starSky

星空特效

<template>
  <canvas ref="canvas" class="xiao-canvas"></canvas>
</template>

<script>
export default {
  name: 'Starsky',

  mounted() {
    var canvas = this.$refs.canvas,
      ctx = canvas.getContext('2d'),
      w = (canvas.width = window.innerWidth),
      h = (canvas.height = window.innerHeight),
      hue = 217,
      stars = [],
      count = 0,
      maxStars = 1200

    var canvas2 = document.createElement('canvas'),
      ctx2 = canvas2.getContext('2d')
    canvas2.width = 100
    canvas2.height = 100
    var half = canvas2.width / 2,
      gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half)
    gradient2.addColorStop(0.025, '#fff')
    gradient2.addColorStop(0.1, 'hsl(' + hue + ', 61%, 33%)')
    gradient2.addColorStop(0.25, 'hsl(' + hue + ', 64%, 6%)')
    gradient2.addColorStop(1, 'transparent')

    ctx2.fillStyle = gradient2
    ctx2.beginPath()
    ctx2.arc(half, half, half, 0, Math.PI * 2)
    ctx2.fill()

    // End cache

    function random(min, max) {
      if (arguments.length < 2) {
        max = min
        min = 0
      }

      if (min > max) {
        var hold = max
        max = min
        min = hold
      }

      return Math.floor(Math.random() * (max - min + 1)) + min
    }

    function maxOrbit(x, y) {
      var max = Math.max(x, y),
        diameter = Math.round(Math.sqrt(max * max + max * max))
      return diameter / 2
    }

    var Star = function () {
      this.orbitRadius = random(maxOrbit(w, h))
      this.radius = random(60, this.orbitRadius) / 12
      this.orbitX = w / 2
      this.orbitY = h / 2
      this.timePassed = random(0, maxStars)
      this.speed = random(this.orbitRadius) / 50000
      this.alpha = random(2, 10) / 10

      count++
      stars[count] = this
    }

    Star.prototype.draw = function () {
      var x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX,
        y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY,
        twinkle = random(10)

      if (twinkle === 1 && this.alpha > 0) {
        this.alpha -= 0.05
      } else if (twinkle === 2 && this.alpha < 1) {
        this.alpha += 0.05
      }

      ctx.globalAlpha = this.alpha
      ctx.drawImage(
        canvas2,
        x - this.radius / 2,
        y - this.radius / 2,
        this.radius,
        this.radius,
      )
      this.timePassed += this.speed
    }

    for (var i = 0; i < maxStars; i++) {
      new Star()
    }

    function animation() {
      ctx.globalCompositeOperation = 'source-over'
      ctx.globalAlpha = 0.8
      ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 1)'
      ctx.fillRect(0, 0, w, h)

      ctx.globalCompositeOperation = 'lighter'
      for (var i = 1, l = stars.length; i < l; i++) {
        stars[i].draw()
      }

      window.requestAnimationFrame(animation)
    }

    animation()
  },

  methods: {},
}
</script>

<style lang="less" scoped>
.xiao-canvas {
  width: 100%;
  height: 100%;
}
</style>