adjustRectangles method 
    
    
    
  Implementation
  Quality? adjustRectangles(Point mouse, bool click) {
  if (!click) return null;
  if (_rectangles == null) return null;
  //print('--- adjustRectangles ---');
  var point = _getMousePointInCanvas(mouse);
  var rectangles = _rectangles.value ?? [];
  var target = nearestRectangle(rectangles, point);
  if (target == null) {
    //rectangles.add(point);
  } else {
    if (target.containsPoint(point)) {
      rectangles.remove(target);
    }
  }
  _rectangles.value = rectangles;
  return Quality.high;
}