Modify a format of codes.
Ignore backup files Emacs generates.
Add 'scene_' and 'view_' to 'MainWindow'.
Create 'Scene' and 'View' classes to customize 'QGraphicsScene' and 'QGraphicsView' by inheritance.
Implement codes for tracking mouse movement.
Put property setting function of 'View' in order.
Create 'Tile' classes such as 'Kite' and 'Dart'.
Enable to put a clone tile of cursor.
Enable to flip cursor.
Enable to rotate cursor.