, wx.downloadFile({
               url: 'https://qqadapt.qpic.cn/adapt/0/7363d9b4-a4d0-46e1-a42a-5fc8b5f24a5f/400?pt=0&ek=1&kp=1&sce=60-2-2',
               success (res) {
               var success_url = res.tempFilePath
               })
             var o = success_url1
             const fileManager = wx.getFileSystemManager(); 
            let base64 = 'data:image/jpg;base64,' +fileManager.readFileSync(o,'base64')
        query.select('#myCanvas')
          .fields({
            node: true,
            size: true
          }).exec((res) => {
            console.log(res)
            const canvas = res[0].node
            const ctx = canvas.getContext('2d')
            const dpr = wx.getSystemInfoSync().windowWidth / 375
            canvas.width = res[0].width * dpr
            canvas.height = res[0].height * dpr
            ctx.scale(dpr, dpr)
            that.roundRectc(canvas, ctx, 0, 0, 262.5 * dpr, 430 * dpr, 15 * dpr, '#transparent', dpr, base64) //大图

          })

我用过base64转码， downloadFile域名也添加了，就是没图片。。QAQ