用getImageInfo把网络图片加载到本地之后，用drawImage方法绘制到画布上依然没有显示图片，并且没有报错
      wx.getImageInfo({
        src: currentValue.image,
        success: function(res) {
          maskCanvas.drawImage(res.path,0, 0, currentValue.width * currentValue.scale * prop, currentValue.height * currentValue.scale * prop);
        }
      });