examples/offscreen-canvas.html

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<html>
  <head>
    <meta charset='utf-8'>
    <meta name='viewport' content='width=device-width, initial-scale=1, user-scalable=no'>
    <meta name='mobile-web-app-capable' content='yes'>
    <meta name='apple-mobile-web-app-capable' content='yes'>

    <title>Offscreen Canvas</title>

    <link href='css/common.css' rel='stylesheet'></link>

    <script src='../build/webxr-polyfill.js'></script>
    <script>
        window.polyfill = new WebXRPolyfill();
    </script>
    <script src='js/gl-matrix-min.js'></script>
    <script src='js/cottontail.js'></script>
    <script src='js/webxr-button.js'></script>
  </head>
  <body>
    <header>
      <details open>
        <summary>Offscreen Canvas</summary>
        <p>
          This sample demonstrates use of a non-immersive XRSession to present
          'Magic Window' rendered from an OffscreenCanvas.
        </p>
      </details>
    </header>
    <script>
      (function () {
      'use strict';

      // XR globals.
      let xrButton = null;
      let xrExclusiveFrameOfRef = null;
      let xrNonExclusiveFrameOfRef = null;

      // WebGL scene globals.
      let gl = null;
      let renderer = null;
      let scene = new CubeSeaScene();

      function initXR() {
        xrButton = new XRDeviceButton({
          onRequestSession: onRequestSession,
          onEndSession: onEndSession
        });
        document.querySelector('header').appendChild(xrButton.domElement);

        if (navigator.xr) {
          navigator.xr.isSessionSupported('immersive-vr').then((supported) => {
            xrButton.enabled = supported;
          });

          // In order for a non-immersive session to be used we must provide
          // an outputContext, which indicates the canvas that will contain
          // results of the session's rendering.
          let outputCanvas = document.createElement('canvas');
          let ctx = outputCanvas.getContext('xrpresent');

          // Pick an arbitrary device for the magic window content and start
          // up a non-immersive session if possible.
          navigator.xr.requestSession('inline')
              .then((session) => {
                // Add the canvas to the document once we know that it will be
                // rendered to.
                document.body.appendChild(outputCanvas);
                onSessionStarted(session);
              });
        }
      }

      function onRequestSession() {
        navigator.xr.requestSession('immersive-vr').then((session) => {
          xrButton.setSession(session);
          onSessionStarted(session);
        });
      }

      function onSessionStarted(session) {
        session.addEventListener('end', onSessionEnded);

        if (!gl) {
          let offscreenCanvas = new OffscreenCanvas(1, 1);
          gl = offscreenCanvas.getContext('webgl', {
            xrCompatible: true
          });

          renderer = new Renderer(gl);

          scene.setRenderer(renderer);
        }

        session.baseLayer = new XRWebGLLayer(session, gl);

        session.requestFrameOfReference('eye-level').then((frameOfRef) => {
          // Since we're dealing with multple sessions now we need to track
          // which XRFrameOfReference is associated with which XRSession.
          if (session.immersive) {
            xrExclusiveFrameOfRef = frameOfRef;
          } else {
            xrNonExclusiveFrameOfRef = frameOfRef;
          }
          session.requestAnimationFrame(onXRFrame);
        });
      }

      function onEndSession(session) {
        session.end();
      }

      function onSessionEnded(event) {
        // Only reset the button when the immersive session ends.
        if (event.session.immersive)
          xrButton.setSession(null);
      }

      // Called every time a XRSession requests that a new frame be drawn.
      function onXRFrame(t, frame) {
        let session = frame.session;
        // Ensure that we're using the right frame of reference for the session.
        let frameOfRef = session.immersive ?
                         xrExclusiveFrameOfRef :
                         xrNonExclusiveFrameOfRef;
        let pose = frame.getViewerPose(frameOfRef);

        scene.startFrame();

        session.requestAnimationFrame(onXRFrame);

        gl.bindFramebuffer(gl.FRAMEBUFFER, session.baseLayer.framebuffer);
        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

        if (pose) {
          for (let view of frame.views) {
            let viewport = session.baseLayer.getViewport(view);
            gl.viewport(viewport.x, viewport.y,
                        viewport.width, viewport.height);

            scene.draw(view.projectionMatrix, pose.getViewMatrix(view));
          }
        }

        scene.endFrame();
      }

      // Start the XR application.
      initXR();
      })();
    </script>
  </body>
</html>