XRSession: selectstart event

The WebXR event selectstart is sent to an XRSession when the user begins a primary action on one of its input sources. Primary actions include things like users pressing triggers or buttons, tapping a touchpad, speaking a command, or performing a recognizable gesture when using a video tracking system or handheld controller with an accelerometer.

For details on how the selectstart, select, and selectend events work, and how you should react to them, see Primary actions in Inputs and input sources.

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, a myBeginTracking() function is called with the target ray pose's matrix. The myBeginTracking() 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, the myDropObject() 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 from doing so (like scheduling an animation of a splash if dropped in water, etc).
• The selectend event results in a myStopTracking() function being called with the object being dragged and the final target ray pose's transform.

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 of course 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:

xrSession.onselectstart = onSelectionEvent;
xrSession.onselect = onSelectionEvent;
xrSession.onselectend = onSelectionEvent;

Specifications

Browser compatibility