/**
  * 用户点击右上角分享
  */
 onShareAppMessage: function() {
  return {
   imageUrl:'',
   title:''
  };
 }

<canvas canvas-id="canvasid" style="width: 375px; height: 500px;" wx:if="{{canvasShow}}"></canvas>

   let context = wx.createCanvasContext('canvasid')
   context.drawImage(back.path, 0, 60, backWidth, backHeight) //绘制下方背景图
   //绘制圆形头像，参考教程：https://www.jianshu.com/p/9a6ee2648d6f 第二种方法

   context.save();
   var d = 2 * 25;
   var cx = 0 + 25;
   var cy = 0 + 25;
   context.arc(cx, cy,25, 0, 2 * Math.PI);
   context.clip();
   context.drawImage(avatar.path, 0,0, d, d);
   context.restore();
   //绘制名字和点赞数
   context.setFontSize(14)
   context.fillText('userName', 70, 32)
   let zanLength = ('100' + '次赞').length
   context.fillText('100'+ '次赞', 375 - 14 * zanLength, 32)
   //执行draw进行渲染 并返回图片url
   context.draw(true, () => {
    //此方法应执行在draw的回调中
    wx.canvasToTempFilePath({
     x: 0,
     y: 0,
     width: 375,
     height: 400,
     destWidth: 375,
     destHeight: 400,
     canvasId: 'canvasid',
     success(res) {
    //设置onShareAppMessage所返回的数据格式
      let shareInfo = {
       title: 'customTitle',
       imageUrl
      }
      //隐藏画布
      that.setData({
       canvasShow: false
      })
     }
    })
   });

     wx.getImageInfo({
        src: imgUrl,
        success: function(res) {
           /**拿到返回值res[0].path,再把该值作为canvas绘制图片的路径 
            context.drawImage(res[0].path,x,x,x)**/
          let drawImgUrl = res[0].path
        }
      });