<xr-ar-tracker>在使用前置摄像头时虚拟物会和目标关于横轴镜像（marker模式），在使用后置摄像头时则一切正常，时刻保持重合，这是为什么？怎么改？

<xr-scene ar-system="modes:Marker;camera:Front;" bind:ready="handleReady">
  <xr-assets bind:loaded="handleAssetsLoaded">
    <xr-asset-load type="texture" asset-id="hikari" src="/images/baidu.png" />
    <xr-asset-material asset-id="mat" effect="simple" uniforms="u_baseColorMap: hikari" />
  </xr-assets>

  <xr-node wx:if="{{loaded}}">
    <xr-ar-tracker
      mode="Marker"
      src="https://mmbizwxaminiprogram-1258344707.cos.ap-guangzhou.myqcloud.com/xr-frame/demo/xr-frame-team/2dmarker/hikari.jpg"
    >
      <xr-mesh node-id="mesh-plane" geometry="plane" material="mat" />
    </xr-ar-tracker>
  </xr-node>

  <xr-camera clear-color="0.4 0.8 0.6 1" background="ar" is-ar-camera />

</xr-scene>