小程序 canvas type="2d"

<!-- 标签是在组件当中使用，组件和页面使用是有区别的 --> <canvas style="width:{{imgWidth}}px;height:{{imgHeight}};position:fixed;left:9999px" type="2d" id="myCanvas" class="canvas"></canvas>     // 下载静态码 myCanvas是我的背景图片 // 这里的处理，调用this.getQRCodeImg生成二维码图片再绘制背景图片     handleDownload() {       this.getQRCodeImg().then(data=> {         wx.createSelectorQuery().in(this).select('#myCanvas').fields({           node: true,           size: true,         })         .exec( async res=> {           const canvas = res[0].node           const width = res[0].width           this.canvasWidth = width           const height = res[0].height           this.canvasHeight = height           const ctx = canvas.getContext('2d')           const dpr = wx.getSystemInfoSync().pixelRatio           canvas.width = res[0].width * dpr           canvas.height = res[0].height * dpr           ctx.scale(dpr, dpr)           ctx.clearRect(0, 0, wx.getSystemInfoSync().windowWidth, wx.getSystemInfoSync().windowHeight)           const img = canvas.createImage()           img.src = '../../image/back-img.png' // 可以是本地地址也可以是网络地址           let imgHeight = null           wx.getImageInfo({             src:'../../image/back-img.png',             success(res){               // 屏幕宽度/图片宽度  *  图片高度               imgHeight = wx.getSystemInfoSync().windowWidth/res.width * res.height               console.log(res);             }           })           img.onload = () => ctx.drawImage(img, 0, 0, wx.getSystemInfoSync().windowWidth, imgHeight)           const codeImg = canvas.createImage()           codeImg.src = data // 可以是本地地址也可以是网络地址           wx.getImageInfo({             src:data,             success(res){               // console.log(res);             }           })           codeImg.onload = () => ctx.drawImage(codeImg, codePosition, 146, 151, 151)           wx.showModal({             title: '提示',             content: '是否下载图片？？',             success: (res)=> {               if (res.confirm) {                 wx.canvasToTempFilePath({                   canvas: canvas,                   success: (res) => {                     // console.log(resx.tempFilePath);                     wx.saveImageToPhotosAlbum({                       filePath: res.tempFilePath,                       success: function (data) {                         wx.showToast({                           title: '已保存到相册',                           icon: 'success',                           duration: 2000                         })                       },                       fail: function (err) {                       },                       complete(res) {                         wx.hideLoading();                         console.log(res);                       }                     })                   },                   fail: (ex) => {                       console.log(ex);                   }                 },this);               }             }           })         })       })     }, // 生成图片 staticCode是我的另外一个Canvas它是一个二维码 getQRCodeImg() {       const ctx = wx.createCanvasContext('staticCode')       return new Promise((resolve,rejects)=> {         setTimeout(() => {           ctx.draw(false, setTimeout(() => {             wx.canvasToTempFilePath({               width: codewidth,               height: codewidth,               canvasId: 'staticCode',               success: res => {                 resolve(res.tempFilePath)               },             fail: error => {               rejects(error)             }             }, this)           },300))         }, 200)       })     },