw + halfRadius) {
        this.x = this.x > 0 ? -halfRadius : this.cw + halfRadius
      }
      if (this.y < -halfRadius || this.y > this.ch + halfRadius) {
        this.y = this.y > 0 ? -halfRadius : this.ch + halfRadius
        this.x = random() * this.cw + this.halfRadius
      }
    }


    function Layer(options) {
      var context = options.ctx
      var count = options.count
      var size = options.size
      var alpha = options.alpha
      var vy = options.vy
      var colors1 = options.colors1
      var colors2 = options.colors2
      var flowers = []
      for (var i = 0; i < count; i++) {
        var rsize = (random() * (size.max - size.min) + size.min) | 1
        var ralpha = random() * (alpha.max - alpha.min) + alpha.min
        var rvy = random() * (vy.max - vy.min) + vy.min
        var colors = [getRandomColor(colors1), getRandomColor(colors2)]
        flowers.push(new Flower(VW, VH, rsize, colors, ralpha, rvy))
      }
      this.context = context
      this.flowers = flowers
    }

    Layer.prototype.zoom = function boom() {
      this.flowers.forEach(flower => {
        flower.zoom()
      })
    }

    Layer.prototype.reverse = function reverse() {
      this.flowers.forEach(flower => {
        flower.reverse()
      })
    }

    Layer.prototype.tick = function tick() {
      this.flowers.forEach(flower => {
        flower.update()
        flower.drow(this.context)
      })
    }

    Layer.prototype.clear = function clear() {
      this.context.clearRect(0, 0, VW, VH)
    }


    var layer = new Layer({
      ctx: context1,
      count: 800,
      size: {
        max: 60,
        min: 10
      },
      alpha: {
        max: 1,
        min: 0.2
      },
      vy: {
        max: 4,
        min: 1
      },
      colors1: colorList1,
      colors2: colorList2
    })

    function drawFrame() {
      window.requestAnimationFrame(drawFrame)
      layer.clear()
      layer.tick()
    }

    drawFrame()

    // 5 秒后静止画面,缩放花瓣
    setTimeout(() => {
      layer.zoom()
    }, 5000)

    // 往后 1 秒花瓣方向运动
    setTimeout(() => {
      layer.reverse()
    }, 6000)

  })()
              
            
!
999px

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