wxml，xr-frame中plane平面默认是趴在场景中的，需要先绕x轴渲染90度，

// 面片    <xr-node id="l" position="-3.0 0 0.0"><xr-mesh rotation="90 0 0" geometry="plane" uniforms="u_baseColorFactor:0.2 0.2 0.4 1, u_metallicRoughnessValues: 0 0.6" states="cullOn: false"></xr-mesh></xr-node>// 模型<xr-node id="b" position="0 0 -3.0"><xr-gltf rotation="0 -90 0" scale="0.01 0.01 0.01" model="door"></xr-gltf></xr-node>

在场景的ready事件中获取相机，模型，并注册tick请求动画帧事件

   handleReady({detail}) {const xrScene = this.scene = detail.value;const xrSystem = wx.getXrFrameSystem();this.mat = new (xrSystem.Matrix4)();const { width, height } = this.scenethis.cameraTrs = this.scene.getElementById('camera').getComponent(xrSystem.Transform);this.leftTRS = this.scene.getElementById('l').getComponent(xrSystem.Transform);this.backTRS = this.scene.getElementById('b').getComponent(xrSystem.Transform);this.FACING = xrSystem.Vector3.createFromNumber(0, 0, 0);this.UP = xrSystem.Vector3.createFromNumber(0, 1, 0);xrScene.event.add('tick', this.handleTick.bind(this));},

 请求动画帧中，计算旋转四元数，更新模型朝向

    handleTick: function () {const xrSystem = wx.getXrFrameSystem();if (this.leftTRS) {const quaternion = this.leftTRS.quaternion;// 算出从物体到相机的向量this.FACING.set(this.cameraTrs.position).sub(this.leftTRS.position, this.FACING);xrSystem.Quaternion.lookRotation(this.FACING, this.UP, quaternion);}if (this.backTRS) {const quaternion = this.backTRS.quaternion;// 算出从物体到相机的向量this.FACING.set(this.cameraTrs.position).sub(this.backTRS.position, this.FACING);xrSystem.Quaternion.lookRotation(this.FACING, this.UP, quaternion);}}