canvas转base64图片以后，图片镜像显示

[codfishzhang]

代码如下，将canvas转成base64图片以后，得到的图片是镜像反转的，不是原图

qrcodeBase64Tools.draw(false, () => {
  wepy.canvasGetImageData({
    canvasId: 'qrcodeBase64Tools',
    x: 0,
    y: 0,
    width: qrcodeRes.width,
    height: qrcodeRes.height
  }).then((res) => {
    let pngData = upng.encode([res.data.buffer], res.width, res.height)
    this.qrcodeBase64 = 'data:image/jpeg;base64,' + wepy.arrayBufferToBase64(pngData)
    this.$apply()
  })
})```