Vue使用自定义指令实现页面底部加水印

<template>
  <div class="water-marker" >
      <div v-waterMarker="{text:'卡洛背心 - 版权所有',textColor:'rgba(180, 180, 180, 0.4)'}">
        <div class="water-marker-item">测试问题啊测试问题啊测试问题啊测试问题啊测试问题啊测试问题啊</div>
      </div>
  </div>
</template>

<script>
import waterMarker from '../../directive/test/waterMarker'
export default {
  directives: {
    waterMarker
  },
  data(){
    return{
    }
  },
  methods:{
  }
}
</script>

<style lang="sCSS">
.water-marker{
  height: 300px;
  .water-marker-item{
    line-height: 300px;
  }
}
</style>

function addWaterMarker(str, parentnode, font, textColor) {
  // 水印文字，父元素，字体，文字颜色
  var can = document.createElement('canvas')
  parentNode.appendChild(can)
  can.width = 200
  can.height = 150
  can.style.display = 'none'
  var cans = can.getContext('2d')
  cans.rotate((-20 * Math.PI) / 180)
  cans.font = font || '16px Microsoft JhengHei'
  cans.fillStyle = textColor || 'rgba(180, 180, 180, 0.3)'
  cans.textAlign = 'left'
  cans.textBaseline = 'Middle'
  cans.fillText(str, can.width / 10, can.height / 2)
  parentNode.style.backgroundImage = 'url(' + can.toDataURL('image/png') + ')'
}

const waterMarker = {
  bind: function (el, binding) {
    addWaterMarker(binding.value.text, el, binding.value.font, binding.value.textColor)
  },
}

export default waterMarker