XRView: isFirstPersonObserver property

The XRView interface's read-only isFirstPersonObserver property is a boolean indicating if the XRView is a first-person observer view.

To create video recordings of AR device cameras, you can't simply use one of the rendered eyes, as there often will be a physical offset. Some devices expose a secondary view, the first-person observer view, which has an eye of none.

To receive a first-person observer view, you need to enable the "secondary-views" feature descriptor explicitly (typically as an optional feature). See XRSystem.requestSession() for details.

The isFirstPersonObserver property then allows you to check which secondary view is a first-person observer view.

// Make sure to enable "secondary-view"
navigator.xr
  .requestSession("immersive-ar", {
    optionalFeatures: ["secondary-views"],
  })
  .then((session) => {
    // …

    session.requestAnimationFrame((frame) => {
      const views = frame.getViewerPose(space);
      // Make sure to iterate over all views
      for (const view of views) {
        if (view.isFirstPersonObserver) {
          renderFPO();
        } else {
          render();
        }
      }
    });
  });