XRSession: selectstart event
Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The WebXR selectstart
event is sent to an XRSession
when the user begins a primary action on one of its input sources.
The beforexrselect
is fired before this event and can prevent this event from being raised.
Syntax
Use the event name in methods like addEventListener()
, or set an event handler property.
js
addEventListener("selectstart", (event) => {});
onselectstart = (event) => {};
Event type
An XRInputSourceEvent
. Inherits from Event
.
Event properties
In addition to the properties listed below, properties from the parent interface, Event
, are available.
frame
Read only-
An
XRFrame
object providing the needed information about the event frame during which the event occurred. This frame may have been rendered in the past rather than being a current frame. Because this is an event frame, not an animation frame, you cannot callXRFrame.getViewerPose()
on it; instead, usegetPose()
. inputSource
Read only-
An
XRInputSource
object indicating which input source generated the input event.
Description
Trigger
Triggered when the user presses triggers or buttons, taps a touchpad, speaks a command, or performs a recognizable gesture when using a video tracking system or handheld controller with an accelerometer.
Use cases
The selectstart
and selectend
events tell you when you might want to display something to the user indicating that the primary action is going on. This might be drawing a controller with the activated button in a new color, or showing the targeted object being grabbed and moved around, starting when selectstart
arrives and stopping when selectend
is received.
The select
event tells your code that the user has completed the action they want to complete. This might be as simple as throwing an object or pulling the trigger of a gun in a game, or as involved as placing a dragged object in a new location.
If your primary action is a simple trigger action and you don't need to animate anything while the trigger is engaged, you can ignore the selectstart
and selectend
events and act on the start event.
Examples
The following example uses addEventListener()
to establish handlers for the selection events: selectstart
, selectend
, and select
. This snippet is the core of an event handler to allow the user to grab objects in the scene and move them around.
In this case, a single function is used to handle all three events, allowing them to share certain code that's the same regardless of which of the three events is received. Only after completing those tasks does the onSelectionEvent()
function below dispatch the action out to a specialized function to handle things.
After checking to ensure that the received event is a tracked-pointer
event (the only kind we handle here), the target ray's pose is obtained using getPose()
.
If the target ray pose was fetched successfully, the code then uses the value of Event
property type
to route control to an appropriate function to handle the event which arrived:
- For
selectstart
events, amyBeginTracking()
function is called with the target ray pose'smatrix
. ThemyBeginTracking()
function would presumably start the presentation of the object-dragging process, using the transform to perform a hit test, determining which object to pick up.myBeginTracking()
returns an object representing the object the user has begun to drag. - Upon receiving a
select
event, themyDropObject()
function is called with the target object, and the current target ray pose transform as inputs. This places the object into its new position in the world and triggers any effects that may arise, like scheduling an animation of a splash if dropped in water, etc. - The
selectend
event results in amyStopTracking()
function being called with the object being dragged and the final target ray pose's transform.
js
xrSession.addEventListener("selectstart", onSelectionEvent);
xrSession.addEventListener("select", onSelectionEvent);
xrSession.addEventListener("selectend", onSelectionEvent);
function onSelectionEvent(event) {
let source = event.inputSource;
let targetObj = null;
if (source.targetRayMode !== "tracked-pointer") {
return;
}
let targetRayPose = event.frame.getPose(source.targetRaySpace, myRefSpace);
if (!targetRayPose) {
return;
}
switch (event.type) {
case "selectstart":
targetObj = myBeginTracking(targetRayPose.matrix);
break;
case "select":
myDropObject(targetObj, targetRayPose.matrix);
break;
case "selectend":
myStopTracking(targetObj, targetRayPose.matrix);
break;
}
}
You can also set up a handler for selectend
events by setting the XRSession
object's onselectend
event handler property to a function that handles the event:
js
xrSession.onselectstart = onSelectionEvent;
xrSession.onselect = onSelectionEvent;
xrSession.onselectend = onSelectionEvent;
Specifications
Specification |
---|
WebXR Device API # eventdef-xrsession-selectstart |
WebXR Device API # dom-xrsession-onselectstart |
Browser compatibility
BCD tables only load in the browser