XRSession: requestAnimationFrame() method
Limited availability
This feature is not Baseline because it does not work in some of the most widely-used browsers.
Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.
The XRSession
method requestAnimationFrame()
, much like the
Window
method of the same name, schedules a callback to be executed the
next time the browser is ready to paint the session's virtual environment to the XR
display. The specified callback is executed once before the next repaint; if
you wish for it to be executed for the following repaint, you must
call requestAnimationFrame()
again. This can be done from within the
callback itself.
The callback takes two parameters as inputs: an XRFrame
describing the
state of all tracked objects for the session, and a timestamp you can use to compute
any animation updates needed.
You can cancel a previously scheduled animation by calling
cancelAnimationFrame()
.
Note:
Despite the obvious similarities between these methods and the
global requestAnimationFrame()
function
provided by the Window
interface, you must not treat these as
interchangeable. There is no guarantee that the latter will work at all while
an immersive XR session is underway.
Syntax
requestAnimationFrame(animationFrameCallback)
Parameters
animationFrameCallback
-
A function which is called before the next repaint in order to allow you to update and render the XR scene based on elapsed time, animation, user input changes, and so forth. The callback receives as input two parameters:
time
-
A
DOMHighResTimeStamp
indicating the time offset at which the updated viewer state was received from the WebXR device. xrFrame
-
An
XRFrame
object describing the state of the objects being tracked by the session. This can be used to obtain the poses of the viewer and the scene itself, as well as other information needed to render a frame of an AR or VR scene.
Return value
An integer value which serves as a unique, non-zero ID or handle you may pass to
cancelAnimationFrame()
if you need to
remove the pending animation frame request.
Examples
The following example requests XRSession
with "inline" mode so that it can
be displayed in an HTML element (without the need for a separate AR or VR device).
Note:
A real application should check that the device and the User
Agent support WebXR API at all and then that they both support the desired session
type via XRSystem.isSessionSupported()
.
// Obtain XR object
const XR = navigator.xr;
// Request a new XRSession
XR.requestSession("inline").then((xrSession) => {
xrSession.requestAnimationFrame((time, xrFrame) => {
const viewer = xrFrame.getViewerPose(xrReferenceSpace);
gl.bindFramebuffer(xrWebGLLayer.framebuffer);
for (const xrView of viewer.views) {
const xrViewport = xrWebGLLayer.getViewport(xrView);
gl.viewport(
xrViewport.x,
xrViewport.y,
xrViewport.width,
xrViewport.height,
);
// WebGL draw calls will now be rendered into the appropriate viewport.
}
});
});
The following example was taken directly from the spec draft. This example demonstrates
a design pattern that ensures seamless transition between non-immersive animations
created via Window.requestAnimationFrame
and immersive XR animations.
let xrSession = null;
function onWindowAnimationFrame(time) {
window.requestAnimationFrame(onWindowAnimationFrame);
// This may be called while an immersive session is running on some devices,
// such as a desktop with a tethered headset. To prevent two loops from
// rendering in parallel, skip drawing in this one until the session ends.
if (!xrSession) {
renderFrame(time, null);
}
}
// The window animation loop can be started immediately upon the page loading.
window.requestAnimationFrame(onWindowAnimationFrame);
function onXRAnimationFrame(time, xrFrame) {
xrSession.requestAnimationFrame(onXRAnimationFrame);
renderFrame(time, xrFrame);
}
function renderFrame(time, xrFrame) {
// Shared rendering logic.
}
// Assumed to be called by a user gesture event elsewhere in code.
function startXRSession() {
navigator.xr.requestSession("immersive-vr").then((session) => {
xrSession = session;
xrSession.addEventListener("end", onXRSessionEnded);
// Do necessary session setup here.
// Begin the session's animation loop.
xrSession.requestAnimationFrame(onXRAnimationFrame);
});
}
function onXRSessionEnded() {
xrSession = null;
}
Specifications
Specification |
---|
WebXR Device API # dom-xrsession-requestanimationframe |
Browser compatibility
BCD tables only load in the browser