This first assignment illustrates the display screen and event-handling features that are used from Pygame. Drawing, erasing, and screen updating are viewed in the Pygame window. Keyboard and mouse events are interpreted and used to control the drawing algorithms. A game loop keeps repeating the process: erase, draw, update the screen. Holding down the "e" key enables screen erasing every time through the game loop. Holding down the "f" inhibits the flip operation that is use to update the screen at the end of the game loop. The two mouse buttons are used to change the color of the circle.
The video starts with the erase feature. With erasing enabled, the ball seems animated (the drawing tail does not persist). Later the flip (screen update) operation is inhibited (these are drawn in memory but not to the screen). Finally a combination of erasing and flip inhibiting cause the ball to lag behind and then catch up to the cursor.