_getController( index ) {

		let controller = this._controllers[ index ];

		if ( controller === undefined ) {

			controller = new WebXRController();
			this._controllers[ index ] = controller;

		}

		return controller;

	}
Returns a WebXR controller for the given controller index.

@private
@param {number} index - The controller index.
@return {WebXRController} The XR controller.