XRSystem: requestSession()
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
requestSession(mode)
requestSession(mode, options)
Parameters
mode
-
A
String
defining the XR session mode. 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'senvironmentBlendMode
indicates the method to be used to blend the content together. -
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. TheenvironmentBlendMode
is expected to beopaque
if possible, but might beadditive
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 available on any user agent offering WebXR API support.
-
options
Optional-
An object to configure the
XRSession
. If none are included, the device will use a default feature configuration for all options.-
requiredFeatures
Optional: An array of values which the returnedXRSession
must support. See Session features below. -
optionalFeatures
Optional: An array of values identifying features which the returnedXRSession
may optionally support. See Session features below. domOverlay
Optional: An object with a requiredroot
property that specifies the overlay element that will be displayed to the user as the content of the DOM overlay. See the example below.depthSensing
Optional: An object with two required propertiesusagePreference
anddataFormatPreference
to configure how to perform depth sensing. See the example below.
-
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
DOMException
-
Returned if 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
DOMException
-
Returned if 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
DOMException
-
Returned if 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.
Session features
The following session features and reference spaces can be requested, either as optionalFeatures
or requiredFeatures
.
anchor
-
Enable use of
XRAnchor
objects. bounded-floor
-
Similar to the
local
type, except the user is not expected to move outside a predetermined boundary, given by theboundsGeometry
in the returned object. depth-sensing
-
Enable the ability to obtain depth information using
XRDepthInformation
objects. dom-overlay
-
Enable allowing to specify a DOM overlay element that will be displayed to the user.
hand-tracking
-
Enable articulated hand pose information from hand-based input controllers (see
XRHand
andXRInputSource.hand
). hit-test
-
Enable hit testing features for performing hit tests against real world geometry.
layers
-
Enable the ability to create various layer types (other than
XRProjectionLayer
). light-estimation
-
Enable the ability to estimate environmental lighting conditions using
XRLightEstimate
objects. local
-
Enable a tracking space whose native origin is located near the viewer's position at the time the session was created. The exact position depends on the underlying platform and implementation. The user isn't expected to move much if at all beyond their starting position, and tracking is optimized for this use case.
local-floor
-
Similar to the
local
type, except the starting position is placed in a safe location for the viewer to stand, where the value of the y axis is 0 at floor level. If that floor level isn't known, the user agent will estimate the floor level. If the estimated floor level is non-zero, the browser is expected to round it such a way as to avoid fingerprinting (likely to the nearest centimeter). secondary-views
-
Enable
XRView
objects to be secondary views. This can be used for first-person observer views used for video capture, or "quad views" where there are two views per eye, with differing resolution and fields of view. unbounded
-
Enable a tracking space which allows the user total freedom of movement, possibly over extremely long distances from their origin point. The viewer isn't tracked at all; tracking is optimized for stability around the user's current position, so the native origin may drift as needed to accommodate that need.
viewer
-
Enable a tracking space whose native origin tracks the viewer's position and orientation.
Security requirements
Several session features and the various reference spaces have minimum security and privacy requirements, like asking for user consent and/or requiring the Feature-Policy
: xr-spatial-tracking
directive to be set. See also Permissions and security for more details.
Session feature | User consent requirement | Feature policy requirement |
---|---|---|
bounded-floor |
Always required | xr-spatial-tracking |
depth-sensing |
— | xr-spatial-tracking |
hand-tracking |
Always required | — |
hit-test |
— | xr-spatial-tracking |
local |
Always required for inline sessions | xr-spatial-tracking |
local-floor |
Always required | xr-spatial-tracking |
unbounded |
Always required | xr-spatial-tracking |
viewer |
Always required | — |
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);
}
}
Requesting a session with required features
Require an unbounded experience in which the user is able to freely move around their physical environment:
navigator.xr.requestSession('immersive-vr', { requiredFeatures: ['unbounded'] })
Requesting a session with a DOM overlay
navigator.xr.requestSession("immersive-ar", {
optionalFeatures: ["dom-overlay"],
domOverlay: {
root: document.getElementById("xr-overlay")
}
}
Requesting a depth-sensing session
Here, the caller is able to handle both CPU- and GPU-optimized usage, as well as both "luminance-alpha" and "float32" formats. The order indicates preference for CPU and "luminance-alpha":
navigator.xr.requestSession("immersive-ar", {
requiredFeatures: ["depth-sensing"],
depthSensing: {
usagePreference: ["cpu-optimized", "gpu-optimized"],
formatPreference: ["luminance-alpha", "float32"]
}
});
Specifications
Specification |
---|
WebXR Device API # dom-xrsystem-requestsession |
Browser compatibility
BCD tables only load in the browser