edit method
Implementation
Quality? edit(Point mouse, bool click) {
  if (!isEditable) return null;
  switch (_editionType) {
    case EditionType.clip:
      return adjustClip(mouse, click);
    case EditionType.points:
      return adjustPoints(mouse, click);
    case EditionType.perspective:
      return adjustPerspective(mouse, click);
    case EditionType.rectangles:
      return adjustRectangles(mouse, click);
    case EditionType.labels:
      return adjustLabels(mouse, click);
    default:
      return null;
  }
}