今天技术团队聚餐，所以没有更新JavaScript的章节，遂找了自己的博客空间，分享一篇这个关于小程序的文字

小程序canvas一键截屏，生成图片并保存，提供源码，

核心代码如下，大家可以参考一下

downImg(list) {
    var that = this
    let imglist = []
    let n = 0

    function up() {
      wx.downloadFile({
        url: list[n],
        success(res) {
          if (res.statusCode == 200) {
            imglist.push(res.tempFilePath)
            n++
            if (n == list.length) {
              that.setData({
                newList: imglist,
              })
              that.Canvas(that)
            } else {
              up(n)
            }
          }
        }
      })
    }
    up()

    // return imglist
  },
  /**
   * 创建画布内容
   */
  Canvas(that) {

    const ctx = wx.createCanvasContext('myCanvas');
    var that = this
    //绘制背景
    ctx.drawImage(that.data.newList[2], 0, 0, this.data.systemInfo.screenWidth, this.data.systemInfo.windowHeight);
    //绘制banner
    ctx.drawImage(that.data.newList[3], that.rem(10), that.rem(20), that.rem(730), that.rem(400))
    ctx.setFontSize(that.rem(26))
    ctx.setTextAlign('left')
    ctx.setFillStyle('white')
    //绘制证书解析标题
    ctx.fillText('证书解析：', that.rem(32), that.rem(500))
    ctx.draw(true)
    that.forlist(that.data.resultlist, that, ctx)
  },

  forlist(list, that, ctx) {
    for (let t = 0; t < list.length; t++) {
      that.drawtitle(ctx, list[t].title, t, that)
      that.tostringLength(list[t].title, t, list[t].main, 20, ctx, that)
    }
    ctx.draw(true)
    wx.hideLoading()
    that.setData({
      isShow: false
    })
  },
  erweima() {
    wx.previewImage({
      current: 'http://www.kiss-me.top/20181103113050.jpg', // 当前显示图片的http链接
      urls: ['http://www.kiss-me.top/20181103113050.jpg'] // 需要预览的图片http链接列表
    })
  },
  save() {
    var that = this
    if (that.data.savatext == '重新测试') {
      wx.reLaunch({
        url: '/pages/index/index'
      })
    } else {
      wx.showLoading({
        title: '正在保存...',
        mask: true,
        success: function(res) {},
        fail: function(res) {},
        complete: function(res) {},
      })
      setTimeout(function() {
        wx.canvasToTempFilePath({
          x: 0,
          y: 0,
          width: that.data.systemInfo.screenWidth,
          height: that.data.systemInfo.screenHeight,
          canvasId: 'myCanvas',
          success: function(res) {
            app.globalData.imgurl = res.tempFilePath
            wx.saveImageToPhotosAlbum({
              filePath: res.tempFilePath,
              success(res) {
                wx.hideLoading()
                wx.showToast({
                  title: '保存成功!',
                  icon: '',
                  image: '',
                  duration: 2000,
                  mask: true,
                  success: function(res) {},
                  fail: function(res) {},
                  complete: function(res) {},
                })
                that.setData({
                  savatext: '重新测试'
                })
              },
              fail(res) {},
              complete(res) {}
            })
          }
        })
      }, 1500)
    }
  },
  drawtitle(ctx, textmain, t, that) {
    //根据奖状的名字长度设置奖状样式
    ctx.drawImage(textmain.length > 4 ? that.data.newList[1] : that.data.newList[0], that.rem(60 + 219 * t), that.rem(200), that.rem(194), that.rem(132))
    ctx.setTextAlign('left')
    ctx.setFillStyle('#2862AB')
    ctx.draw(true)
    //字的展示形式
    if (textmain.length <= 3) {
      ctx.setFontSize(that.rem(55))
      ctx.fillText(textmain, that.rem(75 + 219 * t), that.rem(260))
    } else {
      ctx.setFontSize(that.rem(42))
      ctx.fillText(textmain.substr(0, 4), that.rem(75 + 219 * t), that.rem(255), that.rem(194))
      ctx.fillText(textmain.substr(4, 2), that.rem(75 + 219 * t), that.rem(300), that.rem(100))
    }
    ctx.draw(true)
  },
  tostringLength(title, n, textmain, length, ctx, that) {
    //设置证书类型解释框
    ctx.setFillStyle('white')
    ctx.draw(true)
    ctx.drawImage(that.data.newList[4], that.rem(32), that.rem(550 + 130 * n), that.rem(160), that.rem(40))
    ctx.draw(true)
    ctx.setFontSize(that.rem(26))
    ctx.setTextAlign('center')
    ctx.setFillStyle('#2862AB')
    ctx.draw(true)
    ctx.fillText(title, that.rem(110), that.rem(580 + 130 * n), that.rem(150))
    if (textmain.length / length > 1 && textmain.length / length < 2) {
      ctx.setTextAlign('left')
      ctx.setFillStyle('white')
      ctx.fillText(textmain.substr(0, length), that.rem(210), that.rem(580 + 130 * n), that.rem(500))
      ctx.fillText(textmain.substr(length, length), that.rem(210), that.rem(610 + 130 * n), that.rem(500))
    }
    
    if (textmain.length / length < 1) {
      ctx.setTextAlign('left')
      ctx.setFillStyle('white')
      ctx.fillText(textmain.substr(0, length), that.rem(210), that.rem(580 + 130 * n), that.rem(500))
    }
    if (textmain.length / length > 2 && textmain.length / length < 3) {
      ctx.setTextAlign('left')
      ctx.setFillStyle('white')
      ctx.fillText(textmain.substr(0, length), that.rem(210), that.rem(580 + 130 * n), that.rem(500))
      ctx.fillText(textmain.substr(length, length), that.rem(210), that.rem(610 + 130 * n), that.rem(500))
      ctx.fillText(textmain.substr(2 * length, length), that.rem(210), that.rem(640 + 130 * n), that.rem(500))
    }
    if (textmain.length / length > 3) {
      ctx.setTextAlign('left')
      ctx.setFillStyle('white')
      ctx.fillText(textmain.substr(0, length), that.rem(210), that.rem(580 + 130 * n), that.rem(500))
      ctx.fillText(textmain.substr(length, length), that.rem(210), that.rem(610 + 130 * n), that.rem(500))
      ctx.fillText(textmain.substr(2 * length, length), that.rem(210), that.rem(640 + 130 * n), that.rem(500))
      ctx.fillText(textmain.substr(3 * length, length), that.rem(210), that.rem(670 + 130 * n), that.rem(500))
    }
    ctx.drawImage(that.data.newList[5], that.rem(580), this.data.systemInfo.windowHeight - that.rem(210), that.rem(130), that.rem(180))
    ctx.draw(true)
  },

生成的图片效果如下，纯前端项目，把appid修改一下即可体验，
主要的思路是，首先下载图片到临时本地地址，然后绘制背景，根据坐标绘制文字，然后再给文字样式，字号和颜色，最后一步是合成图片，然后保存到相册

在这里插入图片描述