XRViewerPose
The WebXR Device API interface XRViewerPose
represents the pose (the position and orientation) of a viewer's point of view on the scene. Each XRViewerPose
can have multiple views to represent, for example, the slight separation between the left and right eye.
This view can represent anything from the point-of-view of a user's XR headset to the viewpoint represented by a player's movement of an avatar using mouse and keyboard, presented on the screen, to a virtual camera capturing the scene for a spectator.
Instance properties
In addition to the properties inherited from XRPose
, XRViewerPose
includes the following:
views
Read only-
An array of
XRView
objects, one for each viewpoint on the scene which is needed to represent the scene to the user. A typical headset provides a viewer pose with two views whoseeye
property is eitherleft
orright
, indicating which eye that view represents. Taken together, these views can reproduce the 3D effect when displayed on the XR device.
Usage notes
The XRViewerPose
object is used to describe the state of a viewer of a WebXR scene as it's tracked by the user's XR hardware. The viewer may be the virtual representation of the user, or it may represent another device or interface which may serve as the source of a position and orientation that make up a view upon the scene. For example, every player in a MMORPG might have an instance of XRViewerPose
to provide a way to calculate what they can see; if the game provides a mechanism that tells the player if another player sees them, or that they see another player, this information becomes crucial.
An XRViewerPose
is always obtained and referenced relative to an existing XRReferenceSpace
. This ensures that positions and orientations are reported using the expected relative coordinate system.
To render a scene using the XRViewerPose
representing the user's head, one would iterate over the views in the views
array, rendering them one after another. By calling viewport()
on the WebGL context, specifying the XRView
as input, you can get the viewport to use when rendering in order to draw the frame for that eye into the correct part of the drawing surface.
Also, when rendering the scene for spectators or other players in a multiplayer game, the transform
of the XRViewerPose
can be used to determine both placement and facing direction of the other players in the game, so that they can be drawn in the correct place with the correct facing.
The viewer's pose for the animation frame represented by XRFrame
can be obtained by calling the frame's getViewerPose()
method, specifying the reference space in which the origin's position should be computed. The returned XRViewerPose
tells you where the viewer is and what direction they're facing at the time at which the frame takes place.
Examples
In this example—part of the code to render an XRFrame
,
getViewerPose()
is called to get an XRViewerPose
using the
same reference space the code is using as its base reference space. If a valid pose is
returned, the frame is rendered by clearing the backbuffer and then rendering each of
the views in the pose; these are most likely the views for the left and right eyes.
js
const pose = frame.getViewerPose(xrReferenceSpace);
if (pose) {
const glLayer = xrSession.renderState.baseLayer;
gl.bindFrameBuffer(gl.FRAMEBUFFER, glLayer.framebuffer);
gl.clearColor(0, 0, 0, 1);
gl.clearDepth(1);
gl.clear(gl.COLOR_BUFFER_BIT, gl.DEPTH_BUFFER_BIT);
for (const view of pose.views) {
const viewport = glLayer.getViewport(view);
gl.viewport(viewport.x, viewport.y, viewport.width, viewport.height);
/* render the scene for the eye view.eye */
}
}
Passing each view
to getViewport()
returns the WebGL viewport to apply in order to cause the rendered
output to be positioned correctly in the framebuffer for rendering to the corresponding eye on the output device.
This code is derived from Drawing a frame in our "Movement and motion" WebXR example. You can see more context and see much more on that page.
Specifications
Specification |
---|
WebXR Device API # xrviewerpose-interface |
Browser compatibility
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