微信小程序中生成图片的代码

<!--wxml代码--><view>  <canvas></canvas></view>

const util = require('../../utils/util.js')

//util.jsvar Promise = require('../components/bluebird.min.js')module.exports = {  promisify: api => {    return (options, ...params) => {      return new Promise((resolve, reject) => {        const extras = {          success: resolve,          fail: reject        }        api({ ...options, ...extras }, ...params)      })    }  }}

//获取手机宽高 wx.getSystemInfo({    success: function (res) {      wc.put('phoneInfo', res)    }  });var windowHeight = phoneInfo.windowHeight, windowWidth = phoneInfo.windowWidthself.setData({   windowHeight: windowHeight,   windowWidth: windowWidth })//在这段代码中，我们通过使用wx.getImageInfo这个API来下载一个网络图片到本地（并可获取该图片的尺寸等其他信息），然后调用ctx.drawImage方法将图片绘制到画布上，填满画布。const wxGetImageInfo = util.promisify(wx.getImageInfo)//绘制二维码Promise.all([      //背景图      wxGetImageInfo({        src: 'https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1536213812443&di=753a0a49acfd390fba9fd7884daafa5c&imgtype=0&src=http%3A%2F%2Fi5.hexunimg.cn%2F2016-08-10%2F185422031.jpg'      }),      //二维码      wxGetImageInfo({        src: 'https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=1898297765,3486952215&fm=26&gp=0.jpg'      })    ]).then(res => {      console.log(res)      if (res[0].errMsg == "getImageInfo:ok" && res[1].errMsg == "getImageInfo:ok"){        const ctx = wx.createCanvasContext('shareCanvas')        // 底图        ctx.drawImage(res[0].path, 0, 0, windowWidth, windowHeight)        //写入文字        ctx.setTextAlign('center')    // 文字居中        ctx.setFillStyle('#f3a721')  // 文字颜色：黑色        ctx.setFontSize(22)         // 文字字号：22px        ctx.fillText("作者：墜夢—Eric", windowWidth / 2, windowHeight / 2)        // 小程序码        const qrImgSize = 150        ctx.drawImage(res[1].path, (windowWidth - qrImgSize) / 2, windowHeight / 1.8, qrImgSize, qrImgSize)        ctx.stroke()        ctx.draw()      }else{        wx.showToast({          title: '邀请卡绘制失败!',          image:'../../asset/images/warning.png'        })      } })

  //保存邀请卡  saveInviteCard:function(){    console.log('保存图片')    const wxCanvasToTempFilePath = util.promisify(wx.canvasToTempFilePath)    const wxSaveImageToPhotosAlbum = util.promisify(wx.saveImageToPhotosAlbum)    wxCanvasToTempFilePath({      canvasId: 'shareCanvas'    }, this).then(res => {      return wxSaveImageToPhotosAlbum({        filePath: res.tempFilePath      })    }).then(res => {      wx.showToast({        title: '已保存到相册'      })    })  }