SelectionHelper constructor
      
      SelectionHelper(
    
    
- GlobalKey<PeripheralsState> listenableKey,
- Camera camera, [
- SelectionHelperOptions? options
Implementation
SelectionHelper(this.listenableKey, this.camera, [SelectionHelperOptions? options]) {
    this.options = options ?? SelectionHelperOptions();
	_domElement.addEventListener( PeripheralType.pointerdown, onPointerDown );
	_domElement.addEventListener( PeripheralType.pointermove, onPointerMove );
	_domElement.addEventListener( PeripheralType.pointerup, onPointerUp );
    selectionBox = Mesh(
      PlaneGeometry(),
      MeshStandardMaterial.fromMap({
        'color': this.options.color,
        'transparent': true,
        'opacity': this.options.opacity,
        'side': DoubleSide
      })
    )..name = 'selector';
}