How do I render cesium scene to webxr?

[YHIsMyLove]

I’m trying to make the scene displayed on my oculus quest 2 vr headset using WebXR API. I’ve searched the forum and the internet and the solution I got all seems outdated. I wrote a demo using raw webgl where i call gl.clear and gl.drawArrays in the xrSession.requestAnimationFrame callback function and it works fine. But when I replace them with cesium’s render method, the headset screen only shows the clear color I set with gl.clearColor and nothing else. Currently I only need to make the scene shown on the headset screen. What should I do to achieve this?

Here are part of my code

function initVR() {
var gl = viewer.scene.context._gl;
navigator.xr.requestSession('immersive-vr').then((xrSession) => {
xrSession.requestReferenceSpace("local").then((xrReferenceSpace) => {  
    const xrWebGLLayer = new XRWebGLLayer(xrSession, gl,)
    xrSession.updateRenderState({ baseLayer: xrWebGLLayer })
    xrSession.requestAnimationFrame(animate)
    function animate() {
        xrSession.requestAnimationFrame((time, xrFrame) => {
             let poses = xrFrame.getViewerPose(xrReferenceSpace);
              // gl.clearColor(1,0,1,1)
               gl.bindFramebuffer(gl.FRAMEBUFFER, xrSession.renderState.baseLayer.framebuffer);
                // **draw call here**
                viewer.scene.render()
                 for (let xrView of poses.views) {
                        let xrViewport = xrWebGLLayer.getViewport(xrView);
                         gl.viewport(xrViewport.x, xrViewport.y, xrViewport.width, xrViewport.height);
                  }
                 animate()
             });
         }
       }).catch((err) => {
          console.log(err)
       });
       }).catch((err) => {
          console.log(err)
        });
 }

[cabanier]

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