...
ctx.draw(false, this.canvasToSrc())
...

canvasToSrc: async function() {
    console.log('海报绘制完成')
    const wxCanvasToTempFilePath = promisify(wx.canvasToTempFilePath)
    const posterSrc = (await wxCanvasToTempFilePath({
      canvasId: 'shareCanvas'
    }, this)).tempFilePath
    console.log(posterSrc)
    wx.hideLoading()
    this.setData({
      posterSrc: posterSrc,
      posterShow: true
    })
  },

首次执行，图片为空白，第二次执行才正常。我的理解是draw方法的回调有bug？