vue使用html2canvas截图下载时，存在svg或者img或者特殊字体时截图不全的解决办法

写在前面：

1.网上html2canvas资料少，即使你复制拿来用了，也发现各种问题是不是？
2.它的官网也没有好的demo，不好解决我们的问题。
3.我自己研究了两天，自创魂技，搞定了它。

以下不废话：

vue使用html2canvas截图时，存在svg或者img或者特殊字体时截图时空白，或者不全

如果你的原元素是img，当然再导入canvas，通过img转canvas去替换原来的子节点，再使用html2canvas导出图片。对于组件层级不多的页面是可用的。

 const changeToCanvas = async (element) => {
      const imgElems = element.querySelectorAll('img')
      let svgelems = [...imgElems]
      svgelems.forEach((node) => {
        let parentNode = node.parentNode
        let canvas = document.createElement('canvas')
        canvas.style.zIndex = 999
        //处理img转换canvas
        if (node.tagName == 'IMG') {
          canvas.width = node.width
          canvas.height = node.height
          canvas.getContext('2d').drawImage(node, 0, 0)
          parentNode.removeChild(node)
          let index = parentNode.firstChild
          if (index != null) {
            parentNode.insertBefore(canvas, index)
          } else {
            parentNode.appendChild(canvas)
          }
        }
      })
    }

但是如果你组件层级多时，你会发现这种办法不是很好用，容易出现各种意想不到的问题。

如果你的原元素是svg，那么思路是，遍历div内的svg,把svg转图片，遍历图片转canvas再用html2canvas截图，如果你这么做了成功了，图片没有缺失。那么恭喜你，因为大多数都会存在各种问题。

个人认为：除非你的项目很特殊，根本不需要用canvas去把svg转一下，因为转了以后会出现元素位置问题、删除和新增div节点的延时问题等等。下面自创思路就能完美解决问题。

解决办法如下

第一步，svg或者img先转base64（如果是特殊字体，就把这个字体图形截图转base64）

注意：最好是把转之前的图片尺寸先做好，可以用美图秀秀等把图片尺寸修改一下适配你原来的页面，再转base64，这样就省去了调节css的麻烦。
这里我推荐两个网站，可以将你的svg或img转base64

https://www.chahuo.com/svg2css.html#google_vignette

https://www.bejson.com/image/imgzoom/#google_vignette

第二步，将转换后的base64设置为新元素的content属性：

如下，用新的div的css的content属性代替原来的svg或者img。这样就不需要canvas，只用html2canvas就能实现截图下载。

::v-deep(.vxe-icon-square-minus) {
  pointer-events: none;
  &::before {
    content: url('data:image/svg+xml;base64,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');
    background-repeat: no-repeat;
    background-position: center;
    width: 1em;
    height: 1em;
    display: inline-block;
  }
}

::v-deep(.vxe-icon-square-plus) {
  pointer-events: none;
  &::before {
    content: url('data:image/svg+xml;base64,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');
    background-repeat: no-repeat;
    background-position: center;
    width: 1em;
    height: 1em;
    display: inline-block;
  }
}
::v-deep(.icon_cri_1) {
  &::before {
    content: url('data:image/png;base64,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');
    background-repeat: no-repeat;
    background-position: center;
    width: 1em;
    height: 1em;
    margin-right: 5px;
    margin-top: 3px;
    display: inline-block;
  }
}
::v-deep(.icon_cri) {
  &::before {
    content: url('data:image/png;base64,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');
    background-repeat: no-repeat;
    background-position: center;
    width: 1em;
    height: 1em;
    margin-right: 5px;
    display: inline-block;
    margin-top: 3px;
  }
}

第三步，实现div的截图下载

一：html2canvas npm

npm install html2canvas@1.4.1  

二：引入

import html2canvas from 'html2canvas'

三：实现

   // 生成图片
    const creatImg = async () => {
      try {
        const setup = {
          useCORS: true, // 使用跨域
          backgroundColor: null,
          allowTaint: true,
          logging: true, // 打印日志来检查是否有加载问题
          background: '#ffffff', // 一定要添加背景颜色，否则出来的图片，背景全部都是透明的
          async: true, // 是否异步解析和呈现元素
          scale: 2, // 处理模糊问题
          // dpi: 1000 // 处理模糊问题
          scrollY: 0, // html2canvas默认绘制视图内的页面，需要把scrollY，scrollX设置为0
          scrollX: 0,
          //过滤不需要截图的元素
          ignoreElements: (element) => {
            return element.className === 'vxe-tree--btn-wrapper'
          }
        }
        //找到要截图的div节点，
        //可以用document.getElementById（'aaa'）等获取要截图的节点，根据实际情况而定
        const $image = divImage.value.childNodes[0].childNodes[1]
        
        //html2canvas 把div转图片
        await html2canvas($image, setup).then((canvasimg) => {
          //图片类型
          const link = canvasimg.toDataURL('image/png')
          //图片名称
          const fileName = 'CRI_History_Image_' + getDate()
          //导出
          exportPicture(link, fileName)
        })
      } catch (e) {
        console.log(e)
      }
    }

    // 导出图片
    const exportPicture = (link, name) => {
      try {
        const file = document.createElement('a')
        file.style.display = 'none'
        file.download = decodeURI(name)
        let blob = dataURLtoBlob(link)
        let url = URL.createObjectURL(blob)
        file.href = url
        document.body.appendChild(file)
        file.click()
        document.body.removeChild(file)
      } catch (e) {
        console.log(e)
      }
    }
    
    //图片转Blob类型，避免浏览器报错
    const dataURLtoBlob = (dataurl) => {
      var arr = dataurl.split(',')
      var mime = arr[0].match(/:(.*?);/)[1]
      var bstr = atob(arr[1])
      var n = bstr.length
      var u8arr = new Uint8Array(n)
      while (n--) {
        u8arr[n] = bstr.charCodeAt(n)
      }
      return new Blob([u8arr], { type: mime })
    }