XRReferenceSpace - Web APIs 编辑

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The WebXR Device API's XRReferenceSpace interface describes the coordinate system for a specific tracked entity or object within the virtual world using a specified tracking behavior. The tracking behavior is defined by the selected reference space type. It expands upon the base class, XRSpace, by adding support for several different tracking behaviors as well as to request a new reference space which describes the offset transform between the tracked object and another location in the world.

All reference spaces—with the sole exception being bounded reference spaces—are described using the XRReferenceSpace type. Bounded spaces are implemented as XRBoundedReferenceSpace objects. These are special spaces which let you establish a perimeter within which it's "safe" for the viewer to move. For XR systems that allow the user to physically move around, such as those that track movement with a real-world camera, this boundary establishes the edges of the area the user is able to move around in, whether due to physical obstacles or due to limitations of the XR hardware. See the article Using bounded reference spaces to protect the viewer for more on using boundaries to keep the user from colliding with obstacles both physical and virtual.

Properties

In addition to the properties inherited from XRSpace (of which there are none at this time), XRReferenceSpace also inherits the properties of EventTarget. XRReferenceSpace defines no additional properties.

Methods

In addition to the methods inherited from its parent interface, XRSpace (there are none at this time), XRReferenceSpace inherits methods from  EventTarget. XRReferenceSpace also provides the following methods.

getOffsetReferenceSpace() 

Creates and returns a new reference space object as the same type as the one on which you call the method (so, either XRReferenceSpace or XRBoundedReferenceSpace). The new reference space can be used to transform a coordinate from the reference space of the object on which the method is called into a different coordinate space. This is useful for positioning objects while rendering, and to perform the needed transforms when changing the viewer's position and/or orientation in 3D space.

Events

In addition to other events that may be sent to XRSpace or EventTarget objects, the following also apply to XRReferenceSpace objects.

reset

The reset event is sent to an XRReferenceSpace object when the browser detects a discontinuity has occurred wherein the tracked object's origin  relative to the user's environment or location. This can happen, for example, after the user recalibrates their XR device, or if the device automatically adjusts its origin after losing and regaining tracking.

In addition to using addEventListener(), you can establish a reset event handler by setting the onreset event handler property.

Reference space types

The reference space returned by XRSession.requestReferenceSpace() is either XRReferenceSpace or XRBoundedReferenceSpace. The "Interface" column in the table below indicates which of the two types is returned for each reference space type constant..

Reference space descriptors

The types of reference space are listed in the table below, with brief information about their use cases and which interface is used to implement them.

Usage notes

Creating an XRReferenceSpace

There are two situations in which you need to obtain an XRReferenceSpace. The first is when you set up your scene and need to obtain a reference space to represent the user's viewpoint on the world for the duration of the XRSession. To do that, call the XRSession method requestReferenceSpace(), specifying the reference space type you wish to obtain.

xrSession.requestReferenceSpace("local").then((refSpace) => {
  xrReferenceSpace = refSpace;
  /* ... */
});

The other situation in which you may need to acquire a new reference space is if you need to move the origin to a new position; this is commonly done, for example, when your project allows the user to move through the environment using input devices such as the keyboard, mouse, touchpad, or game controls that are not connected through the XR device. Since the origin will typically be the user's location in the space, you need to change the origin to reflect their movement and any orientation changes they make.

To move or rotate the user's view of the world, you need to change the XRReferenceSpace used to represent that viewpoint. However, XRReferenceSpace is immutable, so you need to instead create a new reference space representing the changed viewpoint. This is easily done using the getOffsetReferenceSpace() method.

let offsetTransform = new XRRigidTransform({x: 2, y: 0, z: 1},
                                           {x: 0, y: 1, z: 0, w: 1});
xrReferenceSpace = xrReferenceSpace.getOffsetReferenceSpace(offsetTransform);

This replaces the XRReferenceSpace with a new one whose origin and orientation are adjusted to place the new origin at (2, 0, 1) relative to the current origin and rotated given a unit quaternion that orients the space to put the viewer facing straight up relative to the previous world orientation.

Geometry

The native origin of any XRReferenceSpace is always configured so that +X is considered to be to the right, +Y is upward, and +Z is "backward" or toward the user.

Specifications

Browser compatibility

BCD tables only load in the browser

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

See also

• Fundamentals of WebXR
• Geometry and reference spaces in WebXR
• Viewpoints and viewers: Simulating cameras in WebXR
• Matrix math for the web
• Movement, orientation, and motion
• Using bounded reference spaces to protect the user