<xr-scene ar-system="modes:Face;camera:{{direction}}" bind:ready="handleReady" bind:tick="handleTick">

  <xr-assets bind:loaded="handleAssetsLoaded">

    <xr-asset-load type="gltf" asset-id="mask" src="{{img}}" />

  </xr-assets>

  <xr-env env-data="xr-frame-team-workspace-day" />

  <xr-light type="ambient" color="1 1 1" intensity="1" />

  <xr-light type="directional" rotation="40 70 0" color="1 1 1" intensity="3" />

  <xr-ar-tracker mode="Face" auto-sync="43">

    <xr-gltf model="mask" rotation="0 180 0" scale="0.5 0.5 0.5" />

  </xr-ar-tracker>

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

</xr-scene>

把camera属性改成动态绑定direction，但是动态修改direction的值，摄像头方向没有变化

 direction: 'Front',// Back