XRSystem: requestSession() - Web APIs 编辑

The XRSystem interface's requestSession() method returns a promise which resolves to an XRSession object through which you can manage the requested type of WebXR session.

While only one immersive VR session can be active at a time, multiple inline sessions can be in progress at once.

Syntax

var sessionPromise = xr.requestSession(sessionMode, sessionInit)

Parameters

 sessionMode

A DOMString whose value is one of those included in the XRSessionMode enum. The supported modes are:

immersive-ar

The session's output will be given exclusive access to the immersive device, but the rendered content will be blended with the real-world environment. The session's environmentBlendMode indicates the method to be used to blend the content together.

Important: The immersive-ar mode is defined by the WebXR Augmented Reality Module, which is not yet stable and should not be used other than for testing and experimentation.

immersive-vr

Indicates that the rendered session will be displayed using an immersive XR device in VR mode; it is not intended to be overlaid or integrated into the surrounding environment. The environmentBlendMode is expected to be opaque if possible, but might be additive if the hardware requires it.

inline

The output is presented inline within the context of an element in a standard HTML document, rather than occupying the full visual space. Inline sessions can be presented in either mono or stereo mode, and may or may not have viewer tracking available. Inline sessions don't require special hardware and should be avalable on any user agent offering WebXR API support.

sessionInit Optional

A XRSessionInit object providing options to configure the new XRSession. See Specifying session options for details on how to configure a WebXR session.

Return value

A Promise that resolves with an XRSession object if the device and user agent support the requested mode and features.

Exceptions

This method doesn't throw true exceptions; instead, it rejects the returned promise, passing into it a DOMException whose name is one of the following:

InvalidStateError

The requested session mode is immersive-vr but there is already an immersive VR session either currently active or in the process of being set up. There can only be one immersive VR session at a time.

NotSupportedError

There is no WebXR-compatible device available, or the device does not support the specified sessionMode; this can also be thrown if any of the required options are unsupported.

SecurityError

Permission to enter the specified XR mode is denied. This can happen for a number of reasons, which are covered in more detail in Permissions and security in WebXR Device API.

Examples

Creating an immersive VR session

The following example calls requestSession() requesting an "immersive-vr" session. If the Promise resolves, it sets up a session and initiates the animation loop.

navigator.xr.requestSession("immersive-vr")
.then((xrSession) => {
  xrSession.addEventListener('end', onXRSessionEnded);
  // Do necessary session setup here.
  // Begin the session’s animation loop.
  xrSession.requestAnimationFrame(onXRAnimationFrame);
}).catch(function(error) {
  // "immersive-vr" sessions are not supported
  console.warn("'immersive-vr' isn't supported, or an error occurred activating VR!");
});

Verifying WebXR support and using a button to start VR mode

The following example shows how to use both isSessionSupported() and requestSession(). First, it checks to see if WebXR is available by verifying the existence of navigator.xr. Next, it calls isSessionSupported(), passing it the desired session option before enabling controls for entering XR. Adding controls is a necessary step because entering XR requires a user action. Finally, the onButtonClicked() method calls requestSession() using the same session option passed to isSessionSupported().

if (navigator.xr) {
  navigator.xr.isSessionSupported('immersive-vr')
  .then((isSupported) => {
    if (isSupported) {
      immersiveButton.addEventListener('click', onButtonClicked);
      immersiveButton.textContent = 'Enter XR';
      immersiveButton.disabled = false;
    } else {
      console.log("WebXR doesn't support immersive-vr mode!");
    }
  });
} else {
  console.log("WebXR is not available!");
}

function onButtonClicked() {
  if (!xrSession) {
    navigator.xr.requestSession('immersive-vr')
    .then((session) => {
      xrSession = session;
      // onSessionStarted() not shown for reasons of brevity and clarity.
      onSessionStarted(xrSession);
    });
  } else {
    // Button is a toggle button.
    xrSession.end().then(() => xrSession = null);
  }
}

Specifications

Browser compatibility

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